3D printing of acellular scaffolds for bone defect regeneration: A review

Materials Today Communications xxx (xxxx) xxxx

Contents lists available at ScienceDirect

Materials Today Communications journal homepage: www.elsevier.com/locate/mtcomm

3D printing of acellular scaffolds for bone defect regeneration: A review Farnaz Ghorbania, Dejian Lia, Shuo Nia, Ying Zhoub, Baoqing Yua,* a b

Department of Orthopedics, Shanghai Pudong Hospital, Fudan University Pudong Medical Center, Shanghai, China Department of Rehabilitation Medicine, Shanghai Pudong Hospital, Fudan University Pudong Medical Center, Shanghai, China

A R T I C LE I N FO

A B S T R A C T

Keywords: 3D printing Additive manufacturing Scaffold Tissue engineering Bone

Bone injuries can be treated using tissue engineering scaffolds, but the conventional constructs have a big challenge in supplying requirements of native tissue, i.e., bioactivity potential, mechanical stability, controllable biodegradability, and proper cellular interaction. In this regard, 3D printing technology with the possibility of controlling the internal microstructure and geometry of synthesized matrixes was introduced as a promising approach for bone defect regeneration. Although a variety of novel materials, which have shown initial potential for bone repair, can be used for preparing the biocompatible matrixes, the 3D printer type and selecting an innovated technology depend on the properties of applied biomaterials. In all the used methods, tunable, controllable, and interconnected porous microstructure can be fabricated even though identification of suitable porosity and microstructure, which can supply required mechanical properties of natural bone and support cellular adhesion, proliferation, and differentiation, need to evaluate. Therefore, this mini-review explains current advances in acellular 3D printed scaffolds, proper microporous structure and geometry for bone repair, and suitable materials for 3D printing the regenerative bone substitutes. Herein, the novel and recent studies were focused and probable limitations, and existing strategies were discussed.

1. Introduction Tissue lesions and defects that create by aging, trauma, infection, accidents, congenital disabilities, tumor resection, etc. are urgent medical problems which require transplantation strategies or implantation of artificial constructs to achieve recovery [1,2]. Although organ transplantation has shown satisfactory results, the costly and expensive process, need for surgery, and tissue adaptability has yielded limited usage [3]. Additionally, a limited number of donors, the viral transmission, lack of osteogenetic properties, and immune rejection can be observed in the case of xeno-transplantation. Accordingly, the artificial matrixes have found lots of attention in clinical treatment. Herein, tissue engineering provides an opportunity to restore and replace injured tissue through the cooperation of scaffolds, cells, and signaling molecules [4]. The scaffolds should prepare a three-dimensional (3D) network microenvironment to mimic the structure and biological performance of native tissue till the cells could adhere, proliferate, and differentiate well. Besides, an ideal tissue engineering constructs should be biodegradable with potential to supply mechanical requirements [5]. It should be noted that the balance between tissue repair rates and scaffold degradation plays a significant role in the efficient reconstruction process. So, the nature of the used materials, the

⁎

construction method, microstructure of the scaffolds, etc. are responsible for supplying physicochemical, mechanical, biological needs, and finally, tissue regeneration [6]. Chemical composition of the bone replacement scaffolds is a critical factor for providing required biocompatibility, hydrophilicity, bioactivity, and finally, osteogenesis in order to the betterment of cellular performance and neo bone formation [7–9]. However, the role of applied materials for supporting load-bearing applications is the principal factor, especially in bone studies [10]. Accordingly, selecting proper composition with a higher level of similarity to the native bone component can be a promising approach for bone repair. Hence, in a large number of investigations, calcium phosphates [11], calcium sulfates [12], calcium silicates [13], bioactive glasses [14], etc. are considered in orthopedic reconstructive scaffolds directly or as reinforcement particles in polymeric matrixes. Selecting a favorable method is another critical issue in tissue engineering. Traditional techniques such as solvent casting [15], gas foaming [16], electrospinning [17], freeze-drying [18], phase separation [19], freeze casting [20], and so on can produce single homogeneous scaffolds without any control on pore size and shape, porosity, and interconnectivity [21]. So the regeneration of the defective sites with different physicochemical and biological requirements same as

Corresponding author. E-mail address: [email protected] (B. Yu).

https://doi.org/10.1016/j.mtcomm.2020.100979 Received 9 August 2019; Received in revised form 10 January 2020; Accepted 4 February 2020 2352-4928/ © 2020 Elsevier Ltd. All rights reserved.

Please cite this article as: Farnaz Ghorbani, et al., Materials Today Communications, https://doi.org/10.1016/j.mtcomm.2020.100979

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

the bone surface that are involved in the breakdown of the bones by secretion of active enzymes against minerals for the production of new bone by osteoblasts [38,39]. In the regeneration process, the bone extracellular matrix can be categorized into three different groups, including decellularized bone ECM, demineralized bone ECM, and deproteinized bovine bone. Decellularization can be a promising approach to reduce immune rejection after implantation through the elimination of antigenic cells. A variety of literature proves the decisive role of the decellularized matrix in alkaline phosphatase activation, stimulating and promoting regeneration process, and finally, vascularization [40–42]. Besides, demineralized bone ECM composed of the organic component of bone in the absence of minerals and can stimulate osteoblast markers for cellular differentiation, enhance alkaline phosphatase activity, and improve regeneration capacity [43,44]. On the contrary, deproteinized ECM is free of organic bone components and can improve osteoblast adhesion and proliferation [45,46], but the investigation of Amerio et al. [47] prove that it can reduce expression of bone morphogenic protein-2. Bone formation is divided into endochondral and intramembranous osteogenesis [48]. Endochondral osteogenesis, which can be observed in long, short, and part of irregular bones, starts with the formation of embryonic cartilage and follow by converting to mature bone. In contrast, intramembranous osteogenesis, which can be observed in parietal, frontal, and clavicle bone, happens through mesenchymal differentiation in embryogenic connective tissue membrane [49,50]. The cells and interaction of cells (especially osteoblasts and osteoclasts) with bones are responsible for bone metabolism [51,52] and finally remodeling of the bone. Therefore, synthesizing and absorbing the bone matrix will be observed continuously due to osteoblasts and osteoclasts' performance, respectively. Herein, functional balance support normal bone formation and prevent any abnormality [53]

subchondral bone and cartilage will be faced a variety of problems [22]. To overcome the mentioned limitations and to revolutionize the traditional treatments, prepare patient-specific scaffolds, and fabrication of multilayered matrixes with different microstructure and materials, additive manufacturing technology has been developed [23,24]. Nonetheless, the possibility of direct printing in the defective site, increasing the accuracy and speed of scaffold preparation, reducing the cost of manufacturing are the other benefits of 3D printing in biomedical applications [25]. The aim of the layer by layer manufactured scaffolds is mimicking the native extracellular matrices (ECM) and providing favor microenvironment for cell growth, transportation of nutrients, waste by-products, and growth factors, and internally vascularization [26,27]. Vascularized tissue accelerates repair and remodeling through regulation of the cellular process such as signaling, proliferation, and differentiation. In this method, which was invented by Charles Hull [28] in the early 1980s, computer-aided manufacturing (CAM) and computer-aided design (CAD) help to fabricate individually designed scaffolds with desirable chemical composition and engineered-structure which have required porosity, uniform pore size, and sophisticated shape. This technology provides an opportunity to produce a synthetic matrix with different intricate shapes that can be incorporated with stem cells and growth factors for rapid regeneration [29]. Hence, the time-consuming and inaccurate procedure of conventional implantation, which was performed by usage of drills, scalpels, or other devices during the surgery, could be solved by the 3D printing strategy [30]. There are some reviews about bone tissue engineering using 3D printing technology, but this mini-review emphasizes the recent development of acellular 3D printing scaffolds for bone reconstruction and aims to summarize the different 3D printing methods, materials, and microstructures for efficient regeneration of defects. First, the chemical properties and physiological function of the bone will be discussed, then different compositions, methods, and microstructures will be compared. Finally, it gives a brief overview of current limitations and future advances in bone-related 3D printing scaffolds.

3. 3D printing technology Different techniques for fabrication of scaffolds have been shown some degree of success for the regeneration of defective sites, but lack of control on the microstructure in conventional methods leads to the development of additive manufacturing technology. Spatial control on the pore size, pore shape, porosity, and interconnectivity, fabrication of individual made constructs, reproducibility [54], printing variety of advanced compositions and multi-material structures [55,56], and coprinting the synthetic materials and biological agents such as peptides, proteins (e.g., fibronectin), polysaccharides, or DNA plasmids [56] are the benefits can be obtained by 3D printing technique. In the first generation of 3D printers that were introduced by Charles Hull in 1984, the 3D object was printed through layer by layer photopolymerization of the fluids. In the next generation, to full-fill the above-mentioned aims 3D computer modeling was prepared by CAD software such as auto desk, auto CAD, solid works, Creo parametric, etc [57]. (computerized tomography scans, photogrammetry [58], and magnetic resonance imaging images [26] can be useful in this step especially in medical applications [1]). Then, the format of computer models should be changed to. stl (stereolithography),. obj (object format),. amf (Additive manufacturing file), and so on [59,60]. The CAD design will be transformed into 2D images by slicer software to create a G-code file and facilitate the layer by layer printing process. Finally, printing the computer model can be done layer by layer [61]. Fig. 1a indicates, schematically, the 3D printing process. There are a variety of 3D printers that are coincident with a special type of material. Selecting the best 3D printer for the fabrication of bone replacement structures depends on production speed, resolution, and raw materials [55]. Stereolithography (SLA) [59], selective laser sintering (SLS), and fused deposition modeling (FDM) are the most available acellular 3D printing systems in medical applications. Table 1 shows a comparison of 3D printing technologies for the fabrication of bone tissue engineering

2. Physiology of the bone Bone is a rigid and dynamic hard tissue which has formed a human skeleton and can be found in different size, shape, structure, and properties. It is responsible for protecting the organs, storing the minerals, and producing different kinds of blood cells. Bone has a honeycomb-like matrix which is composed of 60 % inorganic components (calcium-deficient apatite and trace elements such as magnesium, zinc, copper, strontium, etc.) as reinforcement part of composite structure which is dispersed in 40 % organic matrix (90 % collagen type I and 10 % non-collagenous protein such as osteopontin, osteocalcin, decorin, biglycan, hyaluronan, and chondroitin sulfate) [31,32]. Herein, the required toughness and fracture-resistant of the bone support by collagen type I. This unique composition lead to having a strong tissue with low weight. It seems that this major protein in bone ECM structure is responsible for cellular adhesion, proliferation, and differentiation. Besides, the other non-collagenous compounds regulate bone mineralization and modulate hydroxyapatite orientation [33,34]. Moreover, the bone minerals can supply required hardening and maintain integrity, take part in collagen synthesis, activation of calcium-sensing receptors, inhabitation of osteoclast activity, stimulation of osteoblast proliferation and differentiation, and finally angiogenesis [35–37]. Three kinds of cells that activate bone metabolically are including osteocytes and osteoblasts, which are derived from osteoprogenitor cells and osteoclasts that are derived from differentiated stem cells to monocytes, and macrophages are involved in biomineralization and resorption of bone tissue. The inactive osteoblasts which are located in lacunae are called osteocytes. Osteoblasts are mononucleate cells on the surface of osteon that are involved in osteoid production for mineralization and bone formation. Osteoclasts are multinucleated cells on 2

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

Fig. 1. Schematic of the 3D printing process (a). Stereolithography process (b), irradiation of the light to the photosensitive resin according to CAD information leading to the layer by layer polymerization of the monomer, and finally, the preparation of the porous scaffold. Selective laser sintering technology (c), irradiation of the laser rays to the surface of the powder according to designed pattern terminated to increasing particle temperature till glass transition temperature, surface melting, and finally fusing the particles. Fused deposition modeling method (d), it is composed of the moveable head that extrudes the molten beads or filament layer by layer until the formation of the full structure.

formation of the cell network according to the 3D printed matrix structure was the strength of this study for tissue engineering applications. Based on the literature, the usage of the mask in the first-mentioned strategy resulted in saving more time and energy compared with direct laser irradiation [63,67,68] even though laser-based technology provides better control on the microstructure of the constructs through adjusting the laser beam strength [65]. According to the observation of scientists, the pattern of emission the rays or any extra surface modification can affect the cellular behavior and regeneration condition. Accordingly, in a study, SLA technology was used to print smart soybean oil epoxidized acrylate inks in order to regulate human bone marrow mesenchymal stem cell performance. Herein, the surface pattern lead to pareparation of scaffolds with flower-like structures and four dimensional effects. So the shape memory effect induced to the scaffold. Based on their observations, the scaffold micropattern affects the directional grow of the cells and efficient regeneration [69]. One of the common biodegradable materials which have gained lots of attention in the last three decades is photo cross-linkable poly(propylene fumarate), and it has found versatile application in the fabrication of scaffolds [70]. Fisher et al. [71] proved the possibility of preparing porous scaffolds for orthopedic applications using photo

scaffolds. Table 2 shows different 3D printed scaffolds and their physicomechanical and biological features. 3.1. Stereolithography One of the primitive and high-resolution techniques in the fabrication of tissue engineering structures is SLA technology. Its potential to produce complex shapes with dimensional accuracy made it superior to other conventional scaffolding methods for bone regeneration [62]. SLA technology is categorized in mask-based writing and direct laser writing [63]. In both methods, irradiation of the light to the photosensitive resin according to CAD information leads to the layer by layer polymerization of the monomer, and finally, preparation of the porous scaffold (Fig. 1b) [64]. The type of monomer with a compatible photoinitiator and the concentration of the liquid monomer, its viscosity, affects the microstructure of the final matrix [65]. The composite of gelatin methacryloyl and eosin Y was prepared by Wang et al. [66] via the SLA system (Fig. 2). Accordingly, increasing the content of eosin Y as a photoinitiator could improve the mechanical strength of constructs while the cell viability was reduced. Besides, both compressive Young’s modulus and cellular adhesion were increased as a function of the gelatin methacryloyl concentration. The proliferation of the cells and 3

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

Table 1 Comparison of 3D printing technologies for the fabrication of bone tissue engineering scaffolds. Technology/ Parameters

SLA

Process detail

- Soaking the platform in photopolymer - Layer by layer emission of light based on 3D designed file - Solidification of photopolymer - Removing the liquid non-exposed photopolymer ∼100 (μm) - Produce complex shapes - Dimensional accuracy - Smooth surface - A limited number of applicable materials - Cytotoxic effects of some photoinitiators and emitted light - Restricted cell printing

Resolution Advantages

Disadvantages

Materials

References

-

SLS

Poly(propylene fumarate) Acrylated polycaprolactone Gelatin methacryloyl Soybean oil epoxidized acrylate

[66,70,73,76]

FDM

- feeding the platform by an appropriate amount of powder - Layer by layer addition of powder and its sintering based on 3D designed file - Removing non-sintered powder ∼80 (μm) - Lack of using organic solvents - No need to support - No need to post-processing - Ascending temperature during the radiation of laser - Dependence of pore size to powder particle size and beam diameter - A limited number of applicable materials - Restricted cell printing - Polylactide-calcium carbonate - Poly(L,D) lactic acid-bioactive glass - Polycaprolactone-hydroxyapatite - Polyamide-hydroxyapatite - Poly(D,L-lactide)-β-tricalcium phosphate - Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) - Titanium [83,84,87,88,89,90,91]

- Applying the required temperature to the platform - Extruding of filament through the nozzle

∼50-200 (μm) - Low cost - Fast - Temperature - Low accuracy - Restricted cell printing

- Polycaprolactone - Polycaprolactone–polylactic acid - Polycaprolactonebioactive glass - Polylactic acid - Polyether-ether-ketone - Poly ester urea-hydroxyapatite - Polyvinyl alcohol-β-tricalcium phosphate [94,95,96,103,104,106,193]

composition for preparing SLA-printed scaffolds was performed by Green et al. [76]. Since in-situ decomposition of structures provides a better condition for cell growth and migration, so the regeneration of native tissue can be facilitated. Accordingly, biodegradable and photo cross-linkable polycaprolactone scaffolds can be the right candidate for tissue engineering applications. The functionalization of the polycaprolactone via acrylate groups made it suitable for printing via SLA setups, and the density of the photocurable groups affects the mechanical properties and biodegradability of the constructs. High molecular weight polycaprolactone with low functional groups (PCLDA) was compared with low molecular weight polymer with a high degree of functionality (PCLTA). Herein, PCLDA exhibited a higher level of strain at break and lower modulus compared with PCLTA. Since, in the case of fast biodegradation, the cells have not proliferated perfect, so the redamage of defective target tissue is probable. Herein, the samples with low degree of cross-linking presented 2.5 times faster biodegradation, which can affect efficient regeneration. The biocompatibility of the prepared scaffolds was proved after in-vitro experiments. The SLAprinted scaffolds could support mouse induced pluripotent stem cells attachment and proliferation while PCLTA constructs indicated higher level of proliferation and reach to contact-inhibited state within one week compared with PCLDA. In the other study a mixture of polyurethane resin as an oligomer, trimethylolpropane trimethacrylate as a reactive diluent, and phenyl bis (2, 4, 6-trimethyl benzoyl)-phosphine oxide as a photoinitiator were used as matrix and graphene was added as a reinforcement to preparation of a jawbone with a square architecture and a sternum with a round architecture by SLA 3D printer. The UV curable feature of the graphene-reinforced resin provides an opportunity to prepare patient-specific scaffolds. Besides, the applied composition resulted in achieving tensile strength, flexural strength, and modulus about 68 MPa, 115 MPa, and 5.8 GPa, respectively, which matches the requirement of natural bone [75]. Recently, the development of materials with photocurable potential led to a manifestation variety of applications [77–79]; however, above all the mentioned positive points, some limitations led to the development of other 3D printing technologies. One of the weaknesses of SLA technology is the light beam diameter, which can restrict accuracy, especially when small diameter microstructure is required [80]. Besides, a limited number of relevant materials with required curable

cross-linking of poly(propylene fumarate). Herein, bis(2,4,6-trimethyl benzoyl) phenyl phosphine oxide was used as a photoinitiator, and cross-linking occurred under UV light emission for 30 min. Also, the required interconnectivity of pores was supplied by the addition of NaCl as a porogen. Fabrication of scaffold through photo-crosslinking of resorbable poly(propylene fumarate) was performed in another study by Luo et al. [70] by using the SLA method. In their study, the poly (propylene fumarate) was synthesized by ring-opening copolymerization of maleic anhydride and propylene oxide under the presence of a base-catalyzed isomerization. Mechanical analysis of printed-scaffolds indicated ultimate strength at break above 15 MPa and elastic modulus between 178 and 199 MPa, which was similar to trabecular bone. Accordingly, not only photo cross-linkability of poly(propylene fumarate), spatial and temporal control on polymerization, and excellent osteocompatibilty of final network structure lead to finding versatile application in 3D printing of bone regenerative substitute, but also greater flexibility during implantation of scaffolds compared with other polymerization and cross-linking techniques can be obtained [72]. Besides, achieving the resolution of about 100 μm is one of the strengths of SLAprepared poly(propylene fumarate) scaffolds [73]. Accordingly, a high level of control on the surface area, strut thickness, and pore microstructure such as size, shape, and interconnectivity terminates to better control the diffusion of fluids, nutrients, excretion of cell by-products, and finally infusion and resorption of tissue in-vivo. Nettleton et al. [74] succeeded in fabricating 3D printed scaffolds composed of poly(propylene fumarate) resin for the regeneration of critical-sized cranial defects of a rat model. They compared different molecular mass resins (1000 and 1900 Da), and based on their observation; increasing molecular mass leads to higher stability and slow degradation rate so the new bone can create in defective site sooner. However, the volume of regenerated bone was compared with each other 12 weeks after implantation. According to the results, there was no sign of inflammation after the usage of scaffolds, and both compositions indicate the formation of lamellar bone bridges. But there were no significant differences between scaffolds with a different molecular mass of the polymer. Although poly(propylene fumarate) has shown a versatile application in SLA technology, it is not the only choice, and many acryalted compositions with photocurable groups have found the potential for SLA 3D printing [66,69,75]. Accordingly, the potential of acrylated 4

5 SLS SLS SLS SLS

SLS FDM

FDM FDM

FDM FDM

Polylactide-calcium carbonate

Polycaprolactone-hydroxyapatite

Poly(D,L-lactide)-β-tricalcium phosphate

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)

Titanium matrixes + chitosan-hydroxyapatite coat

Polyether-ether-ketone

Polycaprolactone-bioactive glass

Poly ester urea-hydroxyapatite

Polycaprolactone-decellularized bone ECM

Polyvinyl alcohol-β-tricalcium phosphate

pore size: 1437–87 μm

–

Porosity: 75 %

Pore size: 400−550 μm

–

Porosity: 30–70 %

Porosity: ∼80 %

Compressive modulus: 50−250 MPa Tensile strength: 1.71-3.92 MPa

Tensile strength: 56.6 MPa Bending strength: 56.1 MPa Compressive strength: 60.9 MPa Compressive modulus: ∼120 MPa Compressive modulus under wet conditions: 50 MPa

Biaxial bending strength: 23−62 MPa Compressive modulus: 36.4 MPa Compressive strength: 6.7 MPa –

–

–

Biaxial bending strength: above 75 MPa Young’s modulus: 23−102 MPa

Compressive strength: 11−28 MPa Tensile strength: 9−24 MPa

Tensile modulus: 3.3–6.9 MPa Toughness: 53–150 KJ/m3 Tensile strength: 68 MPa Flexural strength: 115 MPa Modulus: 5.8 GPa Flexural modulus: 10−79 MPa

Elastic modulus: 2.3 ± 0.5 MPa Compressive strength: 0.11 ± 0.02 MPa Ultimate strength at break: above 15 MPa Elastic modulus: 178−199 MPa, –

Porosity: 72 %

SLS

–

Polyamide-hydroxyapatite

SLA

Acrylated PCL

Pore size: ∼621 μm Porosity: ∼82 %

Porosity: 26–30 % Average pore size: 200 μm Porosity: 40–70 % Minimum pore size: 400 μm

SLA

Poly(propylene fumarate) resin

–

SLS

SLA

Resorbable poly(propylene fumarate)

60-78 %

Poly (L, D) lactic acid-bioactive glass

SLA

Photo cross-linkable poly(propylene fumarate)

Young’s modulus 5–15 KPa

–

–

SLA

Gelatin methacryloyl and eosin Y

Mechanical behavior

Microstructure

Graphene-reinforced polyurethane resin

3D printer

Composition

Table 2 Physicomechanical and biological properties of 3D printed scaffolds for bone regeneration.

