Biocompatibility of hydrogel-based scaffolds for tissue engineering applications

Accepted Manuscript Biocompatibility of hydrogel-based engineering applications

scaffolds

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tissue

Sheva Naahidi, Mousa Jafari, Megan Logan, Yujie Wang, Yongfang Yuan, Hojae Bae, Brian Dixon, P. Chen PII: DOI: Reference:

S0734-9750(17)30058-7 doi: 10.1016/j.biotechadv.2017.05.006 JBA 7127

To appear in:

Biotechnology Advances

Received date: Revised date: Accepted date:

14 February 2016 8 May 2017 22 May 2017

Please cite this article as: Sheva Naahidi, Mousa Jafari, Megan Logan, Yujie Wang, Yongfang Yuan, Hojae Bae, Brian Dixon, P. Chen , Biocompatibility of hydrogel-based scaffolds for tissue engineering applications, Biotechnology Advances (2017), doi: 10.1016/j.biotechadv.2017.05.006

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ACCEPTED MANUSCRIPT

Biocompatibility of Hydrogel-Based Scaffolds for

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Tissue Engineering Applications

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Sheva Naahidi1,2,7,8*, Mousa Jafari3#, Megan Logan1#, Yujie Wang4, Yongfang Yuan4, Hojae Bae5,

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Brian Dixon6, P. Chen1,2*

# These authors contributed equally. * Corresponding authors: Sheva Naahidi, Pu Chen

Department of Chemical Engineering, University of Waterloo, 200 University Avenue West,

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Waterloo, Ontario, Canada N2L 3G1

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Waterloo Institute for Nanotechnology, University of Waterloo, ON, Canada Koch Institute for Integrative cancer research, Massachusetts Institute of Technology (MIT), Cambridge, MA, 02139-4307 USA 4 Department of Pharmacy, Shanghai Third People’s Hospital, School of medicine, Shanghai Jiao Tong University, Shanghai 201999, China. 5 College of Animal Bioscience and Technology, Department of Bioindustrial Technologies, Konkuk University, Hwayang-dong, Kwangjin-gu, Seoul 143-701, Korea 6 Department of Biology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario, Canada N2L 3G1 7 Center for Biomedical Engineering, Department of Medicine, Brigham and Women’s Hospital, Harvard Medical School, 65 Landsdowne Street, PRB 252, Cambridge, MA 02139, USA 8 Harvard-MIT Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA 02139, USA

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ABSTRACT

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Recently, understanding of the extracellular matrix (ECM) has expanded rapidly due to the accessibility of cellular and molecular techniques and the growing potential and value for hydrogels in tissue engineering. The fabrication of hydrogel-based cellular scaffolds for the generation of bioengineered tissues has been based on knowledge of the composition and structure of ECM. Attempts at recreating ECM have used either naturally-derived ECM components or synthetic polymers with structural integrity derived from hydrogels. Due to their increasing use, their biocompatibility has been questioned since the use of these biomaterials needs to be effective and safe. It is not surprising then that the evaluation of biocompatibility of these types of biomaterials for regenerative and tissue engineering applications has been expanded from being primarily investigated in a laboratory setting to being applied in the multibillion dollar medicinal industry. This review will aid in the improvement of design of non-invasive, smart hydrogels that can be utilized for tissue engineering and other biomedical applications. In this review, the biocompatibility of hydrogels and design criteria for fabricating effective scaffolds are examined. Examples of natural and synthetic hydrogels, their biocompatibility and use in tissue engineering are discussed. The merits and clinical complications of hydrogel scaffold use are also reviewed. The article concludes with a future outlook of the field of biocompatibility within the context of hydrogel-based scaffolds.

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KEYWORDS: biocompatibility; biomaterials; cellular scaffold; hydrogels; tissue engineering

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ACCEPTED MANUSCRIPT 1. Introduction

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Tissue engineering, a rapidly evolving field, has changed the therapeutic approach to tissue regeneration and replacement. The recent development of this field stems from reparative medicine in addition to the need for tissues and organs required for transplants. According to the U.S. Department of Health and Services, in 2009 only 28,463 patients received a transplant while over 100,000 patients remained on the waiting list (OPTN/SRTR Annual Report, 2009). Tragically, even after the transplant, patients are treated with immunosuppressants to prevent rejection of the transplanted tissue or organs for the remainder of their lives (Anderson, 2010; Marshall and Browner, 2007). This has led to the conclusion that allotransplantation is only a partial solution (Langer and Vacanti, 1999). The ideal way to circumvent these shortcomings is to use the patient’s own cells or a biodegradable material which can promote the ingrowth of neighboring tissues and cells or to serve as a provisional scaffold for transplanted cells to adhere, proliferate, and differentiate within. This strategy is expected to reduce the long waiting time for organ transplants while minimizing the risk of transplant rejection and the necessity for high-risk surgery. Consequently, this led to the creation of a new branch of research called tissue engineering, first introduced by Langer and Vacanti (Langer and Vacanti, 1993; Russell and Monaco, 1964). This interdisciplinary science arose from the combination of cell and developmental biology, basic medical and veterinary sciences, transplantation science, biomaterials, biophysics and biomechanics, bioimmunology and biomedical engineering (Langer and Vacanti, 1993; Lee et al., 2001). Expertise from these fields combined to undertake the immense task of creating living tissues from only a few cells and combining them with biomaterials such as poly(ethylene glycol)(Viola et al., 2003; Zhu, 2010), collagen (Gorgieva and Kokol, 2011), poly(lactic acid) (Majola et al., 1991) or de-cellularized extracellular matrix (ECM) (Badylak, 2004; Sreejit and Verma, 2013). These biomaterials can be used to compensate for donor shortages and allow patients a faster recovery time with fewer complications, increasing quality of life (Slaughter et al., 2009). The key characteristic that differentiates biomaterials from other materials is their ability to coexist and interact in the presence of specific tissues or physiological systems such as blood, interstitial fluids, and immune cells and molecules without inflicting an intolerable amount of damage (Tronci, 2010). A key concept in tissue engineering is selecting the proper biomaterial to design and produce an appropriate scaffold which induces no or minimal immune reaction from the recipient. Following recent technological advances and interests for the design and development of engineered biodegradable scaffold systems, tissue engineering has moved into a modern innovative era. Nevertheless, many, or perhaps most, of these bioengineered systems are being challenged mainly due to a lack of adequate data regarding their toxicity and biocompatibility. Key to understanding biocompatibility is the comprehension of which chemical, biochemical, physiological, physical or other mechanisms are activated by the contact of the biomaterial with the cells in the body and also to understand the consequences of these interactions (Williams, 2008a). Herein, this paper’s focus is to collect and review existing knowledge on the biocompatibility of hydrogel-based scaffolds.

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ACCEPTED MANUSCRIPT 2. Biocompatibility

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Biocompatibility is a field that first attracted the attention of researchers in the 1940s in the context of medical implants and their beneficial and harmful interactions with the body. In 1987, biocompatibility was formally defined as ”the ability of a biomaterial to perform with an appropriate host response in the specific application” (Naahidi et al., 2013; Williams, 1986). In 2010 Kohane and Langer explained biocompatibility in a new context and redefined it as “an expression of the benignity of the relation between a material and its biological environment” (Kohane and Langer, 2010; Naahidi et al., 2013). There is a wide variety of biomaterials that are used in tissue engineering that can generally be categorized as natural materials (derived from autologous (Williams, 2008b), allogenic (Chu et al., 1997; Williams, 2008b), or xenogenic (Anderson, 2001; Böstman et al., 1992) sources) and synthetic materials, or a blend of both types called hybrid materials (Bokhari et al., 2005; Kopeček, 2007). These materials can be processed and manipulated such that they have functional properties which form porous scaffolds that can be used for the restoration or modification of tissues (Anderson, 2010). These functional properties are the ultimate goals for biomaterial-based devices in vivo and include: restoration of the tissue with appropriate function and cellular phenotypic expression, inhibition of macrophage and foreign body giant cell responses that will degrade the material, inhibition of scar formation that may inhibit the function of the biomaterial, and lastly, inhibition of immune responses that could destroy the functionality of the device (Anderson, 2010; Yang et al., 2008). In the past, tissue engineering has attempted to create materials that will control the fate of the transplanted cell populations included in tissue reconstruction (Hwang et al., 2006; Jeong et al., 2006; Langer and Vacanti, 1993; Miroshnikova et al., 2011; Viola et al., 2003). However, cellular interactions have proven to be extremely complicated and consequently, today researchers have shifted their focus from creating bioactive materials to materials which give greater control over inflammatory and immune responses to reduce the chance of rejection in patients (Ishihara et al., 2010; Ratanavaraporn et al., 2012; Tongers et al., 2011). As a result the long-term co-existence of biomaterials and tissues has been the goal of many scientists. As such, biomimetic strategies taken from nature, such as the mechanisms viruses and bacteria use to evade the immune system, are being developed to create immune invisible biomaterials (Novak et al., 2009). Generally, once a biomaterial has been implanted, the body responds with one or more positive and/or negative reactions. These include blood interactions (hemolysis) (Amarnath et al., 2006; Anderson, 1993), stem cell interactions (Korkusuz et al., 2016), provisional matrix formation (Anderson, 2010; Bélanger and Marois, 2001), temporary inflammation (Clark et al., 1982), wound healing (Clark et al., 1982; Yang et al., 2008), the formation of granulation tissue (Anderson et al., 2008; Tabata et al., 1994), foreign body reaction (Anderson et al., 2008; Böstman et al., 1990) and oxidative stress (Mouthuy et al., 2016) . Further, tissue engineered devices can develop a fibrous capsule (scar) that can either surround the implant or infiltrate the porous material (Anderson, 2010). In addition, the body could develop an acquired or innate immune response to the biological component of the device, potentially rendering the biomaterial useless (Anderson, 2010). Therefore, a novel and ideal equation was suggested to quantitatively express biocompatibility (Ratner, 2016). Another problem with preliminary biomaterial testing is that the biomaterial-based implants are generally tested on non-human tissues (i.e. rat, mouse or dog). As a result, species-specific immune responses could be triggered when an engineered tissue that is meant for human is tested using a different species or a device 4

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tested in other animals is applied in humans. Ideally, the engineered tissue would be made using cells or components from one species and subsequently tested using that same target species. This approach would greatly decrease the probability of an immune response, although it does not completely guarantee the absence of one. As a specific example, Harriger et al. used glutaraldehyde-cross-linked bovine collagen as a scaffold to seed human keratinocytes and fibroblasts and then subsequently placed them on full-thickness wounds of athymic mice (Harriger et al., 1997). The work showed that glutaraldehyde crosslinking resulted in a decrease in the rate of degradation of collagen with no change in immunoreactivity in mice, as measured by HLA-ABC staining. However, this does not guarantee that such an implant will work clinically since athymic mice lack a thymus gland resulting in an inhibited immune system and a low number of T-cells capable of initiating reponses. The goal of evaluating the biocompatibility of any material is to determine any toxic effects to the body. Therefore, a biomaterial must be evaluated to determine the biological responses which could cause damage or unwanted side effects to the host (Anderson, 2010). The three major responses that should be taken into account are: inflammation, wound healing, and the immunological reaction/immunotoxicity (Anderson, 2010). Although standards for biological evaluation of medical devices (ISO:10993) have been published by the International Organization for Standardization, the biocompatibility of a substance can also be affected by other factors such as the nature and quality of the medical intervention, the age, sex, genetic background and health of the patient, as well as the presence of any microorganisms or endotoxins (Kohane and Langer, 2010). Therefore, the Standard Practice for “Evaluation of Immune Responses in Biocompatibility Testing of ASTM” (American Society for Testing and Materials) was withdrawn in 2011 due to its limited protocols with no replacement to date. It is hard to unify a standard approach with the development of implantable materials (Reeve and Baldrick, 2017). Taken together these data suggest that by using a biocompatible design based on designs seen in nature, advanced biomaterials can be generated to increase efficacy and lifespan of the implant (Novak et al., 2009). Therefore, tissue engineering would be enhanced upon the acquisition of knowledge and understanding of the interactions between natural materials and tissues, which is usually discussed in the context of biocompatibility.

3. Native Extracellular Matrix and Its Structure

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In all multicellular organisms, cells are structurally supported within a complex and bioactive scaffold, which is known as the ECM. ECM is a relatively structurally stable material that is also involved in dictating the fate of the cell such as migration, differentiation, and apoptosis. Cells generate the macromolecular components of the ECM and control its assembly. The ECM is composed of a complex mixture of proteins and polysaccharides, all of which are arranged in a specific manner that gives tissues their properties (Badylak, 2004). Native ECM is the ideal biological scaffold, since it contains all the components of the tissue from which it was derived except for the living cells (Sreejit and Verma, 2013). For instance, native cardiac extracellular matrix scaffolds could induce pluripotent stem cell-derived cardiomyocytes (Guyette et al., 2016). The nature of the ECM is highly tissue specific and offers many types of tissue specific cues including lending its own mechanical properties, giving bioactive cues to the 5

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microenvironment, acting as a reservoir for growth factors, and have susceptibility to degradation for cellular proliferation and neovascularization (Badylak, 2004; Böstman et al., 1992; Ziats et al., 1988; Kayabolen et al. , 2017). Collagen makes up more than 90% of the dry weight of most ECMs and 28 distinct types have been identified with specialized biological functions (Badylak, 2004; Cen et al., 2008; van der Rest and Garrone, 1991). These different types of collagen provide a diverse range of mechanical and structural properties for the ECM and contain ligands that interact with cells. In the body, the distribution and association of collagen with other proteins is the result of the genetic expression patterns of the cells as they develop and differentiate into organs and tissues. The high complexity of these natural associations between molecules creates difficulty when artificially recreating this delicate structure for bioengineering. The second most abundant protein in the body is fibronectin which is rich in arginine-glycine-aspartate (RGD) subunits, can exist both in tissue and soluble isoforms and contains ligands for adhesion of many different cell types (Hersel et al., 2003; McPherson and Badylak, 1998; Miyamoto et al., 1998; Schwarzbauer, 1991). This protein has also been found in the early stages of embryonic ECM development. For these reasons and because it is critical for normal biological development and cell-cell communication, the RGD peptide sequence is an attractive candidate for tissue engineering purposes. The ECM is also composed of a large mixture of glycosaminoglycans (GAGs), which bind growth factors and enhance water retention while giving the ECM some of its gel-like properties. Hyaluronic acid is one of the most commonly investigated GAGs in tissue engineering due to its high concentration in fetal and newborn tissues and association in wound healing processes (Badylak, 2004). These bioactive molecules, such as growth factors, have unique spatial organizations within the ECM and act as moderators of cell behaviour. Some growth factors have been purified and studied for therapeutic purposes, but therapeutic doses of growth factors are difficult to control and localize in the tissue (Badylak, 2004). Figure 1 is a schematic of all the components of the ECM and their arrangement outside the cell. Researchers have devised physical and chemical methods to decellularize tissues to isolate the ECM which can then be used as a scaffold for tissue regeneration (Hinderer et al., 2016). Decellularized tissues have been used for dermal (Reagan et al., 1997), heart valve (Yao et al., 2003), vascular (Kaushal et al., 2001),corneal (Wilson et al., 2013) and esophageal tissue regeneration. Some of the biocompatibility issues with decellularized ECM arise due to residual detergents, endotoxins, cell debris or changes in ECM fiber structure (Keane et al., 2015; Lee et al., 2014).

