- Email: [email protected]
Bionic design and 3D printing of porous titanium alloy scaffolds for bone tissue repair
Composites Part B 162 (2019) 154–161
Contents lists available at ScienceDirect
Composites Part B journal homepage: www.elsevier.com/locate/compositesb
Bionic design and 3D printing of porous titanium alloy scaffolds for bone tissue repair
T
Li Zhaoa,1, Xuan Peib,1, Lihua Jianga, Cheng Huc, Jianxun Sunc, Fei Xingd, Changchun Zhoub,∗, Yujiang Fanb, Xingdong Zhangb a
Department of Health Policy and Management, West China School of Public Health, Sichuan University, Chengdu, 610041, China National Engineering Research Center for Biomaterials, Sichuan University, 610064, Chengdu, China c State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, 610041, China d Department of Orthopedics, West China Hospital, Sichuan University, Chengdu, 610041, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Public health Ti scaffolds Selective laser melting The bionic pores Bone tissue engineering
Bone defect and osteoporosis are common in clinic which are seriously harmful for public health. Bionic bone tissue engineering scaffolds are very important for bone tissue repair and reconstruction. In this study, different bionic bone tissue engineering scaffolds were constructed by computer-aided design and fabricated by selected laser melting. Novel porous structures were designed by using parameterization modeling. The accurate models with key characteristics such as porosity and the mechanical property of scaffolds were studied. Compared with the designed model, the error of the selective laser melting (SLM) printed scaffold porosity was less than 2.73%. The mechanical properties of the prepared scaffold can be calculated by finite element analysis of 3D models, and the mechanical properties of the 3D printed samples were consistent with the model design. Through the design, manufacture, characterization and evaluation of the scaffold porous structures, the parametric modeling of porous titanium bone tissue engineering scaffold with good mechanical and biological properties was realized. Optimized design and precisely manufactured implants are very important for bone tissue repair and reconstruction.
1. Introduction Natural bone tissue is a complex tissue with precise porous structures. The ideal bone tissue engineering scaffold design requires the implants structures to conform to the anatomical structure of natural bone tissues [1–3]. Meanwhile, it also requires good biological compatibility, bone tissue integration ability, and good bone bonding ability and suitable mechanical property [4]. In order to meet the needs of new bone tissue ingrowth, bone tissue engineering scaffold must be designed with mutual penetration of porous structure [5,6]. Three-dimensional porous structures are benefit for cells adhesion, migration and proliferation and provide the necessary living space, providing transmission channels for nutrients, metabolism and metabolic products [7,8]. A large number of studies have shown that the ideal macropore size of bone tissue engineering scaffold is about 300–900 μm, and the porosity is between 60% and 95% [9–11]. However, porous structures design would affect the biological activity of scaffold, especially the
pores connecting forms will affect the biological function of scaffold [8,12,13]. One key problem for bone tissue scaffold fabrication is that the traditional fabrication methods of porous scaffold [14], such as foaming (including chemical foaming and physical foaming), particle leaching, electrospining method are mostly unable to obtain accurately porosity [15–17], especially unable to control the connecting forms of the porous architecture [15,18]. Therefore, accurate porous architecture design of bone tissue engineering scaffold is a hot spot in biomedical materials research field. Titanium alloy has good biological compatibility, but the mechanical strength of titanium alloy, such as compressive strength, tensile strength, elastic modulus, etc. are higher than that of natural bones [19,20]. The mismatched mechanical strength leads to titanium implants not well restoration in the body, and caused stress shielding phenomenon. It may leads to looseness or breakage of implants. The porous structure design of titanium alloy can effectively solve the problems of stress shielding. Therefore, optimal design of porous titanium, including pore size, porosity, pore connectivity, uniformity of
∗
Corresponding author. E-mail address: [email protected] (C. Zhou). 1 These authors contributed equally. https://doi.org/10.1016/j.compositesb.2018.10.094 Received 12 August 2018; Received in revised form 8 October 2018; Accepted 28 October 2018 Available online 29 October 2018 1359-8368/ © 2018 Elsevier Ltd. All rights reserved.
Composites Part B 162 (2019) 154–161
L. Zhao et al.
printing route. During fabrication process, the roll shaft will spread a very thin layer (50 μm) Ti powders in the forming platform. Two axis servo drive laser illuminated forming part with power of 70 w. The laser scanning speed was 500 mm/s. After each layer was finished, the platform moved down 50 mm, and did next spread of the powders. During processing, no support was used to ensure the accuracy of the scaffolds. After printing, products were heated for4 h to 1000 °C (heating rate: 4.08 °C/min) in vacuum furnace, held for 60 min, and then cooled to room temperature in the furnace.
pore distribution, distortion of pore channels, specific surface area, etc. are vital for the bone tissue scaffold application. However, the traditional technology for fabrication of porous titanium has limitations [14,20–22]. In recent years, the 3D printing technology provides support for fabrication of accurate porous titanium scaffolds [23–26]. 3D printing is an additive manufacturing technology, which produces three-dimensional products by adding materials through layer by layer method [27–31]. 3D printing platform controls the movement of the printer through the products' molding. 3D printing does not need original embryos and molds, it can directly print the shape and structure of the product according to the computer graphics modeling data, which simplifying the manufacturing process of the product, and shorten the manufacturing cycle of the product [32–35]. In this paper, a parameterized modeling based on the selective laser melting (SLM) 3D printing technology was proposed to fabricate porous titanium bone tissue engineering scaffolds with accurate porous structures. Customized mechanical properties and biological functions of the scaffold were predesigned. This study has established a mathematical model of different pore structures. The parameters of porosity and pore diameter are used for finite element analysis. District selective laser melting (SLM) printed the porous titanium bone tissue engineering scaffold based on mathematical models of different pore structures. The porosity characterization and mechanical properties test results indicated that the theoretical design and 3D fabrication process achieved precision manufacturing of porous scaffold. The mechanical properties and biological characteristics of the scaffolds were accurately customized.
2.3. Architecture characterization of porous titanium bone tissue The micropore structure of the scaffold plays an important role in the growth of bone tissue cells and the mechanical properties of the scaffold. The main characteristic parameters of the pore structure include porosity, pore size, pore connectivity, distribution uniformity, pore distortion and specific surface area. 2.3.1. Pore size Pore size refers to the minimum diameter that cells can pass through when they move through the scaffold, and the pore size directly affects the activity ability of cells in the tissue scaffold. When the pore size is too large, cells can easily fall out of the scaffold, which is not conducive to the adhesion and growth of cells in the scaffold. When the pore size is too small, the cells can not enter the scaffold and can not effectively guide the growth of host tissue. For Cube pores, the pore sizes can be controlled by defining the side length of square holes. For Diamond and Gyriod structures, pore sizes can be adjusted by changing parameter equations. It can be calculated by the equation of shape parameters that: For Diamond and Gyriod scaffolds:
2. Materials and methods 2.1. Design of porous titanium bone tissue scaffolds Five different porous titanium bone tissue scaffolds were designed for porous structures building. Diamond (S1), Gyriod (S2), Orthogonal (S3), Truss(S4) and Cube (S5) pore are the basic pore unit of the scaffolds. The scaffolds' porous structure is superimposed with these basic array of pores. The pore connectivity and uniformity of pore distribution were guaranteed by the 3D printing process. The distortion of pore channels are decided by the pore architectures design. In this study, we selected three of them include pore size, porosity and specific surface area were discussed. The modeling design was fixed the micropores at 500 μm. Different porosities were obtained by adjusting the entity proportion in the scaffolds. The shape of the sample dimensions are ϕ 6 × 12 mm. The porous structure of different scaffolds were designed through 3D molding software by stretching and Boolean operation. Diamond(D) and Gyriod(G) porous structure design can effectively improve the distortion degree and specific surface area of the connected pore channel. The theoretical structure function is as follows:
G: f (x , y, z ) = cos(x )·sin(y ) + cos(y )·sin(z ) + cos(z )·sin(x ) = 0 x 2 + y 2 ≤ 16; −4 ≤ x ≤ 4; −4 ≤ y ≤ 4; −4 ≤ z ≤ 4;
(3)
When x = z = 0, f(x,y,z) = sin(y) = 0
(4)
When y = z = 0, f(x,y,z) = sin(x) = 0
(5)
In the x, y and z direction, according to the structure of the pores surface, the pores can be calculated as:
ds =
π × 2
2 = 2.22
(6)
When the surface feature is used to form the channels of the scaffold, the wall thickness of the scaffold is set as b. Then, according to the principle of equal wall thickness migration, the pores of the scaffold, dz, can be calculated as:
d z = ds − 2b
(7)
Then, adjusting the dimension and wall thickness of the pores unit distance to obtain the target pore size of the scaffolds.