–

- Biocompatible for cell adhesion and proliferation

[106]

[104]

[103]

[96]

[94]

[91]

(continued on next page)

- Proliferation and viability of the fibroblast cells - Cell orientation along with the surface pattern - Viability of more than 95 % of MC3T3-E1 preosteoblast cells after 1-week culture - Expression of alkaline phosphatase, bone sialoprotein, and osteocalcin - Deposition of the calcium-rich extracellular matrix after a 4-week culture - Osteoconduction could accelerate bone regeneration

- Promoted proliferation and differentiation - Inducing osteogenesis of MC3T3-E1 cells

[90]

–

[88] [89]

- Growing and spreading the Saos-2 cells - Replication of the Saos-2 cells

[87]

[84] -

Support cell migration Facilitate the exchange of nutrients and waste by-products Expression of alkaline phosphatase Accelerate the new femoral bone formation Supporting viability of the MG-63 osteoblast-like cells

[83]

- High viability of cell line NCTC clone L929 on the scaffolds

[75]

–

–

[76]

[74]

[70]

–

- No sign of inflammation - formation of lamellar bone bridges in critical-sized cranial defects of a rat model - Supporting mouse induced pluripotent stem cells attachment and proliferation

[71]

[66]

Ref.

–

- good cell proliferation - reduction of cell viability by addition of a photoinitiator - betterment of cellular adhesion as a function of gelatin methacryloyl concentration

Biological behavior

F. Ghorbani, et al.

Materials Today Communications xxx (xxxx) xxxx

6 FDM

Poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-calcium sulfate hemihydrate-chitosan

Polycaprolactone-hydroxyapatite

homemade 3D printing equipment

FDM

Biomineralized hydroxyapatite-silk fibroin

β-tricalcium phosphate-bioactive glass

3D Bioplotter

Polydopamine‐laced hydroxyapatite-collagen-calcium silicate

–

Rapid prototyping robotic dispensing system Solidscape printer

chitosan-hydroxyapatite

β-tricalcium phosphate- polycaprolactone

Multi-head deposition system

Polycaprolactone-polylactic-co-glycolic acid-β-tricalcium phosphate

Binder jet system

SLA

Poly(propylene fumarate)- diethyl fumarate

MgO-ZnO-tri calcium phosphate

three-axis robot system supplemented with a dispenser

Polycaprolactone-fish bone extract

Powder-binder ProMetal

3D Bioplotter

Polycaprolactone-bioactive glass-magnetic nanoparticles

Tricalcium phosphate

3D printer

Composition

Table 2 (continued)

Compressive strength: kgf Compressive strength: MPa Compressive modulus MPa bending strengths: 21.39–23.29 MPa, Compressive strength: 6.6 MPa

Pore sizes: 250−500 μm

Pore size: 400 μm

Porosity: 55–60 % Pore size: 400 μm

Porosity: 45–55 % Pore size: 500 μm Pore size: 200−300 μm

Porosity: 27–41 % Pore size: 420–860 μm

Pore size: 100−500 μm 2.7-

< 500

10–20

30–70

Compressive strength: 17.9427.46 MPa Stiffness: 35.7–46.7 N/mm Compressive yield strength: 46.2-56.9 MPa -Compressive strength: 8.34 MPa -Elastic modulus: 208.5 MPa Compressive strength: 16.6 MPa

–

Pore size: 200–1000 μm

Porosity: 70 % Pore size: 400 μm

–

Porosity: 50 % Pore size: 250 μm

–

Young’s modulus: 9 MPa Tensile strength: 82−87 MPa

Porosity: 55 % Pore size: 470−480 μm

Porosity: 60 % Pore size: 200−800 μm

13−16 MPa mechanical strength

Mechanical behavior

Porosity: 60 % Average pore size: 400 μm

Microstructure

–

[12]

[136]

[116]

[134]

[133]

[132]

[130]

[129]

[127]

[111]

[110]

[109]

[108]

Ref.

(continued on next page)

- Supporting adhesion and proliferation of the rat bone marrow stromal cells - Mimic the cell’s extracellular matrix - Similar levels of alanine aminotransferase, aspartate aminotransferase, total protein, blood urea nitrogen creatinine, and uric acid with healthy rats - Any systematic immune responses and organ dysfunction. - Expression of alkaline phosphatase and osteogenic genes, including osteopontin, collagen I, bone morphogenic protein-2, osteocalcin, and Runt-related transcription factor 2 - In-vivo expression of osteogenic genes and bone formation

- Osteogenic behavior - New bone formation eight weeks after implantation in rabbit calvarial defects. - Promoting MC3T3-E1 osteoblast cell proliferation

- Mg2+ induce cellular adhesion, proliferation, and alkaline phosphatase expression - Si4+ has a stimulatory effect on proliferation, osteogenic differentiation, and mineralization of preosteoblasts like bone cells and mesenchymal stem cells. - Si ion releasing induce vascular endothelial growth factor expression - Up-regulating nitric oxide synthase, and nitric oxide production in human endothelial cells - Angiogenesis. - improvement in osteoblast proliferation

- Osteointegration - Peripheral new bone formation - Improvement in adhesion, proliferation, and osteogenic differentiation of the human bone marrow mesenchymal stem cells

- Enhancing cellular growth, - Increasing alkaline phosphatase activity - Expression of gene expression, i.e., bone morphogenic protein-2, collagen type I, runt-related transcription factor 2, bone sialoprotein, and osteocalcin - Osteogenesis - Supporting cell proliferation - Inducing calcium deposition - Expression of osteogenic markers such as bone morphogenic protein-2, osteocalcin, alkaline phosphatase, and osteopontin - Supporting osteoblast migration - Expression of fibroblast growth factor, vascular endothelial growth factor, and transforming growth factor β1 - Controllable transportation of bone-related biological factors - Migration and proliferation of the cells - New bone formation - Enhancement of osteoconductivity

Biological behavior

F. Ghorbani, et al.

Materials Today Communications xxx (xxxx) xxxx

7 FDM Inkjet 3D printer

SLM

Titanium

Titanium coated via chitosan-magnesium-calcium silicate

Motor assisted microsyringe 3D printing machine

Polycaprolactone-strontium contained hydroxyapatite

Poly(lactic acid)- polydopamine- collagen type I

Melt-blending

Polycaprolactone-silanated silica particles

Low-temperature rapid prototyping

FDM

Polycaprolactone-β-tricalcium phosphate

Poly lactic-co-glycolic acid-β-tricalcium phosphate-magnesium

Low temperature dispensing machine

Micro/nanoporous collagen-dECM-silk fibroin

Pore size: ∼450 μm

Pore size: 23-25 μm and 1200-1400 μm Porosity: 65 %

Porosity: ∼80 %

Compressive strength: 50 MPa

MPa

Compressive strength: 9.47 MPa Young’s modulus: 0.40 GPa Compressive strength: ∼50

Compressive strength: 3.7 MPa

Pore size: 392–423 μm Porosity: 60 %

Young’s modulus: 115 MPa

Compressive strength: 2−7 MPa

Young’s modulus: 18−25 MPa

Young’s modulus: 264−1140 MPa

Compressive modulus: 2001200 MPa Compressive strength: 0.030.1 MPa Compressive modulus: 0.030.3 MPa

Compressive strength: 12.1 MPa

Compressive strength: 3−8 MPa Compressive strength: 15−40 MPa

Mechanical behavior

Porosity: 60–65 %

Porosity: 60 % Pore size: 500 μm Pore size: 200 μm

Porosity: 15–60 %

Pore size: ∼600 μm

Pore size: 50 μm

Pore size: 300 μm

Bioprinter

SLA

Porosity: 78 %

Chitosan- polyethylene glycol diacrylate

Mesoporous calcium silicate bioactive glass-gliadinpolycaprolactone

Porosity: 60 % Average pore size: 400 μm Pore size: 170−400 μm

Microstructure

3D

3D Bioplotter three-axis 3D scaffold printer

Pearl-calcium sulfate

Lithium-calcium silicate

3D printer

Composition

Table 2 (continued)

Improve vessel formation No immune responses after surgery ECM deposition Alkaline phosphatase expression Enhancing collagen-producing, alkaline phosphatase activities, and osteocalcin level

Enhancing osteogenic differentiation. Increasing the level of alkaline phosphatase Expression of bone-related gene i.e., osteocalcin Better adhesion and proliferation in the samples containing strontium Inducing differentiation of bone marrow-derived mesenchymal stem cells Improving alkaline phosphatase activity Expression of the osteo-related genes Regeneration of in-vivo cranial defect Enhancing blood perfusion

- The magnesium contained layer improved cell proliferation and differentiation and exhibited both osteogenesis and mineralization - Promoted regeneration of the critical size bone defects

-

-

-

-

- Calcium deposition of preosteoblast cells - Improving cellular proliferation

- Expression of alkaline phosphatase

Expression of collagen type I - In-vitro and in-vivo osteogenesis - New bone formation in femur defect of rabbit - High feed ratio and a higher concentration of photo-initiator leads to lower cell adhesion and viability - Cell viability

- Expression of osteogenic markers such as alkaline phosphatase, osteocalcin, collagen I, and osteopontin - Stimulation of osteogenic differentiation of the rat bone marrow mesenchymal stem cells - Maturation of chondrocytes - Enhancing MC3T3-E1 cells attachment and proliferation

Biological behavior

[176]

[174]

[169]

[164]

[161]

[160]

[100]

[154]

[65]

[149]

[145]

[139]

Ref.

F. Ghorbani, et al.

Materials Today Communications xxx (xxxx) xxxx

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

Fig. 2. Visible light-based stereolithography 3D printing system. Schematic of the single-layer printing procedure (a). Fluorescence images of NIH-3T3 cell-laden scaffolds after five days of culture, which is stained with DAPI for nuclei (blue) and Phalloidin 488 for F-actin (green) (b). Compressive Young’s modulus (c) and 1day cell viability of the eosin Y: gelatin methacryloyl (4X: 10 %, 2X: 15 %, and 1X: 20 %) (d). (Reproduced content is open access) [66] (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article).

functional groups, stability, the viscosity of the resins, and finally restriction in cell printing because of cytotoxic effects of some photo-initiators and emitted light rays made scientist find proper alternative methods [62].

Biocompatibility of scaffolds was proved by MTT assay and observing high-level viability of the human osteosarcoma cell lines on the scaffolds; however, the presence of hydroxyapatite in the structure act as a promoter of alkaline phosphatase expression that is the initial and essential factor to determine the osteogenesis [84]. It should be noted that the ascending temperature during the radiation of laser leading to limitation of its applicability for temperaturesensitive materials [85]; however, lack of using organic solvents, which can reduce biocompatibility, is the strength of this technique [86]. Gayer et al. [87] fabricated solvent-free polylactide (75 %)-calcium carbonate (25 %) composite constructs via SLS technique. The aim of this investigation was the regeneration of large-sized bone defects (Fig. 3). Since the large lesions cannot repair themselves, scaffolds play a positive role in the reconstruction of injuries. According to their observations, the porous microstructure with high strength and slow degradation rate was prepared in this technique while the small particle size showed a faster sintering rate. Additionally, the viscosity was introduced as an effective parameter on 3D printing feasibility in which the lowest inherent viscosity (1.0 dl/g) provides the best condition for SLS. The study of the mechanical behavior of scaffolds indicated a biaxial bending strength of more than 75 MPa, which made them usable for bone tissue engineering. Excellent viability of the MG-63 osteoblastlike cells on the SLS prepared-scaffolds demonstrated appropriate biocompatibility and proved the initial potential of constructs for patientspecific bone replacement applications. On the other hand, the potential for fabrication of a variety of structures, no need to support, and limited requirements of prepared matrixes to post-processing attract several scientists. However, the dependence of pore size to powder particle size and beam diameter have restricted complete control on the microstructure of the scaffold.

3.2. Selective laser sintering SLS is a laser-based technology for printing the constructs through sintering the powder. Irradiation of the laser rays to the surface of the powder according to designed pattern terminated to increasing particle temperature till glass transition temperature, surface melting, and finally fusing the particles [81,82], as indicated schematically in Fig. 1c. A recent investigation was focused on SLS prepared poly (L, D) lactic acid-bioactive glass matrixes for bone repair. Accordingly, observation of a porous microstructure with 26–30 % porosity and an average pore diameter of 200 μm after high sintering degree made scaffolds favorable for tissue engineering applications. Flexural modulus values were about 10−79 MPa depending on the concentration of bioactive glass in the composite, which matches the measured range in human bone. High viability of cell line NCTC clone L929 on the scaffolds indicate their applicability for healing [83]. In the other study on polyamide-hydroxyapatite scaffolds, SLS technology was applied to facilitate the fabrication of complex architecture. Formation of 40–70 % interconnected porosity with minimum pore size 400 μm showed suitable conditions for cell migration. Besides, the pore channels facilitate the exchange of nutrients and waste by-products and accelerate new femoral bone formation. The prepared constructs showed compressive strength and tensile strength of about 11−28 MPa and 9−24 MPa, respectively, depending on the concentration of hydroxyapatite from 0 to 20%, which can supply mechanical requirements of the femur bone. 8

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

Fig. 3. Fabrication of solvent-free polylactide-calcium carbonate composite constructs via SLS technique in order to the regeneration of large-sized bone defects. (Reproduced content is open access) [87].

inside pores and bone inducibility.

Besides, the mechanical strength of SLS prepared matrixes is often lower than natural tissue and need extra modification. Nevertheless, Wiria et al. [88] focused on the effects of laser scan speed on properties of SLS printed-polycaprolactone-hydroxyapatite scaffolds while hydroxyapatite had small and large particle size. They proved that scan speed has an impressive effect on sintering the powders and porous microstructure. Based on their observations, lower scan speed leads to the fabrication of structurally stable specimens. An enhancement in necking intensity under lower scan speed, the particles fused, and stability of constructs can improve by the formation of bigger clusters. Additionally, growing and spreading the Saos-2 cells on the surface indicated the supportive behavior of 3D printed matrixes form cellscaffolds interactions. Replication of the Saos-2 cells presented the favorable potential of SLS prepared scaffolds for tissue engineering applications. Besides, in a recent investigation, the poor mechanical properties were controlled through powder particle size and melt viscosity during the printing procedure. Herein, poly(D,L-lactide) (50 %)-β-tricalcium phosphate (50 % composite powder was used for 3D printing process. Comparing different particle sizes 35 μm vs. 50 μm and melt viscosity 5800 Pa∙s vs. 17,900 Pa∙s indicated an increase in biaxial bending strength from 23 to 62 MPa when the particle size and melting viscosity enhanced. So filtering the particle size or molecular weight can improve the laser-sintering process and supply mechanical needs [89]. The dependence of the microstructure of scaffolds to laser energy density was also examined by Diermann et al. [90]. Herein, interconnected porous poly(3-hydroxybutyrate-co-3-hydroxyvalerate) scaffolds with large surface areas and porosity about 80 % were fabricated by SLS technology. According to their observations, relative density and interlayer connections enhanced when the laser energy density increased; moreover, the quantity of residual powder inside the pores reduced by an increase of this parameter. An increase in compressive modulus (36.4 MPa) and strength (6.7 MPa) arise from enhancement in relative density from 20.3–41.1%. Since SLS can be used for the fabrication of metal-based constructs. Titanium powder with great osteointegration can be applicable for the preparation of reconstructive bone substitute. In the investigation of Wei et al. [91], titanium matrixes were fabricated using SLS technology, and the surface was coated with a layer of chitosan-hydroxyapatite. They observed that quasi-elastic gradient of constructs with 30 and 70 % porosity was near to cortical and cancellous bone, respectively, that arise from the porosity-dependent behavior of the scaffolds. Besides, porosity can depend on the power of laser, speed of scan, molecular weight, etc. in SLS procedure. Coating the chitosan-hydroxyapatite on the surface of matrixes promoted proliferation, differentiation, induced osteogenesis of MC3T3-E1 cells, and provided a condition for growing the new bone

3.3. Fused deposition modeling FDM is a developed technology for printing the thermoplastic filaments or beads, and finally, the preparation of 3D microstructure [92]. This method is more common and cheaper than other printing technologies and enables the fabrication of scaffolds with controllable geometry and architecture; nonetheless, the final cost depends on print quality and complexity of the setup such as the number of applicable heads. FDM setup (Fig. 1d) is composed of the moveable head that extrudes the molten beads or filament layer by layer until the formation of the full structure. Fusing the layers supported by applied heat and molten thermoplastics [93]; moreover, dimensional accuracy and controlling porosity, interconnectivity, and pore size and shape can be supplied by adjusting the angle between the bed and printed structure, layer thickness, and gap width [94]. Investigation Wu et al. [94] on FDM printed polyether-ether-ketone scaffolds were focused on the determination of the influence of layer thickness and the angle between the bed and printed structure on the mechanical performance of scaffolds. Accordingly, the scaffolds with a layer thickness of 200, 300, and 400 μm and angle of 0°, 30°, and 45° were printed. Herein, tensile strength (56.6 MPa), bending strength (56.1 MPa), and compressive strength (60.9 MPa) received to a higher amount when the layer thickness was 300 μm, and similar condition was observed in angle of 0°. So optimal mechanical properties were found at layer thickness of 300 μm and angle of 0°. Since the type of materials can be an effective factor on performance of FDM printed scaffolds, mechanical behavior of acrylonitrile butadiene styrene, a common material in FDM technology, was compared with polyether-ether-ketone constructs in similar printing condition. Based on observations, average tensile strengths, compressive strengths, and bending strengths were increased about 108, 114, and 1.5 %, respectively. The result of study on FDM printed poly lactic acid confirmed that the pore dimension affected by printing procedure since a slight shrinkage in the fabricated scaffolds was observed compared with 3D designed file. Additionally, the FDM printing process resulted in a reduction in degradation temperature and molecular weight while no special effect on crystallinity was observed [95]. Moreover, the porosity level is the other factor that can be controlled by FDM technology parameters and affect final mechanical behavior of scaffold, which is one of the critical factors in bone tissue engineering. Evaluating the mechanical strength of FDM printed polycaprolactonebioactive glass scaffolds proved the role of this method to provide reasonable mechanical properties. Accordingly, increasing the pore size from 400 to 550 μm terminated to a reduction in compressive modulus 9