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Badylak et al. reviewed the host response to artificial ECM based scaffolds (Badylak and Gilbert, 2009). It is not surprising, then, that one of the first key issues in generating artificial tissue is the ability to design a biocompatible scaffold, which would closely mimic ECM of a specific tissue.

4. Artificial Scaffold For a long time the ECM was known as an inert supporting material, synthesized by the cells as mere scaffolding on or within which cells are situated. Inert substances have already 6

ACCEPTED MANUSCRIPT been shown to have superior biocompatibility and are usually chosen for their non-toxic, nonimmunogenic, and non-thrombogenic capabilities (Williams, 2009, 2008a). Having inert properties allows for biomaterials to be used for many applications in a multitude of tissues such as concealing foreign materials from the body as in hip replacements (Heimann, 1999) or stents (Zamiri et al., 2010). Recently, however, with the merging of tissue engineering and material sciences and in light of the active role of ECM described above, the definition of biomaterials has gone from an inert material to:

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‘a scaffold or matrix for a tissue engineering product refers to the ability to perform as a substrate that will support the appropriate cellular activity, including the facilitation of molecular and mechanical signalling systems, in order to optimize tissue regeneration, without eliciting any undesirable local or systemic response in the eventual host’ (Williams, 2008a)

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Thus the current goal of artificial scaffold engineers is to facilitate ECM production, host cell adhesion and proliferation since most cells in the body, with a few exceptions such as red blood cells, are anchorage-dependent (Chan and Leong, 2008). There are an enormous variety of scaffolds made from polymeric biomaterials capable of encapsulating cells, mitigating immune responses, tissue regeneration, or even acting as a barrier between tissues (Slaughter et al., 2009). For instance, hydrogels have long stood out because of their natural structural and compositional resemblances to the ECM. Additionally, hydrogels can be engineered to control cellular attachment, molecular responses, structural integrity, biodegradability and biocompatibility (Slaughter et al., 2009). While hydrogels possess these advantageous characteristics, researchers often have to compromise biocompatibility to increase structural integrity and degradability (Discher et al., 2005; Slaughter et al., 2009). For example, the degradability, cellular response, interaction with scaffold and biocompatibility of PEG hydrogels can be changed and regulated by adjusting the length of hydrolytically degradable lactic acid units within the polymer crosslink(Kong et al., 2004).

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The use of hydrogels for tissue engineering is relatively new and there is only a modest amount of data about their precise mechanisms and performance regarding biocompatibility. However, there are a wide range of materials and processing techniques that have been employed to create a hydrogel-based scaffold that mimic the native ECM. When designing an artificial ECM, engineers understand that scaffolds represent the space for tissues to develop and provide the physical cues for cell growth and 3D arrangement. Therefore, the overall goal of a biocompatible scaffold is to directly influence cells, support cell signalling and degrade in a controllable, non-toxic manner. The 3D structure and pore size of a scaffold should match that of the target cells and is fundamental for providing enough space for cells to migrate and for vascularization to occur (Karageorgiou and Kaplan, 2005). In addition, the pores should be large enough to allow for nutrients, metabolites and wastes to diffuse through the scaffold so that cells continue to remain viable deep within the scaffold (Slaughter et al., 2009). For instance, fibroblasts and endothelial cells were cultured in scaffolds with pore sizes ranging from 5 to 90 µm and fibroblasts were found to be able to connect to neighbouring cells in scaffolds with pore sizes larger than their cell dimensions using a bridging mechanism, while endothelial cells did not show this behaviour (Salem et al., 2002). The size of the pores has a direct influence on how the cells grow and proliferate on the material and should be determined by the type of tissue 7

ACCEPTED MANUSCRIPT being designed and the kinds of cells that it will incorporate, as well as allowing for adequate mass transfer.

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After the cells have populated the scaffold and started to produce their own ECM, the hydrogel should degrade into biocompatible by-products that can easily be excreted from the body (Hedberg et al., 2005). The degradation process must not incite an immune or inflammatory response from the body and if the polymer is synthetic, the breakdown products will be monomers, oligomers or fragments of the polymer. In some instances the polymer fragments may influence the behaviour of cells and in extreme cases these fragments can be cytotoxic, altering cell metabolism or respiration (Williams, 2008a). It is important for engineers to be able to control the degradation rate of a scaffold so that it can be tailored for different tissue types and cell growth rates. If the degradation products are pro-inflammatory, the host’s immune system will respond with an overwhelming number of macrophages and foreign body giant cells that may lead to the compromise the intended function of the material(Anderson et al., 2008). Furthermore, the scaffold needs to be bioactive in order to promote cell attachment and interact with cells to regulate their activity in a similar manner as the native ECM would. The biomaterial should include biological cues such as adhesion ligands as well as growth factors to enhance regeneration of the tissue (Drury and Mooney, 2003). For example, many materials have been functionalized with RGD peptide sequences to enhance cell adhesion and can also aid in cell selectivity and cause specific cell responses (Hersel et al., 2003). In recent years, a mathematical model was used to investigate the interplay among cell proliferation, ECM deposition and scaffold degradation (O’Dea et al., 2013). Use of the continuum model could predict the heterogeneity and relationship between cell proliferation rate and ECM deposition rate.

5. Hydrogels

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In this section, the application of natural and synthetic hydrogels in tissue engineering will be discussed. The application of hydrogels dates back to 1960, when Wichterle and Lim introduced the use of hydrophilic networks of cross-linked poly (2-hydroxyethyl methacrylate) as soft contact lens material (Van Vlierberghe et al., 2011; Wichterle and Lim, 1960). Hydrogels are a class of hydrated polymeric materials with a water content of ≥ 90% by weight (Drury and Mooney, 2003; Park and Lakes, 1992; Singh, 2009). They have been used since the 1960s for applications such as contact lenses and intraocular lenses due to their lack of foreign body response and high oxygen permeability (Singh, 2009). However, there are several biocompatibility issues with silicon hydrogel contact lenses which causes inflammatory responses in some individuals (Hall et al., 2014). Hydrogels were the first types of polymers developed for use in the human body (Blackshaw et al., 1997; Wichterle and Lim, 1960). Even before the field of tissue engineering gained momentum, hydrogels were already being used to encapsulate cells in the 1980s (Lim and Sun, 1980). Today, hydrogels are being employed for clinical applications such as wound healing (Singh, 2009) and more recently, they are being used as scaffolds to provide a biomimetic 3D microenvironment for the growth of cells (Blackshaw et al., 1997; Dillon et al., 1998; Kopeček, 2007; Yang et al., 2008). Numerous classifications have been applied to hydrogels based on their origin, durability, response to environmental stimuli, charge, structure or composition (El-Sherbiny and Yacoub, 2013). 8

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Additionally, hydrogels have long stood out because of their structural and compositional resemblance to the natural ECM. These materials can be easily engineered to control cellular attachment, molecular responses, structural integrity, biodegradability and biocompatibility (Slaughter et al., 2009). The ideal hydrogel scaffold will mimic the properties of the native ECM, and also will allow cell attachment and migration (Chan and Leong, 2008; Schwarzbauer, 1999), deliver and retain cells and biochemical factors(Chan and Leong, 2008), enable diffusion of nutrients and products (Slaughter et al., 2009), and finally exert mechanical and biological influences to modify the behaviour of the cell (Anderson, 2001; Kim and Mooney, 1998). To create such a scaffold, engineers use natural and/or synthetic hydrogels that are able to create a high surface area to volume ratio that closely mimics the natural pore size, mechanical strength, cellular attachment, molecular response, biodegradability, biocompatibility and solute transport of the target tissue (Chan and Leong, 2008; Slaughter et al., 2009). Table 1 lists the functions of the native ECM and the corresponding design characteristics for an engineered scaffold. Table 1- Functions of native ECM and how scaffolds are designed to mimic these properties Designed features for scaffolding

Reference(s)

Possess the correct porosity to allow for cell anchorage, proliferation, void volume for vascularization and be degradable. The scaffold should also actively influence cell morphology with such things as exogenous growth-stimulating factors.

(Chan and Leong, 2008; Hutmacher, 2000)

Allows for diffusion of nutrients, metabolites, and growth factors Storage depot for growth factors

Provide appropriate mass transfer ability to allow nutrients, growth factors and waste products to diffuse throughout the matrix

(Carletti et al., 2011)

Structures are available in the matrix to retain bioactive agents

(Kim and Mooney, 1998)

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Functions of Native ECM Provides the correct 3D environment and bioactive cues for interaction with cells

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Mechanical support to the tissue

Enable stress transfer and load bearing, while also giving shape stability to the tissue. Studies have shown that mature cell types are able to sense the stiffness of the material and response to the change. Addition of sodium N-lauroyl sarcosinate enhances the failure strain of the silk protein fibroin hydrogels.

(Discher et al., 2005)

(Zhang et al., 2015)

Although hydrogels have the advantageous features, some suffer from poor biocompatibility and recently many researchers have focused on improving their performance in this area (Aziz et al., 2015; Beenken-Rothkopf et al., 2012; Darnell et al., 2013; Popa et al., 2014). Conjugation methods and ionic charges on the polymer are some of the aspects that could 9

ACCEPTED MANUSCRIPT be modified to improve poor biocompatibility (Silva-Correia et al., 2013; Zhu and Marchant, 2011). For instance, cations control the swelling and viscoelastic properties in many alginate hydrogels, but the presence of cations adversely affects the biocompatibility of the hydrogel (Hyland et al., 2013; Lee et al., 2013).

5.1. Natural Materials used in Hydrogels

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Naturally derived scaffolds such as decellularized ECM, collagen, chitosan, elastin, alginates, hyaluronic acid, pullulan and fibrin have been processed from living organisms and possess good biocompatibility properties with low cytotoxicity. These compounds, depending on concentration and purity, do not induce a chronic inflammatory response (Gomes et al., 2008). Despite these advantages, these polymers suffer from batch-to-batch variability, difficult processing, and poor control over material properties (Hutmacher, 2000). Methods used to control the material strength, degradation rate, or decrease the immune response generally result in the scaffold material becoming less biocompatible (Badylak, 2004). Table 2 summarizes the natural polymers and the type of application.

Cell Types Studied

Collagen

Chondrocytes, Astroglial cells

Applications

Cartilage, Neural, Skin, Spinal Cord, Vocal Cord

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Table 2-Overview of Natural Polymers and their Applications

Chondrocytes, Fibroblasts

Cartilage, ECM

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Gelatin

Hyaluronic Acid

Chondrocytes, Fibroblasts, Human Embryonic Stem Cells

Cartilage, Connective Tissue, ECM, Eye, Facial, Intraperitoneal, Skin, Vascular

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References (Hahn et al., 2006; Itoh et al., 2002; Joosten et al., 2004; Liao et al., 2007; Tang et al., 2007; Thacharodi and Panduranga Rao, 1996; Willers et al., 2005) (Gong et al., 2007; Shu et al., 2006; Tabata et al., 1994) (Burns et al., 1995; Duranti et al., 1998; Gerecht et al., 2007; Ghosh et al., 2006; Liao et al., 2007; Pape and Balazs, 1980; Peattie et al., 2004; Shu et al., 2006, 2004; Stevens et al., 2005; Tabata et al., 1994; Tang et al.,

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Pullulan

Stem cell culture, Vascular, Skin, Cartilage, Soft tissues

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5.1.1. Collagen

(Autissier et al., 2007; Bae et al., 2011a; Bulman et al., 2015; Li et al., 2016; Wong et al., 2011)

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Collagen is the most abundant protein found in mammalian ECM and therefore this makes it a very attractive molecule for tissue engineering applications (Lee et al., 2001). Collagen fibers are self-aggregating triple-stranded helical structures that are held together by both hydrogen and covalent bonds. Collagens are also found in strong connective tissues such as fibrocartilage or articular cartilage (Lee et al., 2001). These fibers can be easily manipulated and their mechanical strength can be altered to inhibit in vivo degradation (Gomes et al., 2008; Park and Lakes, 1992) by using chemical crosslinkers (Slaughter et al., 2009), crosslinking with physical treatment (Weadock et al., 1995), or by blending with other polymers (Park et al., 2002). Collagen is degraded naturally by collagenase and serine proteases, allowing degradation to be locally controlled by the cells present in the specific tissue (Lee et al., 2001; Park and Lakes, 1992). Collagen has been blended with other natural materials, such as alginate (Hahn et al., 2006), chitosan (Tan et al., 2001; Tangsadthakun et al., 2006), hyaluronic acid (Liao et al., 2007; Park et al., 2002; Tang et al., 2007), and synthetic materials such as poly(glycolic acid), poly(lactic acid), or poly(ethylene oxide) (Chen et al., 2001; Huang et al., 2001; Park and Lakes, 1992). Collagen can also take many different forms such as sponges, granules and gels, which are controlled by the arrangement of the collagen strands and the amount of crosslinking induced. Collagen is a good material for generating hydrogels since it is a natural ECM protein that contains the signals that promote cell adhesion and function. It can support many different cell types and has been used for creating synthetic tissues such as heart valves (Taylor et al., 2006), cartilage (DeLustro et al., 1986), skin (Tangsadthakun et al., 2006), spinal cord (Joosten et al., 2004) , vocal cord (Hahn et al., 2006; Slaughter et al., 2009) and breast reconstruction (Cavallo et al., 2015) . Recently, Calabrace et al. reported that a collagen-based scaffold induces early chondrogenic commitment and its combination with bioactive factors induces in vitro complete differentiation (Calabrese et al., 2017). They have also shown that a collagen/hydroxyapatite biomimetic scaffold in combination with human MSCs could induce new bone formation in vitro (Calabrese et al., 2016a)and in vivo, after implantation of the empty scaffold into the dorsum of mice (Calabrese et al., 2016b). Wong and Lo have reviewed the properties and design considerations of collagen-based scaffolds for brain tissue engineering (Amy CY Lo and Lo, 2015). Most of the collagen used in tissue engineering is derived from human or animal sources which can lead to disease transmission and other immunological problems, but in fact marine collagen matrices perform better in in vitro compatibility tests (Benedetto et al., 2014). Understanding of the immunochemical responses of implants containing collagen can be blurred by the presence of non-collagenous proteins (DeLustro et al., 1986), cells and cell remnants (Allaire et al., 1994; Esses and Halloran, 1983) and residues left from crosslinking (Dahm et al., 11

ACCEPTED MANUSCRIPT 1990; Jayakrishnan and Jameela, 1996; Speer et al., 1980; Yan et al., 2010). Unfortunately, there is almost a complete absence of standard methods for purification and characterization of reconstituted collagen, which in turn makes it extremely difficult to distinguish the exact causes of immunological reactions and whether or not collagen is the actual cause of the reaction (Lynn et al., 2004). In this article, for simplicity, we will only consider the reactions due to collagen itself.