(1)
2.3.2. Porosity Porosity refers the description of the void and solid parts of the scaffold. The porosity directly affects the specific surface area of the scaffold and the mechanical properties of the scaffold. Suitable porosity provides the cells with the reproductive space, while biomimic the mechanical strength of the natural bone. Porosity may be characterized as,
D: f (x , y , z ) = sin(x )·sin(y )·sin(z ) + sin(x )·cos(y )·cos(z ) + cos(x )·sin(y )·cos(z ) + cos(x )·cos(y )·sin(z ) = 0 x 2 + y 2 ≤ 16; −4 ≤ x ≤ 4; −4 ≤ y ≤ 4; −4 ≤ z ≤ 4;
When x = y = 0, f(x,y,z) = sin(z) = 0
(2)
2.2. 3D printing of porous titanium scaffolds
η= The porous titanium samples were all prepared by M2 SLM printer (CONCEPT LASER, Germany). According to the data of computer graphics modeling, the shape and structure of the product are directly printed by layer-by-layer printing. According to different types of porous scaffold surface functions, the 3D molding software built up framework of STL file. Then the printer would using the adaptive slicing and trajectory planning algorithm to develop a framework of best
Vp Vz
× 100% =
1 − Vs 4(1 − Vs ) × 100% = × 100% Vz πd 2h
(8)
Where: Vp represents the pore volume of scaffold. Vs is the solid volume of scaffold (which can be automatically assessed). Vz is the total volume of cylindrical supports. d and h are cylinder diameter and height. 2.3.3. Specific surface area Specific surface area refers the surface area of the internal pore 155
Composites Part B 162 (2019) 154–161
L. Zhao et al.
Fig. 1. Schematic diagram of 3D printing of metal products with complex microporous structure and its application in biomedicine.
image and its size distribution were shown in Fig. 2. Most printing powders sizes were distributed between 10 and 100 μm, of which 50 μm particle size were the most distribution. After the porous titanium sample was printed and formed, the sample was prepared for metallographic observation by electro spark wire cutting on the sample. Microstructure was observed by HITACHI S-4800 scanning electron microscopy (SEM) after 15 s corrosion by HF:HNO3:H2O = 1:6:7. The characteristics of scaffold pore structure play an important role in the proliferation and metabolism of bone tissue cells. As shown in Fig. 3 (a), (b) and (c) respectively represented the porous structures SEM images of Gyriod (S2) scaffold. It observed that the surfaces were respectively connected with each other surfaces with certain roughness. (d) were the corresponding 3D printed samples of porous titanium. The first-level pores on the surface are consistent with the theoretical parameter model. Due to the molding process and data characteristics of parts, the connecting surface between pores is composed of many pits, which were residual print powders. These roughness was conducive to the adsorption and metabolic movement of cells. Interpenetrating communication channels increase the movement track of
space of the scaffold. Larger specific surface area provide more protein and cell adsorption sites, which is conducive to cell adsorption, migration and reproduction. Meanwhile, it also provides greater interaction space for the secretion and deposition of extracellular matrix and enhances the biological activity of scaffold. Specific surface area ε can be represented as:
ε=
Sp VP
× 100% =
SP × 100% Vz − VS
(9)
Where: Sp is the surface area of the pores (which can be automatically assessed by the design software). 3. Results and discussion 3.1. Pore structure characterization Fig. 1 showed the schematic diagram of 3D printing of metal products with complex microporous structure and its application in biomedicine. The spherical printing powders scanning electron microscope
Fig. 2. SEM of printing powders and its size distribution. 156
Composites Part B 162 (2019) 154–161
L. Zhao et al.
Fig. 3. Porous structures SEM images of scaffolds. (a) Gyriod (S2) scaffold magnified X50, (B) Gyriod (S2) scaffold magnified X100, (C) Gyriod (S2) scaffold magnified X500, (D) Different printed real samples of porous scaffolds.
length was longer but irregular, and the length is about 500 μm. The size tissue in the original grains was relatively short, with a diameter of 15 μm and a length-diameter ratio of 5–10 μm. Small clusters of interlacing arrangement were observed. Table 1 showed the design porosity and measured porosity data of different samples. The structural units with different pore size and porosity have different biological activities and mechanical properties. It is very important to design and manufacture bone tissue engineering scaffolds. As shown in Table 1, the theoretical and experimental values of three structures were compared in different porosity. According to the comparative analysis, the porosity deviation rate of porous titanium bone tissue scaffold model formed by SLM remain within the range of about 2.73%, which indicated that SLM method can control the pore
cells, which was more conducive to cell implantation reproduction and migration. Fig. 4 showed the metallographic photographs of different printed porous Ti samples. (a)-(e) were metallographic photographs for S1 to S5. (f) was the metallographic photograph of cast titanium alloy. Through the analysis of the metallographic photographs of different printed porous Ti samples, it was observed that the printed and the cast titanium alloy samples shown no too much difference between them. Because of the rapid cooling process during SLM printing, the metallographic should be hexagonal martensite. In these samples, the structure showed smaller size than that of cast titanium alloy samples. The vertical surface was a long strip with no obvious boundaries, parallel to the direction of printing. The width was about 100 μm, the
Fig. 4. Metallographic photographs of different printed samples. (a)–(e) are metallographic photographs for S1 to S5. (f) is the metallographic photograph of cast titanium alloy. Magnification: 50X. 157
Composites Part B 162 (2019) 154–161
L. Zhao et al.
Table 1 Design porosity and measured porosity data of different samples. Sample
designed porosity
Measured porosity by weighing method
errors
Measured porosity by Archimedes method
errors
S1 S2 S3 S4 S5
80.00% 75.00% 70.00% 65.00% 60.00%
78.85% 73.44% 68.18% 63.47% 58.01%
−1.15% −1.56% −1.82% −1.53% −1.99%
78.24% 73.04% 67.27% 62.71% 57.68%
−1.76% −1.96% −2.73% −2.29% −2.32%
Fig. 5. Comparison data of the designed porosity, measured porosity by weighing and Archimedes methods.