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

provide all of the mentioned requirements, but there is no precise control on microstructure in none of them that lead to the development of 3D printing scaffolds [27]. The porous microstructure of the scaffolds is a critical factor in supporting cellular interactions. Not only the porosity of scaffolds should support cell migration and osteogenic behavior, but also it is responsible for providing desired mechanical stability. In an investigation, 3D printed polycaprolactone-bioactive glass scaffolds were incorporated via magnetic nanoparticles. According to the observation, a high porous microstructure (60 %) with an average pore diameter of 400 μm could express 13−16 MPa mechanical strength, which is suitable for reconstructive bone constructs. Besides, the prepared scaffolds could enhance cellular growth, alkaline phosphatase activity, and stimulate gene expression, i.e., bone morphogenic protein-2, collagen type I, runt-related transcription factor 2, bone sialoprotein, and osteocalcin which are an indicator for osteogenesis [108]. Besides, Heo et al. [109] fabricated polycaprolactone-fish bone extract composite scaffolds by 3D printing technology and also coated the surface via fish bone extract. According to their observation, interconnected porous microstructure with pore size between 470−480 μm and porosity 55 % was prepared in this technique which can support cell proliferation, induce calcium deposition, and express osteogenic markers such as bone morphogenic protein-2, osteocalcin, alkaline phosphatase, and osteopontin which are an indication of bone regeneration. Although porosity is a critical issue in tissue engineering, the pore size has a significant role in maintaining efficient regeneration. The SLA printed poly(propylene fumarate)- diethyl fumarate showed 60 % porosity while the interconnected pores were distributed in the range of 200−800 μm. herein, the 3D printed scaffolds by Kim et al. [110], presented osteoblast migration and expression of fibroblast growth factor, vascular endothelial growth factor, and transforming growth factor β1 compared with the same composition which is prepared with traditional technologies. In other study by Shim et al. [111], the polycaprolactone-polylactic-co-glycolic acid-β-tricalcium phosphate scaffolds were prepared by 3D printing technology to achieve guided bone regeneration membrane. Herein, membranes with 50 % of 250 μm fully interconnected pores were fabricated, which was suitable for controllable transportation of bone-related biological factors, migration and proliferation of the cells, and finally, new bone formation. Implantation of recombinant human bone morphogenic protein-2 loaded membranes resulted in the repairing of calvaria defects within eight weeks. Since a balance between porosity and pore size with mechanical strength of scaffolds is required, the investigation of Salmoria et al. [83] proved that polylactic acid-bioactive glass scaffolds which are prepared via SLS technology can supply mechanical needs (Flexural modulus values was about 10−79 MPa) of injured bone while scaffolds have 26–30 % porosity with 200 μm diameter. Additionally, the viability and proliferation of the cells on the printed matrix confirmed that the porous microstructure could supply in-vitro needs. Furthermore, the SLS printed polyamide-hydroxyapatite with 40–70 % interconnected porosity and pore size 400 μm showed cell migration and osteogenesis behavior. The compressive strength (11−28 MPa) and tensile strength (9−24 MPa) of the porous scaffolds were suitable for femur bone regeneration that proved the selection of pore size and porosity in the processing window according to bone requirements [84]. The quasielastic gradient of SLS printed constructs with 30 and 70 % porosity was near to cortical and cancellous bone, respectively, which was proved by Wei et al. [91]. Although a variety of 3D printed scaffolds has been promoted for bone regeneration, the pore shape is another useful factor in maintaining mechanical requirements, osteogenic behavior of constructs, and finally, bone ingrowth, but there is no exact statement about the best microstructure up to now. The worthy study on interconnected and regular honeycomb microstructure of the 3D printed polycaprolactonepoly ethylene glycol scaffolds demonstrated that honeycomb pores

from approximately 120 to 100 MPa (z-axis direction), respectively [96]. In the other investigation by Carlier et al. [97], PLA filaments were used to prepare the scaffolds with FDM printer. According to their observations, ductility of the constructs was increased as a function of layer thickness enhancement and temperature reduction; in contrast, a reduction in layer thickness and an increase in temperature improved layer adhesion. Kind of thermoplastics or their combination with other temperatureresistant biomaterials can be used in FDM systems for the fabrication of porous scaffolds [98–100]. Higher stiffness and excellent in-vivo bone regeneration compared with prepared scaffolds with conventional technologies and the same materials made FDM printed matrixes favorable for tissue regeneration [42,101,102]. Yu et al. [103] fabricated poly ester urea-hydroxyapatite scaffolds with 75 % porosity using FDM printing technology. Observation of about 50 MPa compressive modulus under wet conditions demonstrated the decisive role of applied materials and scaffolding technology on supplying mechanical needs. Besides, viability of more than 95 % of MC3T3-E1 preosteoblast cells after 1-week culture confirmed the biocompatibility of scaffolds. Additionally, incorporation of hydroxyapatite played an undeniable role in the expression of alkaline phosphatase, bone sialoprotein, and osteocalcin that are favorable for bone reconstruction. The deposition of calcium-rich extracellular matrix after a 4-week culture proved the suitability of scaffolds for bone repair. Composite of polycaprolactonedecellularized bone ECM was printed via FDM printers in the investigation of Rindone et al. [104]. The exact matching the scaffold geometry and lesion site was the strength of this study that arise from application of 3D printing technology. Potential of porous microstructure for osteoconduction could accelerate bone regeneration. However, the role of decellularized ECM on increasing surface roughness and betterment of cellular adhesion should not be ignored. Printing temperature is the most crucial factor in the final microstructure and quality of printed construct [105]. Accordingly, FDM technology was applied for the fabrication of polyvinyl alcohol-β-tricalcium phosphate scaffolds with interconnected channels. Results presented that increasing the printing temperature resulted in a decrease in flow viscosity. Accordingly, it is better to set the printing temperature above the melting temperature of the polymer to have an extrudable microstructure. In fact, in high temperatures, the exact microstructure cannot be obtained with a high level of accuracy since the molten polymer does not have enough strength, and its volatilization will happen. In this study, the highest resolution of the printed structure was obtained at 165 °C while increasing the temperature until 190 lead to the formation of a rough surface. In this research, improvement of thermal processability of the composite filament was provided by water and glycerin as co-plasticizer. Based on the observations, the printing temperature affects interlayer adhesion strength. Increasing tensile strength from 1.71 MPa to 3.92 MPa by decreasing the printing temperature form 185 °C to 175 °C proves the claim. Beside the printing parameters, the composition can affect the final properties. The presence of β-tricalcium phosphate, especially in concentration of more than 20 wt.%, could promote load-bearing capacity since maximum stress increase from 8.3–10.7 K Pa [106]. Although a large number of studies can be found on FDM 3D printers, applied temperature provide limitation for using thermalsensitive polymers or biological macromolecules. Furthermore, low accuracy and restriction of cell printing reduced its application in regenerative medicine [56]. 4. microstructure and architecture of 3D printed scaffolds The microstructure and architecture of the scaffolds, including pore size and shape, the interconnectivity of the pores, porosity, etc. are undeniable factors in supplying the required mechanical strength, cellular proliferation, migration, differentiation, and finally neo-tissue formation [107]. There are a variety of scaffolding methods that 10

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

Fig. 4. Effect of pore geometries on the enrichment and differentiation of mesenchymal stem cells (Reproduced content is open access) [114].

materials for creating 3D printed bone scaffolds should be biocompatible, biodegradable or bioresorbable, support biomineralization, and provide required physicochemical and mechanical needs [102]. The printability of the materials, reproducibility, and cost-effectively are essential factors in the field of 3D printing [121]. In a published study about 3D printing process, researcher creates scaffolds with > 99 % precision, totally interconnection with proper pore morphology and size, and high mechanical strength for a range of load-bearing and tissue healing process [102]. Different kinds of polymeric, ceramic, and metallic materials have been used in the fabrication of reconstructive bone constructs. Nevertheless, all of them have some strong and weak points to supply the requirements, so to overcome the limitations; usually, the hybrid compositions are preferred to simulate natural bone ECM [122]. It means that polymers especially natural ones can be a better choice for ameliorating biological activity while the required bioactivity for neo-bone formation can be supplied by bioactive ceramics [123]. Metallic particles can improve mechanical strength or induce special features such as magnetic or electrical properties [124]. Furthermore, the addition of some biological factors such as growth factors, particular ions, and even cells can provide a better microenvironment for cell adhesion and growth.

could support cellular diffusion inside the structure, provide a bridge for cells for cell-cell interactions, cell-ECM network formation, and production of ECM [112]. Investigation of Lee et al. [113] on pore geometry of poly(propylene fumarate)- diethyl fumarate matrixes indicated that osteoblasts could proliferate on staggered pores more than orthogonal geometry when both scaffolds had same pore size and porosity. Investigation of Ferlin et al. [114] on the effect of pore geometries on the enrichment and differentiation of mesenchymal stem cells indicated that cubic pores have the potential to support the expression of cell markers. Accordingly, cubic pores increase gene and protein expression and promote adipogenesis and chondrogenesis compared with a cylindrical one (Fig. 4). Gong et al. [115] investigation indicated that 3D printed polylactic acid scaffolds with 60 % interconnected porosity have different mechanical properties while the pore geometry changed from triangular to circular. Accordingly, circular pores showed a high degree of fatigue resistance, while the circular pores could not tolerate cyclic loads. As a conclusion, a variety of studies indicated the pore size between 100−400 μm and porosity about 50–60 % could be suitable for fluid transfer, cell and tissue growth, cell migration and differentiation, and finally bone repair [108,111,116,117]. However, according to one study, the minimum pore size for bone reconstruction is 150 μm [118]. But as indicated by Salvatore et al. [119], the optimum pore size for accelerated bone regeneration is less than 280 μm. Besides, the honeycomb geometry can have a better simulation from bone microstructure and will be a suitable selection for the fabrication of reconstructive substitutes. Also, it can provide higher mechanical strength during neo bone formation.

5.1. Ceramic-based scaffolds Bioceramics are a class of biomaterials which use frequently used in hard tissue applications. Ceramics are high-density inorganic metal oxide materials, which are usually biocompatible with high corrosion and temperature resistance [121]. They divide into two groups of bioinert and bioactive ceramics based on their biomineralization potential [125]. Some of the most usable ceramic for bone scaffold fabrications include calcium phosphates, calcium sulfate, calcium silicates, bioactive glasses, etc. The most important 3D printed ceramic-based scaffolds will be discussed below.

5. Materials used for 3D printing of hard tissue There is a wide range of materials which has been used in the 3D printing process, including solid or liquid state [120]. The selected 11

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

on the surface of hydroxyapatite and formation of heterogeneous nucleation, which leads to higher crystalline nature and perfection compared with pure polycaprolactone crystals. Although the printed pores for both scaffolds were rectangular and were in the range of 100−500 μm, which are essential for bone tissue engineering, 3D printed hydroxyapatite-polycaprolactone scaffolds with micro-particles showed lower pore dimensions. The tensile and bending strengths were approximately 23.29 and 21.39 MPa, for micro and nanoparticulate systems, respectively, which were 26.0 and 33.1 % higher than pure polycaprolactone scaffolds. The mechanical properties showed that the 3D printed scaffold with nano-hydroxyapatite fillers is the better choice. This increment in mechanical properties is mainly related to higher modulus of hydroxyapatite compared with polymers such as polycaprolactone. Furthermore, the rough surface arises from added nano-hydroxyapatite can generate friction and create an interface with a polycaprolactone matrix to withstand some of the applied stresses. Also, the more mechanical properties of nano-particles compared with micro ones can be attributed to the more homogenous dispersion of nano-hydroxyapatite particles in the matrix. Although hydroxyapatite contained constructs have shown desirable osteogenic performance, owing to lack of biodegradation, its application has been restricted; hence, the addition of polymers can modulate its performance.

5.1.1. Calcium phosphates 5.1.1.1. Hydroxyapatite. Blending hydroxyapatite, one of the main and essential components of natural bone matrix to supply required rigidity, with natural polymers improve mechanical strength, bioactivity, and biological aspects of the polymeric bone substitutions [126]. In this regard, Ang et al. [127] fabricated chitosan-hydroxyapatite scaffolds with interconnected porous microstructure via dispensing rapid prototyping technology. Enhancement of mechanical stability and osteoconductivity was the benefit of the addition of hydroxyapatite to the composite structure. In another study on hydroxyapatite based matrixes, Stevanovic et al. [128] fabricate hydroxyapatite scaffolds using a powder-based 3D printer. For better mimicking the natural bone structure and rapid osteointegration, the hydroxyapatite constructs were infiltrated via polymers such as polyvinyl alcohol, polycaprolactone, ethyl acetate, and gelatin. According to their observation, the coating layer could simulate the elastic behavior of the collagen phase in natural bone, which affects mechanical strength and control the biodegradation rate. Mechanical investigations demonstrate that after the infiltration of 4X gelatin, the compressive strength reached 3.7 MPa, while 10X one improved strength to 12.6 MPa, which are significantly higher than gelatin-free constructs (0.8 MPa). The observation confirms the positive effect of polymeric infiltration on the mechanical properties of hydroxyapatite scaffolds. Besides, it should be noted that the more infiltration leads to higher mechanical properties even though it reduces the porosity of the scaffolds. Accordingly, the infiltration times should be modulated based on the required porosity. The potential of bone regeneration was investigated using polydopamine‐laced hydroxyapatite-collagencalcium silicate matrixes, which were prepared via mold printing technology. Herein, different pore sizes (250 μm and 500 μm) were compared with each other. Accordingly, higher pore size support osteointegration, peripheral new bone formation, and the formed neobone could diffuse inside the scaffolds [129]. Fabrication of 3D biomineralized hydroxyapatite-silk fibroin nanocomposite constructs was followed by Ting et al. [130]. 70 % porosity with a diameter of 400 μm was produced by a 3D printing setup. According to their observation, although the scaffolds possess high porosity, regular pore channels supplied high mechanical strength. Improvement in adhesion, proliferation, and osteogenic differentiation of the human bone marrow mesenchymal stem cells is the strength of using 3D printed scaffolds. They used sodium alginate as paste binders due to its biocompatibility and biodegradability, which is approved by the Food & Drug Administration (FDA). Furthermore, the bivalent cations such as Ca2+ are amicable in bone tissue engineering. The mechanical investigation of the prepared scaffolds demonstrated that higher silk fibroin reduces mechanical properties. Although all printed scaffolds had compressive strength in the range of human trabecular bone, the highest compressive strength was achieved in the scaffold with similar weight ratio of silk fibroin and hydroxyapatite. However, the best mechanical properties were obtained in the scaffold with lower silk fibroin, while higher silk fibroin weight ratio improves cellular interactions. On the other hand, one of the most effective parameters on the properties of the final scaffolds, which should be considered is the shape and the size of used particles as raw materials [131]. In a recent study [132], the internal structure and mechanical properties of FDM 3D-printed polycaprolactone-hydroxyapatite scaffolds were analyzed. For this purpose, nano and micro hydroxyapatite were incorporated in the polycaprolactone scaffolds, which were printed by a self-developed melt differential FDM 3D printer. According to their results, microhydroxyapatite particles were agglomerated, while nano-hydroxyapatite were evenly distributed in the polycaprolactone substrate. These phenomena lead to the higher tensile strength and flexural strength of nano-hydroxyapatite-polycaprolactone scaffolds. In addition to uniformity, the hydroxyapatite addition affects the crystallization temperature of the constructs. It was observed that hydroxyapatite increases the crystallization temperature due to chain absorption of PCL

5.1.1.2. Tricalcium phosphate. The other important material in the regeneration of bone defects is tricalcium phosphate. So many different studies focused on the fabrication of its scaffolds in pure or composite form to accelerate bone reconstruction and take advantage of biodegradability. Bose et al. [133] investigated Mg and Si ion release from tricalcium phosphate 3D printed scaffolds. Their analysis confirmed the higher bone and vascular formations as a function of incorporation of ions in the chemical structure of constructs. The Mg2+ can induce cellular adhesion, proliferation, and alkaline phosphatase expression; besides, Si4+ ion release has a stimulatory effect on proliferation, osteogenic differentiation, and mineralization of preosteoblasts like bone cells and mesenchymal stem cells. Si ions have a high impact on collagen synthesize and stabilization, which causes bone healing. It has been shown that Si ion releasing can induce vascular endothelial growth factor expression, up-regulating nitric oxide synthase, and nitric oxide production in human endothelial cells; additionally, produced Mg ion by nitric oxide in endothelial cells can increases angiogenesis. Moreover, it was concluded that tartrate-resistant acid phosphatase activity and the balance between the bone resorption and formation could be modulated by Mg ions. Investigation of Ke et al. [134] on printed MgO-ZnO-tricalcium phosphate scaffolds via binder jet system indicated the formation of a dense core and porous surface with an average diameter of 500 μm. Accordingly, the formation of the rough surface as a result of surface pores and doping Mg and Zn ions in tricalcium constructs lead to an improvement in osteoblast proliferation, which is a promising parameter for orthopedic application. The aim of Pae et al. [116] study was to evaluate the effect of βtricalcium phosphate addition to polycaprolactone scaffolds and study the biocompatibility and osteogenesis. Accordingly, 3D-printed scaffolds with 10 wt.% β-tricalcium phosphate were prepared. The mechanical analysis showed an increase in the level of β-tricalcium phosphate that lead to a decrease in stiffness and compressive yield strength of the constructs from 46.7 ± 1.7 N/mm to 35.7 ± 3.1 N/ mm and from 56.9 ± 2.3 MPa to 46.2 ± 3.1 MPa, respectively. The addition of β-tricalcium phosphate could induce hydrophilicity, osteoconductivity, and cell affinity. It demonstrated enhancement in osteogenic efficacy and new bone formation eight weeks after implantation in rabbit calvarial defects. Decoration of 3D printed β-tricalcium phosphate scaffolds with melatonin as a promising osteogenic factor, increased cell viability and proliferation, promoted osteogenesis significantly, exhibited the highest degree of bone ingrowth, and repaired bone defects as observed in investigation of Miao et al. [135]. They 12

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

used dopamine to loading the melatonin on β-tricalcium phosphate scaffolds by van der Waals forces, hydrogen bonding, and π-π stacking. According to gene expression studies, the level of osteopontin gene expression was improved in melatonin-dopamine-β-tricalcium phosphate 3D printed scaffolds. Also, the expression trends of alkaline phosphatase and collagen type I revealed that the prepared scaffolds could start earlier osteogenic differentiation process. Osteocalcin gene expression, which is related to mineralization, proved high bone mineralizations of the modified matrixes. Furthermore, due to the high vascular endothelial growth factor expression, it can be concluded that scaffolds can promote osteogenesis. The better in-vivo osteogenesis, mineral density, angiogenesis, and blood vessel formation observed in melatonin-dopamine-β-tricalcium phosphate 3D printed scaffold. In another recent study by Ma et al. [136], different weight ratio of bioactive glass was added to the 3D printed β-tricalcium phosphate scaffolds in order to reduce the sintering temperature and to enhance the biodegradability. The mechanical analysis demonstrated that the addition of bioactive glass improves the compressive strength of the scaffolds and the β-tricalcium phosphate with 20 wt.% bioactive glass showed compressive strength and elastic modulus about 8.34 MPa and 208.5 MPa, respectively. In addition, the biodegradability was modulated after bioactive glass addition to the β-tricalcium phosphate scaffolds. Cell proliferation assays approved better behavior of β-tricalcium phosphate-bioactive glass scaffolds compared with pure β-tricalcium phosphate ones. Ben et al. [137] examined another additive to improve the performance of printed β-tricalcium phosphate. They claimed that although β-tricalcium phosphate has an active role in repairing bone tissue, it cannot meet the needs for bone repair completely in pure form. Accordingly, β-tricalcium phosphate powders were dopped by different concentrations of silica for 3D printing the scaffolds and study about the effect of additives on sintering. The aim of this investigation was to obtain a powder for 3D printing procedures with excellent dispersity, flowability, and high density. Results demonstrated that the silica addition reduces agglomeration of the powders and improves the formability. Moreover, silica can absorb on the surfaces of the β-tricalcium phosphate fractures and penetrates into the deep cracks. This phenomenon leads to packaging the newly formed interfaces and inhibit powder recombination. It can enhance grinding efficiently and therefore less agglomerated particles were prepared for 3D printing.