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The electrospinning technique has been used to fabricate well-aligned composite fibers from collagen and other proteins. The collagen becomes biocompatible due to homogeneous mixing in the electrospun fibers (Zhu et al., 2015). Heat and low pressure cause weak denaturation and combine to form cross-links between the collagen fibers and thus elevate biocompatibility (Nakada et al., 2013). Carbodiimide cross-linking had also been certified useful to enhance the biostability and biocompatibility of collagen-chitosan scaffolds (Chen et al. , 2016).

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Immunogenic responses caused by collagen are dependent on both the donor and recipient species and include reactions such as granulomatous foreign body reaction (McGregor et al., 1986) and induced collagen allergy (Nelson et al., 2001). Antibodies interact with collagen, mainly as a weak antigen, in three ways: helical, central and terminal (Lynn et al., 2004). Helical interactions occur when the antibodies recognize epitopes in the 3D conformation of the triple helix. Central recognition occurs within the triple helix and is determined solely by the amino acid sequence and not the 3D structure (Lynn et al., 2004). Terminal epitopes are located at the end of the protein in the non-helical portion of the protein (Lynn et al., 2004). The amino acid sequences of the helical region of collagen vary no more than a few percent between mammalian species, whilst up to half of the amino acid sequences at the terminal regions have been found to vary between species (Fietzek and Kühn, 1976; Furthmayr and Timpl, 1976; Lynn et al., 2004). In order to overcome these variations scientists have removed the terminal telopeptides to create atelocollagens (Kohmura et al., 1999; Onodera et al., 2002; Vizárová et al., 1994; Yamamoto et al., 1992), although this has not yet shown a lot of clinically significant immunological benefit (Lynn et al., 2004). However, recently a scaffold containing atelocollagen and poly(D, L-lactide-co-glycolic acid: PLGA) did show superior biocompatibility in soft tissues (Takechi et al., 2012). Other documented reactions to collagen devices for such uses as dermal (for wound dressing and wound closure), osseous (for bone defect and bone grafting), and cosmetic replacement such as skin needling, show that immunological reactions occur very infrequently (Lynn et al., 2004). Lynn et al. have written a comprehensive review on the antigenicity and immunogenicity of collagen in relation to its clinical applications (Lynn et al., 2004).

5.1.2. Gelatin Gelatin is a useful material since it is the denatured form of collagen which retains bioactive properties such as RGD sequences and matrix metalloproteinase (MMP) sensitive degradation sites, and is very inexpensive (Barker et al., 1980; Elzoghby, 2013; Panduranga Rao, 1996). Gelatin forms a thermally reversible gel that dissolves at body temperature and is the product of partial hydrolysis of collagen. This polymer is attractive for tissue engineering due to 12

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its ease of modification, low level of immunogenicity and cytotoxicity, and its use as a clotting agent (Panduranga Rao, 1996). Like most hydrogels, gelatin lacks significant mechanical strength and is subject to rapid enzymatic degradation which is commonly overcome by chemical or physical crosslinking (Choi et al., 1999a). Chemical crosslinking agents such as glutaraldehyde (Gendler et al., 1984), carbodiimide, diphenylphosphoryl azide and methacrylic anhydride (Nichol et al., 2010) have been used to crosslink gelatin, however, these crosslinking agents are often cytotoxic or elicit immunological responses from the host (Choi et al., 1999a, 1999b; Crescenzi et al., 2002; Liang et al., 2003; Park and Lakes, 1992; Stevens et al., 2002). Also, cell viability is decreased in proportion to longer crosslinking times (Shin et al., 2012). Recently, it has been noted that mechanical strength can be increased by a double-network strategy (DN) in order to engineer photo-crosslinkable gelatin and gellan gum (Shin et al., 2012). However, the potency of the DN hydrogels was reduced when they were arranged in cellcompatible conditions, and the encapsulated cells in the DN hydrogels did not function as well as gelatin hydrogels. Therefore they proposed microgel-reinforced hydrogels from the same gelatin and gellan gum, with a better mechanical strength and biological properties in comparison to the DN hydrogels (Shin et al., 2014). Good biocompatibility can also be obtained by blending gelatin with biocompatible and nontoxic materials, such as chitosan (Han et al., 2014) or dextran aldehyde (Jalaja et al., 2014).

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The alternative is to physically crosslink the polymeric strands with UV irradiation or thermal conduction (Panduranga Rao, 1996; Weadock et al., n.d.). Gelatin has shown no antigenicity in physiological conditions (Sela and Arnon, 1960), although it has been shown to activate macrophages to some extent (Anderson and Miller, 2006; Tabata and Ikada, 1987) and exhibits high hemostatic effect (Chvapil, 1982). Biocompatibility of gelatin and gelatin-based biomaterials can be improved by including a surface-modified hydroxyapatite sponge scaffold (Carpena et al., 2015; Li et al., 2014). Nano-hydroxyapatite can be deposited on the surface by alternating a soaking process and an electrospinning process. The alternate soaking process promotes better cellular adhesion and proliferation (Jaiswal et al., 2013). In addition, methacrylated gelatin (GelMA) has been shown to be a potent inducer of nascent blood vessel formation in vivo compared to collagen-based hydrogels (Chen et al., 2012).

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5.1.3. Hyaluronic Acid

Hyaluronic acid (HA) is a relatively simple GAG present in mammals, characterized by repeating disaccharide units made up of (β-1,4)-linked D-glucuronic acid and (β-1,3)-linked Nacetyl-D-glucosamine (Slaughter et al., 2009). It is found in almost all tissues in adult mammals including skin, umbilical cord, synovial fluid (Park and Lakes, 1992) and vitreous humor, and is essential for cell growth, embryonic development, wound healing, and tumor development (Noble, 2002; Plattt and Szoka, 2008; Toole, 2004). HA is commonly extracted from rooster combs and human umbilical cords or is manufactured by bacterial fermentation (Lapč k et al., 1998). Hyaluronidase degrades HA into smaller oligosaccharides, but in addition to enzymatic degradation, reactive oxygen intermediates can also degrade HA (Stern et al., 2006). Hyaluronic acid fillers typically fall into one of two categories, monophasic or biphasic, based on variations 13

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in crosslinking (Flynn et al., 2011). There is no cell toxicity in monophasic and biphasic fillers, moreover biphasic hyaluronic acid fillers have some advantages in hyaluronidase resistance and syringeability (Park et al., 2013). High molecular weight HA is water soluble, biodegradable, angiogenic and non-immunogenic. On the other hand, low molecular weight HA is seen as inflammatory, immunostimulatory and angiogenic (Lapč k et al., 1998; Stern et al., 2006). Thus, crosslinking is introduced in order to reduce the rapid in vivo degradation of HA, but it can also slow the release of drugs from the gel in therapeutic applications. HA hydrogels are made by covalent crosslinking with hydrazide derivatives (Gamini et al., 2002; Mensitieri et al., 1996), by esterification (Prestwich et al., 1998; Vercruysse et al., 1997;(Sahapaibounkit et al. , 2016)), by annealing (Fujiwara et al., 2000; Park and Lakes, 1992), or by electrospinning cryogelation (Kemence and Bolgen, 2017). Transglutaminase cross-linked gelatin hydrogels also showed greater biocompatibility (Alarake et al. , 2017). Photopolymerization with UV-initiators can enhance the biocompatibility of hyaluronic acid based materials during crosslinking (Kim et al., 2015). UV-initiators which react to visible light can be helpful for the phase transfer-catalyzed synthesis of highly acrylated hyaluronan forming dimensionally stable hydrogels (Becher et al., 2013). Due to HA’s hydrophilic nature, cell adhesion is limited which makes it useful for postsurgical adhesion barriers (Slaughter et al., 2009). Thiol-modified HA can be further modified with RGD sequences in order to increase cell recruitment and proliferation of the material (Massia and Hubbell, 1991; Park et al., 2006). HA has been the subject of many reviews focusing on its biological functions medical applications such as visco-supplementation (Moreland, 2003), and wound healing (Jiang et al., 2007). However, Collins and Birkinshaw (Collins and Birkinshaw, 2013) reviewed HA and HA derivatives that have been used specifically for tissue engineering applications.

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5.1.4. Pullulan

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Pullulan is produced by the fungus species Aureobasidium pullulans and is a linear, water soluble exopolysaccharide composed of α-1,6-linked maltotriose residues (Ball et al., 1992; Bruneel and Schacht, 1995; Coviello et al., 2007). This polysaccharide favors cell adhesion and is biodegradable, hemocompatible, non-immunogenic, non-carcinogenic, and as a result is FDAapproved for numerous applications (Bae et al., 2011b; Bruneel and Schacht, 1995; Kimoto et al., 1997; Leathers, 2003; Rekha and Sharma, 2007). Recently, pullulan has been used for tissue engineering, wound healing, and both drug and gene delivery (Coviello et al., 2007; Dionísio et al., 2013; Leathers, 2003; Li et al., 2011; Nitta and Numata, 2013; Thébaud et al., 2007). However, the hydrophilic nature of pullulan-based polysaccharide scaffolds may prevent the adsorption of proteins, limiting support for cellular attachment and spreading (Lavergne et al., 2012). Cutiongco et al. indicated that cell interaction and spatial distribution could be enhanced by the combination of pullulan-dextran polysaccharide scaffolds with interfacial polyelectrolyte complexation (PEC) fibers (Cutiongco et al., 2014). Yim et al also reported PEC fiber as a biostructural unit and biological construct for tissue engineering applications (Yim et al., 2007). Bae et al. showed that by adding methacrylate groups for the hydroxyl groups on pullulan they were able control the physical properties to yield tunable mechanical and swelling properties 14

ACCEPTED MANUSCRIPT (Bae et al., 2011b). They also integrated gelatin methacrylate with the pullulan methacrylate (PulMA) and found that the biological properties (i.e. cell adhesion, proliferation and elongation) were enhanced leading to the suggestion that PulMA can be used for applications such as hepatic and embryonic stem cell cultures (Bae et al., 2011b).

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Pullulan has excellent film-forming properties, but low mechanical properties (Bumbu et al., 2003; Cascone et al., 1997). Mechanical properties of pullulan can be increased by crosslinking the pullulan with the dextran (Aschenbrenner et al., 2013) or human-like collagen (HLC) (Li et al. , 2016). However, dextran is known to reduce cell adhesion and spreading (Massia et al., 2000) while HLC has good biocompatibility, biodegradability, workability and no risk of viral infection (Zhu et al. , 2009). Dextran and pullulan synthesized by crosslinking can promote the proliferation of endothelial cells (Machy et al., 2000) and inhibit the creation of vascular smooth muscle cells in vitro (Autissier et al., 2007). However, Abed et al. demonstrated that adding more than 25% pullulan to dextran induced an increased inflammatory reaction (Abed et al., 2011). The inflammatory reaction seems to be solely due to the degradation of pullulan gel fragments. Amrita et al. showed the potential of pullulan-based composite scaffolds in bone tissue engineering with improved osteoconductivity by pore wall mineralization (Amrita et al., 2015). Therefore, if pullulan is used at a suitable concentration with proper techniques, it demonstrates tremendous potential for applications in the medical and pharmaceutical fields.

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5.2. Synthetic Materials used in hydrogels

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Synthetic polymers offer engineers highly versatile materials with physical and chemical properties that can be easily controlled and altered (Park and Lakes, 1992). One such property is degradability, which can be altered by creating copolymers or polymer blends. These polymers and blends are generally easier to process than natural polymers and have more predictable results. Conversely, synthetic polymers are less biocompatible than naturally derived polymers and not as bioactive.

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5.2.1. Poly(lactic acid) and Poly(glycolic acid)

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These thermoplastic aliphatic polyesters are some of the most studied synthetic biomaterials in the past, have proven to be of satisfactory biocompatibility (Athanasiou et al., 1996; Christel et al., 1983; Ignatius and Claes, 1996) and have been approved by the US Food and Drug Administration for certain human clinical applications (Ratner, 2013). The use of these biodegradable polyesters for appropriate and faster fixation of long bone fractures was first clinically put into practice in Finland in 1984 (Rokkanen et al., 1985). Since the 1990s, the applications of poly(lactic acid) (PLA) and poly(glycolic acid) (PGA) and their copolymers, poly(lactic acid-co-glycolic acid) (PLGA) have been extensively investigated for tissue engineering (Gunatillake and Adhikari, 2003); and mostly used for bone or cartilage engineering due to their mechanical strength and biodegradability(Böstman, 1991; Gentile et al., 2014; Moran et al., 2003; M. Vert et al., 1992)

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Degradation of PLA and PGA primarily occurs through random hydrolytic chain scission (Böstman et al., 1990). Several studies have shown a high rate of inflammation and osteolytic reactions when PLGA/PGA constructs with molecular weights of 10,000-20,000 Dalton were implanted in bone. In this case researchers attributed the inflammation to the degradation of PLA and PGA into their soluble forms (Ali et al., 1993; Böstman et al., 1992; Matsusue et al., 1992; Schakenraad et al., 1990; Spenlehauer et al., 1989; Suganuma and Alexander, 1993). Enzymatic degradation of these polymers and acceleration of their breakdown by free radicals which are released from activated macrophages and neutrophils has also been demonstrated (Ali et al., 1993; Suganuma and Alexander, 1993; Williams and Mort, 1977; Williams, 2006). Thus, a major concern for the use of these polymers is their degradation. In the case of bone tissue engineering, intermediate degradation products decreases the local pH which induces an inflammatory reaction and damages bone cells at the implant site. Furthermore, the rapid drop of pH in vivo accelerates the polymer’s degradation. This results in a loss of mechanical properties before new bone formation occurs (Liu et al., 2006). The ratio of lactic acid to glycolic acid could influence the degradation as well. A higher proportion of lactic acid conferred a longer biodegradation time which would provide sufficient support for tissue regeneration during wound healing (Rogers et al., 2013). Recently, nano-hydroxyapatite/PLA scaffolds have been found to be more biocompatible with human bone marrow-derived mesenchymal stem cells (hMSCs) (Zong et al., 2014), osteoblast-like human bone fibroblast (MG-63) cells (Cecen et al., 2014, Nga et al. , 2015) and bovine amniotic epithelial stem cells (Russo et al. , 2016). Although, poly-glycolic acid scaffolds were biocompatible, N-Methyl-2-pyrrolidone, a stabilizer used to produce PLGA scaffold, increased the expression of IL-8 by human dental pulp stem cells (Leong et al. , 2016). The electrospinning technique (Hidalgo et al., 2013), room temperature ionic liquids (RTILs) (Lee et al., 2012) and organic solvent-free extraction (Zhao et al., 2011) are other effective methods to improve the biocompatibility of PLA scaffolds. PLA, PGA and PLGA are also used for the temporary management of pathologically altered tissue architectures including ligaments, skin, vascular tissues and skeletal muscle (Dhandayuthapani et al., 2011). These implanted scaffolds have shown structural support, the ability to guide new tissue formation and to degrade completely in the body. For a detailed review on the biocompatibility of PLA/PGA materials, see Anthanasoiu et al. (Athanasiou et al., 1996).