Fig. 6. XRD data of specimen1, 2 and 3. the bottom data show standard Ti and the printing powders XRD.
158
Composites Part B 162 (2019) 154–161
L. Zhao et al.
Fig. 7. The mechanical performance simulation. (a) and (b) are overall mesh division and local magnification of the finite element analysis model. (c) and (d) are the equivalent stress cloud diagram and strain cloud diagram of von mises of bionic porous titanium scaffolds.
characteristics of scaffold structure very accurate. Through the design of theoretical porosity, the porous structure of target scaffolds can be realized. Comparison data of the designed porosity, measured porosity by weighing and Archimedes methods were shown as in Fig. 5. The designed porosity refers to the porosity calculated by the SolidWorks measurement of the scaffold models. The designed porosity of different scaffold were 60%–80%. However, the measured porosity by weighing and Archimedes methods were little bit lower than the designed data. the error gap with the designed porosity ranged from −1.15% to −2.73%. The porosity measured by weighing method and drainage method is similar, but it can be found that the porosity measured by weighing method is larger than that by drainage method. This is because the drainage method is measured by measuring its volume indirectly and then calculating its porosity, while the weighing method is measured by measuring its mass and then calculating its porosity by formulas. As shown in Fig. 6, from the bottom to top were standard Ti, the printing powders, specimen1, 2 and 3 XRD data, respectively. Three
Fig. 8. Experimental mechanical properties data of different scaffolds.
159
Composites Part B 162 (2019) 154–161
L. Zhao et al.
area compared with S1 and S2. By analyzing the stress and strain of different scaffold structures under different porosities, the mechanical strength of the scaffolds can be effectively designed. Therefore, the mechanical strength scaffold similar to natural bone tissue can be predesigned and fabricated.
peaks of were compared. In all samples, the type of uncovered phase was found, and the peak value was larger than that of the standard XRD of titanium, while the Al and V alloy elements added in Ti6Al4v were all replacement elements of titanium alloy, and their atomic sizes were smaller than those of titanium atom. Therefore, the formed type of uncovered phase structure was smaller than that of pure titanium, indicated the right XRD peaks. XRD results indicated that there were no other elements were added into the scaffolds.
4. Conclusion In this paper, parameterization modeling, SLM manufacturing and porous structure characterization were carried out for different porous Ti scaffolds. The parameterized construction method can be used to accurately design the model with key characteristics such as porosity and the mechanical property of bone tissue engineering scaffolds can be obtained. Selected laser melting technology has effectively fabricated different porous titanium bone tissue engineering scaffolds. Compared with the designed model, the error of the main pores parameters were less than 2.73%. The mechanical properties of the prepared titanium bone tissue engineering scaffold can be calculated by finite element analysis of 3D models, and the mechanical properties of the 3D printed samples were consistent with the model design. Through the design, manufacture, characterization and evaluation of the scaffold porous structures, the parametric modeling of porous titanium bone tissue engineering scaffold with good mechanical and biological properties was realized and verified.
3.2. Mechanical performance simulation and test analysis 3.2.1. Mechanical performance simulation The static analysis of porous scaffold based on finite element method of scaffold structure can obtain the theoretical mechanical strength of scaffolds. In the analysis, the whole model was discretized into several small high-order units, and the stress and strain transfer was realized through the nodes between the units. During the analysis, one end of the support was set as a fixed constraint, and the other end was applied with 200N, 250N, 300N and 350N forces along the axis, and a gravity field was applied along the axis to obtain the stress and strain at different boundary conditions. Meshing is an important step in finite element analysis. The quality of meshing plays a decisive role in computing time and accuracy of simulation results. In this study, because of the complex porous structures, the grid adopts the tetrahedral and the jacobian point was 4. Meshing method adopted global seed control, whose approximate global size was 0.05 mm. The overall mesh division and local magnification of the finite element analysis model of bionic porous titanium structure are shown in Fig. 7 (a) and (b). It can be seen that the grid is closely distributed in structure, orderly and uniform in size, the high and wide proportions of the untwisted grid were similar, the grid transition at the structural corner was smooth, and there ass no grid distortion. When the stress at any position of the porous structure reaches the yield strength point, the yield of the porous structure is defined. As shown in Fig. 7 (c) and (d), the equivalent stress cloud diagram and strain cloud diagram of von mises at the yield of each porous structure were showed. The analysis step time in this study was set as maximum 0.1, minimum 1e-8, adjustment number was 5, maximum balance iteration was 20, and convergence tolerance was 0.001. It can be found that the maximum stress point of the bar was at the joint between the truss, and the maximum strain observed right there.
Acknowledgments This work was supported by the National Key Research and Development Program of China (No. 2018YFB1105600, 2018YFC1106800). Key R & D project of Sichuan Province (2018GZ0142). Sichuan Province Major Scientific & Technological Achievements Transformation Demonstration Project (2016CZYD0004). Sichuan Province Science & Technology Department Key Projects (2017SZ0001). The "111" Project (No. B16033). References [1] Zhang JW, Xiao DQ, He X, Shi F, Luo PF, Zhi W, et al. A novel porous bioceramic scaffold by accumulating hydroxyapatite spheres for large bone tissue engineering. III: characterization of porous structure. Mater Sci Eng C-Mater Biol Appli 2018;89:223–9. [2] Vetrik M, Parizek M, Hadraba D, Kukackova O, Brus J, Hlidkova H, et al. Porous heat-treated polyacrylonitrile scaffolds for bone tissue engineering. Acs Appl Mater Inter 2018;10(10):8496–506. [3] Yao QQ, Liu YX, Selvaratnam B, Koodali RT, Sun HL. Mesoporous silicate nanoparticles/3D nanofibrous scaffold-mediated dual-drug delivery for bone tissue engineering. J Contr Release 2018;279:69–78. [4] Sharma A, Molla S, Katti KS, Katti DR. Multiscale models of degradation and healing of bone tissue engineering nanocomposite scaffolds. J Nanomechanics Micr 2017;7(4). [5] Tang QG, Piard C, Lin J, Nan K, Guo T, Caccamese J, et al. Imaging stem cell distribution, growth, migration, and differentiation in 3-D scaffolds for bone tissue engineering using mesoscopic fluorescence tomography. Biotechnol Bioeng 2018;115(1):257–65. [6] Wu SY, Wang JD, Zou LY, Jin L, Wang ZL, Li Y. A three-dimensional hydroxyapatite/polyacrylonitrile composite scaffold designed for bone tissue engineering. RSC Adv 2018;8(4):1730–6. [7] Yan Y, Kang YJ, Li D, Yu K, Xiao T, Wang QY, et al. Microstructure, mechanical properties and corrosion behavior of porous Mg-6 wt.% Zn scaffolds for bone tissue engineering. J Mater Eng Perform 2018;27(3):970–84. [8] Zhou CC, Ye XJ, Fan YJ, Ma L, Tan YF, Qing FZ, et al. Biomimetic fabrication of a three-level hierarchical calcium phosphate/collagen/hydroxyapatite scaffold for bone tissue engineering. Biofabrication 2014;6(3). [9] Zhang K, Fan YB, Dunne N, Li XM. Effect of microporosity on scaffolds for bone tissue engineering. Regen Biomater 2018;5(2):115–24. [10] Arabi N, Zamanian A, Rashvand SN, Ghorbani F. The tunable porous structure of gelatin-bioglass nanocomposite scaffolds for bone tissue engineering applications: physicochemical, mechanical, and in vitro properties. Macromol Mater Eng 2018;303(3). [11] Arahira T, Maruta M, Matsuya S, Todo M. Development and characterization of a novel porous beta-TCP scaffold with a three-dimensional PLLA network structure for use in bone tissue engineering. Mater Lett 2015;152:148–50. [12] Li SH, de Groot K, Layrolle P. Bioceramic scaffold with controlled porous structure for bone tissue engineering. Bioceramics 2002;218–2:25–9. 14.