osteopontin, collagen I, bone morphogenic protein-2, osteocalcin, and Runt-related transcription factor 2 were observed after implantation. Strongly enhancement in adhesion and proliferation of the rat bone marrow stromal cells, an increase in osteogenesis and expression of osteogenic genes, resulting in a better bone formation in-vivo. In addition, Masson's trichrome staining visualized more regular and thicker collagen fibers in the prepared constructs compared with calcium sulfate-free scaffolds [12]. The previous investigation on 3D printed pearlcalcium sulfate scaffolds indicated the formation of interconnected porous structure (60 % porosity with an average size of 400 μm) with enhanced compressive strength. The mechanical properties of the cured pure CaSO4 and pearl-CaSO4 were about 5.4 MPa, and 7.8 MPa, respectively. Results revealed that pearl addition to calcium sulfate 3D printed scaffold could improve mechanical strength and meets the needs of trabecular bone (2−12 MPa). Also, the mineralization investigation proved the capability of the scaffolds to deposit apatite with the Ca/P ratio of 1.63 which is near to Ca/P of natural bone apatite. The dissolution of calcium sulfate and pearl as well as binding between organic compounds and Ca2+ ions of pearl creates a suitable microenvironment for hydroxyapatite deposition. Also, 3D printed pearlCaSO4 scaffolds demonstrated higher alkaline phosphatase activity and osteogenic marker expressions such as osteocalcin, collagen I, and osteopontin. Accordingly, One of the advantages of the scaffolds is the rapid curing and self-setting of CaSO4·0.5H2O that leads to the formation of CaSO4·2H2O (CSD). Moreover, the addition of polycaprolactone to the scaffolds as a binder reduced scaffold brittleness. One of the primary considerations about calcium sulfate is its rapid biodegradation compared with the speed of new bone formation. Furthermore, calcium sulfate biodegradation products are acidic that is not suitable for cell interactions. Therefore, the addition of pearl with alkaline nature can modulate the pH. Additionally, the biodegradation ratio of pearl is slower than calcium sulfate, so it can regulate the biodegradation ratio and create a balance between degradation and regeneration ratio. New bone formation within eight weeks in rabbit femoral condyle defects proves the supportive behavior of scaffolds in bone reconstruction [139]. 5.1.3. Calcium silicate The other category of ceramic-based materials with osseointegration potential is calcium silicates, which are known as wollastonite [140]. The potential of silicate ions for the absorption of calcium and phosphate ions in body fluid leads to hydroxyapatite deposition, which is the advantage of a reconstructive bone substitute [141]. The addition of calcium silicate to polymeric substrates increases mechanical properties in addition to accelerating apatite depositions. Furthermore, it was demonstrated that released silicon and calcium ions from calcium silicate could stimulate human mesenchymal stem cell proliferation and osteogenic differentiation [142]. Pei et al. [143] investigated the effect of calcium sulfate addition on the physicochemical and biological properties of 3D printed calcium silicate scaffolds. Calcium silicate was chosen due to its bioactivity and higher mechanical strength compared with other bioactive materials such as bioactive glass. Herein, mesoporous calcium silicate was preferred owing to the potential for more apatite formation, sustained drug delivery, and overstimulation. In order to have hardened ceramic powders and fill the pores, calcium sulfate was added to the scaffolds. The calcium species in calcium sulfate are released quickly; accordingly, hydrolyzation of Ca2+ terminates to produce OH contained group, pH enhancement, and higher biodegradation. Biodegradation of calcium sulfate creates micropores in the scaffolds which support cell migration and fluid flow. According to other studies, lack of bioactivity and positive osteoinduction of calcium sulfate have restricted its application in bone tissue engineering, but in present study calcium sulfate addition to mesoporous calcium silicate did not show negative effect on the bioactivity of the scaffolds, whereas increases its mechanical properties. The composite of calcium silicate and polycaprolactone was printed in different ratios of calcium

5.1.2. Calcium sulfate Calcium sulfate, known as plaster of Paris, is the other classification of bio-inert ceramics, which numerously used in bone reconstruction studies owing to its osteoconductive properties, supporting neovascularization, and potential of bone formation [138]. In this regard, FDM printed poly(3-hydroxybutyrate-co-3-hydroxyvalerate)-calcium sulfate hemihydrate-chitosan scaffolds presented porous microstructure with required mechanical stability. The scaffolds were prepared with different content of calcium sulfate, and the constructs with 20 wt.% calcium sulfate presented maximum stress-strain and breaking strength, while its elongation at the break had the lowest level. The compressive strength of the scaffolds reached 16.6 MPa and revealed the decisive role of calcium sulfate for the improvement of mechanical properties. On the other hand, biological assays proved that scaffolds had a high capability to support cell adhesion and proliferation. The promoted cell adhesion can be attributed to the chitosan coating, which can mimic the cell’s extracellular matrix and provide a suitable microenvironment for cell adhesion, growth, and proliferation. The implanted 3D printed poly (3-hydroxybutyrate-co-3-hydroxyvalerate)-calcium sulfate hemihydrate-chitosan showed typical results in blood examination (white blood cells, red blood cells, hemoglobin, and platelets) and the levels of alanine aminotransferase, aspartate aminotransferase, total protein, blood urea nitrogen creatinine, and uric acid were same as healthy rats. Accordingly, biodegradation products of the scaffolds had any systematic immune responses and organ dysfunction. Besides, the increasing levels of alkaline phosphatase and osteogenic genes, including 13

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

the addition of bioactive glass with proper weight ratio to the 3D printed β-tricalcium phosphate scaffolds can reduce sintering temperature, increase mechanical properties, enhance biodegradability ratio, and promote cell-scaffold interactions [136].

silicate from 0 to 50 wt.%. Results indicated that improvement of hydrophilicity and mechanical stability as a function of calcium silicate content as well as precipitation of bone-like apatite is the strength of prepared scaffolds for bone regeneration. The more calcium silicates lead to higher mechanical properties and higher brittleness of the scaffolds. The high degree of mechanical strength can be attributed to the more homogenous dispersion of calcium silicate in the polymeric matrix. In addition to mechanical properties, the higher concentration of calcium silicates leads to faster biodegradation due to the hydrolyzing process. Moreover, porous 3D printed constructs exhibited ameliorated human Wharton’s Jelly mesenchymal stem cells adhesion, proliferation, and differentiation. The best cell adhesion, spreading, and osteogenic gene expressions were observed on the scaffolds with highest calcium silicate content. Alizarin red staining demonstrated higher calcium deposition on the surface of calcium silicate contained 3D printed scaffolds compared with the pure PCL ones after 2 and 3 weeks. Observation of osteogenic performance and angiogenesis proteins expression proved the applicability of scaffolds for bone tissue engineering [144]. Chen et al. [145] fabricate bioscaffold with suitable ionic components and beneficial for the regeneration of osteochondral defects. So 3D printed lithium-calcium silicate scaffolds with pore diameter between 170−400 μm indicated required mechanical strength (15−40 MPa) and support biomineralization. The composite structures could stimulate osteogenic differentiation of the rat bone marrow mesenchymal stem cells and promote maturation of chondrocytes, which are singe of osteochondral regeneration.

5.2. Polymeric-based scaffolds Providing a printable polymeric ink, solution, filament, granules, etc. which could supply required porosity, mechanical properties, and biodegradation rate is an important parameter that affects efficient bone regeneration. 5.2.1. Natural polymers Among the variety of polymeric materials, natural polymers, i.e., chitosan, collagen, alginate, hyaluronic acid, etc. and their composited have gained lots of attraction for bone regenerative substitute owing to hydrophilicity, biodegradability, and potential for simulation of natural tissue component. The presence of biofunctional molecules in the chemical structure of natural polymers is responsible for this phenomenon [150,151]. 5.2.1.1. Chitosan. Chitosan is a hydrophilic, biocompatible, biodegradable, antibacterial printable polymer which gained lots of attention in tissue engineering, especially in bone regeneration [6,152]. However, the degree of deacetylation of chitosan should be considered for tissue engineering applications. Lower deacetylation create high inflammatory responses due to the high biodegradation ratio of chitosan and the accumulation of monosaccharides, while minimal responses occurred in a high degree of deacetylation [12]. In a novel study, chitosan-calcium phosphate ink showed suitable shear thinning properties for 3D printing by robocasting and based on observation of Caballero et al. [153] the concentration of hydrogel and percentage of dispersed particles can control rheological features of the ink and affect printability and final microstructure of hydrogels. The chitosan and salt solutions were mixed to maintain the calcium to the phosphorous molar ratio of 1.67. In this investigation, the calcium phosphate phase evolved from dicalcium phosphate dihydrate in the extruded inks to hydroxyapatite in the 3D printed scaffolds. The rheological analysis demonstrated that the modulus level was constant overtime for all samples, which can supply the required stability of all samples. Also, according to the shear-thinning behavior, the inks showed dependent shear-thinning and viscosity behavior to chitosan concentration for robocasting. Besides, the investigating of ink properties demonstrated that the chitosan concentration affects the polymer chain entanglement, and the inorganic to organic ratio determines the mineral content and ionic strength of the printed inks. On the other hand, increasing the inorganic compositions can enhance ionic strength due to charge screening and higher levels of Newtonian fluid behavior. The results of this study demonstrated that the composition and ratio of inorganic-organic components, pH, and rheological properties have significant impacts on the final ink behavior and 3D printed structure. Since the mechanical behavior of the chitosan scaffolds cannot meet the requirements of the bone, in another study, chitosan was incorporated with hydroxyapatite and was printed via a robocasting dispensing system. Hydroxyapatite could improve osteoconductivity and control biodegradation of the porous scaffolds beside supplying the mechanical strength. In order to enhance construct stability, NaOH was added to this composition. The optimal concentration of NaOH was achieved 0.75–1.5 % (V/V). Herein, a high concentration of NaOH leads to rapid precipitation and no attachments between the layers. In contrast, the low concentration of NaOH resulted in a low precipitation rate, which was not fast enough to hold its shape. Since the in-vitro behavior of the scaffolds can introduce as underlying factor, the cellscaffold interactions were studied, and according to the results, composite constructs could support cell adhesion and proliferation well [127].

5.1.4. Bioactive glass Bioactive glass is silica-based glass, which is incorporated with P2O5, Na2O, and CaO [146] that have shown strong biomineralization potential for bone applications [123]. 3D printing the bioactive glass scaffolds possess interconnected porous microstructure in which the pore size controlled via 3D printer adjustment. Additionally, cell viability and osteogenesis confirmed the potential of constructs for bone growth induction [14]. Sharifi et al. [147] demonstrated that Cudopped bioactive glass and its incorporation in gelatin-collagen fibrous scaffolds enhance cellular biocompatibility and osteoblastic growth. Also, in another study by Estrada et al. [148], the composite of 45S5 bioactive glass-poly lactic acid was applied for 3D printing of bone tissue engineering scaffolds. According to the SEM observations, the addition of bioactive glass to polylactic acid provides a rough surface that can be suitable for cell anchorage. Besides, the bioactivity evaluations revealed that the presence of bioactive glass could induce a high level of biomineralization to the polylactic acid constructs since one day after soaking the samples in the simulated body fluid the surface was covered with precipitated particles. After three days, cauliflower-like structure was observed, and after seven days, apatite-like crystals cover the surface of matrixes, which is suitable for bone regeneration process. In the investigation of Zhang et al. [149], 3D printed scaffolds composed of mesoporous calcium silicate bioactive glass, gliadin, and polycaprolactone were used for inducing new bone ingrowth. Herein, bioactive glass was added to polycaprolactone scaffolds to improve the bioactivity and biodegradability and gliadin could enhance bio-performance. The printed scaffolds showed pores size about 300 μm and interconnected porosity of 78 %. As expected, gliadin contained scaffolds showed faster biodegradation. The highest level of compressive strength (12.1 MPa) was observed in the scaffolds with higher bioactive glass and gliadin. Accordingly, not only bioactive glass fibers provide mechanical requirements, but also they could enhance MC3T3-E1 cells attachment and proliferation. The collagen staining revealed that collagen type I was expressed more in the samples with more bioactive glass. The ions of mesoporous calcium silicate bioactive glass such as Si, Ca, and Mg promoted the functions of osteoblasts and enhanced osteogenesis both in-vitro and in-vivo. Implantation of constructs in femur defect of rabbit and observation of new bone formation confirmed the applicability of scaffolds for bone repair. Additionally, 14

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

and 604.5 ± 17.1 μm, respectively. Additionally, the mechanical properties of scaffolds were obtained 0.03 ± 0.002 MPa, 0.03 ± 0.003 MPa, and 0.04 ± 0.002 MPa, respectively. Besides, the viability of more number of cells, higher level of alkaline phosphatase expression, and calcium deposition of preosteoblast cells on the collagen-dECM-silk fibroin scaffolds proved its applicability for bone repair.

In the investigation of Morris et al. [65], chitosan- polyethylene glycol diacrylate scaffolds were printed using the stereolithography technique, and the effect of polymer concentration and molecular weight on the properties of printed scaffolds was discussed. According to their observations, a porous microstructure with a pore diameter of 50 μm was prepared, which could support mechanical requirements and supply a biocompatible matrix for cellular adhesion, proliferation, and tissue reconstruction. The minimum concentration for polyethylene glycol diacrylate for 3D printing the scaffolds was 30 % (w/v). The addition of chitosan terminated to reduction of polyethylene glycol diacrylate concentration to 6.5 % (w/v) due to enhancement in viscosity. The result of swelling analysis demonstrated that the addition of both high and low molecular weight chitosan to polyethylene glycol diacrylate increases the swelling ratio. In addition, chitosan enhancement improved mechanical properties seven times more than pure polyethylene glycol diacrylate scaffolds. It was observed that the molecular weight has a great impact on 3D printing accuracy. The low molecular weight chitosan showed higher dimensional accuracy for printing compared with high molecular weight one. The concentration of photo-initiator also is a useful parameter in cell adhesion and viability. The high concentration of photo-initiator (here above 0.0275 % (w/v) leads to low cell viability. In addition to molecular weight, the feed ratio is another useful parameter in chitosan 3D printed structures. It was demonstrated that high feed ratio arises from higher concentration of photo-initiator leads to lower cell adhesion and viability.

5.2.1.4. Alginate. alginate is another natural polymer which has found versatile application in bone tissue engineering. In a study by Luo et al. [156], the alginate-gelatin matrixes with controlled morphology were prepared via a 3D printing setup and coated via nano-hydroxyapatite. Tunable pore structure and presence of apatite coating layer played an undeniable role in the enhancement of young modulus and full-fill bone mechanical requirements. The 3D printed scaffolds had enough structural integrity and retained shape after printing without collapsing. Herein, calcium ions were used as alginate cross-linker. The calcium diffusion inhibited by fast apatite formation. According to the swelling test, the deposited minerals had a low impact on the swelling behavior of the scaffolds due to high swelling capability of alginate and gelatin hydrogels. The compressive strength of the scaffolds achieved 20.7 ± 4.7 MPa and 23.9 ± 1.5 MPa for the scaffolds with 0.5 M and 1 M Na2HPO4, respectively. According to the cell proliferation results, the number of viable cells on the surface of nano hydroxyapatite-coated alginate-gelatin scaffolds were significantly higher than non-coated ones. RT-PCR analysis demonstrated that the nano hydroxyapatite-coated 3D printed scaffolds had higher capability to regulate osteogenic marker genes such as osteopontin, osteocalcin, Runt-related transcription factor, and alkaline phosphatase. On the other hand, the porous nanohydroxyapatite provide suitable place for protein absorption. The more absorbed protein provides more suitable microenvironment for cell adhesion and proliferation due to ligands binding created by proteins for cells. Potential of absorption proteins improved precipitation of component after in-situ biomineralization and act as a stimulator for significant osteogenic differentiation of rat bone marrow stem cells that made the scaffolds suitable candidate for bone reconstruction [156]. In a similar study by Wu et al. [157] on sodium alginate-gelatin bioinks incorporated with mesoporous bioactive glasses. 80 % interconnected porosity with cubic structure, rough surface, and bioactivity was prepared by 3D printing technology. Herein, the naringin or calcitonin gene-related peptide co-printed into the scaffolds and leading to the expression of osteogenic genes that can be an indicator in bone regeneration.

5.2.1.2. Collagen. Collagen is another suitable ink for reconstruction bone injuries. Low-temperature 3D printing provides an opportunity to print collagen-based constructs; however, low mechanical strength restricts its applicability in pure form. Accordingly, to promote the hydrogel properties, silk fibroin and decellularized ECM were blended with collagen, and according to the observation, better mechanical strength and cellular activity were achieved. The osteogenic expression after culturing the pre-osteoblast (MC3T3-E1) cells confirmed its applicability for bone reconstruction [154]. Montalbano et al. [155] simulate bone structure by printing the collagen type I hydrogels incorporated with bioactive components (strontium-containing mesoporous bioactive glasses). The shear-thinning properties of hydrogels proved its printability. According to the results of the bioactivity, the acidic groups of collagen fibers (derived from aspartic and glutamic acid) provide more sites for nucleation of hydroxyapatite that can enhance the bioactivity of the constructs. The 3D printed scaffolds showed a high swelling ratio, and this can be related to the ability of the construct to form hydrogen bonding with water molecules. According to the rheological investigations, the prepared solution has pseudo-plastic (shear thinning) behavior. So the rapid decrease in material viscosity leads to an increase in shear rate from 50 Pa·s at 0.01 s−1 to 0.28 Pa·s at 200 s−1. The observed phenomenon mainly attributed to the chain orientation of collagen, which showed shear thinning behavior to applied stress. Furthermore, osteogenic expression of the hybrid constructs that is a promising factor in bone healing was improved as a function of strontium ion release.