5.2.2. Poly(ethylene oxide) and Poly(ethylene glycol)

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Poly(ethylene oxide) (PEO) and poly(ethylene glycol) (PEG) are FDA-approved and are some of the most commonly used materials for synthesizing hydrogels in tissue engineering (Park and Lakes, 1992). PEO is a hydrophilic polymer that is generally inert with limited immunogenicity, antigenicity, protein binding and cell adhesion (Alcantar et al., 2000; Merrill and Salzman, 1983). Its inhibition of protein binding is thought to be due to the lack of hydrogen donating groups (Ostuni et al., 2001). PEG, the shorter version of PEO with lower molecular weight, became popular in the 1970s as scientists discovered the polymer’s ability to block protein adsorption (Ostuni et al., 2001). Both PEO and PEG hydrogels are capable of photo-polymerization, have adjustable mechanical properties, plus easy control of scaffold architecture and chemical composition, all of which make them attractive scaffolds to produce 3D templates for tissue regeneration. However, 16

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these two hydrogels alone cannot provide a complete environment to support cell adhesion and tissue formation due to their bio-inert nature. Block copolymers of PEO with poly(L-lactic acid) (PLLA) (Huh and Bae, 1999; M. Saffer et al., 2011), and PEG with PLLA (Jeong et al., 1997) have been combined to form thermally reversible hydrogels. In addition, degradable PEO and PEG hydrogels have been created by combining them with carboxymethyl cellulose (Lee et al. , 2015), hydrolytically degradable PLA (Mann et al., 2001a) or with enzyme cleavage sequences of oligopeptides (Metters et al., 2000; Park and Lakes, 1992; West and Hubbell, 1999). Therefore, PLLA/PEG composites have good adhesion prevention and a high degradation rate, which can reduce the production of inflammatory cytokines, such as tumor growth factors (TGF-β) (Ehashi et al., 2014). An electrospun nanoweb of short-term absorbable PLGA with PEO shows good biocompatibility (Böhm et al., 2011). Also, PEG-PLGA based thermosensitive injectable hydrogels have better biocompatibility and biodegradability than Poloxamer, which is a triblock copolymer composed of polyoxypropylene (PPO), central hydrophobic chains and two hydrophilic chains of PEO (Saraf et al., 2013). Hou et al. reviewed different material designs and fabrication approaches for the development of bioactive PEG-based scaffolds for tissue engineering application (Hou et al., 2010). PEG has extensively been used for coating purposes. For instance, it has been used to coat the carrier and/or toxic drugs for delivery. This has been shown to increase biocompatibility due to PEG’s nonimmunogenicity, nonantigenicity and protein rejection properties (Alcantar et al., 2000). Additionally, it has been shown that by grafting PEG to solid surfaces, protein adsorption and cell adhesion can be reduced (Andrade et al., 1996; Harris, 1992; Lee et al., 1995). Also adding PEG, both in vitro and in vivo, can suppress platelet adhesion. This suppression in turns minimizes the risk of thrombus formation, tissue damage, and other cytotoxic effects (Alcantar et al., 2000; Nagaoka and Nakao, 1990). Researchers have also incorporated RGD sequences to PEG to increase cell attachment and spreading (Bezwada et al., 1995; Yang et al., 2005; Zhu, 2010). A number of cell lines including fibroblasts, chondrocytes, vascular smooth muscle cells (SMCs), endothelial cells (ECs), osteoblasts, neural cells, and stem cells have been immobilized on bioactive PEG hydrogels (Lutolf and Hubbell, 2005; Tibbitt and Anseth, 2009). Burdick et al. have shown that Acr-PEG-RGD increased osteoblast attachment, spreading and mineralization of rat calvarial osteoblasts (Burdick and Anseth, 2002). PEG-RGD can significantly decrease the nonspecific adsorption of proteins from serum and fibrinogen from plasma, thus decreasing the risk of thrombus formation and improving the blood compatibility of implanted materials as well (Wang et al., 2011). Recent work has shown good biocompatibility of PEG, PEG-chitosan, multi-arm PEG and PEG- polypeptides (Escudero-Castellanos et al., 2016), (Cheng, 2016). For a comprehensive review of the physical characteristics and hemocompatibility of PEG, please refer to reference (Lee et al., 1995).

5.2.3. Poly(caprolactone) Poly (caprolactone) (PCL) is semi-crystalline, restorable aliphatic polyester, which has been approved by the FDA for medical devices and drug delivery vehicles (Darney et al., 1989; Marra et al., 1998). It has more recently been used as a bone graft substitute and is used extensively in bone tissue engineering (Hutmacher et al., 2001a; Kweon et al., 2003; Marra et al., 17

ACCEPTED MANUSCRIPT 1999). PCL has exhibited excellent biocompatibility in human fibroblasts and periosteal cell culture systems (Salgado et al., 2012).

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Nevertheless, the application of PCL has been limited due to its degradation and resorption kinetics; they are considerably slower than other aliphatic polyesters because they take over three years for complete degradation (Böstman et al., 1989; Sun et al., 2006). This is because of their hydrophobic character and high crystallinity (Kweon et al., 2003). Degradation of PCL initially occurs in amorphous domains of the material and as a result the crystal domains remain untouched (Chen et al., 2000). This stage involves non-enzymatic bulk hydrolysis of the ester linkages, which are catalyzed by the carboxylic acid end groups (Pitt et al., 1981). After the material becomes very brittle with extensive hydrolysis, a foreign body response consisting of giant cells and macrophages with a few neutrophils occurs (Anderson and Langone, 1999; Woodward et al., 1985). One percent chitosan and eight percent PCL blended at a 1:3 ratio can enhance bioactivity and protein adsorption with no cytotoxicity (Shalumon et al., 2011). Thrombus formation on PCL can been significantly decreased by surface engineering of poly caprolactone with curdlan sulphate and heparin (Khandwekar et al., 2011). However, the channel size of the scaffold can also influence cell proliferation (Sharaf et al., 2012). Using electrospinning and crosslinking techniques to combine PCL and PEG, one can develop a product that exhibits good biocompatibility (Yu et al., 2014). However, chemical crosslinking can produce chemical residuals, which might cause toxicity and irritation. A two-step modification via air plasma and carbodiimide crosslinking could enhance the biocompatibility of polycaprolactone (Sahapaibounkit, Prasertsung, 2016). Table 3 summarizes the application and biocompatibility characteristics of most commonly used synthetic materials in tissue engineering.

Degradable Polymer

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Table 3- Comparison of the biocompatibility, degradation and application of a selected number of synthetic materials commonly used in tissue engineering. Biocompatibility

PLA PGA

Enzymatic hydrolysis Degradation PLGA products in metabolic pathway Localized inflammation

poly(ε-

PCL

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ploy(lactic acid) poly(glycolic acid) poly(lactic-coglycolic acid)

Hydrolysis

Degradation Time Bulk: 5 months to ~5 years Bulk: 1 to ~12 months Bulk: 1 to ~12 months

Applications

References

Skin, Cartilage, Bone, Ligament, Tendon, Vessels, Nerve, Bladder, Liver, Kidney, Tumor

(Anderson and Langone, 1999; Athanasiou et al., 1996; Babensee et al., 2000; Böstman et al., 1989; Chu et al., 1997; Freed et al., 1993; Fu et al., 2000; Honda et al., 2000; Sarazin et al., 2004; Schakenraad et al., 1990;) (Lih et al. , 2016); (Li et al. , 2015); (Tajbakhsh and Hajiali, 2017); (Santoro et al. , 2016)

Bulk: more

Skin, Cartilage,

(Choi and Park, 2002;

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than 3 years

PEO

Hydrolysis Bulk: 1 Mild foreign body month to ~5 reaction years No inflammation

poly(ethylene glycol)

PEG

Hydrolysis Minimal foreign body reaction

Skin, Cartilage, Bone, Muscle

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Bine, Ligament, Honda et al., 2000; Tendon, Vessels, Hutmacher et al., 2001b; Wang, 1989;) Nerve, Retina (Naghashzargar et al. , 2015); (Sepahvandi et al. , 2016)

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Varies with composition

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Skin, Vessels, Nerve, Bone, Cardiovascular, Cartilage, Intraperitoneal, Liver,

(Bakker et al., 1988; Beumer et al., 1994; Bezemer et al., 1999; Bulstra et al., 1996; Deschamps et al., 2002; Mahmood et al., 2004; Mensik et al., 2002; Olde Riekerink et al., 2003; van Blitterswijk et al., 1993; Van Dijkhuizen-Radersma et al., 2002) (Behravesh et al., 1999; Bryant et al., 2004; Burdick et al., 2001; Chowdhury and Hubbell, 1996; Cruise et al., 1999; Elbert and Hubbell, 2001; Elbert et al., 2001; Elisseeff et al., 1999; Fischer et al., 2001; He et al., 2000, 2001; Hill-West et al., 1995, 1994; Hwang et al., 2006; Kraehenbuehl et al., 2008; Kuo and Ma, 2001; Lee et al., 2006; Lutolf et al., 2003; Mann et al., 2001a, 2001b; Seliktar et al., 2004; Sharma et al., 2007; Varghese et al., 2008; West and Hubbell, 1996; Williams et al., 2003; Yang et al., 2005; Zisch et al., 2003;) (Stevens et al. , 2015)

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Engineers and material scientists have reported mostly on the effects of the composition and physicochemical properties of hydrogels in the context of hydrogel-based scaffolds for tissue engineering and regenerative medicine. Nevertheless, adverse immune reactions to hydrogels have posed crucial challenges that require expert attention. Thus, this review has surveyed and summarized the recent findings on biocompatibility of hydrogel-based scaffolds used in tissue engineering applications. Biocompatibility is a term that is used broadly within biomaterial science, but there is still a great deal of uncertainty about its meaning as well as about the mechanisms that collectively need to be inhibited to produce biocompatibility. While effective and biocompatible cellular hydrogel scaffolds have been the the goal of scientists and engineers for many years, we are still far from the ultimate goal of designing perfectly biocompatible cellular scaffolds for effective tissue engineering, which points to the growing importance of this research area in relation to human health. As hydrogels have promising potential to mimic native ECM, uncertainty over the mechanisms and conditions of biocompatibility are becoming a serious obstacle to the development of new hydrogel-based scaffolds. Consequently, the question of whether hydrogel materials could mark an end to the necessity for biocompatible smart cellular scaffolds rests upon understanding and clarification of the concept of biocompatibility and represents a major area of interest in the field of tissue engineering. Currently, the advancement of hydrogels for use in tissue engineering rests on the ability to predict the possible toxicological reactions to the material and on characterizing the ideal structural and chemical properties of the polymer in the appropriate host to reduce the immune response and chance of rejection in patients. However, future work should focus on engineering of hydrogels that control and modulate the immune cells such as macrophages and controlling the plasticity and reprogramming (modulating M1– M2 polarization) to form/repair/reconstruct tissues. Additionally, and perhaps of equal importance, is to engineer smart regenerative hydrogels to guide the spatial organization, growth, proliferation, and differentiation of cells with integrated spreading, and that provide an orientation that promotes clinical implementations of tissue engineering.

Acknowledgments

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The authors would like to thank Faramarz Edalat for the proofreading of the initial draft. The authors are grateful for the financial support from the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Foundation for Innovation (CFI), Waterloo Institute of Nanotechnology (WIN) and the Canadian Research Chairs (CRC) program.

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ACCEPTED MANUSCRIPT References 2009 OPTN/SRTR Annual Report of the U.S. Organ Procurement and Transplantation Network and the Scientific Registry of Transplant Recipients: Transplant Data 1999-2008, n.d. . Rockville, MD.

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Abed, A., Assoul, N., Ba, M., Derkaoui, S.M., Portes, P., Louedec, L., Flaud, P., Bataille, I., Letourneur, D., Meddahi-Pellé, A., 2011. Influence of polysaccharide composition on the biocompatibility of pullulan/dextran-based hydrogels. J. Biomed. Mater. Res. - Part A 96 A, 535–542. doi:10.1002/jbm.a.33007

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Alcantar, N.A., Aydil, E.S., Israelachvili, J.N., 2000. Polyethylene glycol-coated biocompatible surfaces. J. Biomed. Mater. Res. 51, 343–351. doi:10.1002/1097-4636(20000905)51:3<343::AIDJBM7>3.0.CO;2-D

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Ali, S.A., Doherty, P.J., Williams, D.F., 1993. Mechanisms of polymer degradation in implantable devices. 2. Poly(DL-lactic acid). J. Biomed. Mater. Res. 27, 1409–1418. doi:10.1002/jbm.820271108

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Allaire, E., Guettier, C., Bruneval, P., Plissonnier, D., Michel, J.B., 1994. Cell-free arterial grafts: morphologic characteristics of aortic isografts, allografts, and xenografts in rats. J. Vasc. Surg. Off. Publ. Soc. Vasc. Surg. [and] Int. Soc. Cardiovasc. Surgery, North Am. Chapter 19, 446–456. doi:10.1016/S0741-5214(94)70071-0 Amarnath, L.P., Srinivas, A., Ramamurthi, A., 2006. In vitro hemocompatibility testing of UV-modified hyaluronan hydrogels. Biomaterials 27, 1416–1424. doi:10.1016/j.biomaterials.2005.08.008

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Amrita, Arora, A., Sharma, P., Katti, D.S., 2015. Pullulan-based composite scaffolds for bone tissue engineering: Improved osteoconductivity by pore wall mineralization. Carbohydr. Polym. 123, 180– 189. doi:10.1016/j.carbpol.2015.01.038

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Amy CY Lo, F.S., Lo, A.C., 2015. Collagen-Based Scaffolds for Cell Therapies in the Injured Brain. J. Stem Cell Res. Ther. 5. doi:10.4172/2157-7633.1000267

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Anderson, J., 2010. Biocompatibility and Bioresponse to Biomaterials, in: Principles of Regenerative Medicine. pp. 693–716.