3.2.2. Mechanical properties test analysis Fig. 8 showed the experimental mechanical properties data of different scaffolds. Mechanical properties were tested in accordance with ISO 13314:2011 (E) (Precision Universal Tester Autograph AG-X, Japan). Standard test samples were fabricated as cylinder ϕ10 × 18 mm and with 1 mm compact base at both ends. Loading speed was set to 1 mm/min. The load-displacement curve of the porous titanium sample of porous structures can be obtained by the data of the displacement of the pressure head and the reaction force of the sensor. Through the conversion formula, it can be transformed into stress - strain curve. By observing the stress and strain curves of the porous titanium samples structure, it can be found that the stress and strain graphs present the spoon-like curve of the non-yielding platform and the ductile materials. The scaffolds with diamond pore unit specimens (S1) showed lowest compressive strength, it was only about 38.2 MPa. The scaffolds with gyriod pore unit specimens (S2) showed lower compressive strength (57.0 MPa). Orthogonal specimens (S3) showed compressive strength of 83.7 MPa. Because of the complex porosities of the diamond and gyriod structures, their solid bearing surface in the vertical direction was smaller. Therefore, it showed lower compressive strength. The scaffolds with Truss(S4) and Cube (S5) pore unit specimens showed higher compressive strength, which were 114.9 MPa and 142.8 MPa, respectively. This was because their porosities were simpler and more conducive to supporting vertical forces. But they showed smaller surface 160
Composites Part B 162 (2019) 154–161
L. Zhao et al.
scaffolds for bone regeneration. J Mater Chem B 2018;6(3):499–509. [25] He HY, Zhang JY, Mi X, Hu Y, Gu XY. Rapid prototyping for tissue-engineered bone scaffold by 3D printing and biocompatibility study. Int J Clin Exp Med 2015;8(7):11777–85. [26] Helguero CG, Mustahsan VM, Parmar S, Pentyala S, Pfail JP, Kao I, et al. Biomechanical properties of 3D-printed bone scaffolds are improved by treatment with CRFP. J Orthop Surg Res 2017;12. [27] Hong JK, Roman M. Mechanical performance of 3D-printed porous nanocomposite bone scaffolds. Abstr Pap Am Chem Soc 2016;251. [28] Huan ZJ, Chu HK, Liu HB, Yang J, Sun D. Engineered bone scaffolds with Dielectrophoresis-based patterning using 3D printing. Biomed Microdevices 2017;19(4). [29] Huang BY, Bartlo PJ. Rheological characterization of polymer/ceramic blends for 3D printing of bone scaffolds. Polym Test 2018;68:365–78. [30] Tran P, Ngo TD, Ghazlan A, Hui D. Bimaterial 3D printing and numerical analysis of bio-inspired composite structures under in-plane and transverse loadings. Compos B Eng 2017;108:210–23. [31] Henriques B, Pinto P, Silva FS, Fredel MC, Fabris D, Souza JCM, et al. On the mechanical properties of monolithic and laminated nano-ceramic resin structures obtained by laser printing. Compos B Eng 2018;141:76–83. [32] Iraimudi V, Begum SR, Arumaikkannu G, Narayanan R. Design and fabrication of customised scaffold for femur bone using 3D printing. Mater Indus Manufac Eng Res Adv 2014;845:920–4. 11. [33] Jariwala SH, Lewis GS, Bushman ZJ, Adair JH, Donahue HJ. 3D printing of personalized artificial bone scaffolds. 3D Print Addit Manuf 2015;2(2):56–64. [34] Leukers B, Gulkan H, Irsen SH, Milz S, Tille C, Schieker M, et al. Hydroxyapatite scaffolds for bone tissue engineering made by 3D printing. J Mater Sci Mater Med 2005;16(12):1121–4. [35] Leukers B, Gulkan H, Irsen SH, Milz S, Tille C, Seitz H, et al. Biocompatibility of ceramic scaffolds for bone replacement made by 3D printing. Mater Werkst 2005;36(12):781–7.
[13] Lin LL, Zhang HC, Zhao L, Hu QX, Fang ML. Design and preparation of bone tissue engineering scaffolds with porous controllable structure. J Wuhan Univ Technol 2009;24(2):174–80. [14] Zhou CC, Ye XJ, Fan YJ, Qing FZ, Chen HJ, Zhang XD. Synthesis and characterization of CaP/Col composite scaffolds for load-bearing bone tissue engineering. Compos B Eng 2014;62:242–8. [15] Delabarde C, Plummer CJG, Bourban PE, Manson JAE. Biodegradable polylactide/ hydroxyapatite nanocomposite foam scaffolds for bone tissue engineering applications. J Mater Sci Mater Med 2012;23(6):1371–85. [16] Bak TY, Kook MS, Jung SC, Kim BH. Biological effect of gas plasma treatment on CO2 gas foaming/salt leaching fabricated porous polycaprolactone scaffolds in bone tissue engineering. J Nanomater 2014;8:1–16. [17] Fiorilli S, Baino F, Cauda V, Crepaldi M, Vitale-Brovarone C, Demarchi D, et al. Electrophoretic deposition of mesoporous bioactive glass on glass-ceramic foam scaffolds for bone tissue engineering. J Mater Sci Mater Med 2015;26(1). [18] Dong SJ, Wang L, Li QS, Chen XS, Liu SJ, Zhou YM. Poly(L-lactide)-grafted bioglass/poly(lactide-co-glycolide) scaffolds with supercritical CO2 foaming reprocessing for bone tissue engineering. Chem Res Chin Univ 2017;33(3):499–506. [19] Zhang BQ, Pei X, Zhou CC, Fan YJ, Jiang Q, Ronca A, et al. The biomimetic design and 3D printing of customized mechanical properties porous Ti6Al4V scaffold for load-bearing bone reconstruction. Mater Des 2018;152:30–9. [20] Deng ZB, Zhou CC, Fan YJ, Peng JP, Zhu XD, Pei X, et al. Design and characterization of porous titanium scaffold for bone tissue engineering. Rare Metal Mater Eng 2016;45(9):2287–92. [21] Ngo TD, Kashani A, Imbalzano G, Nguyen KTQ, Hui D. Additive manufacturing (3D printing): a review of materials, methods, applications and challenges. Compos B Eng 2018;143:172–96. [22] Wang X, Jiang M, Zhou ZW, Gou JH, Hui D. 3D printing of polymer matrix composites: a review and prospective. Compos B Eng 2017;110:442–58. [23] Du XY, Fu SY, Zhu YF. 3D printing of ceramic-based scaffolds for bone tissue engineering: an overview. J Mater Chem B 2018;6(27):4397–412. [24] Du XY, Yu B, Pei P, Ding HF, Yu BQ, Zhu YF. 3D printing of pearl/CaSO4 composite
161
Contents lists available at ScienceDirect
Composites Part B journal homepage: www.elsevier.com/locate/compositesb
Bionic design and 3D printing of porous titanium alloy scaffolds for bone tissue repair
T
Li Zhaoa,1, Xuan Peib,1, Lihua Jianga, Cheng Huc, Jianxun Sunc, Fei Xingd, Changchun Zhoub,∗, Yujiang Fanb, Xingdong Zhangb a
Department of Health Policy and Management, West China School of Public Health, Sichuan University, Chengdu, 610041, China National Engineering Research Center for Biomaterials, Sichuan University, 610064, Chengdu, China c State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, 610041, China d Department of Orthopedics, West China Hospital, Sichuan University, Chengdu, 610041, China b
A R T I C LE I N FO
A B S T R A C T
Keywords: Public health Ti scaffolds Selective laser melting The bionic pores Bone tissue engineering
Bone defect and osteoporosis are common in clinic which are seriously harmful for public health. Bionic bone tissue engineering scaffolds are very important for bone tissue repair and reconstruction. In this study, different bionic bone tissue engineering scaffolds were constructed by computer-aided design and fabricated by selected laser melting. Novel porous structures were designed by using parameterization modeling. The accurate models with key characteristics such as porosity and the mechanical property of scaffolds were studied. Compared with the designed model, the error of the selective laser melting (SLM) printed scaffold porosity was less than 2.73%. The mechanical properties of the prepared scaffold can be calculated by finite element analysis of 3D models, and the mechanical properties of the 3D printed samples were consistent with the model design. Through the design, manufacture, characterization and evaluation of the scaffold porous structures, the parametric modeling of porous titanium bone tissue engineering scaffold with good mechanical and biological properties was realized. Optimized design and precisely manufactured implants are very important for bone tissue repair and reconstruction.