5.2.2. Synthetic polymers Despite the benefits of natural materials, controllable biodegradation, higher mechanical properties, and convenient processing of synthetic polymers and the potential of endotoxicity in natural polymers resulted in the versatile application of synthetic polymers and their copolymers in bone healing issue [158]. 5.2.2.1. Polycaprolactone. The low melting points of polycaprolactone facilitated its application for 3D printing the scaffolds. Polycaprolactone also has resilient physical properties that are near to natural bones [144]. Although polycaprolactone is a polymer with proper mechanical properties for bone tissue engineering, its hydrophobic nature, low degradation ratio, and weak cell-interactions limited its application. In order to increase hydrophilicity or inducing bioactivity, it usually mixed with other polymers, ceramics, or metals. In this regard, Moncal et al. [159] fabricate polycaprolactone-poly lactic-co-glycolic acid-hydroxyapatite bioink for 3D printing the scaffold. Based on observation, composite inks supported mechanical needs and improved cellular performance compared with pure polycaprolactone one. Moreover, the positive role of printed matrixes on bone regeneration in an animal model is the other strength of

5.2.1.3. Silk fibroin. Silk fibroin can be considered as a proper candidate for bone regeneration due to its biocompatibility, lower immunogenic, lack of inflammatory responses, and suitable mechanical properties. Furthermore, it showed a significant influence on inducing calcium salt deposition, which can accelerate bone reconstruction; besides, its capability to improve cell-interactions cannot be ignored. So, it can be a favorable choice among other polymers, especially in blending with ceramics such as hydroxyapatite. It has observed that silk fibroin degradation reduces pH, which may activate osteoclast in acidic conditions [130]. Lee et al. [154] used silk fibroin to fabricate micro/ nanoporous collagen-dECM-silk fibroin scaffolds for bone tissue engineering. The macrospore size of pure collagen, collagen-dECM, collagen-dECM-silk fibroin were 600.6 ± 22.1 μm, 614.1 ± 25.3 μm, 15

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

Fig. 5. Optical image (a) and scanning electron microscopy image (b) of 3D printed polycaprolactone scaffolds. Scanning electron microscopy micrographs of chitosan infiltrated in porous polycaprolactone constructs (c) (Reproduced content is open access) [162].

strontium hydroxyapatite indicated better properties for bone repair. Accordingly, the cultured cells on the surface of the scaffolds showed better adhesion and proliferation in the samples containing strontium. Additionally, the more alkaline phosphatase level for strontiumhydroxyapatite contained scaffolds proved the higher ability of the scaffolds for bone reconstruction. Inducing differentiation of bone marrow-derived mesenchymal stem cells, improving alkaline phosphatase activity, and expression of the osteo-related genes in presence of scaffolds confirmed the initial potential of hybrid constructs for bone healing. Regeneration of in-vivo cranial defect proved all the in-vitro claims and showed applicability of constructs in the orthopedic field. In another study, thermoresponsive chitosan incorporated with rabbit bone marrow mesenchymal stem cells and bone morphogenetic protein-2 and was injected in 3D printed polycaprolactone scaffolds in order to betterment of cellular performance and osteoinductivity (Fig. 5). Their observation confirmed that not only 3D printed constructs provide substrate for improved cell adhesion and proliferation, but also hybrid structure with cells and growth factors support osteogenesis and new bone formation more [162].

printable inks that was proved by observing biomineralized layer and vascular network formation. In a similar investigation, 3D printed (FDM technology) polycaprolactone-β-tricalcium phosphate scaffolds were fabricated by Bruyas et al. [100] for orthopedic application. According to their observation, β-tricalcium phosphate concentration can improve cellular proliferation through increasing surface roughness and enhance osteogenic differentiation. Besides, the mechanical properties of the scaffolds were increased after β-tricalcium phosphate additions. The young’s modulus was 264, 355, 495, and 1140 MPa, respectively, for the polycaprolactone scaffolds contains 0, 20, 40, and 60 wt.% β-tricalcium phosphate, respectively. The biodegradation investigation of the scaffolds demonstrated that by adjusting the ceramic content, a suitable biodegradation ratio could be obtained. The proliferation ratio of the cultured cells on the surface of the scaffolds was higher in ceramic contained scaffolds. The more ceramic content increases roughness, which provides larger surface area for cell anchorage. Moreover, the alkaline phosphatase level was increased by β-tricalcium phosphate addition to the scaffolds. Also, the potential of FDM technology to control pore size was the strength of 3D printing methods and indicated that a reduction in porosity terminate to an enhancement in young modulus. The other investigation on polycaprolactone-based scaffolds for bone regeneration indicated a significant bone osteogenic performance. Herein, a composite matrix composed of polycaprolactone and silanated silica particles were prepared via melt-blending procedure and 3D bioprinting method. Accordingly, homogeneous distribution of silica particles leading to an improvement in the mechanical stability of the constructs and increase young modulus 1.4 times higher than pure polycaprolactone scaffolds. Silica is an effective material in bone tissue engineering scaffolds due to the interactions of silanol groups with calcium and phosphate ions and formation of calcium phosphate layers. Moreover, the homogenous distribution of these particles improved the wettability; besides, the water absorption was higher in the sacffolds with higher silica content. Additionally, the cell viability on the ceramic contained 3D printed scaffolds was significantly higher than pure polycaprolactone scaffolds. Increasing the level of alkaline phosphatase level and bone related gene expression were observed by additions of ceramic. The more silica absorbed, the more calcium on the surface of the scaffolds deposited. The accumulated calcium provided more favorable environment for bone differentiation and maturation. Osteocalcin is a biomarker and expresses in differentiated bone cells. This protein has the most important function in bone resorption and bone reformation during changing osteoblast to osteocyte. Osteocalcin was detected in all samples after 21 days, but its expression was significantly higher in samples with higher silica. The supportive behavior of silica from precipitation of hydroxyapatite-like layers and osteogenic differentiation proves the capability of scaffolds for bone therapies [160]. In the novel investigation by Liu et al. [161], polycaprolactonestrontium contained hydroxyapatite were prepared by 3D printing technology. The strontium degree showed great impact on the synthesized nano-hydroxyapatite shape. The scaffolds with 30 wt.%

5.2.2.2. Poly lactic-co-glycolic acid/ polylactic acid. Poly lactic-coglycolic acid is one of the suitable polymers for bone tissue engineering due to its biocompatibility, controllable biodegradation, and mechanical properties by modulating copolymer compositions [163]. Lai et al. [164] used low-temperature rapid prototyping techniques to fabricate poly lactic-co-glycolic acid-β-tricalcium phosphate-magnesium scaffolds for the regeneration of bone defects (Fig. 6). SEM-EDS analysis proved the homogenous distribution of the magnesium and tricalcium phosphate in the structure. The porosity and pore size of the scaffolds was analyzed, and the results demonstrated that the porosity, pore size, and pore connectivity was not significantly different for scaffolds with or without magnesium. The scaffolds young’s modulus and compressive strength of the scaffolds with 15 wt.% magnesium were 114.9 ± 15.4 and 3.7 ± 0.2 MPa, respectively, which is higher than magnesium-free scaffolds. Besides, the 3D printed constructs could enhance blood perfusion and improve vessel formation after implantation of scaffolds in the rabbit model. Ingrowth of new bone with suitable mechanical properties 12 weeks after implantation was the strength of novel constructs with osteogenic and angiogenic abilities. Although Mg ion concentration is a big concern, the serum Mg ion releasing analysis tests demonstrated normal release level with no immune responses after surgery. In the other study, scaffold with interconnected pores and osteoinductivity potential was prepared through the polydopamine coating on 3D printed poly lactic-co-glycolic acid scaffolds. Herein, polydopamine mediate BMP-2, and ponericin G1 immobilization leads to improvement in preosteoblasts (MC3T3-E1) attachment and proliferation and regulates osteogenic differentiation [165]. 3Dprinted poly lactic-co-glycolic acid-TiO2 scaffolds showed the porous structure and supply the required mechanical strength for bone repair 16

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

Fig. 6. Low-temperature rapid prototyping technique to fabricate poly lactic-co-glycolic acid -β-tricalcium phosphate-magnesium scaffolds for the regeneration of bone defects (Reproduced content is open access) [164].

support required mechanical stiffness of the bone and supply bioactivity, which is necessary for bone regeneration. The compressive strength was achieved 49.3 ± 0.9, 49.7 ± 1.7, 48.5 ± 1.4, and 50.3 ± 1.6 MPa, respectively for the Ti-6Al-4 V, Ti-6Al-4V-chitosan scaffolds with 0, 0.2, and 0.5 wt.% magnesium-calcium silicate. Ca and Si ion releasing revealed that the ion releasing was higher for the samples with 0.2 and 0.5 wt.% magnesium and calcium silicate. The Ca release can modulate cell behavior, proliferation, and differentiation. On the other hand, Si ion releasing enhances collagen producing, alkaline phosphatase activities, and osteocalcin level. The cellular assays demonstrated that the cells cultured on the surfaces of the scaffolds with 0.2 and 0.5 wt.% magnesium and calcium silicate had higher cell activity. Moreover, the cell spreading, alkaline phosphatase level, and calcium deposition were highly better on the surface of the scaffolds with 0.5 wt.% magnesium and calcium silicate. In another study, strontium ion incorporated zeolite was used for inducing strong bioactivity to 3D printed titanium scaffolds. Releasing strontium ion provide an opportunity for ion exchange with body fluid and promotes apatite formation. The strong ability of the scaffolds to support alkaline phosphatase expression and improvement of osteogenesis and osteointegration indicate the applicability of 3D printed scaffolds to use as a bone reconstructive implants. Formation of new bone, especially around the pores of scaffolds in a rabbit model within four weeks proved the ability of functionalized scaffolds for orthopedic applications [175]. In other investigations by Tsai et al. [176], the surface of 3D printed titanium scaffolds was coated via chitosan-magnesium-calcium silicate composition in order to induce bioactivity to the constructs. Accordingly, the exhibited morphology and pore structure of the scaffolds played a positive role in hard tissue regeneration. Moreover, the coating layer terminated to a higher degree of hydrophilicity and mechanical stability according to the requirement of natural bone. Modification of the scaffolds with magnesium contained layer improved cell proliferation and differentiation and exhibit both osteogenesis and mineralization downstream. Promoted regeneration of the critical size bone defects of rabbits in magnesium contained constructs proved the applicability of the 3D printed scaffolds for orthopedic application. Biodegradable and bioactive metallic scaffolds composed of magnesium were prepared via 3D printing technology. Results showed fabrication of microporous scaffolds with 65 % porosity and pore diameter about 450 μm and high stable constructs through printing the paste (magnesium powder, 2-hydroxyethyl cellulose, polyethylene glycol, glycerol trioleate, ammonia, deionized water, and absolute ethanol) by pneumatic extrusion printing setup. High mechanical strength (∼0.87 MPa)

while the presence of TiO2 nanoparticles enhanced the mechanical properties more. Arising wettability as a function of TiO2 addition affects osteoblast proliferation. Besides, alkaline phosphatase expression level confirmed the potential of 3D printed scaffolds for bone substitute [166]. Polylactic acid is a thermoplastic aliphatic polyester that is derived from agricultural products. Its biocompatibility, high stiffness, thermoplasticity, availability, and low cost made it suitable in different areas of tissue engineering, especially bone regeneration [167]. Although polylactic acid is a well-known polymer in bone tissue engineering, it affects the inflammatory responses. This phenomenon is mainly attributed to acidic biodegradation by-products of polylactic acid [168]. Teixeira et al. [169] immobilized collagen type I on polydopaminecoated poly(lactic acid) scaffolds, which were fabricated by 3D printing technology and introduced it as an applicable construct for bone tissue engineering. The 3D printed poly (lactic acid) scaffolds had the porosity of 60 ± 1.5 %, which is in the range of cancellous bone. The mechanical investigations demonstrated that compressive strength and young’s modulus were 9.47 ± 0.48 MPa and 0.40 ± 0.006 GPa, respectively. Herein, the synergistic effect of polydopamine and collagen type I lead to rapid cell response during the initial seven days, ECM deposition within the first fourteen days, and alkaline phosphatase expression during twenty-one days after culturing the mesenchymal stem cells proved the applicability of the constructs for bone repair.

5.3. Metallic-based scaffolds High mechanical stability and foreseeable fracture toughness of the metallic biomaterials made them favorable for replacement or regeneration of the injured bone [170,171]. Both bioactivity potential and biodegradation behavior, which are required in bone tissue engineering constructs, have restricted the application of metals as a temporary matrix. So the most used metals for printing the reconstructive bone substitute are titanium, magnesium, and their alloys [172]. Ti and its alloys, especially Ti-6Al-4 V, are considered as the optimal materials for producing orthopedic implants due to biocompatibility, corrosion resistance, and mechanical properties [173]. Maleksaeedi et al. [174] fabricated titanium scaffolds with customized pores and geometry using an inkjet 3D printer, and the surface of the scaffolds were coated through electrochemical deposition of hydroxyapatite. The result of their analysis confirmed that prepared constructs could 17

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

parameters, a suitable scaffold for bone tissue engineering can be designed. Bioprinting a functional tissue/organ with the type of cells, proteins, or growth factors, etc. is a complicated topic that needs more effort to progress [181]. Further progress in multi-material printing the scaffolds to support all the physicochemical, mechanical, and biological requirements, printing a cell-laden matrix with higher accuracy and possibility of brings extensive development in bone reconstruction. Although a variety of hydrogels have been used to full-fill this dream and received excellent results, the possibility of printing ECM based bioinks with a higher degree of simulation of natural tissue is under evaluation. In fact, a printable and stable bioink which simulate physicochemical features of natural bone with a suitable rheological performance for tolerating applied stresses is required. Since the number of human models has been restricted extent of research, translation of the discoveries in the laboratory to human patients needs more effort even though a high level of success was observed in the human investigations, which are evaluating the functionality of the constructs. Accordingly, due to accessibility to animal models, in-vivo experiments have been concentrated for determining the effectiveness of scaffolds before implantation in the human body. It should be noted that the recent investigations and the result of the experiment on animals indicated the feasibility of this technology for reconstruction of lesions. Accordingly, regeneration of cranial defect in the goats 24 weeks after surgery through the usage of bioactive scaffolds showed the decisive role of 3D printed constructs for bone regeneration [182]. Laser bioprinting of the 30 layers nano-hydroxyapatite leads to regeneration of 4 mm calvarial defect in a mouse model and X-Ray tomography observations confirmed repair the defects within 3 months in 96 % of mousse [183]. Additionally, an increase in in-vivo osteogenesis of rat adipose stem cells which are incorporated in collagen I-contained gels led to the improvement of regeneration in 15-mm length critical-sized segmental radial defect [184]. Extrusion-based bioprinted alginate-demineralized bone matrixes-gelatin-based bioinks which was crosslinked via CaSO4 indicated a high degree of accuracy (mean surface errors < 0.1 mm) that prove the applicability of the constructs for insitu regeneration of defective sites (4 mm-deep chondral defects, 4 mmdeep condyle, and 4 mm bone for osteochondral defect) [185]. In another study, Matrigel-alginate-biphasic calcium phosphate microparticulate systems were incorporated with goat bone marrow mesenchymal stem cells and epithelial cells in order to bioprinting a matrix for subcutaneous implantation in mice. ECM production, vascularization, and integration with the natural tissue was the indication of in-vivo regeneration [186]. New bone formation in calvarial bone defects in rats after 5 months was achieved by Kang et al. through usage of human amniotic fluid-derived stem cell-laden fibrin-based gels [26]. Furthermore, mature bone was formed in calvarial bone defects in mice within 2 months as a result of implantation of bioprinted-mesenchymal stromal cells-laden collagen-nanohydroxyapatite discs [187]. Laser-assisted bioprinting collagen containing mesenchymal stem cells and vascular endothelial growth factor was used for in-situ organization of printed endothelial cells to facilitate prevascularization and improve calvarial bone reconstruction in mouse model. During the 2 months vascularization rate and regeneration rate was +203.6 % and +294.1 % for disc pattern, respectively, and +355 % and +602.1 % for crossed circle pattern, respectively. Based on observation of Kérourédan et al. [188], in-situ printed constructs showed effectiveness for regeneration of bone defects. Accordingly, there are number of studies on the animals which evaluate the decisive role of single/multi-materials printed scaffolds and their microstructure, cell-scaffolds interactions, etc. on efficient regeneration of the defective sites. Based on the in-vivo results, positive interaction was observed between 3D printed scaffolds and cells or biomolecules; additionally, osteoconductive scaffolds and the osteoinductive properties of the cells indicate synergistic effect in regeneration of lesions. Further to the applied materials, both internal and external microstructure of the scaffolds, including, printing pattern,

and controllable biodegradation rate (∼10 mm/year) made them favorable for bone regeneration [177]. 6. Challenges, future perspectives, and conclusion Although there are a variety of technologies to fabricate reconstructive bone substitute [178–180], 3D printing has emerged and led to a significant revolution in the tissue engineering scaffolds owing to controllable geometry and microstructure, preparation of patientspecific constructs, fabrication of multi-layered and multi-material scaffolds with a range of properties. In this review, recent advances in 3D printing technologies for the regeneration of defective sites in the bone were evaluated. Novel research on 3D printed bone substitute over the past decade indicates the versatile application of new generation scaffolds with controllable geometry and microstructure in the bone regeneration area. So, the main aim of scientists in this filed is to propose a promising strategy for promoting osteogenic expression, vascularization, and efficient bone ingrowth, which can be achievable by selecting proper 3D printing techniques, designing a suitable microstructure, and choosing a novel, printable, and bioactive materials. However, the same as any new technologies, there are some considerable challenges and disadvantages in this area. One of the challenges in this area is the usage of organic additives and binders or photoinitiators in some 3D printing methods. These components cannot remove entirely after heating or sintering processes and may compromise biocompatibility of the constructs. Also, applying the temperature in some of the technologies restrict applicability of materials. Besides, in powder-based techniques, the powder features and build parameters affect the porous microstructure and influence dimensional accuracy, especially when pore size less than 300 μm is required. Trapped powders inside the small pores take part in sintering process and change the pore size and interconnectivity and finally prevent appropriate cellular migration. Additionally, requirement of some techniques to post-processing can negatively affect the final geometry, microstructure, and properties and restrict applicability of different kinds of materials. There are different 3D printing technologies introduced in this paper, and all of them have advantages and disadvantages. However, the lack of potential to print the cells and signaling molecules is the limitation of all the introduced technologies. Although bioprinting techniques had developments extensively, it needs more evaluation to receive excellent results for efficient regeneration. However, in the mentioned methods, according to the target tissue, types of applied materials, required resolution and dimensional accuracy, cost of production, etc., different strategies can be applied for the fabrication of reconstructive substitutes. It appears that each of the polymeric, metal, ceramic scaffolds can show some positive points and level of applicability for bone regeneration. However, bioactive components with potential to support mineralization of hydroxyapatite-like layers are preferred; besides, the load bearing behavior of final constructs should be considered to prevent stress shielding. Accordingly, composite structures offer better properties compared with the pure composition of scaffolds. However, among these scaffolds, it seems that calcium phosphate scaffolds can produce better properties due to their similarity to the bone mineral phase. According to Jiao et al. [132], adding ceramics such as hydroxyapatite to the polymeric substrates enhances the mechanical properties, and the composite of these materials can be a better choice for the bone application. Herein, the polymeric matrixes can improve the biological properties of final matrix. On the other hand, Mg and Si ion releasing scaffolds can improve bone healing and angiogenesis [133], which can be loaded in the scaffolds. Nevertheless, for successful 3D printing of bone scaffolds, many parameters such as feeding rate, the additives, rheological properties of materials, pore size, porosity and interconnectivity, released ions, degradation products, etc. should be considered. By carefully selecting materials and adjusting print 18

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

References

porosity, pore size, interconnectivity, surface roughness, etc. influence in-vivo performance of synthetic matrixes through acting as a barrier for fibrous tissue, affecting cell colonization, and ECM secretion [189]. Since the in-vivo vascularization within the implants happen slowly (rate of < 1 mm per day) [190], the restriction in access of cells in center of constructs to required nutrients and cell viability is a major concern in this field. Besides, need to co-culture of both osteogenic cells and epithelial cells to achieve both bone and vascular network formation may provide a problem since some stimulatory parameters such as hypoxia in angiogenesis can inhibit osteogenesis [191]. However, the ability of encapsulation of viable cells, supplying survivability of the cells, and carry out the bone-related proteins, drug, and growth factors for regulating osteogenic expression and complete formation of the vascular network for the nutrition of neo-tissue need more investigation to be commercial [192]. Although 3D printed scaffolds reach the highest similarity to natural tissue compared with other conventional technologies; however, there is a long way to fabricate functional scaffolds or simulated vital tissue/ organ. The accelerated development of 3D printed and bioprinted bone substitute for the regeneration of the defects over the recent years demonstrated that the products would be available commercially for helping the patients who suffer from bone disease.