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Anderson, J.M., 2001. Biological responses to materials. Annu. Rev. Mater. Res. 31, 81–110. doi:10.1146/annurev.matsci.31.1.81 Anderson, J.M., 1993. Mechanisms of inflammation and infection with implanted devices, in: Cardiovascular Pathology. pp. 33–41. doi:10.1016/1054-8807(93)90045-4

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Anderson, J.M., Langone, J.J., 1999. Issues and perspectives on the biocompatibility and immunotoxicity evaluation of implanted controlled release systems. J. Control. Release 57, 107–113. doi:10.1016/S0168-3659(98)00178-3 Anderson, J.M., Miller, K.M., 2006. Biomaterial biocompatibility and the macrophage, in: The Biomaterials: Silver Jubilee Compendium. pp. 21–26. doi:10.1016/B978-008045154-1.50004-6 Anderson, J.M., Rodriguez, A., Chang, D.T., 2008. Foreign body reaction to biomaterials. Semin. Immunol. doi:10.1016/j.smim.2007.11.004 Andrade, J.D., Hlady, V., Jeon, S.-I., 1996. Poly(ethylene oxide) and Protein Resistance: Principles, Problems and Possibilities, in: Hydrophilic Polymers. American Chemial Society, pp. 51–59. doi:10.1021/ba-1996-0248 Aschenbrenner, E.M., Bley, K., Koynov, K., Makowski, M.M., Kappl, M., Landfester, K., Weiss, C.K., 21

ACCEPTED MANUSCRIPT 2013. Using the “Polymeric Ouzo-Effect” for the preparation of polysaccharide based nanoparticles. Langmuir. doi:10.1021/la4017867 Athanasiou, K.A., Niederauer, G.G., Agrawal, C.M., 1996. Sterilization, toxicity, biocompatibility and clinical applications of polylactic acid/polyglycolic acid copolymers. Biomaterials. doi:10.1016/0142-9612(96)85754-1 Autissier, A., Letourneur, D., Le Visage, C., 2007. Pullulan-based hydrogel for smooth muscle cell culture. J. Biomed. Mater. Res. - Part A 82, 336–342. doi:10.1002/jbm.a.30998

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Aziz, M. a., Cabral, J.D., Brooks, H.J.L., McConnell, M. a., Fitzpatrick, C., Hanton, L.R., Moratti, S.C., 2015. In vitro biocompatibility and cellular interactions of a chitosan/dextran-based hydrogel for postsurgical adhesion prevention. J. Biomed. Mater. Res. Part B Appl. Biomater. 103, 332–341. doi:10.1002/jbm.b.33206

CR

Babensee, J.E., McIntire, L. V., Mikos, A.G., 2000. Growth factor delivery for tissue engineering. Pharm. Res. 17, 497–504. doi:10.1023/A:1007502828372 Badylak, S.F., 2004. Xenogeneic extracellular matrix as a scaffold for tissue reconstruction. Transpl. Immunol. 12, 367–377. doi:10.1016/j.trim.2003.12.016

US

Badylak, S.F., Gilbert, T.W., 2009. Immnue Response to Biologic Scaffold Materials. Semin. Immunol. 20, 109–116. doi:10.1016/j.smim.2007.11.003.Immune

AN

Bae, H., Ahari, A.F., Shin, H., Nichol, J.W., Hutson, C.B., Masaeli, M., Kim, S.-H., Aubin, H., Yamanlar, S., Khademhosseini, A., 2011a. Cell-laden microengineered pullulan methacrylate hydrogels promote cell proliferation and 3D cluster formation. Soft Matter 7, 1903. doi:10.1039/c0sm00697a

M

Bae, H., Ahari, A.F., Shin, H., Nichol, J.W., Hutson, C.B., Masaeli, M., Kim, S.-H., Aubin, H., Yamanlar, S., Khademhosseini, A., 2011b. Cell-laden microengineered pullulan methacrylate hydrogels promote cell proliferation and 3D cluster formation. Soft Matter. doi:10.1039/c0sm00697a

ED

Bakker, D., van Blitterswijk, C.A., Hesseling, S.C., Grote, J.J., 1988. Effect of implantation site on phagocyte/polymer interaction and fibrous capsule formation. Biomaterials 9, 14–23. doi:10.1016/0142-9612(88)90064-6

PT

Ball, D.H., Wiley, B.J., Reese, E.T., 1992. Effect of substitution at C-6 on the susceptibility of pullulan to pullulanases. Enzymatic degradation of modified pullulans. Can. J. Microbiol. 38, 324–327. doi:10.1139/m92-054

CE

Barker, H., Oliver, R., Grant, R., Stephen, L., 1980. Formaldehyde as a pre-treatment for dermal collagen heterografts. Biochim. Biophys. Acta 632, 589–597. doi:10.1016/0304-4165(80)90335-9

AC

Becher, J., Möller, S., Schnabelrauch, M., 2013. Phase transfer-catalyzed synthesis of highly acrylated hyaluronan. Carbohydr. Polym. 93, 438–441. doi:10.1016/j.carbpol.2012.12.056 Beenken-Rothkopf, L.N., Karfeld-Sulzer, L.S., Zhang, X., Kissler, H., Michie, S. a., Kaufman, D.B., Fontaine, M.J., Barron, a. E., 2012. Protein polymer hydrogels: Effects of endotoxin on biocompatibility. J. Biomater. Appl. 28, 395–406. doi:10.1177/0885328212454555 Behravesh, E., Yasko, A.W., Engel, P.S., Mikos, A.G., 1999. Synthetic biodegradable polymers for orthopaedic applications. Clin. Orthop. Relat. Res. S118–S129. doi:10.1097/00003086-19991000100012 Bélanger, M.C., Marois, Y., 2001. Hemocompatibility, biocompatibility, inflammatory and in vivo studies of primary reference materials low-density polyethylene and polydimethylsiloxane: A review. J. Biomed. Mater. Res. 58, 467–477. doi:10.1002/jbm.1043 Benedetto, C., Barbaglio, A., Martinello, T., Alongi, V., Fassini, D., Cullorà, E., Patruno, M., Bonasoro, 22

ACCEPTED MANUSCRIPT F., Barbosa, M., Carnevali, M., Sugni, M., 2014. Production, Characterization and Biocompatibility of Marine Collagen Matrices from an Alternative and Sustainable Source: The Sea Urchin Paracentrotus lividus. Mar. Drugs 12, 4912–4933. doi:10.3390/md12094912 Beumer, G.J., Van Blitterswijk, C.A., Ponec, M., 1994. Degradative behaviour of polymeric matrices in (sub)dermal and muscle tissue of the rat: A quantitative study. Biomaterials 15, 551–559. doi:10.1016/0142-9612(94)90022-1

T

Bezemer, J.M., Grijpma, D.W., Dijkstra, P.J., Van Blitterswijk, C.A., Feijen, J., 1999. A controlled release system for proteins based on poly(ether ester) block-copolymers: Polymer network characterization. J. Control. Release 62, 393–405. doi:10.1016/S0168-3659(99)00170-4

IP

Bezwada, R.S., Jamiolkowski, D.D., Lee, I.Y., Agarwal, V., Persivale, J., Trenka-Benthin, S., Erneta, M., Suryadevara, J., Yang, A., Liu, S., 1995. Monocryl suture, a new ultra-pliable absorbable monofilament suture. Biomaterials 16, 1141–1148. doi:10.1016/0142-9612(95)93577-Z

CR

Blackshaw, S.E., Arkison, S., Cameron, C., Davies, J.A., 1997. Promotion of regeneration and axon growth following injury in an invertebrate nervous system by the use of three-dimensional collagen gels. Proc. Biol. Sci. 264, 657–661. doi:10.1098/rspb.1997.0093

US

Böhm, G., Ushakova, Y., Alizai, H.P., Braunschweig, T., Lente, C., Heffels, K.H., Groll, J., Neumann, U.P., Junge, K., 2011. Biocompatibility of PLGA/sP(EO-stat-PO)-coated mesh surfaces under constant shearing stress. Eur. Surg. Res. 47, 118–129. doi:10.1159/000329412

AN

Bokhari, M.A., Akay, G., Zhang, S., Birch, M.A., 2005. The enhancement of osteoblast growth and differentiation in vitro on a peptide hydrogel-polyHIPE polymer hybrid material. Biomaterials 26, 5198–5208. doi:10.1016/j.biomaterials.2005.01.040

M

Böstman, O., Hirvensalo, E., Mäkinen, J., Rokkanen, P., 1990. Foreign-body reactions to fracture fixation implants of biodegradable synthetic polymers. J. Bone Joint Surg. Br. 72, 592–596.

ED

Böstman, O., Hirvensalo, E., Vainionpää, S., Mäkelä, A., Vihtonen, K., Törmälä, P., Rokkanen, P., 1989. Ankle fractures treated using biodegradable internal fixation. Clin. Orthop. Relat. Res. 195–203.

PT

Böstman, O., Päivärinta, U., Partio, E., Vasenius, J., Manninen, M., Rokkanen, P., 1992. Degradation and tissue replacement of an absorbable polyglycolide screw in the fixation of rabbit femoral osteotomies. J. Bone Joint Surg. Am. 74, 1021–1031.

CE

Böstman, O.M., 1991. Osteolytic changes accompanying degradation of absorbable fracture fixation implants. J. Bone Joint Surg. Br. 73, 679–682. Bruneel, D., Schacht, E., 1995. Enzymatic degradation of pullulan and pullulan derivatives. J. Bioact. Compat. Polym. 10, 299–312. doi:10.1177/088391159501000402

AC

Bryant, S.J., Chowdhury, T.T., Lee, D. a., Bader, D.L., Anseth, K.S., 2004. Crosslinking density influences chondrocyte metabolism in dynamically loaded photocrosslinked poly(ethylene glycol) hydrogels. Ann. Biomed. Eng. 32, 407–417. doi:10.1023/B:ABME.0000017535.00602.ca Bulman, S.E., Coleman, C.M., Murphy, J.M., Medcalf, N., Ryan, A.E., Barry, F., 2015. Pullulan: a new cytoadhesive for cell-mediated cartilage repair. Stem Cell Res. Ther. 6, 34. doi:10.1186/s13287-0150011-7 Bulstra, S.K., Geesink, R.G., Bakker, D., Bulstra, T.H., Bouwmeester, S.J., van der Linden, A.J., 1996. Femoral canal occlusion in total hip replacement using a resorbable and flexible cement restrictor. J. Bone Joint Surg. Br. 78, 892–898. Bumbu, G.-G., Vasile, C., Popescu, M.C., Darie, H., Charlotte Chiţanu, G., Singurel, G., Carpov, A., 2003. Compatibility of polysaccharide/maleic copolymer blends. IV. Thermal behavior of hydroxypropyl cellulose-containing blends. J. Appl. Polym. Sci. 88, 2585–2597. 23

ACCEPTED MANUSCRIPT doi:10.1002/app.11853 Burdick, J.A., Anseth, K.S., 2002. Photoencapsulation of osteoblasts in injectable RGD-modified PEG hydrogels for bone tissue engineering. Biomaterials 23, 4315–4323. doi:10.1016/S01429612(02)00176-X Burdick, J.A., Peterson, A.J., Anseth, K.S., 2001. Conversion and temperature profiles during the photoinitiated polymerization of thick orthopaedic biomaterials. Biomaterials 22, 1779–1786. doi:10.1016/S0142-9612(00)00347-1

IP

T

Burns, J.W., Skinner, K., Colt, J., Sheidlin, A., Bronson, R., Yaacobi, Y., Goldberg, E.P., 1995. Prevention of tissue injury and postsurgical adhesions by precoating tissues with hyaluronic acid solutions. J. Surg. Res. 59, 644–652. doi:10.1006/jsre.1995.1218

CR

Calabrese, G., Forte, S., Gulino, R., Cefalì, F., Figallo, E., Salvatorelli, L., Maniscalchi, E.T., Angelico, G., Parenti, R., Gulisano, M., Memeo, L., Giuffrida, R., 2017. Combination of Collagen-Based Scaffold and Bioactive Factors Induces Adipose-Derived Mesenchymal Stem Cells Chondrogenic Differentiation In vitro. Front. Physiol. 8, 50. doi:10.3389/fphys.2017.00050

US

Calabrese, G., Giuffrida, R., Fabbi, C., Figallo, E., Furno, D. Lo, Gulino, R., Colarossi, C., Fullone, F., Giuffrida, R., Parenti, R., Memeo, L., Forte, S., 2016a. Collagen-Hydroxyapatite scaffolds induce human adipose derived stem cells osteogenic differentiation in Vitro. PLoS One 11, e0151181. doi:10.1371/journal.pone.0151181

M

AN

Calabrese, G., Giuffrida, R., Forte, S., Salvatorelli, L., Fabbi, C., Figallo, E., Gulisano, M., Parenti, R., Magro, G., Colarossi, C., Memeo, L., Gulino, R., 2016b. Bone augmentation after ectopic implantation of a cell-free collagen-hydroxyapatite scaffold in the mouse. Sci. Rep. 6, 36399. doi:10.1038/srep36399 Carletti, E., Motta, A., Migliaresi, C., 2011. Scaffolds for tissue engineering and 3D cell culture. Methods Mol. Biol. 695, 17–39. doi:10.1007/978-1-60761-984-0_2

ED

Carpena, N.T., Min, Y.-K., Lee, B.-T., 2015. Improved In Vitro Biocompatibility of Surface-Modified Hydroxyapatite Sponge Scaffold with Gelatin and BMP-2 in Comparison Against a Commercial Bone Allograft. ASAIO J. 61, 78–86. doi:10.1097/MAT.0000000000000155

PT

Cascone, M.G., Polacco, G., Lazzeri, L., Barbani, N., 1997. Dextran / Poly ( acrylic acid ) Mixtures as Miscible Blends. J. Appl. Polym. Sci. 66, 2089–2094.