1. Introduction Natural bone tissue is a complex tissue with precise porous structures. The ideal bone tissue engineering scaffold design requires the implants structures to conform to the anatomical structure of natural bone tissues [1–3]. Meanwhile, it also requires good biological compatibility, bone tissue integration ability, and good bone bonding ability and suitable mechanical property [4]. In order to meet the needs of new bone tissue ingrowth, bone tissue engineering scaffold must be designed with mutual penetration of porous structure [5,6]. Three-dimensional porous structures are benefit for cells adhesion, migration and proliferation and provide the necessary living space, providing transmission channels for nutrients, metabolism and metabolic products [7,8]. A large number of studies have shown that the ideal macropore size of bone tissue engineering scaffold is about 300–900 μm, and the porosity is between 60% and 95% [9–11]. However, porous structures design would affect the biological activity of scaffold, especially the
pores connecting forms will affect the biological function of scaffold [8,12,13]. One key problem for bone tissue scaffold fabrication is that the traditional fabrication methods of porous scaffold [14], such as foaming (including chemical foaming and physical foaming), particle leaching, electrospining method are mostly unable to obtain accurately porosity [15–17], especially unable to control the connecting forms of the porous architecture [15,18]. Therefore, accurate porous architecture design of bone tissue engineering scaffold is a hot spot in biomedical materials research field. Titanium alloy has good biological compatibility, but the mechanical strength of titanium alloy, such as compressive strength, tensile strength, elastic modulus, etc. are higher than that of natural bones [19,20]. The mismatched mechanical strength leads to titanium implants not well restoration in the body, and caused stress shielding phenomenon. It may leads to looseness or breakage of implants. The porous structure design of titanium alloy can effectively solve the problems of stress shielding. Therefore, optimal design of porous titanium, including pore size, porosity, pore connectivity, uniformity of
∗
Corresponding author. E-mail address: [email protected] (C. Zhou). 1 These authors contributed equally. https://doi.org/10.1016/j.compositesb.2018.10.094 Received 12 August 2018; Received in revised form 8 October 2018; Accepted 28 October 2018 Available online 29 October 2018 1359-8368/ © 2018 Elsevier Ltd. All rights reserved.
Composites Part B 162 (2019) 154–161
L. Zhao et al.
printing route. During fabrication process, the roll shaft will spread a very thin layer (50 μm) Ti powders in the forming platform. Two axis servo drive laser illuminated forming part with power of 70 w. The laser scanning speed was 500 mm/s. After each layer was finished, the platform moved down 50 mm, and did next spread of the powders. During processing, no support was used to ensure the accuracy of the scaffolds. After printing, products were heated for4 h to 1000 °C (heating rate: 4.08 °C/min) in vacuum furnace, held for 60 min, and then cooled to room temperature in the furnace.
pore distribution, distortion of pore channels, specific surface area, etc. are vital for the bone tissue scaffold application. However, the traditional technology for fabrication of porous titanium has limitations [14,20–22]. In recent years, the 3D printing technology provides support for fabrication of accurate porous titanium scaffolds [23–26]. 3D printing is an additive manufacturing technology, which produces three-dimensional products by adding materials through layer by layer method [27–31]. 3D printing platform controls the movement of the printer through the products' molding. 3D printing does not need original embryos and molds, it can directly print the shape and structure of the product according to the computer graphics modeling data, which simplifying the manufacturing process of the product, and shorten the manufacturing cycle of the product [32–35]. In this paper, a parameterized modeling based on the selective laser melting (SLM) 3D printing technology was proposed to fabricate porous titanium bone tissue engineering scaffolds with accurate porous structures. Customized mechanical properties and biological functions of the scaffold were predesigned. This study has established a mathematical model of different pore structures. The parameters of porosity and pore diameter are used for finite element analysis. District selective laser melting (SLM) printed the porous titanium bone tissue engineering scaffold based on mathematical models of different pore structures. The porosity characterization and mechanical properties test results indicated that the theoretical design and 3D fabrication process achieved precision manufacturing of porous scaffold. The mechanical properties and biological characteristics of the scaffolds were accurately customized.
2.3. Architecture characterization of porous titanium bone tissue The micropore structure of the scaffold plays an important role in the growth of bone tissue cells and the mechanical properties of the scaffold. The main characteristic parameters of the pore structure include porosity, pore size, pore connectivity, distribution uniformity, pore distortion and specific surface area. 2.3.1. Pore size Pore size refers to the minimum diameter that cells can pass through when they move through the scaffold, and the pore size directly affects the activity ability of cells in the tissue scaffold. When the pore size is too large, cells can easily fall out of the scaffold, which is not conducive to the adhesion and growth of cells in the scaffold. When the pore size is too small, the cells can not enter the scaffold and can not effectively guide the growth of host tissue. For Cube pores, the pore sizes can be controlled by defining the side length of square holes. For Diamond and Gyriod structures, pore sizes can be adjusted by changing parameter equations. It can be calculated by the equation of shape parameters that: For Diamond and Gyriod scaffolds:
2. Materials and methods 2.1. Design of porous titanium bone tissue scaffolds Five different porous titanium bone tissue scaffolds were designed for porous structures building. Diamond (S1), Gyriod (S2), Orthogonal (S3), Truss(S4) and Cube (S5) pore are the basic pore unit of the scaffolds. The scaffolds' porous structure is superimposed with these basic array of pores. The pore connectivity and uniformity of pore distribution were guaranteed by the 3D printing process. The distortion of pore channels are decided by the pore architectures design. In this study, we selected three of them include pore size, porosity and specific surface area were discussed. The modeling design was fixed the micropores at 500 μm. Different porosities were obtained by adjusting the entity proportion in the scaffolds. The shape of the sample dimensions are ϕ 6 × 12 mm. The porous structure of different scaffolds were designed through 3D molding software by stretching and Boolean operation. Diamond(D) and Gyriod(G) porous structure design can effectively improve the distortion degree and specific surface area of the connected pore channel. The theoretical structure function is as follows:
G: f (x , y, z ) = cos(x )·sin(y ) + cos(y )·sin(z ) + cos(z )·sin(x ) = 0 x 2 + y 2 ≤ 16; −4 ≤ x ≤ 4; −4 ≤ y ≤ 4; −4 ≤ z ≤ 4;
(3)
When x = z = 0, f(x,y,z) = sin(y) = 0
(4)
When y = z = 0, f(x,y,z) = sin(x) = 0
(5)
In the x, y and z direction, according to the structure of the pores surface, the pores can be calculated as:
ds =
π × 2
2 = 2.22
(6)
When the surface feature is used to form the channels of the scaffold, the wall thickness of the scaffold is set as b. Then, according to the principle of equal wall thickness migration, the pores of the scaffold, dz, can be calculated as:
d z = ds − 2b
(7)
Then, adjusting the dimension and wall thickness of the pores unit distance to obtain the target pore size of the scaffolds.