[1] X. Cui, T. Boland, D.D. D’Lima, M.K. Lotz, Thermal inkjet printing in tissue engineering and regenerative medicine, Recent Patents Drug Deliv. Formul. 6 (2012) 149–155. [2] R.A. Wolfe, E.C. Roys, R.M. Merion, Trends in organ donation and transplantation in the United States, 1999–2008, Am. J. Transplant. 10 (2010) 961–972, https:// doi.org/10.1111/j.1600-6143.2010.03021.x. [3] M.M. Safikhani, A. Zamanian, F. Ghorbani, Synergistic effects of retinoic acid and graphene oxide on the physicochemical and in-vitro properties of electrospun polyurethane scaffolds for bone tissue engineering, E-Polymers 17 (2017) 363–371, https://doi.org/10.1515/epoly-2016-0304. [4] A. Ehterami, M. Kazemi, B. Nazari, P. Saraeian, M. Azami, Fabrication and characterization of highly porous barium titanate based scaffold coated by Gel/HA nanocomposite with high piezoelectric coefficient for bone tissue engineering applications, J. Mech. Behav. Biomed. Mater. 79 (2018) 195–202, https://doi.org/ 10.1016/j.jmbbm.2017.12.034. [5] A. Huang, X. Peng, L. Geng, L. Zhang, K. Huang, B. Chen, Z. Gu, T. Kuang, Electrospun poly (butylene succinate)/cellulose nanocrystals bio-nanocomposite scaffolds for tissue engineering: preparation, characterization and in vitro evaluation, Polym. Test. 71 (2018) 101–109, https://doi.org/10.1016/j. polymertesting.2018.08.027. [6] A. Aidun, A. Safaei Firoozabady, M. Moharrami, A. Ahmadi, N. Haghighipour, S. Bonakdar, S. Faghihi, Graphene oxide incorporated polycaprolactone/chitosan/ collagen electrospun scaffold: enhanced osteogenic properties for bone tissue engineering, Artif. Organs 43 (2019), https://doi.org/10.1111/aor.13474 aor. 13474. [7] F. Ghorbani, A. Zamanian, A. Behnamghader, M.D. Joupari, A facile method to synthesize mussel-inspired polydopamine nanospheres as an active template for in situ formation of biomimetic hydroxyapatite, Mater. Sci. Eng. C 94 (2019) 729–739, https://doi.org/10.1016/j.msec.2018.10.010. [8] F. Ghorbani, A. Zamanian, A. Behnamghader, M.D. Joupari, Microwave-induced rapid formation of biomimetic hydroxyapatite coating on gelatin-siloxane hybrid microspheres in 10X-SBF solution, E-Polymers 18 (2018) 247–255, https://doi. org/10.1515/epoly-2017-0196. [9] F. Ghorbani, A. Zamanian, A. Behnamghader, M. Daliri-Joupari, Bone-like hydroxyapatite mineralization on the bio-inspired PDA nanoparticles using microwave irradiation, Surf. Interfaces 15 (2019) 38–42, https://doi.org/10.1016/j. surfin.2019.01.007. [10] B. Derby, Printing and prototyping of tissues and scaffolds, Science (80-.) 338 (2012) 921–926, https://doi.org/10.1126/science.1226340. [11] R. Meißner, L. Bertol, M.A.U. Rehman, L.A.L. dos Santos, A.R. Boccaccini, Bioprinted 3D calcium phosphate scaffolds with gentamicin releasing capability, Ceram. Int. 45 (2019) 7090–7094, https://doi.org/10.1016/j.ceramint.2018.12. 212. [12] X. Ye, L. Li, Z. Lin, W. Yang, M. Duan, L. Chen, Y. Xia, Z. Chen, Y. Lu, Y. Zhang, Integrating 3D-printed PHBV/Calcium sulfate hemihydrate scaffold and chitosan hydrogel for enhanced osteogenic property, Carbohydr. Polym. 202 (2018) 106–114, https://doi.org/10.1016/j.carbpol.2018.08.117. [13] X. Feng, Y. Wu, F. Bao, X. Chen, J. Gong, Comparison of 3D-printed mesoporous calcium silicate/polycaprolactone and mesoporous Bioacive glass/polycaprolactone scaffolds for bone regeneration, Microporous Mesoporous Mater. 278 (2019) 348–353, https://doi.org/10.1016/j.micromeso.2019.01.007. [14] L. Li, H. Hu, Y. Zhu, M. Zhu, Z. Liu, 3D-printed ternary SiO2CaO P2O5 bioglassceramic scaffolds with tunable compositions and properties for bone regeneration, Ceram. Int. 45 (2019) 10997–11005, https://doi.org/10.1016/j.ceramint.2019. 02.183. [15] A. Sola, J. Bertacchini, D. D’Avella, L. Anselmi, T. Maraldi, S. Marmiroli, M. Messori, Development of solvent-casting particulate leaching (SCPL) polymer scaffolds as improved three-dimensional supports to mimic the bone marrow niche, Mater. Sci. Eng. C 96 (2019) 153–165, https://doi.org/10.1016/j.msec. 2018.10.086. [16] I. Manavitehrani, T.Y.L. Le, S. Daly, Y. Wang, P.K. Maitz, A. Schindeler, F. Dehghani, Formation of porous biodegradable scaffolds based on poly(propylene carbonate) using gas foaming technology, Mater. Sci. Eng. C 96 (2019) 824–830, https://doi.org/10.1016/j.msec.2018.11.088. [17] F. Ghorbani, A. Zamanian, A. Aidun, Conductive electrospun polyurethane-polyaniline scaffolds coated with poly(vinyl alcohol)-GPTMS under oxygen plasma surface modification, Mater. Today Commun. (2019) 100752, https://doi.org/10. 1016/j.mtcomm.2019.100752. [18] A. Zamanian, F. Ghorbani, H. Nojehdehian, Morphological comparison of PLGA/ Gelatin scaffolds produced by freeze casting and freeze drying methods, Appl. Mech. Mater. 467 (2013) 108–111, https://doi.org/10.4028/www.scientific.net/ AMM.467.108. [19] N. Abzan, M. Kharaziha, S. Labbaf, Development of three-dimensional piezoelectric polyvinylidene fluoride-graphene oxide scaffold by non-solvent induced phase separation method for nerve tissue engineering, Mater. Des. 167 (2019) 107636, , https://doi.org/10.1016/j.matdes.2019.107636. [20] F. Ghorbani, A. Zamanian, A. Shams, A. Shamoosi, A. Aidun, Fabrication and characterisation of super-paramagnetic responsive PLGA–gelatine–magnetite scaffolds with the unidirectional porous structure: a physicochemical, mechanical, and in vitro evaluation, IET Nanobiotechnol. 13 (2019) 860–867, https://doi.org/ 10.1049/iet-nbt.2018.5305. [21] B.S.I. Gibson, D. Rosen, Additive Manufacturing Technologies: 3D Printing, Rapid Prototyping, and Direct Digital Manufacturing, Springer, 2014.

Author statement Farnaz Ghorbani: Ideas and evolution of overarching goals and aims -Development and creation of models -Conducting an investigation process, specifically data collection -Preparation, creation and presentation of the published work, specifically writing the initial draft -Preparation, creation and presentation of the published work by those from the original research group, specifically critical review, commentary or revision Dejian Li: Coordination responsibility for the activity planning Shuo Ni: Conducting an investigation process, specifically data collection Ying Zhou: Conducting an investigation process, specifically data collection Baoqing Yu: Leadership responsibility for the activity planning and execution, including mentorship external to the core team -Acquisition of the financial support for the project leading to this publication

Declaration of Competing Interest The authors whose names are listed certify that they have NO affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patentlicensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.

Acknowledgment This work was supported by the National Natural Science Foundation of China (Grant No. 81971753), the Outstanding Clinical Discipline Project of Shanghai Pudong (Grant No. PWYgy2018-09), the Key Disciplines Group Construction Project of Pudong Health Bureau of Shanghai (Grant No. PWZxq2017–11), and Program for Outstanding Leader of Shanghai (Grant No. 046). 19

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

[22] J. Liu, L. Li, H. Suo, M. Yan, J. Yin, J. Fu, 3D printing of biomimetic multi-layered GelMA/nHA scaffold for osteochondral defect repair, Mater. Des. 171 (2019) 107708, , https://doi.org/10.1016/j.matdes.2019.107708. [23] A. Farzadi, V. Waran, M. Solati-Hashjin, Z.A.A. Rahman, M. Asadi, N.A.A. Osman, Effect of layer printing delay on mechanical properties and dimensional accuracy of 3D printed porous prototypes in bone tissue engineering, Ceram. Int. 41 (2015) 8320–8330, https://doi.org/10.1016/j.ceramint.2015.03.004. [24] N. Jones, Science in three dimensions: the print revolution, Nature 487 (2012) 22–23, https://doi.org/10.1038/487022a. [25] W.L. Ng, C.K. Chua, Y.-F. Shen, Print me an organ! Why we are not there yet, Prog. Polym. Sci. 97 (2019) 101145, , https://doi.org/10.1016/j.progpolymsci.2019. 101145. [26] H.-W. Kang, S.J. Lee, I.K. Ko, C. Kengla, J.J. Yoo, A. Atala, A 3D bioprinting system to produce human-scale tissue constructs with structural integrity, Nat. Biotechnol. 34 (2016) 312–319, https://doi.org/10.1038/nbt.3413. [27] F. Kabirian, B. Ditkowski, A. Zamanian, M.F. Hoylaerts, M. Mozafari, R. Heying, Controlled NO-Release from 3D-Printed small-diameter vascular grafts prevents platelet activation and bacterial infectivity, ACS Biomater. Sci. Eng. 5 (2019) 2284–2296, https://doi.org/10.1021/acsbiomaterials.9b00220. [28] C. Hull, Apparatus for Production of Three-Dimensional Object by Stereolithography, U. S. Patent 4,575,330, 1986. [29] T.N. Vo, F.K. Kasper, A.G. Mikos, Strategies for controlled delivery of growth factors and cells for bone regeneration, Adv. Drug Deliv. Rev. 64 (2012) 1292–1309, https://doi.org/10.1016/j.addr.2012.01.016. [30] J. Banks, Adding value in additive manufacturing: researchers in the United Kingdom and Europe look to 3D printing for customization, IEEE Pulse 4 (2013) 22–26, https://doi.org/10.1109/MPUL.2013.2279617. [31] M.B. Habal, Biomaterials and bioengineering handbook, J. Craniofac. Surg. 12 (2001) 200, https://doi.org/10.1097/00001665-200103000-00022. [32] A.L. Boskey, Noncollagenous matrix proteins and their role in mineralization, Bone Miner. 6 (1989) 111–123. [33] S. Viguet-Carrin, P. Garnero, P.D. Delmas, The role of collagen in bone strength, Osteoporos. Int. 17 (2006) 319–336, https://doi.org/10.1007/s00198-0052035-9. [34] S. Morgan, A.A. Poundarik, D. Vashishth, Do Non-collagenous Proteins Affect Skeletal Mechanical Properties? Calcif. Tissue Int. 97 (2015) 281–291, https://doi. org/10.1007/s00223-015-0016-3. [35] F.I. Wolf, A. Cittadini, Magnesium in cell proliferation and differentiation, Front Biosci. 4 (1999) D607–D617. [36] M. Yamaguchi, Role of zinc in bone formation and bone resorption, J. Trace Elem. Exp. Med. 11 (1998) 119–135 doi:10.1002/(SICI)1520-670X(1998)11:2/ 3 < 119::AID-JTRA5 > 3.0.CO;2-3.. [37] N. Chattopadhyay, S.J. Quinn, O. Kifor, C. Ye, E.M. Brown, The calcium-sensing receptor (CaR) is involved in strontium ranelate-induced osteoblast proliferation, Biochem. Pharmacol. 74 (2007) 438–447. [38] N.E. Balaban, J.E. Bobick, The Handy Anatomy Answer Book, Visible Ink Press, 2008. [39] B. Young, P. Woodford, G. O’Dowd, Wheater’s Functional Histology E-Book: A Text and Colour Atlas, Elsevier Health Sciences, (2013). [40] Y. Hashimoto, S. Funamoto, T. Kimura, K. Nam, T. Fujisato, A. Kishida, The effect of decellularized bone/bone marrow produced by high-hydrostatic pressurization on the osteogenic differentiation of mesenchymal stem cells, Biomaterials 32 (2011) 7060–7067, https://doi.org/10.1016/j.biomaterials.2011.06.008. [41] D.J. Lee, S. Diachina, Y.T. Lee, L. Zhao, R. Zou, N. Tang, H. Han, X. Chen, C.-C. Ko, Decellularized bone matrix grafts for calvaria regeneration, J. Tissue Eng. 7 (2016) 204173141668030, , https://doi.org/10.1177/2041731416680306. [42] B.P. Hung, B.A. Naved, E.L. Nyberg, M. Dias, C.A. Holmes, J.H. Elisseeff, A.H. Dorafshar, W.L. Grayson, Three-dimensional printing of bone extracellular matrix for craniofacial regeneration, ACS Biomater. Sci. Eng. 2 (2016) 1806–1816, https://doi.org/10.1021/acsbiomaterials.6b00101. [43] S. Tuli, A. Singh, The osteoninductive property of decalcified bone matrix. An experimental study, J. Bone Joint Surg. Br. 60-B (1978) 116–123, https://doi.org/ 10.1302/0301-620X.60B1.342532. [44] T. Komori, Regulation of osteoblast differentiation by transcription factors, J. Cell. Biochem. 99 (2006) 1233–1239, https://doi.org/10.1002/jcb.20958. [45] Z. Schwartz, T. Weesner, S. Van Dijk, D.L. Cochran, J.T. Mellonig, C.H. Lohmann, D.L. Carnes, M. Goldstein, D.D. Dean, B.D. Boyan, Ability of deproteinized cancellous bovine bone to induce new bone formation, J. Periodontol. 71 (2000) 1258–1269, https://doi.org/10.1902/jop.2000.71.8.1258. [46] E.B. Stephan, D. Jiang, S. Lynch, P. Bush, R. Dziak, Anorganic bovine bone supports osteoblastic cell attachment and proliferation, J. Periodontol. 70 (1999) 364–369, https://doi.org/10.1902/jop.1999.70.4.364. [47] P. Amerio, G. Vianale, M. Reale, R. Muraro, A. Tulli, A. Piattelli, The effect of deproteinized bovine bone on osteoblast growth factors and proinflammatory cytokine production, Clin. Oral Implants Res. 21 (2010) 650–655, https://doi.org/ 10.1111/j.1600-0501.2009.01881.x. [48] E. Ruiz-Hitzky, M. Darder, P. Aranda, K. Ariga, Advances in biomimetic and nanostructured biohybrid materials, Adv. Mater. 22 (2010) 323–336, https://doi. org/10.1002/adma.200901134. [49] M.S. Rahman, N. Akhtar, H.M. Jamil, R.S. Banik, S.M. Asaduzzaman, TGF-β/BMP signaling and other molecular events: regulation of osteoblastogenesis and bone formation, Bone Res. 3 (2015) 15005, https://doi.org/10.1038/boneres.2015.5. [50] A.R. Derubeis, R. Cancedda, Bone marrow stromal cells (BMSCs) in bone engineering: limitations and recent advances, Ann. Biomed. Eng. 32 (2004) 160–165, https://doi.org/10.1023/B:ABME.0000007800.89194.95. [51] A. Asti, L. Gioglio, Natural and synthetic biodegradable polymers: different

[52]

[53]

[54]

[55] [56] [57]

[58] [59]

[60]

[61]

[62]

[63]

[64]

[65]

[66]

[67]

[68]

[69]

[70]

[71]

[72]

[73]

[74]

[75]

20

scaffolds for cell expansion and tissue formation, Int. J. Artif. Organs 37 (2014) 187–205 doi:10.530/ijao.5000307. S. Tajbakhsh, F. Hajiali, A comprehensive study on the fabrication and properties of biocomposites of poly(lactic acid)/ceramics for bone tissue engineering, Mater. Sci. Eng. C Mater. Biol. Appl. 70 (2017) 897–912, https://doi.org/10.1016/j.msec. 2016.09.008. N.E.E. Fedorovich, J. Alblas, W.E.E. Hennink, F.C. Öner, W.J.A.J.A. Dhert, F.C. Oner, W.J.A.J.A. Dhert, F.C. Öner, W.J.A.J.A. Dhert, Organ printing: the future of bone regeneration? Trends Biotechnol. 29 (2011) 601–606, https://doi. org/10.1016/j.tibtech.2011.07.001. S. Patra, V. Young, A review of 3D printing techniques and the future in biofabrication of bioprinted tissue, Cell Biochem. Biophys. 74 (2016) 93–98, https://doi. org/10.1007/s12013-016-0730-0. C.L. Ventola, Medical applications for 3D printing: current and projected uses, P T 39 (2014) 704–711, https://doi.org/10.1016/j.infsof.2008.09.005. H.N. Chia, B.M. Wu, Recent advances in 3D printing of biomaterials, J. Biol. Eng. 9 (2015) 4, https://doi.org/10.1186/s13036-015-0001-4. J.A. Inzana, D. Olvera, S.M. Fuller, J.P. Kelly, O.A. Graeve, E.M. Schwarz, S.L. Kates, H.A. Awad, 3D printing of composite calcium phosphate and collagen scaffolds for bone regeneration, Biomaterials 35 (2014) 4026–4034, https://doi. org/10.1016/j.biomaterials.2014.01.064. M.G. Mitchell, Applications of 3D printing in cell biology, Cell Biol, Elsevier, 2016, pp. 121–162, https://doi.org/10.1016/B978-0-12-801853-8.00002-8. O. Guillaume, M.A. Geven, C.M. Sprecher, V.A. Stadelmann, D.W. Grijpma, T.T. Tang, L. Qin, Y. Lai, M. Alini, J.D. de Bruijn, H. Yuan, R.G. Richards, D. Eglin, Surface-enrichment with hydroxyapatite nanoparticles in stereolithography-fabricated composite polymer scaffolds promotes bone repair, Acta Biomater. (2017), https://doi.org/10.1016/j.actbio.2017.03.006. E.L. Doubrovski, E.Y. Tsai, D. Dikovsky, J.M.P. Geraedts, H. Herr, N. Oxman, Voxel-based fabrication through material property mapping: a design method for bitmap printing, Comput. Des. 60 (2015) 3–13, https://doi.org/10.1016/j.cad. 2014.05.010. A. Colin, J.Y. Boire, A novel tool for rapid prototyping and development of simple 3D medical image processing applications on PCs, Comput. Methods Programs Biomed. 53 (1997) 87–92, https://doi.org/10.1016/j.minpro.2006.07.009. F.P.W. Melchels, J. Feijen, D.W. Grijpma, A review on stereolithography and its applications in biomedical engineering, Biomaterials 31 (2010) 6121–6130, https://doi.org/10.1016/j.biomaterials.2010.04.050. V. Chan, P. Zorlutuna, J.H. Jeong, H. Kong, R. Bashir, Three-dimensional photopatterning of hydrogels using stereolithography for long-term cell encapsulation, Lab Chip 10 (2010) 2062, https://doi.org/10.1039/c004285d. E. Sachlos, J.T. Czernuszka, Making tissue engineering scaffolds work. Review on the application of solid freeform fabrication technology to the production of tissue engineering scaffolds, Eur. Cells Mater. 5 (2003) 29–40, https://doi.org/10. 22203/eCM.v005a03. V.B. Morris, S. Nimbalkar, M. Younesi, P. McClellan, O. Akkus, mechanical properties, cytocompatibility and manufacturability of chitosan:PEGDA hybrid-gel scaffolds by stereolithography, Ann. Biomed. Eng. (2016) 1–11, https://doi.org/ 10.1007/s10439-016-1643-1. Z. Wang, H. Kumar, Z. Tian, X. Jin, J.F. Holzman, F. Menard, K. Kim, Visible light photoinitiation of cell-adhesive gelatin methacryloyl hydrogels for stereolithography 3D bioprinting, ACS Appl. Mater. Interfaces 10 (2018) 26859–26869, https://doi.org/10.1021/acsami.8b06607. V. Melissinaki, aa Gill, I. Ortega, M. Vamvakaki, A. Ranella, J.W. Haycock, C. Fotakis, M. Farsari, F. Claeyssens, Direct laser writing of 3D scaffolds for neural tissue engineering applications, Biofabrication 3 (2011) 045005, , https://doi.org/ 10.1088/1758-5082/3/4/045005. S. Wadnap, S. Krishnamoorthy, Z. Zhang, C. Xu, Biofabrication of 3D cell-encapsulated tubular constructs using dynamic optical projection stereolithography, J. Mater. Sci. Mater. Med. 30 (2019) 36, https://doi.org/10.1007/s10856-0196239-5. S. Miao, H. Cui, M. Nowicki, S. Lee, J. Almeida, X. Zhou, W. Zhu, X. Yao, F. Masood, M.W. Plesniak, M. Mohiuddin, L.G. Zhang, Photolithographic-stereolithographic-tandem fabrication of 4D smart scaffolds for improved stem cell cardiomyogenic differentiation, Biofabrication 10 (2018) 035007, , https://doi. org/10.1088/1758-5090/aabe0b. Y. Luo, G. Le Fer, D. Dean, M.L. Becker, 3D printing of poly(propylene fumarate) oligomers: evaluation of resin viscosity, printing characteristics and mechanical properties, Biomacromolecules 20 (2019) 1699–1708, https://doi.org/10.1021/ acs.biomac.9b00076. J.P. Fisher, T.A. Holland, D. Dean, P.S. Engel, A.G. Mikos, Synthesis and properties of photocross-linked poly(propylene fumarate) scaffolds, J. Biomater. Sci. Polym. Ed. 12 (2001) 673–687, https://doi.org/10.1163/156856201316883476. K.S. Anseth, V.R. Shastri, R. Langer, Photopolymerizable degradable polyanhydrides with osteocompatibility, Nat. Biotechnol. 17 (1999) 156–159, https:// doi.org/10.1038/6152. S.A. Skoog, P.L. Goering, R.J. Narayan, Stereolithography in tissue engineering, J. Mater. Sci. Mater. Med. 25 (2014) 845–856, https://doi.org/10.1007/s10856013-5107-y. K. Nettleton, D. Luong, A.P. Kleinfehn, L. Savariau, C. Premanandan, M.L. Becker, Molecular mass‐dependent resorption and bone regeneration of 3D printed PPF scaffolds in a critical‐sized rat cranial defect model, Adv. Healthc. Mater. 8 (2019) 1900646, , https://doi.org/10.1002/adhm.201900646. Z. Feng, Y. Li, L. Hao, Y. Yang, T. Tang, D. Tang, W. Xiong, Graphene-reinforced biodegradable resin composites for stereolithographic 3D printing of bone structure scaffolds, J. Nanomater. 2019 (2019) 1–13, https://doi.org/10.1155/2019/