AC

CE

Cavallo, J.A., Gangopadhyay, N., Dudas, J., Roma, A.A., Jasielec, M.S., Baty, J., Baalman, S., Frisella, M.M., Tenenbaum, M.M., Myckatyn, T.M., Matthews, B.D., Deeken, C.R., 2015. Remodeling Characteristics and Collagen Distributions of Biologic Scaffold Materials Biopsied From Postmastectomy Breast Reconstruction Sites. Ann. Plast. Surg. 75, 74–83. doi:10.1097/SAP.0000000000000538 Cecen, B., Kozaci, D., Yuksel, M., Erdemli, D., Bagriyanik, A., Havitcioglu, H., 2014. Biocompatibility of MG-63 cells on collagen, poly-L-lactic acid, hydroxyapatite scaffolds with different parameters. J. Appl. Biomater. Funct. Mater. 0–0. doi:10.5301/jabfm.5000182 Cen, L., Liu, W.E.I., Cui, L.E.I., Zhang, W., Cao, Y., L, R.S.W., People, S., Tong, S.J., 2008. Collagen Tissue Engineering : Development of Novel Biomaterials. Pediatr. Res. 63, 492–496. Chan, B.P., Leong, K.W., 2008. Scaffolding in tissue engineering: General approaches and tissue-specific considerations. Eur. Spine J. 17, S467–S479. doi:10.1007/s00586-008-0745-3 Chen, D.R., Bei, J.Z., Wang, S.G., 2000. Polycaprolactone microparticles and their biodegradation. Polym. Degrad. Stab. 67, 455–459. doi:10.1016/S0141-3910(99)00145-7 Chen, G., Ushida, T., Tateishi, T., 2001. Development of biodegradable porous scaffolds for tissue 24

ACCEPTED MANUSCRIPT engineering. Mater. Sci. Eng. C 17, 63–69. doi:10.1016/S0928-4931(01)00338-1 Chen, Y.C., Lin, R.Z., Qi, H., Yang, Y., Bae, H., Melero-Martin, J.M., Khademhosseini, A., 2012. Functional human vascular network generated in photocrosslinkable gelatin methacrylate hydrogels. Adv. Funct. Mater. 22, 2027–2039. doi:10.1002/adfm.201101662 Choi, S.H., Park, T.G., 2002. Synthesis and characterization of elastic PLGA/PCL/PLGA tri-block copolymers. J. Biomater. Sci. Polym. Ed. 13, 1163–1173. doi:10.1163/156856202320813864

IP

T

Choi, Y.S., Hong, S.R., Lee, Y.M., Song, K.W., Park, M.H., Nam, Y.S., 1999a. Studies on gelatincontaining artificial skin: II. Preparation and characterization of cross-linked gelatin-hyaluronate sponge. J. Biomed. Mater. Res. 48, 631–639. doi:10.1002/(SICI)1097-4636(1999)48:5<631::AIDJBM6>3.0.CO;2-Y

CR

Choi, Y.S., Hong, S.R., Lee, Y.M., Song, K.W., Park, M.H., Nam, Y.S., 1999b. Study on gelatincontaining artificial skin: I. Preparation and characteristics of novel gelatin-alginate sponge. Biomaterials 20, 409–417. doi:10.1016/S0142-9612(98)00180-X Chowdhury, S.M., Hubbell, J.A., 1996. Adhesion prevention with ancrod released via a tissue-adherent hydrogel. J. Surg. Res. 61, 58–64. doi:10.1006/jsre.1996.0081

AN

US

Christel, P., Vert, M., Chabot, F., Abols, Y., LEary, J., 1983. Polylactic acid for intramedullary plugging, in: Biomaterials and Biomechanics, 1983: Proceedings of the 4th European Conference on Biomaterials, Leuven, Belgium, Aug. 31-Sept. 2, 1983Biomaterials and Biomechanics, 1983: Proceedings of the 4th European Conference on Biomaterials, Leuven, Belgium, Aug. 3. Elsevier Science, Amsterdam.

M

Chu, C.R., Dounchis, J.S., Yoshioka, M., Sah, R.L., Coutts, R.D., Amiel, D., 1997. Osteochondral repair using perichondrial cells. A 1-year study in rabbits. Clin. Orthop. Relat. Res. 220–229. doi:10.1097/00003086-199707000-00029

ED

Chvapil, M., 1982. Considerations on manufacturing principles of a synthetic burn dressing: a review. J. Biomed. Mater. Res. 16, 245–263. doi:10.1002/jbm.820160306

PT

Clark, R.A.F., Lanigan, J.M., DellaPelle, P., Manseau, E., Dvorak, H.F., Colvin, R.B., 1982. Fibronectin and fibrin provide a provisional matrix for epidermal cell migration during wound reepithelialization. J. Invest. Dermatol. 79, 264–269. doi:10.1111/1523-1747.ep12500075

CE

Collins, M.N., Birkinshaw, C., 2013. Hyaluronic acid based scaffolds for tissue engineering—A review. Carbohydr. Polym. 92, 1262–1279. doi:10.1016/j.carbpol.2012.10.028 Coviello, T., Matricardi, P., Marianecci, C., Alhaique, F., 2007. Polysaccharide hydrogels for modified release formulations. J. Control. Release 119, 5–24. doi:10.1016/j.jconrel.2007.01.004

AC

Crescenzi, V., Fancescangeli, A., Taglienti, A., 2002. New gelatin-based hydrogels via enzymatic networking. Biomacromolecules 3, 1384–1391. doi:10.1021/bm025657m Cruise, G.M., Hegre, O.D., Lamberti, F. V., Hager, S.R., Hill, R., Scharp, D.S., Hubbell, J.A., 1999. In vitro and in vivo performance of porcine islets encapsulated in interfacially photopolymerized poly(ethylene glycol) diacrylate membranes. Cell Transplant. 8, 293–306. Cutiongco, M.F.A., Tan, M.H., Ng, M.Y.K., Le Visage, C., Yim, E.K.F., 2014. Composite pullulandextran polysaccharide scaffold with interfacial polyelectrolyte complexation fibers: A platform with enhanced cell interaction and spatial distribution. Acta Biomater. doi:10.1016/j.actbio.2014.06.029 Dahm, M., Lyman, W.D., Schwell, A.B., Factor, S.M., Frater, R.W., 1990. Immunogenicity of glutaraldehyde-tanned bovine pericardium. J. Thorac. Cardiovasc. Surg. 99, 1082–1090. 25

ACCEPTED MANUSCRIPT Darnell, M.C., Sun, J.Y., Mehta, M., Johnson, C., Arany, P.R., Suo, Z., Mooney, D.J., 2013. Performance and biocompatibility of extremely tough alginate/polyacrylamide hydrogels. Biomaterials 34, 8042– 8048. doi:10.1016/j.biomaterials.2013.06.061 Darney, P.D., Monroe, S.E., Klaisle, C.M., Alvarado, A., 1989. Clinical evaluation of the Capronor contraceptive implant: preliminary report., American journal of obstetrics and gynecology. doi:10.1016/S0002-9378(89)80015-8

T

DeLustro, F., Condell, R.A., Nguyen, M.A., McPherson, J.M., 1986. A comparative study of the biologic and immunologic response to medical devices derived from dermal collagen. J. Biomed. Mater. Res. 20, 109–120. doi:10.1002/jbm.820200110

IP

Deschamps, A.A., Claase, M.B., Sleijster, W.J., De Bruijn, J.D., Grijpma, D.W., Feijen, J., 2002. Design of segmented poly(ether ester) materials and structures for the tissue engineering of bone. J. Control. Release 78, 175–186. doi:10.1016/S0168-3659(01)00497-7

CR

Dhandayuthapani, B., Yoshida, Y., Maekawa, T., Kumar, D.S., 2011. Polymeric scaffolds in tissue engineering application: A review. Int. J. Polym. Sci. doi:10.1155/2011/290602

US

Dillon, G.P., Yu, X., Sridharan, A., Ranieri, J.P., Bellamkonda, R. V, 1998. The influence of physical structure and charge on neurite extension in a 3D hydrogel scaffold. J. Biomater. Sci. Polym. Ed. 9, 1049–1069. doi:10.1163/156856298X00325

AN

Dionísio, M., Cordeiro, C., Remuñán-López, C., Seijo, B., Da Costa, A.M.R., Grenha, A., 2013. Pullulanbased nanoparticles as carriers for transmucosal protein delivery. Eur. J. Pharm. Sci. 50, 102–113. doi:10.1016/j.ejps.2013.04.018

M

Discher, D.E., Janmey, P., Wang, Y.-L., 2005. Tissue cells feel and respond to the stiffness of their substrate. Science 310, 1139–1143. doi:10.1126/science.1116995

ED

Drury, J.L., Mooney, D.J., 2003. Hydrogels for tissue engineering: Scaffold design variables and applications. Biomaterials. doi:10.1016/S0142-9612(03)00340-5 Duranti, F., Salti, G., Bovani, B., Calandra, M., Rosati, M.L., 1998. Injectable hyaluronic acid gel for soft tissue augmentation. A clinical and histological study. Dermatol. Surg. 24, 1317–1325.

PT

Ehashi, T., Kakinoki, S., Yamaoka, T., 2014. Water absorbing and quick degradable PLLA/PEG multiblock copolymers reduce the encapsulation and inflammatory cytokine production. J. Artif. Organs 17, 321–328. doi:10.1007/s10047-014-0791-z

CE

El-Sherbiny, I., Yacoub, M., 2013. Hydrogel scaffolds for tissue engineering: Progress and challenges. Glob. Cardiol. Sci. Pract. 2013, 316–42. doi:10.5339/gcsp.2013.38

AC

Elbert, D.L., Hubbell, J.A., 2001. Conjugate addition reactions combined with free-radical cross-linking for the design of materials for tissue engineering. Biomacromolecules 2, 430–441. doi:10.1021/bm0056299 Elbert, D.L., Pratt, A.B., Lutolf, M.P., Halstenberg, S., Hubbell, J.A., 2001. Protein delivery from materials formed by self-selective conjugate addition reactions. J. Control. Release 76, 11–25. doi:10.1016/S0168-3659(01)00398-4 Elisseeff, J., Anseth, K., Sims, D., McIntosh, W., Randolph, M., Yaremchuk, M., Langer, R., 1999. Transdermal photopolymerization of poly(ethylene oxide)-based injectable hydrogels for tissueengineered cartilage. Plast. Reconstr. Surg. 104, 1014–1022. doi:10.1097/00006534-19990904000017 Elzoghby, A.O., 2013. Gelatin-based nanoparticles as drug and gene delivery systems: Reviewing three decades of research. J. Control. Release 172, 1075–1091. doi:10.1016/j.jconrel.2013.09.019 26

ACCEPTED MANUSCRIPT Esses, S.I., Halloran, P.F., 1983. Donor marrow-derived cells as immunogens and targets for the immune response to bone and skin allografts. Transplantation 35, 169–174. doi:10.1097/00007890198302000-00012 Fietzek, P.P., Kühn, K., 1976. The primary structure of collagen. Int. Rev. Connect. Tissue Res. 7, 1–60. Fischer, N.O., Mbuy, G.N.., Woodruff, R.I., 2001. HSV-2 disrupts gap junctional intercellular communication between mammalian cells in vitro. J. Virol. Methods 91, 157–166. doi:10.1016/S0166-0934(00)00260-3

IP

T

Flynn, T.C., Sarazin, D., Bezzola, A., Terrani, C., Micheels, P., 2011. Comparative histology of intradermal implantation of mono and biphasic hyaluronic acid fillers. Dermatologic Surg. 37, 637– 643. doi:10.1111/j.1524-4725.2010.01852.x

CR

Freed, L.E., Marquis, J.C., Nohria, A., Emmanual, J., Mikos, A.G., Langer, R., 1993. Neocartilage formation in vitro and in vivo using cells cultured on synthetic biodegradable polymers. J. Biomed. Mater. Res. 27, 11–23. doi:10.1002/jbm.820270104

US

Fu, K., Pack, D.W., Klibanov, A.M., Langer, R., 2000. Visual evidence of acidic environment within degrading poly(lactic-co- glycolic acid) (PLGA) microspheres. Pharm. Res. 17, 100–106. doi:10.1023/A:1007582911958

AN

Fujiwara, J., Takahashi, M., Hatakeyama, T., Hatakeyama, H., 2000. Gelation of hyaluronic acid through annealing. Polym. Int. 49, 1604–1608. doi:10.1002/1097-0126(200012)49:12<1604::AIDPI558>3.0.CO;2-4 Furthmayr, H., Timpl, R., 1976. Immunochemistry of collagens and procollagens. Int. Rev. Connect. Tissue Res. 7, 61–99.