(1)
2.3.2. Porosity Porosity refers the description of the void and solid parts of the scaffold. The porosity directly affects the specific surface area of the scaffold and the mechanical properties of the scaffold. Suitable porosity provides the cells with the reproductive space, while biomimic the mechanical strength of the natural bone. Porosity may be characterized as,
D: f (x , y , z ) = sin(x )·sin(y )·sin(z ) + sin(x )·cos(y )·cos(z ) + cos(x )·sin(y )·cos(z ) + cos(x )·cos(y )·sin(z ) = 0 x 2 + y 2 ≤ 16; −4 ≤ x ≤ 4; −4 ≤ y ≤ 4; −4 ≤ z ≤ 4;
When x = y = 0, f(x,y,z) = sin(z) = 0
(2)
2.2. 3D printing of porous titanium scaffolds
η= The porous titanium samples were all prepared by M2 SLM printer (CONCEPT LASER, Germany). According to the data of computer graphics modeling, the shape and structure of the product are directly printed by layer-by-layer printing. According to different types of porous scaffold surface functions, the 3D molding software built up framework of STL file. Then the printer would using the adaptive slicing and trajectory planning algorithm to develop a framework of best
Vp Vz
× 100% =
1 − Vs 4(1 − Vs ) × 100% = × 100% Vz πd 2h
(8)
Where: Vp represents the pore volume of scaffold. Vs is the solid volume of scaffold (which can be automatically assessed). Vz is the total volume of cylindrical supports. d and h are cylinder diameter and height. 2.3.3. Specific surface area Specific surface area refers the surface area of the internal pore 155
Composites Part B 162 (2019) 154–161
L. Zhao et al.
Fig. 1. Schematic diagram of 3D printing of metal products with complex microporous structure and its application in biomedicine.
image and its size distribution were shown in Fig. 2. Most printing powders sizes were distributed between 10 and 100 μm, of which 50 μm particle size were the most distribution. After the porous titanium sample was printed and formed, the sample was prepared for metallographic observation by electro spark wire cutting on the sample. Microstructure was observed by HITACHI S-4800 scanning electron microscopy (SEM) after 15 s corrosion by HF:HNO3:H2O = 1:6:7. The characteristics of scaffold pore structure play an important role in the proliferation and metabolism of bone tissue cells. As shown in Fig. 3 (a), (b) and (c) respectively represented the porous structures SEM images of Gyriod (S2) scaffold. It observed that the surfaces were respectively connected with each other surfaces with certain roughness. (d) were the corresponding 3D printed samples of porous titanium. The first-level pores on the surface are consistent with the theoretical parameter model. Due to the molding process and data characteristics of parts, the connecting surface between pores is composed of many pits, which were residual print powders. These roughness was conducive to the adsorption and metabolic movement of cells. Interpenetrating communication channels increase the movement track of
space of the scaffold. Larger specific surface area provide more protein and cell adsorption sites, which is conducive to cell adsorption, migration and reproduction. Meanwhile, it also provides greater interaction space for the secretion and deposition of extracellular matrix and enhances the biological activity of scaffold. Specific surface area ε can be represented as:
ε=
Sp VP
× 100% =
SP × 100% Vz − VS
(9)
Where: Sp is the surface area of the pores (which can be automatically assessed by the design software). 3. Results and discussion 3.1. Pore structure characterization Fig. 1 showed the schematic diagram of 3D printing of metal products with complex microporous structure and its application in biomedicine. The spherical printing powders scanning electron microscope
Fig. 2. SEM of printing powders and its size distribution. 156
Composites Part B 162 (2019) 154–161
L. Zhao et al.
Fig. 3. Porous structures SEM images of scaffolds. (a) Gyriod (S2) scaffold magnified X50, (B) Gyriod (S2) scaffold magnified X100, (C) Gyriod (S2) scaffold magnified X500, (D) Different printed real samples of porous scaffolds.
length was longer but irregular, and the length is about 500 μm. The size tissue in the original grains was relatively short, with a diameter of 15 μm and a length-diameter ratio of 5–10 μm. Small clusters of interlacing arrangement were observed. Table 1 showed the design porosity and measured porosity data of different samples. The structural units with different pore size and porosity have different biological activities and mechanical properties. It is very important to design and manufacture bone tissue engineering scaffolds. As shown in Table 1, the theoretical and experimental values of three structures were compared in different porosity. According to the comparative analysis, the porosity deviation rate of porous titanium bone tissue scaffold model formed by SLM remain within the range of about 2.73%, which indicated that SLM method can control the pore
cells, which was more conducive to cell implantation reproduction and migration. Fig. 4 showed the metallographic photographs of different printed porous Ti samples. (a)-(e) were metallographic photographs for S1 to S5. (f) was the metallographic photograph of cast titanium alloy. Through the analysis of the metallographic photographs of different printed porous Ti samples, it was observed that the printed and the cast titanium alloy samples shown no too much difference between them. Because of the rapid cooling process during SLM printing, the metallographic should be hexagonal martensite. In these samples, the structure showed smaller size than that of cast titanium alloy samples. The vertical surface was a long strip with no obvious boundaries, parallel to the direction of printing. The width was about 100 μm, the
Fig. 4. Metallographic photographs of different printed samples. (a)–(e) are metallographic photographs for S1 to S5. (f) is the metallographic photograph of cast titanium alloy. Magnification: 50X. 157
Composites Part B 162 (2019) 154–161
L. Zhao et al.
Table 1 Design porosity and measured porosity data of different samples. Sample
designed porosity
Measured porosity by weighing method
errors
Measured porosity by Archimedes method
errors
S1 S2 S3 S4 S5
80.00% 75.00% 70.00% 65.00% 60.00%
78.85% 73.44% 68.18% 63.47% 58.01%
−1.15% −1.56% −1.82% −1.53% −1.99%
78.24% 73.04% 67.27% 62.71% 57.68%
−1.76% −1.96% −2.73% −2.29% −2.32%
Fig. 5. Comparison data of the designed porosity, measured porosity by weighing and Archimedes methods.