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

[98] A. Haryńska, J. Kucinska-Lipka, A. Sulowska, I. Gubanska, M. Kostrzewa, H. Janik, Medical-grade PCL based polyurethane system for FDM 3D printing—characterization and fabrication, Materials (Basel) 12 (2019) 887, https://doi.org/10.3390/ ma12060887. [99] W. Lin, H. Shen, G. Xu, L. Zhang, J. Fu, X. Deng, Single-layer temperature-adjusting transition method to improve the bond strength of 3D-printed PCL/PLA parts, Compos. Part A Appl. Sci. Manuf. 115 (2018) 22–30, https://doi.org/10. 1016/j.compositesa.2018.09.008. [100] A. Bruyas, F. Lou, A.M. Stahl, M. Gardner, W. Maloney, S. Goodman, Y.P. Yang, Systematic characterization of 3D-printed PCL/β-TCP scaffolds for biomedical devices and bone tissue engineering: influence of composition and porosity, J. Mater. Res. 33 (2018) 1948–1959, https://doi.org/10.1557/jmr.2018.112. [101] H. Dodziuk, Applications of 3D printing in healthcare, Polish J. Cardio-Thoracic Surg. 3 (2016) 283–293, https://doi.org/10.5114/kitp.2016.62625. [102] A.-V. Do, B. Khorsand, S.M. Geary, A.K. Salem, 3D printing of scaffolds for tissue regeneration applications, Adv. Healthc. Mater. 4 (2015) 1742–1762, https://doi. org/10.1002/adhm.201500168. [103] J. Yu, Y. Xu, S. Li, G.V. Seifert, M.L. Becker, Three-dimensional printing of nano Hydroxyapatite/Poly(ester urea) composite scaffolds with enhanced bioactivity, Biomacromolecules 18 (2017) 4171–4183, https://doi.org/10.1021/acs.biomac. 7b01222. [104] A.N. Rindone, E. Nyberg, W.L. Grayson, 3D-printing Composite Polycaprolactonedecellularized Bone Matrix Scaffolds for Bone Tissue Engineering Applications, (2017), https://doi.org/10.1007/7651. [105] C. Yang, X. Tian, D. Li, Y. Cao, F. Zhao, C. Shi, Influence of thermal processing conditions in 3D printing on the crystallinity and mechanical properties of PEEK material, J. Mater. Process. Technol. 248 (2017) 1–7, https://doi.org/10.1016/j. jmatprotec.2017.04.027. [106] G. Chen, N. Chen, Q. Wang, Fabrication and properties of poly(vinyl alcohol)/βtricalcium phosphate composite scaffolds via fused deposition modeling for bone tissue engineering, Compos. Sci. Technol. 172 (2019) 17–28, https://doi.org/10. 1016/j.compscitech.2019.01.004. [107] F. Ghorbani, A. Zamanian, Oriented microstructure in neural tissue engineering : a review, Tissue Sci. Eng. 7 (2016) 2–5, https://doi.org/10.4172/2157-7552. 1000182. [108] J. Zhang, S. Zhao, M. Zhu, Y. Zhu, Y. Zhang, Z. Liu, C. Zhang, 3D-printed magnetic Fe3O4/MBG/PCL composite scaffolds with multifunctionality of bone regeneration, local anticancer drug delivery and hyperthermia, J. Mater. Chem. B 2 (2014) 7583–7595, https://doi.org/10.1039/c4tb01063a. [109] S.Y. Heo, S.C. Ko, G.W. Oh, N. Kim, I.W. Choi, W.S. Park, W.K. Jung, Fabrication and characterization of the 3D-printed polycaprolactone/fish bone extract scaffolds for bone tissue regeneration, J. Biomed. Mater. Res. - Part B Appl. Biomater. (2018) 1–8, https://doi.org/10.1002/jbm.b.34286. [110] K. Kim, A. Yeatts, D. Dean, J.P. Fisher, Stereolithographic bone scaffold design parameters: osteogenic differentiation and signal expression, Tissue Eng. Part B Rev. 16 (2010) 523–539, https://doi.org/10.1089/ten.teb.2010.0171. [111] J.H. Shim, M.C. Yoon, C.M. Jeong, J. Jang, S.I. Jeong, D.W. Cho, J.B. Huh, Efficacy of rhBMP-2 loaded PCL/PLGA/β-TCP guided bone regeneration membrane fabricated by 3D printing technology for reconstruction of calvaria defects in rabbit, Biomed. Mater. 9 (2014), https://doi.org/10.1088/1748-6041/9/6/065006. [112] M.E. Hoque, W.Y. San, F. Wei, S. Li, M.-H. Huang, M. Vert, D.W. Hutmacher, Processing of polycaprolactone and polycaprolactone-based copolymers into 3D scaffolds, and their cellular responses, Tissue Eng. Part A 15 (2009) 3013–3024, https://doi.org/10.1089/ten.tea.2008.0355. [113] J.W. Lee, G. Ahn, J.Y. Kim, D.-W. Cho, Evaluating cell proliferation based on internal pore size and 3D scaffold architecture fabricated using solid freeform fabrication technology, J. Mater. Sci. Mater. Med. 21 (2010) 3195–3205, https://doi. org/10.1007/s10856-010-4173-7. [114] K.M. Ferlin, M.E. Prendergast, M.L. Miller, S. David, J.P. Fisher, Influence of 3D printed porous architecture on mesenchymal stem cell enrichment, Acta Biomater. (2016), https://doi.org/10.1016/j.actbio.2016.01.007. [115] B. Gong, S. Cui, Y. Zhao, Y. Sun, Q. Ding, Strain-controlled fatigue behaviors of porous PLA-based scaffolds by 3D-printing technology, J. Biomater. Sci. Polym. Ed. 28 (2017) 2196–2204, https://doi.org/10.1080/09205063.2017.1388993. [116] H.C. Pae, J.H. Kang, J.K. Cha, J.S. Lee, J.W. Paik, U.W. Jung, B.H. Kim, S.H. Choi, 3D-printed polycaprolactone scaffold mixed with β-tricalcium phosphate as a bone regenerative material in rabbit calvarial defects, J. Biomed. Mater. Res. - Part B Appl. Biomater. (2018) 1–10, https://doi.org/10.1002/jbm.b.34218. [117] F. Pati, T.-H. Song, G. Rijal, J. Jang, S. Won, D. Cho, S.W. Kim, D. Cho, Ornamenting 3D printed scaffolds with cell-laid extracellular matrix for bone tissue regeneration, Biomaterials 37 (2015) 230–241, https://doi.org/10.1016/j. biomaterials.2014.10.012. [118] R. Gutta, R.A. Baker, A.A. Bartolucci, P.J. Louis, Barrier membranes used for ridge augmentation: is there an optimal pore size? J. Oral Maxillofac. Surg. 67 (2009) 1218–1225, https://doi.org/10.1016/j.joms.2008.11.022. [119] J.E. Salvatore, W.S. Gilmer, M. Kashgarian, W.R. Barbee, An experimental study of the influence of pore size of implanted polyurethane sponges upon subsequent tissue formation, Surg. Gynecol. Obstet. 112 (1961) 463–468 http://www.ncbi. nlm.nih.gov/pubmed/13745795. [120] T. Billiet, M. Vandenhaute, J. Schelfhout, S. Van Vlierberghe, P. Dubruel, A review of trends and limitations in hydrogel-rapid prototyping for tissue engineering, Biomaterials 33 (2012) 6020–6041, https://doi.org/10.1016/j.biomaterials.2012. 04.050. [121] N. Nagarajan, A. Dupret-Bories, E. Karabulut, P. Zorlutuna, N.E. Vrana, Enabling personalized implant and controllable biosystem development through 3D printing, Biotechnol. Adv. 36 (2018) 521–533, https://doi.org/10.1016/j.

9710264. [76] B.J. Green, K.S. Worthington, J.R. Thompson, S.J. Bunn, M. Rethwisch, E.E. Kaalberg, C. Jiao, L.A. Wiley, R.F. Mullins, E.M. Stone, E.H. Sohn, B.A. Tucker, C.A. Guymon, Effect of molecular weight and functionality on acrylated poly(caprolactone) for stereolithography and biomedical applications, Biomacromolecules 19 (2018) 3682–3692, https://doi.org/10.1021/acs.biomac. 8b00784. [77] F.P.W. Melchels, J. Feijen, D.W. Grijpma, A poly(d,l-lactide) resin for the preparation of tissue engineering scaffolds by stereolithography, Biomaterials 30 (2009) 3801–3809, https://doi.org/10.1016/j.biomaterials.2009.03.055. [78] L. Elomaa, S. Teixeira, R. Hakala, H. Korhonen, D.W. Grijpma, J.V. Seppälä, Preparation of poly(ε-caprolactone)-based tissue engineering scaffolds by stereolithography, Acta Biomater. 7 (2011) 3850–3856, https://doi.org/10.1016/j. actbio.2011.06.039. [79] N.J. Castro, J. O’Brien, L.G. Zhang, Integrating biologically inspired nanomaterials and table-top stereolithography for 3D printed biomimetic osteochondral scaffolds, Nanoscale 7 (2015) 14010–14022, https://doi.org/10.1039/C5NR03425F. [80] E.A. Aisenbrey, A. Tomaschke, E. Kleinjan, A. Muralidharan, C. Pascual-Garrido, R.R. McLeod, V.L. Ferguson, S.J. Bryant, A stereolithography-based 3D printed hybrid scaffold for in situ cartilage defect repair, Macromol. Biosci. 18 (2018) 1700267, , https://doi.org/10.1002/mabi.201700267. [81] Y.-J. Seol, T.-Y. Kang, D.-W. Cho, Solid freeform fabrication technology applied to tissue engineering with various biomaterials, Soft Matter 8 (2012) 1730, https:// doi.org/10.1039/c1sm06863f. [82] W.-Y. Yeong, W.Y. Yeong, C.-K. Chua, C.K. Chua, K.-F. Leong, K.F. Leong, M. Chandrasekaran, Rapid prototyping in tissue engineering: challenges and potential, Trends Biotechnol. 22 (2004) 643–652, https://doi.org/10.1016/j.tibtech. 2004.10.004. [83] G.V. Salmoria, R.V. Pereira, M.C. Fredel, A.P.M. Casadei, Properties of PLDLA/ bioglass scaffolds produced by selective laser sintering, Polym. Bull. 75 (2018) 1299–1309, https://doi.org/10.1007/s00289-017-2093-0. [84] M. Ramu, M. Ananthasubramanian, T. Kumaresan, R. Gandhinathan, S. Jothi, Optimization of the configuration of porous bone scaffolds made of Polyamide/ Hydroxyapatite composites using Selective Laser Sintering for tissue engineering applications, Biomed. Mater. Eng. 29 (2018) 739–755, https://doi.org/10.3233/ BME-181020. [85] A. Mazzoli, Selective laser sintering in biomedical engineering, Med. Biol. Eng. Comput. 51 (2013) 245–256, https://doi.org/10.1007/s11517-012-1001-x. [86] K. Tan, C. Chua, K. Leong, C. Cheah, P. Cheang, M. Abu Bakar, S. Cha, Scaffold development using selective laser sintering of polyetheretherketone–hydroxyapatite biocomposite blends, Biomaterials 24 (2003) 3115–3123, https://doi.org/10.1016/S0142-9612(03)00131-5. [87] C. Gayer, J. Ritter, M. Bullemer, S. Grom, L. Jauer, W. Meiners, A. Pfister, F. Reinauer, M. Vučak, K. Wissenbach, H. Fischer, R. Poprawe, J.H. Schleifenbaum, Development of a solvent-free polylactide/calcium carbonate composite for selective laser sintering of bone tissue engineering scaffolds, Mater. Sci. Eng. C 101 (2019) 660–673, https://doi.org/10.1016/j.msec.2019.03.101. [88] F.E. Wiria, K.F. Leong, C.K. Chua, Y. Liu, Poly-ε-caprolactone/hydroxyapatite for tissue engineering scaffold fabrication via selective laser sintering, Acta Biomater. 3 (2007) 1–12, https://doi.org/10.1016/j.actbio.2006.07.008. [89] C. Gayer, J. Abert, M. Bullemer, S. Grom, L. Jauer, W. Meiners, F. Reinauer, M. Vučak, K. Wissenbach, R. Poprawe, J.H. Schleifenbaum, H. Fischer, Influence of the material properties of a poly(D,L-lactide)/β-tricalcium phosphate composite on the processability by selective laser sintering, J. Mech. Behav. Biomed. Mater. 87 (2018) 267–278, https://doi.org/10.1016/j.jmbbm.2018.07.021. [90] S.H. Diermann, M. Lu, Y. Zhao, L.-J. Vandi, M. Dargusch, H. Huang, Synthesis, microstructure, and mechanical behaviour of a unique porous PHBV scaffold manufactured using selective laser sintering, J. Mech. Behav. Biomed. Mater. 84 (2018) 151–160, https://doi.org/10.1016/j.jmbbm.2018.05.007. [91] T. Wei, X.-W. Zhang, H.-Q. Sun, M.-Y. Mao, Selective laser sintering and performances of porous titanium implants, Hua Xi Kou Qiang Yi Xue Za Zhi 36 (2018) 532–538, https://doi.org/10.7518/hxkq.2018.05.013. [92] I. Zein, D.W. Hutmacher, K.C. Tan, S.H. Teoh, Fused deposition modeling of novel scaffold architectures for tissue engineering applications, Biomaterials 23 (2002) 1169–1185, https://doi.org/10.1016/S0142-9612(01)00232-0. [93] S. Naghieh, M.R. Karamooz Ravari, M. Badrossamay, E. Foroozmehr, M. Kadkhodaei, Numerical investigation of the mechanical properties of the additive manufactured bone scaffolds fabricated by FDM: the effect of layer penetration and post-heating, J. Mech. Behav. Biomed. Mater. 59 (2016) 241–250, https://doi.org/10.1016/j.jmbbm.2016.01.031. [94] W. Wu, P. Geng, G. Li, D. Zhao, H. Zhang, J. Zhao, Influence of layer thickness and raster angle on the mechanical properties of 3D-Printed PEEK and a comparative mechanical study between PEEK and ABS, Materials (Basel) 8 (2015) 5834–5846, https://doi.org/10.3390/ma8095271. [95] A. Grémare, V. Guduric, R. Bareille, V. Heroguez, S. Latour, N. L’heureux, J.C. Fricain, S. Catros, D. Le Nihouannen, Characterization of printed PLA scaffolds for bone tissue engineering, J. Biomed. Mater. Res. Part A 106 (2018) 887–894, https://doi.org/10.1002/jbm.a.36289. [96] J. Korpela, A. Kokkari, H. Korhonen, M. Malin, T. Närhi, J. Seppälä, Biodegradable and bioactive porous scaffold structures prepared using fused deposition modeling, J. Biomed. Mater. Res. Part B Appl. Biomater. 101B (2013) 610–619, https://doi.org/10.1002/jbm.b.32863. [97] E. Carlier, S. Marquette, C. Peerboom, L. Denis, S. Benali, J.-M. Raquez, K. Amighi, J. Goole, Investigation of the parameters used in fused deposition modeling of poly (lactic acid) to optimize 3D printing sessions, Int. J. Pharm. 565 (2019) 367–377, https://doi.org/10.1016/j.ijpharm.2019.05.008.

21

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

biotechadv.2018.02.004. [122] H. Lee, S. Ahn, L.J. Bonassar, G. Kim, Cell(MC3T3-E1)-Printed Poly(ε -caprolactone)/alginate hybrid scaffolds for tissue regeneration, Macromol. Rapid Commun. 34 (2013) 142–149, https://doi.org/10.1002/marc.201200524. [123] N. Arabi, A. Zamanian, S.N. Rashvand, F. Ghorbani, The tunable porous structure of gelatin-bioglass nanocomposite scaffolds for bone tissue engineering applications: physicochemical, mechanical, and in-vitro properties, Macromol. Mater. Eng. 303 (2018) 1700539, , https://doi.org/10.1002/mame.201700539. [124] S. Aliramaji, A. Zamanian, M. Mozafari, Super-paramagnetic responsive silk fibroin/chitosan/magnetite scaffolds with tunable pore structures for bone tissue engineering applications, Mater. Sci. Eng. C 70 (2017) 736–744, https://doi.org/ 10.1016/j.msec.2016.09.039. [125] M. Ebrahimi, M.G. Botelho, S.V. Dorozhkin, Biphasic calcium phosphates bioceramics (HA/TCP): concept, physicochemical properties and the impact of standardization of study protocols in biomaterials research, Mater. Sci. Eng. C 71 (2017) 1293–1312, https://doi.org/10.1016/j.msec.2016.11.039. [126] C. Sharma, A.K. Dinda, P.D. Potdar, C.F. Chou, N.C. Mishra, Fabrication and characterization of novel nano-biocomposite scaffold of chitosan-gelatin-alginatehydroxyapatite for bone tissue engineering, Mater. Sci. Eng. C 64 (2016) 416–427, https://doi.org/10.1016/j.msec.2016.03.060. [127] T. Ang, F.S. Sultana, D. Hutmacher, Y. Wong, J.Y. Fuh, X. Mo, H. Loh, E. Burdet, S. Teoh, Fabrication of 3D chitosan–hydroxyapatite scaffolds using a robotic dispensing system, Mater. Sci. Eng. C 20 (2002) 35–42, https://doi.org/10.1016/ S0928-4931(02)00010-3. [128] S. S, C. P, Improvement of mechanical properties of 3d printed hydroxyapatite scaffolds by polymeric infiltration, Bioceram. Dev. Appl. 3 (2016) 10–12, https:// doi.org/10.4172/2090-5025.s1-012. [129] D.J. Lee, J. Kwon, Y. Kim, X. Wang, T. Wu, Y. Lee, S. Kim, P. Miguez, C. Ko, Effect of pore size in bone regeneration using polydopamine‐laced hydroxyapatite collagen calcium silicate scaffolds fabricated by 3D mould printing technology, Orthod. Craniofac. Res. 22 (2019) 127–133, https://doi.org/10.1111/ocr.12261. [130] T. Huang, C. Fan, M. Zhu, Y. Zhu, W. Zhang, L. Li, 3D-printed scaffolds of biomineralized hydroxyapatite nanocomposite on silk fibroin for improving bone regeneration, Appl. Surf. Sci. 467–468 (2019) 345–353, https://doi.org/10.1016/ j.apsusc.2018.10.166. [131] A. Zamanian, S. Farhangdoust, M. Yasaei, M. Khorami, M. Hafezi, The effect of particle size on the mechanical and microstructural properties of freeze-casted macroporous hydroxyapatite scaffolds, Int. J. Appl. Ceram. Technol. 11 (2014) 12–21, https://doi.org/10.1111/ijac.12031. [132] Z. Jiao, B. Luo, S. Xiang, H. Ma, Y. Yu, W. Yang, 3D printing of HA / PCL composite tissue engineering scaffolds, Adv. Ind. Eng. Polym. Res. (2019), https://doi.org/ 10.1016/j.aiepr.2019.09.003. [133] S. Bose, S. Tarafder, A. Bandyopadhyay, Effect of chemistry on osteogenesis and angiogenesis towards bone tissue engineering using 3D printed scaffolds, Ann. Biomed. Eng. 45 (2017) 261–272, https://doi.org/10.1007/s10439-016-1646-y. [134] D. Ke, S. Bose, Effects of pore distribution and chemistry on physical, mechanical, and biological properties of tricalcium phosphate scaffolds by binder-jet 3D printing, Addit. Manuf. 22 (2018) 111–117, https://doi.org/10.1016/j.addma. 2018.04.020. [135] Y. Miao, Y. Chen, X. Liu, J. Diao, N. Zhao, X. Shi, Y. Wang, Melatonin decorated 3D-printed beta-tricalcium phosphate scaffolds promoting bone regeneration in a rat calvarial defect model, J. Mater. Chem. B (2019), https://doi.org/10.1039/ c8tb03361g. [136] Y. Ma, H. Dai, X. Huang, Y. Long, 3D printing of bioglass-reinforced β-TCP porous bioceramic scaffolds, J. Mater. Sci. 54 (2019) 10437–10446, https://doi.org/10. 1007/s10853-019-03632-3. [137] Y. Ben, L. Zhang, S. Wei, T. Zhou, Z. Li, H. Yang, C. Wong, H. Chen, Improved forming performance of β-TCP powders by doping silica for 3D ceramic printing, J. Mater. Sci. Mater. Electron. 28 (2017) 5391–5397, https://doi.org/10.1007/ s10854-016-6199-1. [138] Y. Kumar, C, calcium sulfate as bone graft substitute in the treatment of osseous bone defects, a prospective study, J. Clin. Diagn. Res. (2013), https://doi.org/10. 7860/JCDR/2013/6404.3791. [139] X. Du, B. Yu, P. Pei, H. Ding, B. Yu, Y. Zhu, 3D printing of pearl/CaSO 4 composite scaffolds for bone regeneration, J. Mater. Chem. B 6 (2018) 499–509, https://doi. org/10.1039/C7TB02667F. [140] M. Sanmartin de Almeida, G.Vde O. Fernandes, A.M. de Oliveira, J.M. Granjeiro, Calcium silicate as a graft material for bone fractures: a systematic review, J. Int. Med. Res. 46 (2018) 2537–2548, https://doi.org/10.1177/0300060518770940. [141] F. Ghorbani, A. Zamanian, A. Behnamghader, M. Daliri Joupari, A novel pathway for in situ synthesis of modified gelatin microspheres by silane coupling agents as a bioactive platform, J. Appl. Polym. Sci. 135 (2018) 46739, https://doi.org/10. 1002/app.46739. [142] C. Shuai, W. Guo, C. Gao, Y. Yang, Y. Xu, L. Liu, T. Qin, H. Sun, S. Yang, P. Feng, P. Wu, Calcium silicate improved bioactivity and mechanical properties of poly(3hydroxybutyrate-co-3-hydroxyvalerate) scaffolds, Polymers (Basel) 9 (2017) 1–15, https://doi.org/10.3390/polym9050175. [143] P. Pei, D. Wei, M. Zhu, X. Du, Y. Zhu, The effect of calcium sulfate incorporation on physiochemical and biological properties of 3D-printed mesoporous calcium silicate cement scaffolds, Microporous Mesoporous Mater. 241 (2017) 11–20, https://doi.org/10.1016/j.micromeso.2016.11.031. [144] Y.-H.H. Lin, Y.-C.C. Chiu, Y.-F.F. Shen, Y.-H.A.H.A. Wu, M.-Y.Y. Shie, Bioactive calcium silicate/poly-ε-caprolactone composite scaffolds 3D printed under mild conditions for bone tissue engineering, J. Mater. Sci. Mater. Med. 29 (2018) 11, https://doi.org/10.1007/s10856-017-6020-6. [145] L. Chen, C. Deng, J. Li, Q. Yao, J. Chang, L. Wang, C. Wu, 3D printing of a lithium-