ED

M

Gamini, A., Paoletti, S., Toffanin, R., Micali, F., Michielin, L., Bevilacqua, C., 2002. Structural investigations of cross-linked hyaluronan. Biomaterials 23, 1161–1167. doi:10.1016/S01429612(01)00231-9

PT

Gendler, E., Gendler, S., Nimni, M.E., 1984. Toxic reactions evoked by glutaraldehyde-fixed pericardium and cardiac valve tissue bioprosthesis. J. Biomed. Mater. Res. 18, 727–736. doi:10.1002/jbm.820180703

CE

Gentile, P., Chiono, V., Carmagnola, I., Hatton, P. V., 2014. An overview of poly(lactic-co-glycolic) Acid (PLGA)-based biomaterials for bone tissue engineering. Int. J. Mol. Sci. doi:10.3390/ijms15033640

AC

Gerecht, S., Burdick, J.A., Ferreira, L.S., Townsend, S.A., Langer, R., Vunjak-Novakovic, G., 2007. Hyaluronic acid hydrogel for controlled self-renewal and differentiation of human embryonic stem cells. Proc. Natl. Acad. Sci. U. S. A. 104, 11298–11303. doi:10.1073/pnas.0703723104 Ghosh, K., Ren, X.-D., Shu, X.Z., Prestwich, G.D., Clark, R.A.F., 2006. Fibronectin functional domains coupled to hyaluronan stimulate adult human dermal fibroblast responses critical for wound healing. Tissue Eng. 12, 601–613. doi:10.1089/ten.2006.12.601 Gomes, M., Azevedo, H., Malafaya, P., Silva, S., Oliveira, J., Silva, G., Sousa, R., Mano, J., Reis, R., 2008. Natural Polymers in Tissue Engineering Applications, in: Tissue Engineering. pp. 145–192. doi:10.1016/B978-0-12-370869-4.00006-9 Gong, Y., He, L., Li, J., Zhou, Q., Ma, Z., Gao, C., Shen, J., 2007. Hydrogel-filled polylactide porous scaffolds for cartilage tissue engineering. J. Biomed. Mater. Res. - Part B Appl. Biomater. 82, 192– 204. doi:10.1002/jbm.b.30721 Gorgieva, S., Kokol, V., 2011. Collagen- vs. Gelatine-Based Biomaterials and Their Biocompatibility: Review and Perspectives, Biomaterials Applications for Nanomedicine, in: Pignatello, R. (Ed.), 27

ACCEPTED MANUSCRIPT Biomaterials Applications for Nanomedicine. pp. 1–36. doi:10.5772/1957 Gunatillake, P.A., Adhikari, R., 2003. Biodegradable synthetic polymers for tissue engineering. Eur. Cell. Mater. 5, 1–16; discussion 16. Guyette, J.P., Charest, J.M., Mills, R.W., Jank, B.J., Moser, P.T., Gilpin, S.E., Gershlak, J.R., Okamoto, T., Gonzalez, G., Milan, D.J., Gaudette, G.R., Ott, H.C., 2016. Bioengineering Human Myocardium on Native Extracellular Matrix. Circ. Res. 118, 56–72. doi:10.1161/CIRCRESAHA.115.306874

T

Hahn, M.S., Teply, B.A., Stevens, M.M., Zeitels, S.M., Langer, R., 2006. Collagen composite hydrogels for vocal fold lamina propria restoration. Biomaterials 27, 1104–1109. doi:10.1016/j.biomaterials.2005.07.022

IP

Hall, B.J., Jones, L.W., Dixon, B., 2014. Silicone allergies and the eye: fact or fiction? Eye Contact Lens 40, 51–7. doi:10.1097/ICL.0000000000000010

CR

Han, F., Dong, Y., Su, Z., Yin, R., Song, A., Li, S., 2014. Preparation, characteristics and assessment of a novel gelatin–chitosan sponge scaffold as skin tissue engineering material. Int. J. Pharm. 476, 124– 133. doi:10.1016/j.ijpharm.2014.09.036

US

Harriger, M.D., Supp, A.P., Warden, G.D., Boyce, S.T., 1997. Glutaraldehyde crosslinking of collagen substrates inhibits degradation in skin substitutes grafted to athymic mice. J. Biomed. Mater. Res. 35, 137–145. doi:10.1002/(SICI)1097-4636(199705)35:2<137::AID-JBM1>3.0.CO;2-O

AN

Harris, M.J. (Ed.), 1992. Poly(Ethylene Glycol) Chemistry. New York, New York. doi:10.1007/978-14899-0703-5

M

He, S., Timmer, M.., Yaszemski, M.., Yasko, A.., Engel, P.., Mikos, A.., 2001. Synthesis of biodegradable poly(propylene fumarate) networks with poly(propylene fumarate)–diacrylate macromers as crosslinking agents and characterization of their degradation products. Polymer (Guildf). 42, 1251–1260. doi:10.1016/S0032-3861(00)00479-1

ED

He, S., Yaszemski, M.J., Yasko, A.W., Engel, P.S., Mikos, A.G., 2000. Injectable biodegradable polymer composites based on poly(propylene fumarate) crosslinked with poly(ethylene glycol)dimethacrylate. Biomaterials 21, 2389–2394. doi:10.1016/S0142-9612(00)00106-X

PT

Hedberg, E.L., Shih, C.K., Lemoine, J.J., Timmer, M.D., Liebschner, M.A.K., Jansen, J.A., Mikos, A.G., 2005. In vitro degradation of porous poly(propylene fumarate)/poly(DL-lactic-co-glycolic acid) composite scaffolds. Biomaterials 26, 3215–3225. doi:10.1016/j.biomaterials.2004.09.012

CE

Heimann, R.B., 1999. Design of Novel Plasma Sprayed Hydroxyapatite-Bond Coat Bioceramic Systems. J. Therm. Spray Technol. 8, 597–603. doi:10.1361/105996399770350304

AC

Hersel, U., Dahmen, C., Kessler, H., 2003. RGD modified polymers: Biomaterials for stimulated cell adhesion and beyond. Biomaterials 24, 4385–4415. doi:10.1016/S0142-9612(03)00343-0 Hidalgo, I.A., Sojot, F., Arvelo, F., Sabino, M.A., 2013. Functional electrospun poly (lactic acid) scaffolds for biomedical applications: experimental conditions, degradation and biocompatibility study. Mol. Cell. Biomech. 10, 85–105. Hill-West, J.L., Chowdhury, S.M., Slepian, M.J., Hubbell, J.A., 1994. Inhibition of thrombosis and intimal thickening by in situ photopolymerization of thin hydrogel barriers. Proc. Natl. Acad. Sci. U. S. A. 91, 5967–5971. doi:10.1073/pnas.91.13.5967 Hill-West, J.L., Dunn, R.C., Hubbell, J.A., 1995. Local release of fibrinolytic agents for adhesion prevention. J. Surg. Res. 59, 759–763. doi:10.1006/jsre.1995.1236 Hinderer, S., Layland, S.L., Schenke-Layland, K., 2016. ECM and ECM-like materials - Biomaterials for applications in regenerative medicine and cancer therapy. Adv. Drug Deliv. Rev. 97, 260–269. 28

ACCEPTED MANUSCRIPT doi:10.1016/j.addr.2015.11.019 Honda, M., Yada, T., Ueda, M., Kimata, K., 2000. Cartilage formation by cultured chondrocytes in a new scaffold made of poly(L-lactide-epsilon-caprolactone) sponge. J. Oral Maxillofac. Surg. 58, 767– 775. doi:10.1053/joms.2000.7262 Hou, Y., Schoener, C.A., Regan, K.R., Munoz-Pinto, D., Hahn, M.S., Grunlan, M.A., 2010. Photo-crosslinked PDMSstar-PEG hydrogels: Synthesis, characterization, and potential application for tissue engineering scaffolds. Biomacromolecules 11, 648–656. doi:10.1021/bm9012293

T

Huang, L., Nagapudi, K., Apkarian, R.P., Chaikof, E.L., 2001. Engineered collagen-PEO nanofibers and fabrics. J. Biomater. Sci. Polym. Ed. 12, 979–993. doi:10.1163/156856201753252516

CR

IP

Huh, K.M., Bae, Y.H., 1999. Synthesis and characterization of poly(ethylene glycol)/poly(l-lactic acid) alternating multiblock copolymers. Polymer (Guildf). 40, 6147–6155. doi:10.1016/S00323861(98)00822-2 Hutmacher, D.W., 2000. Scaffolds in tissue engineering bone and cartilage. Biomaterials 21, 2529–2543. doi:10.1016/S0142-9612(00)00121-6

US

Hutmacher, D.W., Schantz, T., Zein, I., Ng, K.W., Teoh, S.H., Tan, K.C., 2001a. Mechanical properties and cell cultural response of polycaprolactone scaffolds designed and fabricated via fused deposition modeling. J. Biomed. Mater. Res. 55, 203–216. doi:10.1002/1097-4636(200105)55:2<203::AIDJBM1007>3.0.CO;2-7

M

AN

Hutmacher, D.W., Schantz, T., Zein, I., Ng, K.W., Teoh, S.H., Tan, K.C., 2001b. Mechanical properties and cell cultural response of polycaprolactone scaffolds designed and fabricated via fused deposition modeling. J. Biomed. Mater. Res. 55, 203–216. doi:10.1002/1097-4636(200105)55:2<203::AIDJBM1007>3.0.CO;2-7

ED

Hwang, N.S., Varghese, S., Theprungsirikul, P., Canver, A., Elisseeff, J., 2006. Enhanced chondrogenic differentiation of murine embryonic stem cells in hydrogels with glucosamine. Biomaterials 27, 6015–6023. doi:10.1016/j.biomaterials.2006.06.033

PT

Hyland, L.L., Twomey, J.D., Vogel, S., Hsieh, A.H., Yu, Y.B., 2013. Enhancing biocompatibility of D oligopeptide hydrogels by negative charges. Biomacromolecules 14, 406–412. doi:10.1021/bm301598g

CE

Ignatius, A.A., Claes, L.E., 1996. In vitro biocompatibility of bioresorbable polymers: Poly(L,DL-lactide) and poly(L-lactide-co-glycolide). Biomaterials 17, 831–839.

AC

Ishihara, T., Takahashi, M., Higaki, M., Mizushima, Y., Mizushima, T., 2010. Preparation and characterization of a nanoparticulate formulation composed of PEG-PLA and PLA as antiinflammatory agents. Int. J. Pharm. 385, 170–175. doi:10.1016/j.ijpharm.2009.10.025 Itoh, S., Takakuda, K., Kawabata, S., Aso, Y., Kasai, K., Itoh, H., Shinomiya, K., 2002. Evaluation of cross-linking procedures of collagen tubes used in peripheral nerve repair. Biomaterials 23, 4475– 4481. doi:10.1016/S0142-9612(02)00166-7 Jaiswal, a. K., Chhabra, H., Soni, V.P., Bellare, J.R., 2013. Enhanced mechanical strength and biocompatibility of electrospun polycaprolactone-gelatin scaffold with surface deposited nanohydroxyapatite. Mater. Sci. Eng. C 33, 2376–2385. doi:10.1016/j.msec.2013.02.003 Jalaja, K., Kumar, P.R.A., Dey, T., Kundu, S.C., James, N.R., 2014. Modified dextran cross-linked electrospun gelatin nanofibres for biomedical applications. Carbohydr. Polym. 114, 467–475. doi:10.1016/j.carbpol.2014.08.023 Jayakrishnan, A., Jameela, S.R., 1996. Glutaraldehyde as a fixative in bioprostheses and drug delivery matrices. Biomaterials 17, 471–484. doi:10.1016/0142-9612(96)82721-9 29

ACCEPTED MANUSCRIPT Jeong, B., Bae, Y.H., Lee, D.S., Kim, S.W., 1997. Biodegradable block copolymers as injectable drugdelivery systems. Nature 388, 860–862. doi:10.1038/42218 Jeong, H.Ã., Lee, S.Ã., Moon, P.Ã., Na, H., Park, R., Um, J., Kim, H., Hong, S.Ã., 2006. Alginic acid has anti-anaphylactic effects and inhibits inflammatory cytokine expression via suppression of nuclear factor- j B activation Clinical and Experimental Allergy. Clin. Exp. Allergy 36, 785–794. Jiang, D., Liang, J., Noble, P.W., 2007. Hyaluronan in Tissue Injury and Repair. Annu. Rev. Cell Dev. Biol. 23, 435–461. doi:10.1146/annurev.cellbio.23.090506.123337

IP

T

Joosten, E.A.J., Veldhuis, W.B., Hamers, F.P.T., 2004. Collagen containing neonatal astrocytes stimulates regrowth of injured fibers and promotes modest locomotor recovery after spinal cord injury. J. Neurosci. Res. 77, 127–142. doi:10.1002/jnr.20088

CR

Karageorgiou, V., Kaplan, D., 2005. Porosity of 3D biomaterial scaffolds and osteogenesis. Biomaterials 26, 5474–5491. doi:10.1016/j.biomaterials.2005.02.002

US

Kaushal, S., Amiel, G.E., Guleserian, K.J., Shapira, O.M., Perry, T., Sutherland, F.W., Rabkin, E., Moran, A.M., Schoen, F.J., Atala, A., Soker, S., Bischoff, J., Mayer, J.E., 2001. Functional smalldiameter neovessels created using endothelial progenitor cells expanded ex vivo. Nat. Med. 7, 1035– 40. doi:10.1038/nm0901-1035 Keane, T.J., Swinehart, I.T., Badylak, S.F., 2015. Methods of tissue decellularization used for preparation of biologic scaffolds and in vivo relevance. Methods 84, 25–34. doi:10.1016/j.ymeth.2015.03.005

AN

Khandwekar, A.P., Patil, D.P., Shouche, Y., Doble, M., 2011. Surface Engineering of Polycaprolactone by Biomacromolecules and their Blood Compatibility. J. Biomater. Appl. 26, 227–252. doi:10.1177/0885328210367442

M

Kim, B.S., Mooney, D.J., 1998. Development of biocompatible synthetic extracellular matrices for tissue engineering. Trends Biotechnol. 16, 224–229. doi:10.1016/S0167-7799(98)01191-3

ED

Kim, D.H., Martin, J.T., Elliott, D.M., Smith, L.J., Mauck, R.L., 2015. Phenotypic stability, matrix elaboration and functional maturation of nucleus pulposus cells encapsulated in photocrosslinkable hyaluronic acid hydrogels. Acta Biomater. 12, 21–29. doi:10.1016/j.actbio.2014.10.030

PT

Kimoto, T., Shibuya, T., Shiobara, S., 1997. Safety studies of a novel starch, pullulan: Chronic toxicity in rats and bacterial mutagenicity. Food Chem. Toxicol. 35, 323–329. doi:10.1016/S02786915(97)00001-X

CE

Kohane, D.S., Langer, R., 2010. Biocompatibility and drug delivery systems. Chem. Sci. doi:10.1039/c0sc00203h

AC

Kohmura, E., Yuguchi, T., Yoshimine, T., Fujinaka, T., Koseki, N., Sano, A., Kishino, A., Nakayama, C., Sakaki, T., Nonaka, M., Takemoto, O., Hayakawa, T., 1999. BDNF atelocollagen mini-pellet accelerates facial nerve regeneration. Brain Res. doi:10.1016/S0006-8993(99)02163-0 Kong, H.J., Kaigler, D., Kim, K., Mooney, D.J., 2004. Controlling rigidity and degradation of alginate hydrogels via molecular weight distribution. Biomacromolecules 5, 1720–1727. doi:10.1021/bm049879r Kopeček, J., 2007. Hydrogel biomaterials: A smart future? Biomaterials 28, 5185–5192. doi:10.1016/j.biomaterials.2007.07.044 Korkusuz, P., Kose, S., Kopru, C.Z., 2016. Biomaterial and stem cell interactions: Histological biocompatibility. Curr. Stem Cell Res. Ther. 11, 475–486. doi:10.2174/1574888X10666150306160027 Kraehenbuehl, T.P., Zammaretti, P., Van der Vlies, A.J., Schoenmakers, R.G., Lutolf, M.P., Jaconi, M.E., 30

ACCEPTED MANUSCRIPT Hubbell, J.A., 2008. Three-dimensional extracellular matrix-directed cardioprogenitor differentiation: Systematic modulation of a synthetic cell-responsive PEG-hydrogel. Biomaterials 29, 2757–2766. doi:10.1016/j.biomaterials.2008.03.016 Kuo, C.K., Ma, P.X., 2001. Ionically crosslinked alginate hydrogels as scaffolds for tissue engineering: Part 1. Structure, gelation rate and mechanical properties. Biomaterials 22, 511–521. doi:10.1016/S0142-9612(00)00201-5

T

Kweon, H., Yoo, M.K., Park, I.K., Kim, T.H., Lee, H.C., Lee, H.S., Oh, J.S., Akaike, T., Cho, C.S., 2003. A novel degradable polycaprolactone networks for tissue engineering. Biomaterials 24, 801–808. doi:10.1016/S0142-9612(02)00370-8

IP

Langer, R., Vacanti, J.P., 1999. Tissue Engineering: The Challenges Ahead. Sci. Am. 280, 86–89. Langer, R., Vacanti, J.P., 1993. Tissue engineering. Science (80-. ). 260, 920–926.