Fig. 6. XRD data of specimen1, 2 and 3. the bottom data show standard Ti and the printing powders XRD.
158
Composites Part B 162 (2019) 154–161
L. Zhao et al.
Fig. 7. The mechanical performance simulation. (a) and (b) are overall mesh division and local magnification of the finite element analysis model. (c) and (d) are the equivalent stress cloud diagram and strain cloud diagram of von mises of bionic porous titanium scaffolds.
characteristics of scaffold structure very accurate. Through the design of theoretical porosity, the porous structure of target scaffolds can be realized. Comparison data of the designed porosity, measured porosity by weighing and Archimedes methods were shown as in Fig. 5. The designed porosity refers to the porosity calculated by the SolidWorks measurement of the scaffold models. The designed porosity of different scaffold were 60%–80%. However, the measured porosity by weighing and Archimedes methods were little bit lower than the designed data. the error gap with the designed porosity ranged from −1.15% to −2.73%. The porosity measured by weighing method and drainage method is similar, but it can be found that the porosity measured by weighing method is larger than that by drainage method. This is because the drainage method is measured by measuring its volume indirectly and then calculating its porosity, while the weighing method is measured by measuring its mass and then calculating its porosity by formulas. As shown in Fig. 6, from the bottom to top were standard Ti, the printing powders, specimen1, 2 and 3 XRD data, respectively. Three
Fig. 8. Experimental mechanical properties data of different scaffolds.
159
Composites Part B 162 (2019) 154–161
L. Zhao et al.
area compared with S1 and S2. By analyzing the stress and strain of different scaffold structures under different porosities, the mechanical strength of the scaffolds can be effectively designed. Therefore, the mechanical strength scaffold similar to natural bone tissue can be predesigned and fabricated.
peaks of were compared. In all samples, the type of uncovered phase was found, and the peak value was larger than that of the standard XRD of titanium, while the Al and V alloy elements added in Ti6Al4v were all replacement elements of titanium alloy, and their atomic sizes were smaller than those of titanium atom. Therefore, the formed type of uncovered phase structure was smaller than that of pure titanium, indicated the right XRD peaks. XRD results indicated that there were no other elements were added into the scaffolds.
4. Conclusion In this paper, parameterization modeling, SLM manufacturing and porous structure characterization were carried out for different porous Ti scaffolds. The parameterized construction method can be used to accurately design the model with key characteristics such as porosity and the mechanical property of bone tissue engineering scaffolds can be obtained. Selected laser melting technology has effectively fabricated different porous titanium bone tissue engineering scaffolds. Compared with the designed model, the error of the main pores parameters were less than 2.73%. The mechanical properties of the prepared titanium bone tissue engineering scaffold can be calculated by finite element analysis of 3D models, and the mechanical properties of the 3D printed samples were consistent with the model design. Through the design, manufacture, characterization and evaluation of the scaffold porous structures, the parametric modeling of porous titanium bone tissue engineering scaffold with good mechanical and biological properties was realized and verified.
3.2. Mechanical performance simulation and test analysis 3.2.1. Mechanical performance simulation The static analysis of porous scaffold based on finite element method of scaffold structure can obtain the theoretical mechanical strength of scaffolds. In the analysis, the whole model was discretized into several small high-order units, and the stress and strain transfer was realized through the nodes between the units. During the analysis, one end of the support was set as a fixed constraint, and the other end was applied with 200N, 250N, 300N and 350N forces along the axis, and a gravity field was applied along the axis to obtain the stress and strain at different boundary conditions. Meshing is an important step in finite element analysis. The quality of meshing plays a decisive role in computing time and accuracy of simulation results. In this study, because of the complex porous structures, the grid adopts the tetrahedral and the jacobian point was 4. Meshing method adopted global seed control, whose approximate global size was 0.05 mm. The overall mesh division and local magnification of the finite element analysis model of bionic porous titanium structure are shown in Fig. 7 (a) and (b). It can be seen that the grid is closely distributed in structure, orderly and uniform in size, the high and wide proportions of the untwisted grid were similar, the grid transition at the structural corner was smooth, and there ass no grid distortion. When the stress at any position of the porous structure reaches the yield strength point, the yield of the porous structure is defined. As shown in Fig. 7 (c) and (d), the equivalent stress cloud diagram and strain cloud diagram of von mises at the yield of each porous structure were showed. The analysis step time in this study was set as maximum 0.1, minimum 1e-8, adjustment number was 5, maximum balance iteration was 20, and convergence tolerance was 0.001. It can be found that the maximum stress point of the bar was at the joint between the truss, and the maximum strain observed right there.
Acknowledgments This work was supported by the National Key Research and Development Program of China (No. 2018YFB1105600, 2018YFC1106800). Key R & D project of Sichuan Province (2018GZ0142). Sichuan Province Major Scientific & Technological Achievements Transformation Demonstration Project (2016CZYD0004). Sichuan Province Science & Technology Department Key Projects (2017SZ0001). The "111" Project (No. B16033). References [1] Zhang JW, Xiao DQ, He X, Shi F, Luo PF, Zhi W, et al. A novel porous bioceramic scaffold by accumulating hydroxyapatite spheres for large bone tissue engineering. III: characterization of porous structure. Mater Sci Eng C-Mater Biol Appli 2018;89:223–9. [2] Vetrik M, Parizek M, Hadraba D, Kukackova O, Brus J, Hlidkova H, et al. Porous heat-treated polyacrylonitrile scaffolds for bone tissue engineering. Acs Appl Mater Inter 2018;10(10):8496–506. [3] Yao QQ, Liu YX, Selvaratnam B, Koodali RT, Sun HL. Mesoporous silicate nanoparticles/3D nanofibrous scaffold-mediated dual-drug delivery for bone tissue engineering. J Contr Release 2018;279:69–78. [4] Sharma A, Molla S, Katti KS, Katti DR. Multiscale models of degradation and healing of bone tissue engineering nanocomposite scaffolds. J Nanomechanics Micr 2017;7(4). [5] Tang QG, Piard C, Lin J, Nan K, Guo T, Caccamese J, et al. Imaging stem cell distribution, growth, migration, and differentiation in 3-D scaffolds for bone tissue engineering using mesoscopic fluorescence tomography. Biotechnol Bioeng 2018;115(1):257–65. [6] Wu SY, Wang JD, Zou LY, Jin L, Wang ZL, Li Y. A three-dimensional hydroxyapatite/polyacrylonitrile composite scaffold designed for bone tissue engineering. RSC Adv 2018;8(4):1730–6. [7] Yan Y, Kang YJ, Li D, Yu K, Xiao T, Wang QY, et al. Microstructure, mechanical properties and corrosion behavior of porous Mg-6 wt.% Zn scaffolds for bone tissue engineering. J Mater Eng Perform 2018;27(3):970–84. [8] Zhou CC, Ye XJ, Fan YJ, Ma L, Tan YF, Qing FZ, et al. Biomimetic fabrication of a three-level hierarchical calcium phosphate/collagen/hydroxyapatite scaffold for bone tissue engineering. Biofabrication 2014;6(3). [9] Zhang K, Fan YB, Dunne N, Li XM. Effect of microporosity on scaffolds for bone tissue engineering. Regen Biomater 2018;5(2):115–24. [10] Arabi N, Zamanian A, Rashvand SN, Ghorbani F. The tunable porous structure of gelatin-bioglass nanocomposite scaffolds for bone tissue engineering applications: physicochemical, mechanical, and in vitro properties. Macromol Mater Eng 2018;303(3). [11] Arahira T, Maruta M, Matsuya S, Todo M. Development and characterization of a novel porous beta-TCP scaffold with a three-dimensional PLLA network structure for use in bone tissue engineering. Mater Lett 2015;152:148–50. [12] Li SH, de Groot K, Layrolle P. Bioceramic scaffold with controlled porous structure for bone tissue engineering. Bioceramics 2002;218–2:25–9. 14.