[146]

[147]

[148]

[149]

[150]

[151]

[152]

[153]

[154]

[155]

[156]

[157]

[158]

[159]

[160]

[161]

[162]

[163]

[164]

[165]

[166]

22

calcium-silicate crystal bioscaffold with dual bioactivities for osteochondral interface reconstruction, Biomaterials 196 (2019) 138–150, https://doi.org/10. 1016/j.biomaterials.2018.04.005. M.E. Pecquet Goad, D.L. Goad, Biomedical materials and devices, Haschek Rousseaux’s Handb. Toxicol. Pathol, Elsevier, 2013, pp. 783–806, https://doi.org/ 10.1016/B978-0-12-415759-0.00026-1. E. Sharifi, M. Azami, A.M. Kajbafzadeh, F. Moztarzadeh, R. Faridi-Majidi, A. Shamousi, R. Karimi, J. Ai, Preparation of a biomimetic composite scaffold from gelatin/collagen and bioactive glass fibers for bone tissue engineering, Mater. Sci. Eng. C 59 (2016) 533–541, https://doi.org/10.1016/j.msec.2015.09.037. S. Adriana Martel Estrada, I. Olivas Armendáriz, A. Torres García, J. Francisco Hernández Paz, C. Alejandra Rodríguez González, Evaluation of in vitro bioactivity of 45S5 bioactive glass / poly lactic acid scaffolds produced by 3D printing, Int. J. Compos. Mater. 7 (2017) 144–149, https://doi.org/10.5923/j.cmaterials. 20170705.03. Y. Zhang, W. Yu, Z. Ba, S. Cui, J. Wei, H. Li, 3D-printed scaffolds of mesoporous bioglass/gliadin/polycaprolactone ternary composite for enhancement of compressive strength, degradability, cell responses and new bone tissue ingrowth, Int. J. Nanomed. 13 (2018) 5433–5447, https://doi.org/10.2147/IJN.S164869. A.R. Akkineni, Y. Luo, M. Schumacher, B. Nies, A. Lode, M. Gelinsky, 3D plotting of growth factor loaded calcium phosphate cement scaffolds, Acta Biomater. 27 (2015) 264–274, https://doi.org/10.1016/j.actbio.2015.08.036. Z. Shafaei, B. Ghalandari, A. Vaseghi, A. Divsalar, T. Haertlé, A.A. Saboury, L. Sawyer, β-Lactoglobulin: an efficient nanocarrier for advanced delivery systems, Nanomed. Nanotechnol. Biol. Med. 13 (2017) 1685–1692, https://doi.org/10. 1016/j.nano.2017.03.007. M. Sahranavard, A. Zamanian, F. Ghorbani, M.H. Shahrezaee, A Critical Review on Three Dimensional-Printed Chitosan Hydrogels for Development of Tissue Engineering, Bioprinting, 2019, p. e00063, https://doi.org/10.1016/j.bprint. 2019.e00063. S.S. Ramirez Caballero, E. Saiz, A. Montembault, S. Tadier, E. Maire, L. David, T. Delair, L. Grémillard, 3-D printing of chitosan-calcium phosphate inks: rheology, interactions and characterization, J. Mater. Sci. Mater. Med. 30 (2019) 6, https://doi.org/10.1007/s10856-018-6201-y. H. Lee, G.H. Yang, M. Kim, J. Lee, J. Huh, G. Kim, Fabrication of micro/nanoporous collagen/dECM/silk-fibroin biocomposite scaffolds using a low temperature 3D printing process for bone tissue regeneration, Mater. Sci. Eng. C 84 (2018) 140–147, https://doi.org/10.1016/j.msec.2017.11.013. G. Montalbano, S. Fiorilli, A. Caneschi, C. Vitale-Brovarone, Type I collagen and strontium-containing mesoporous glass particles as hybrid material for 3D printing of bone-like materials, Materials (Basel) 11 (2018) 700, https://doi.org/10.3390/ ma11050700. Y. Luo, Y. Li, X. Qin, Q. Wa, 3D printing of concentrated alginate/gelatin scaffolds with homogeneous nano apatite coating for bone tissue engineering, Mater. Des. 146 (2018) 12–19, https://doi.org/10.1016/j.matdes.2018.03.002. J. Wu, G. Miao, Z. Zheng, Z. Li, W. Ren, C. Wu, Y. Li, Z. Huang, L. Yang, L. Guo, 3D printing mesoporous bioactive glass/sodium alginate/gelatin sustained release scaffolds for bone repair, J. Biomater. Appl. 33 (2019) 755–765, https://doi.org/ 10.1177/0885328218810269. S. Oh, Fabrication and characterization of hydrophilic poly(lactic-co-glycolic acid)/poly(vinyl alcohol) blend cell scaffolds by melt-molding particulate-leaching method, Biomaterials 24 (2003) 4011–4021, https://doi.org/10.1016/S01429612(03)00284-9. K.K. Moncal, D.N. Heo, K.P. Godzik, D.M. Sosnoski, O.D. Mrowczynski, E. Rizk, V. Ozbolat, S.M. Tucker, E.M. Gerhard, M. Dey, G.S. Lewis, J. Yang, I.T. Ozbolat, 3D printing of poly(ε-caprolactone)/poly(D,L-lactide- co -glycolide)/hydroxyapatite composite constructs for bone tissue engineering, J. Mater. Res. 33 (2018) 1972–1986, https://doi.org/10.1557/jmr.2018.111. H.J. Jeon, M. Lee, S. Yun, D. Kang, K. ho Park, S. Choi, E. Choi, S. Jin, J.H.H. Shim, W.-S.S. Yun, B.-J.J. Yoon, J. Park, Fabrication and characterization of 3D-printed biocomposite scaffolds based on PCL and silanated silica particles for bone tissue regeneration, Chem. Eng. J. 360 (2019) 519–530, https://doi.org/10. 1016/j.cej.2018.11.176. D. Liu, W. Nie, D. Li, W. Wang, L. Zheng, J. Zhang, 3D printed PCL / SrHA sca ff old for enhanced bone regeneration, Chem. Eng. J. 362 (2019) 269–279, https:// doi.org/10.1016/j.cej.2019.01.015. L. Dong, S.-J. Wang, X.-R. Zhao, Y.-F. Zhu, J.-K. Yu, 3D- printed poly(ε-caprolactone) scaffold integrated with cell-laden chitosan hydrogels for bone tissue engineering, Sci. Rep. 7 (2017) 13412, https://doi.org/10.1038/s41598-01713838-7. M. Schardosim, J. Souli??, D. Poquillon, S. Cazalbou, B. Duployer, C. Tenailleau, C. Rey, R. H??bler, C. Combes, Freeze-casting for PLGA/carbonated apatite composite scaffolds: structure and properties, Mater. Sci. Eng. C 77 (2017) 731–738, https://doi.org/10.1016/j.msec.2017.03.302. Y. Lai, Y. Li, H. Cao, J. Long, X. Wang, L. Li, C. Li, Q. Jia, B. Teng, T. Tang, J. Peng, D. Eglin, M. Alini, D.W. Grijpma, G. Richards, L. Qin, Osteogenic magnesium incorporated into PLGA/TCP porous scaffold by 3D printing for repairing challenging bone defect, Biomaterials 197 (2019) 207–219, https://doi.org/10.1016/j. biomaterials.2019.01.013. L. Chen, L. Shao, F. Wang, Y. Huang, F. Gao, Enhancement in sustained release of antimicrobial peptide and BMP-2 from degradable three dimensional-printed PLGA scaffold for bone regeneration, RSC Adv. 9 (2019) 10494–10507, https:// doi.org/10.1039/C8RA08788A. M. Rasoulianboroujeni, F. Fahimipour, P. Shah, K. Khoshroo, M. Tahriri, H. Eslami, A. Yadegari, E. Dashtimoghadam, L. Tayebi, Development of 3D-printed PLGA/TiO2 nanocomposite scaffolds for bone tissue engineering applications,

Materials Today Communications xxx (xxxx) xxxx

F. Ghorbani, et al.

[167]

[168]

[169]

[170]

[171]

[172]

[173]

[174]

[175]

[176]

[177]

[178]

[179]

1002/btpr.2918 btpr.2918. [180] F. Ghorbani, A. Zamanian, M. Sahranavard, Mussel-inspired polydopaminemediated surface modification of freeze-cast poly (ε-caprolactone) scaffolds for bone tissue engineering applications, Biomed. Eng. / Biomed. Tech. (2019), https://doi.org/10.1515/bmt-2019-0061. [181] I.T. Ozbolat, Bioprinting scale-up tissue and organ constructs for transplantation, Trends Biotechnol. 33 (2015) 395–400, https://doi.org/10.1016/j.tibtech.2015. 04.005. [182] D. Yu, Q. Li, X. Mu, T. Chang, Z. Xiong, Bone regeneration of critical calvarial defect in goat model by PLGA/TCP/rhBMP-2 scaffolds prepared by low-temperature rapid-prototyping technology, Int. J. Oral Maxillofac. Surg. (2008), https://doi.org/10.1016/j.ijom.2008.07.012. [183] V. Keriquel, F. Guillemot, I. Arnault, B. Guillotin, S. Miraux, J. Amédée, J.C. Fricain, S. Catros, In vivo bioprinting for computer- and robotic-assisted medical intervention: preliminary study in mice, Biofabrication 2 (2010) 014101, , https://doi.org/10.1088/1758-5082/2/1/014101. [184] W. Hao, L. Pang, M. Jiang, R. Lv, Z. Xiong, Y.Y. Hu, Skeletal repair in rabbits using a novel biomimetic composite based on adipose-derived stem cells encapsulated in collagen I gel with PLGA-β-TCP Scaffold, J. Orthop. Res. (2010), https://doi.org/ 10.1002/jor.20969. [185] D.L. Cohen, J.I. Lipton, L.J. Bonassar, H. Lipson, Additive manufacturing for in situ repair of osteochondral defects, Biofabrication 2 (2010) 035004, , https://doi.org/ 10.1088/1758-5082/2/3/035004. [186] N.E. Fedorovich, H.M. Wijnberg, W.J.A. Dhert, J. Alblas, Distinct tissue formation by heterogeneous printing of Osteo- and endothelial progenitor cells, Tissue Eng. Part A 17 (2011) 2113–2121, https://doi.org/10.1089/ten.tea.2011.0019. [187] V. Keriquel, H. Oliveira, M. Rémy, S. Ziane, S. Delmond, B. Rousseau, S. Rey, S. Catros, J. Amédée, F. Guillemot, J.C. Fricain, In situ printing of mesenchymal stromal cells, by laserassisted bioprinting, for in vivo bone regeneration applications, Sci. Rep. 7 (2017) 1778. [188] O. Kérourédan, D. Hakobyan, M. Rémy, S. Ziane, N. Dusserre, J.-C. Fricain, S. Delmond, N.B. Thébaud, R. Devillard, In situ prevascularization designed by laser-assisted bioprinting: effect on bone regeneration, Biofabrication 11 (2019) 045002, , https://doi.org/10.1088/1758-5090/ab2620. [189] M. Maroulakos, G. Kamperos, L. Tayebi, D. Halazonetis, Y. Ren, Applications of 3D printing on craniofacial bone repair: a systematic review, J. Dent. 80 (2019) 1–14, https://doi.org/10.1016/j.jdent.2018.11.004. [190] S. Stegen, N. van Gastel, G. Carmeliet, Bringing new life to damaged bone: the importance of angiogenesis in bone repair and regeneration, Bone 70 (2015) 19–27, https://doi.org/10.1016/j.bone.2014.09.017. [191] J. Baldwin, M. Antille, U. Bonda, E.M. De-Juan-Pardo, K. Khosrotehrani, S. Ivanovski, E. Petcu, D. Hutmacher, In vitro pre-vascularisation of tissue-engineered constructs A co-culture perspective, Vasc. Cell. 6 (2014) 13, https://doi. org/10.1186/2045-824X-6-13. [192] V. Mironov, R.P. Visconti, V. Kasyanov, G. Forgacs, C.J. Drake, R.R. Markwald, Organ printing: tissue spheroids as building blocks, Biomaterials 30 (2009) 2164–2174, https://doi.org/10.1016/j.biomaterials.2008.12.084. [193] A. Guerra, P. Cano, M. Rabionet, T. Puig, J. Ciurana, 3D-printed PCL/PLA composite stents: towards a new solution to cardiovascular problems, Materials (Basel) 11 (2018) 1679, https://doi.org/10.3390/ma11091679.

Mater. Sci. Eng. C 96 (2019) 105–113, https://doi.org/10.1016/j.msec.2018.10. 077. M.A. Elsawy, K.H. Kim, J.W. Park, A. Deep, Hydrolytic degradation of polylactic acid (PLA) and its composites, Renew. Sustain. Energy Rev. 79 (2017) 1346–1352, https://doi.org/10.1016/j.rser.2017.05.143. C.R. Almeida, T. Serra, M.I. Oliveira, J.A. Planell, M.A. Barbosa, M. Navarro, Impact of 3-D printed PLA- and chitosan-based scaffolds on human monocyte/ macrophage responses: unraveling the effect of 3-D structures on inflammation, Acta Biomater. 10 (2014) 613–622, https://doi.org/10.1016/j.actbio.2013.10. 035. B.N. Teixeira, P. Aprile, R.H. Mendonça, D.J. Kelly, R.M. da S.M. Thiré, Evaluation of bone marrow stem cell response to PLA scaffolds manufactured by 3D printing and coated with polydopamine and type I collagen, J. Biomed. Mater. Res. Part B Appl. Biomater. 107 (2019) 37–49, https://doi.org/10.1002/jbm.b.34093. G. Radenković, D. Petković, Metallic biomaterials, Biomater. Clin. Pract. Springer International Publishing, Cham, 2018, pp. 183–224, https://doi.org/10.1007/ 978-3-319-68025-5_8. V. Hosseini, M. Mirrahimi, A. Shakeri-Zadeh, F. Koosha, B. Ghalandari, S. Maleki, A. Komeili, S.K. Kamrava, Multimodal cancer cell therapy using Au@Fe2O3 core–shell nanoparticles in combination with photo-thermo-radiotherapy, Photodiagnosis Photodyn. Ther. 24 (2018) 129–135, https://doi.org/10.1016/j. pdpdt.2018.08.003. J.L. Gilbert, G.W. Kubacki, Oxidative stress, inflammation, and the corrosion of metallic biomaterials, Oxidative Stress Biomater, Elsevier, 2016, pp. 59–88, https://doi.org/10.1016/B978-0-12-803269-5.00003-6. X.P. Tan, Y.J. Tan, C.S.L. Chow, S.B. Tor, W.Y. Yeong, Metallic powder-bed based 3D printing of cellular scaffolds for orthopaedic implants: a state-of-the-art review on manufacturing, topological design, mechanical properties and biocompatibility, Mater. Sci. Eng. C 76 (2017) 1328–1343, https://doi.org/10.1016/j.msec. 2017.02.094. S. Maleksaeedi, J.K. Wang, A. El-Hajje, L. Harb, V. Guneta, Z. He, F.E. Wiria, C. Choong, A.J. Ruys, Toward 3D printed bioactive titanium scaffolds with bimodal pore size distribution for bone ingrowth, Procedia Cirp 5 (2013) 158–163, https://doi.org/10.1016/j.procir.2013.01.032. S. Wang, R. Li, D. Li, Z.-Y. Zhang, G. Liu, H. Liang, Y. Qin, J. Yu, Y. Li, Fabrication of bioactive 3D printed porous titanium implants with Sr ion-incorporated zeolite coatings for bone ingrowth, J. Mater. Chem. B 6 (2018) 3254–3261, https://doi. org/10.1039/C8TB00328A. C.-H. Tsai, C.-H. Hung, C.-N. Kuo, C.-Y. Chen, Y.-N. Peng, M.-Y. Shie, Improved bioactivity of 3D printed porous titanium alloy scaffold with chitosan/magnesiumcalcium silicate composite for orthopaedic applications, Materials (Basel) 12 (2019) 203, https://doi.org/10.3390/ma12020203. Y. LI, Q. WU, G. TANG, H. LI, L.-Y. SHANG, Preparation and characterization of printed magnesium scaffolds for bone tissue engineering, Chin. J. Tissue Eng. Res. 22 (2018) 827–832. A. Aidun, A. Zamanian, F. Ghorbani, Immobilization of polyvinyl alcohol-siloxane on the oxygen plasma-modified polyurethane-carbon nanotube composite matrix, J. Appl. Polym. Sci. (2019) 1–12, https://doi.org/10.1002/app.48477. F. Ghorbani, A. Zamanian, F. Kermanian, A. Shamoosi, A bio‐inspired 3D shape olibanum‐collagen‐gelatin scaffolds with tunable porous microstructure for efficient neural tissue regeneration, Biotechnol. Prog. (2019), https://doi.org/10.

23