3.2.2. Mechanical properties test analysis Fig. 8 showed the experimental mechanical properties data of different scaffolds. Mechanical properties were tested in accordance with ISO 13314:2011 (E) (Precision Universal Tester Autograph AG-X, Japan). Standard test samples were fabricated as cylinder ϕ10 × 18 mm and with 1 mm compact base at both ends. Loading speed was set to 1 mm/min. The load-displacement curve of the porous titanium sample of porous structures can be obtained by the data of the displacement of the pressure head and the reaction force of the sensor. Through the conversion formula, it can be transformed into stress - strain curve. By observing the stress and strain curves of the porous titanium samples structure, it can be found that the stress and strain graphs present the spoon-like curve of the non-yielding platform and the ductile materials. The scaffolds with diamond pore unit specimens (S1) showed lowest compressive strength, it was only about 38.2 MPa. The scaffolds with gyriod pore unit specimens (S2) showed lower compressive strength (57.0 MPa). Orthogonal specimens (S3) showed compressive strength of 83.7 MPa. Because of the complex porosities of the diamond and gyriod structures, their solid bearing surface in the vertical direction was smaller. Therefore, it showed lower compressive strength. The scaffolds with Truss(S4) and Cube (S5) pore unit specimens showed higher compressive strength, which were 114.9 MPa and 142.8 MPa, respectively. This was because their porosities were simpler and more conducive to supporting vertical forces. But they showed smaller surface 160
Composites Part B 162 (2019) 154–161
L. Zhao et al.
scaffolds for bone regeneration. J Mater Chem B 2018;6(3):499–509. [25] He HY, Zhang JY, Mi X, Hu Y, Gu XY. Rapid prototyping for tissue-engineered bone scaffold by 3D printing and biocompatibility study. Int J Clin Exp Med 2015;8(7):11777–85. [26] Helguero CG, Mustahsan VM, Parmar S, Pentyala S, Pfail JP, Kao I, et al. Biomechanical properties of 3D-printed bone scaffolds are improved by treatment with CRFP. J Orthop Surg Res 2017;12. [27] Hong JK, Roman M. Mechanical performance of 3D-printed porous nanocomposite bone scaffolds. Abstr Pap Am Chem Soc 2016;251. [28] Huan ZJ, Chu HK, Liu HB, Yang J, Sun D. Engineered bone scaffolds with Dielectrophoresis-based patterning using 3D printing. Biomed Microdevices 2017;19(4). [29] Huang BY, Bartlo PJ. Rheological characterization of polymer/ceramic blends for 3D printing of bone scaffolds. Polym Test 2018;68:365–78. [30] Tran P, Ngo TD, Ghazlan A, Hui D. Bimaterial 3D printing and numerical analysis of bio-inspired composite structures under in-plane and transverse loadings. Compos B Eng 2017;108:210–23. [31] Henriques B, Pinto P, Silva FS, Fredel MC, Fabris D, Souza JCM, et al. On the mechanical properties of monolithic and laminated nano-ceramic resin structures obtained by laser printing. Compos B Eng 2018;141:76–83. [32] Iraimudi V, Begum SR, Arumaikkannu G, Narayanan R. Design and fabrication of customised scaffold for femur bone using 3D printing. Mater Indus Manufac Eng Res Adv 2014;845:920–4. 11. [33] Jariwala SH, Lewis GS, Bushman ZJ, Adair JH, Donahue HJ. 3D printing of personalized artificial bone scaffolds. 3D Print Addit Manuf 2015;2(2):56–64. [34] Leukers B, Gulkan H, Irsen SH, Milz S, Tille C, Schieker M, et al. Hydroxyapatite scaffolds for bone tissue engineering made by 3D printing. J Mater Sci Mater Med 2005;16(12):1121–4. [35] Leukers B, Gulkan H, Irsen SH, Milz S, Tille C, Seitz H, et al. Biocompatibility of ceramic scaffolds for bone replacement made by 3D printing. Mater Werkst 2005;36(12):781–7.
[13] Lin LL, Zhang HC, Zhao L, Hu QX, Fang ML. Design and preparation of bone tissue engineering scaffolds with porous controllable structure. J Wuhan Univ Technol 2009;24(2):174–80. [14] Zhou CC, Ye XJ, Fan YJ, Qing FZ, Chen HJ, Zhang XD. Synthesis and characterization of CaP/Col composite scaffolds for load-bearing bone tissue engineering. Compos B Eng 2014;62:242–8. [15] Delabarde C, Plummer CJG, Bourban PE, Manson JAE. Biodegradable polylactide/ hydroxyapatite nanocomposite foam scaffolds for bone tissue engineering applications. J Mater Sci Mater Med 2012;23(6):1371–85. [16] Bak TY, Kook MS, Jung SC, Kim BH. Biological effect of gas plasma treatment on CO2 gas foaming/salt leaching fabricated porous polycaprolactone scaffolds in bone tissue engineering. J Nanomater 2014;8:1–16. [17] Fiorilli S, Baino F, Cauda V, Crepaldi M, Vitale-Brovarone C, Demarchi D, et al. Electrophoretic deposition of mesoporous bioactive glass on glass-ceramic foam scaffolds for bone tissue engineering. J Mater Sci Mater Med 2015;26(1). [18] Dong SJ, Wang L, Li QS, Chen XS, Liu SJ, Zhou YM. Poly(L-lactide)-grafted bioglass/poly(lactide-co-glycolide) scaffolds with supercritical CO2 foaming reprocessing for bone tissue engineering. Chem Res Chin Univ 2017;33(3):499–506. [19] Zhang BQ, Pei X, Zhou CC, Fan YJ, Jiang Q, Ronca A, et al. The biomimetic design and 3D printing of customized mechanical properties porous Ti6Al4V scaffold for load-bearing bone reconstruction. Mater Des 2018;152:30–9. [20] Deng ZB, Zhou CC, Fan YJ, Peng JP, Zhu XD, Pei X, et al. Design and characterization of porous titanium scaffold for bone tissue engineering. Rare Metal Mater Eng 2016;45(9):2287–92. [21] Ngo TD, Kashani A, Imbalzano G, Nguyen KTQ, Hui D. Additive manufacturing (3D printing): a review of materials, methods, applications and challenges. Compos B Eng 2018;143:172–96. [22] Wang X, Jiang M, Zhou ZW, Gou JH, Hui D. 3D printing of polymer matrix composites: a review and prospective. Compos B Eng 2017;110:442–58. [23] Du XY, Fu SY, Zhu YF. 3D printing of ceramic-based scaffolds for bone tissue engineering: an overview. J Mater Chem B 2018;6(27):4397–412. [24] Du XY, Yu B, Pei P, Ding HF, Yu BQ, Zhu YF. 3D printing of pearl/CaSO4 composite
161