CR

Lapč k, L., De Smedt, S., Demeester, J., Chabreček, P., 1998. Hyaluronan: Preparation, Structure, Properties, and Applications. Chem. Rev. 98, 2663–2684. doi:10.1021/cr941199z

US

Lavergne, M., Derkaoui, M., Delmau, C., Letourneur, D., Uzan, G., Le Visage, C., 2012. Porous Polysaccharide-Based Scaffolds for Human Endothelial Progenitor Cells. Macromol. Biosci. 12, 901–910. doi:10.1002/mabi.201100431

AN

Leathers, T.D., 2003. Biotechnological production and applications of pullulan. Appl. Microbiol. Biotechnol. 62, 468–473. doi:10.1007/s00253-003-1386-4

M

Lee, C., Shin, J., Lee, J.S., Byun, E., Ryu, J.H., Um, S.H., Kim, D.I., Lee, H., Cho, S.W., 2013. Bioinspired, calcium-free alginate hydrogels with tunable physical and mechanical properties and improved biocompatibility. Biomacromolecules 14, 2004–2013. doi:10.1021/bm400352d Lee, C.H., Singla, A., Lee, Y., 2001. Biomedical applications of collagen. Int. J. Pharm. 221, 1–22. doi:10.1016/S0378-5173(01)00691-3

ED

Lee, H.J., Lee, J.S., Chansakul, T., Yu, C., Elisseeff, J.H., Yu, S.M., 2006. Collagen mimetic peptideconjugated photopolymerizable PEG hydrogel. Biomaterials 27, 5268–5276. doi:10.1016/j.biomaterials.2006.06.001

PT

Lee, H.Y., Jin, G.Z., Shin, U.S., Kim, J.H., Kim, H.W., 2012. Novel porous scaffolds of poly(lactic acid) produced by phase-separation using room temperature ionic liquid and the assessments of biocompatibility. J. Mater. Sci. Mater. Med. 23, 1271–1279. doi:10.1007/s10856-012-4588-4

CE

Lee, J.H., Lee, H.B., Andrade, J.D., 1995. Blood compatibility of polyethylene oxide surfaces. Prog. Polym. Sci. 20, 1043–1079. doi:10.1016/0079-6700(95)00011-9

AC

Lee, W., Miyagawa, Y., Long, C.L., Cooper, D.K.C., Hara, H., 2014. A comparison of three methods of decellularization of pig corneas to reduce immunogenicity. Int. J. Ophthalmol. 7, 587–593. doi:10.3980/j.issn.2222-3959.2014.04.01 Li, D., Sun, H., Jiang, L., Zhang, K., Liu, W., Zhu, Y., Fangteng, J., Shi, C., Zhao, L., Sun, H., Yang, B., 2014. Enhanced biocompatibility of PLGA nanofibers with gelatin/nano- hydroxyapatite bone biomimetics incorporation. ACS Appl. Mater. Interfaces 6, 9402–9410. doi:10.1021/am5017792 Li, H., Yang, J., Hu, X., Liang, J., Fan, Y., Zhang, X., 2011. Superabsorbent polysaccharide hydrogels based on pullulan derivate as antibacterial release wound dressing. J. Biomed. Mater. Res. - Part A 98 A, 31–39. doi:10.1002/jbm.a.33045 Li, X., Xue, W., Liu, Y., Li, W., Fan, D., Zhu, C., Wang, Y., 2016. HLC/pullulan and pullulan hydrogels: their microstructure, engineering process and biocompatibility. Mater. Sci. Eng. C 58, 1046–1057. doi:10.1016/j.msec.2015.09.039 31

ACCEPTED MANUSCRIPT Liang, H.-C., Chang, W.-H., Lin, K.-J., Sung, H.-W., 2003. Genipin-crosslinked gelatin microspheres as a drug carrier for intramuscular administration: in vitro and in vivo studies. J. Biomed. Mater. Res. A 65, 271–282. doi:10.1002/jbm.a.10476 Liao, E., Yaszemski, M., Krebsbach, P., Hollister, S., 2007. Tissue-engineered cartilage constructs using composite hyaluronic acid/collagen I hydrogels and designed poly(propylene fumarate) scaffolds. Tissue Eng. 13, 537–550. doi:10.1089/ten.2006.0117 Lim, F., Sun, A.M., 1980. Microencapsulated islets as bioartificial endocrine pancreas. Science 210, 908– 910. doi:10.1126/science.6776628

IP

T

Liu, H., Slamovich, E.B., Webster, T.J., 2006. Less harmful acidic degradation of poly(lactic-co-glycolic acid) bone tissue engineering scaffolds through titania nanoparticle addition. Int. J. Nanomedicine 1, 541–545. doi:10.2147/nano.2006.1.4.541

CR

Lutolf, M.P., Hubbell, J.A., 2005. Synthetic biomaterials as instructive extracellular microenvironments for morphogenesis in tissue engineering. Nat. Biotechnol. 23, 47–55. doi:10.1038/nbt1055

US

Lutolf, M.P., Lauer-Fields, J.L., Schmoekel, H.G., Metters, A.T., Weber, F.E., Fields, G.B., Hubbell, J.A., 2003. Synthetic matrix metalloproteinase-sensitive hydrogels for the conduction of tissue regeneration: engineering cell-invasion characteristics. Proc. Natl. Acad. Sci. U. S. A. 100, 5413– 5418. doi:10.1073/pnas.0737381100

AN

Lynn, A.K., Yannas, I. V., Bonfield, W., 2004. Antigenicity and immunogenicity of collagen. J. Biomed. Mater. Res. - Part B Appl. Biomater. doi:10.1002/jbm.b.30096

M

M. Saffer, E., N. Tew, G., R. Bhatia, S., 2011. Poly(lactic acid)-poly(ethylene oxide) Block Copolymers: New Directions in Self-Assembly and Biomedical Applications. Curr. Med. Chem. doi:10.2174/092986711798347324

ED

Machy, D., Jozefonvicz, J., Letourneur, D., 2000. Vascular prosthesis impregnated with crosslinked dextran. US6991648 B2.

PT

Mahmood, T.A., De Jong, R., Riesle, J., Langer, R., Van Blitterswijk, C.A., 2004. Adhesion-mediated signal transduction in human articular chondrocytes: The influence of biomaterial chemistry and tenascin-C. Exp. Cell Res. 301, 179–188. doi:10.1016/j.yexcr.2004.07.027

CE

Majola, A., Vainionpää, S., Vihtonen, K., Mero, M., Vasenius, J., Törmälä, P., Rokkanen, P., 1991. Absorption, biocompatibility, and fixation properties of polylactic acid in bone tissue: an experimental study in rats. Clin. Orthop. Relat. Res. 260–269.

AC

Mann, B.K., Gobin, A.S., Tsai, A.T., Schmedlen, R.H., West, J.L., 2001a. Smooth muscle cell growth in photopolymerized hydrogels with cell adhesive and proteolytically degradable domains: Synthetic ECM analogs for tissue engineering. Biomaterials 22, 3045–3051. doi:10.1016/S01429612(01)00051-5 Mann, B.K., Schmedlen, R.H., West, J.L., 2001b. Tethered-TGF-β increases extracellular matrix production of vascular smooth muscle cells. Biomaterials 22, 439–444. doi:10.1016/S01429612(00)00196-4 Marra, K.G., Campbell, P.G., Dimilla, P.A., Kumta, P.N., Mooney, M.P., Szem, J.W., Weiss, L.E., 1998. Novel three Dimensional Biodegradable Scaffolds for Bone Tissue Engineering. MRS Proc. 550, 155–160. doi:10.1557/PROC-550-155 Marra, K.G., Szem, J.W., Kumta, P.N., DiMilla, P.A., Weiss, L.E., 1999. In vitro analysis of biodegradable polymer blend/hydroxyapatite composites for bone tissue engineering. J. Biomed. Mater. Res. 47, 324–335. doi:10.1002/(SICI)1097-4636(19991205)47:3<324::AIDJBM6>3.0.CO;2-Y 32

ACCEPTED MANUSCRIPT Marshall, S.T., Browner, B., 2007. Emergency Care of Musculoskeletal Injuries, in: Sabiston Textbook of Surgery:The Biological Basis of Modern Surgical Practice. Massia, S.P., Hubbell, J.A., 1991. An RGD spacing of 440 nm is sufficient for integrin alpha-v-betamediated fibroblast spreading and 140 nm for focal contact and stress fiber formation. J. Cell Biol. 114, 1089–1100. doi:10.1083/jcb.114.5.1089 Massia, S.P., Stark, J., Letbetter, D.S., 2000. Surface-immobilized dextran limits cell adhesion and spreading. Biomaterials 21, 2253–2261. doi:10.1016/S0142-9612(00)00151-4

IP

T

Matsusue, Y., Yamamuro, T., Oka, M., Shikinami, Y., Hyon, S.H., Ikada, Y., 1992. In vitro and in vivo studies on bioabsorbable ultra-high-strength poly(L-lactide) rods. J. Biomed. Mater. Res. 26, 1553– 1567. doi:10.1002/jbm.820261203

CR

McGregor, D.H., MacArthur, R.I., Carter, T., 1986. Avitene granulomas of colonic serosa. Ann. Clin. Lab. Sci. 16, 296–302. McPherson, T.B., Badylak, S.F., 1998. Characterization of Fibronectin Derived from Porcine Small Intestinal Submucosa. Tissue Eng. 4, 75–83. doi:10.1089/ten.1998.4.75

US

Mensik, I., Lamme, E.N., Riesle, J., Brychta, P., 2002. Effectiveness and safety of the PEGT/PBT copolymer scafford as dermal substitute in scar reconstruction wounds (feasibility trial). Cell Tissue Bank. 3, 245–253. doi:10.1023/A:1024674325253

AN

Mensitieri, M., Ambrosio, L., Nicolais, L., Bellini, D., O’Regan, M., 1996. Viscoelastic properties modulation of a novel autocrosslinked hyaluronic acid polymer. J. Mater. Sci. Mater. Med. 7, 695– 698. doi:10.1007/BF00123409

M

Merrill, E.W., Salzman, W., 1983. Polyethylene oxide as a biomaterial. ASAIO J. 6, 60–64. Metters, A.T., Anseth, K.S., Bowman, C.N., 2000. Fundamental studies of a novel, biodegradable PEG-bPLA hydrogel. Polymer (Guildf). 41, 3993–4004. doi:10.1016/S0032-3861(99)00629-1

PT

ED

Miroshnikova, Y.A., Jorgens, D.M., Spirio, L., Auer, M., Sarang-Sieminski, A.L., Weaver, V.M., 2011. Engineering strategies to recapitulate epithelial morphogenesis within synthetic three-dimensional extracellular matrix with tunable mechanical properties. Phys. Biol. 8, 26013. doi:10.1088/14783975/8/2/026013

CE

Miyamoto, S., Katz, B.Z., Lafrenie, R.M., Yamada, K.M., 1998. Fibronectin and integrins in cell adhesion, signaling, and morphogenesis. Ann. N. Y. Acad. Sci. 857, 119–129. doi:10.1111/j.13652907.2008.00120.x

AC

Moran, J.M., Pazzano, D., Bonassar, L.J., 2003. Characterization of Polylactic Acid–Polyglycolic Acid Composites for Cartilage Tissue Engineering. Tissue Eng. 9, 63–70. doi:10.1089/107632703762687546 Moreland, L.W., 2003. Intra-articular hyaluronan (hyaluronic acid) and hylans for the treatment of osteoarthritis: mechanisms of action. Arthritis Res. Ther. 5, 54–67. Mouthuy, P.A., Snelling, S.J.B., Dakin, S.G., Milković, L., Gašparović, A.Č., Carr, A.J., Žarković, N., 2016. Biocompatibility of implantable materials: An oxidative stress viewpoint. Biomaterials. doi:10.1016/j.biomaterials.2016.09.010 Naahidi, S., Jafari, M., Edalat, F., Raymond, K., Khademhosseini, A., Chen, P., 2013. Biocompatibility of engineered nanoparticles for drug delivery. J. Control. Release 166, 182–194. doi:10.1016/j.jconrel.2012.12.013 Nagaoka, S., Nakao, A., 1990. Clinical application of antithrombogenic hydrogel with long poly(ethylene oxide) chains. Biomaterials 11, 119–121. doi:10.1016/0142-9612(90)90126-B 33

ACCEPTED MANUSCRIPT Nakada, a, Shigeno, K., Sato, T., Kobayashi, T., Wakatsuki, M., Uji, M., Nakamura, T., 2013. Manufacture of a weakly denatured collagen fiber scaffold with excellent biocompatibility and space maintenance ability. Biomed. Mater. 8, 45010. doi:10.1088/1748-6041/8/4/045010 Nelson, P.A., Nol Powers, J., Estridge, T.D., Elder, E.A., Alea, A.D., Sidhu, P.K., Sehl, L.C., Delustro, F.A., 2001. Serological analysis of patients treated with a new surgical hemostat containing bovine proteins and autologous plasma. J. Biomed. Mater. Res. 58, 710–719. doi:10.1002/jbm.10025

T

Nichol, J.W., Koshy, S.T., Bae, H., Hwang, C.M., Yamanlar, S., Khademhosseini, A., 2010. Cell-laden microengineered gelatin methacrylate hydrogels. Biomaterials 31, 5536–5544. doi:10.1016/j.biomaterials.2010.03.064

IP

Nitta, S.K., Numata, K., 2013. Biopolymer-based nanoparticles for drug/gene delivery and tissue engineering. Int. J. Mol. Sci. 14, 1629–1654. doi:10.3390/ijms14011629

CR

Noble, P.W., 2002. Hyaluronan and its catabolic products in tissue injury and repair. Matrix Biol. 21, 25– 29. doi:10.1016/S0945-053X(01)00184-6

US

Novak, M.T., Bryers, J.D., Reichert, W.M., 2009. Biomimetic strategies based on viruses and bacteria for the development of immune evasive biomaterials. Biomaterials. doi:10.1016/j.biomaterials.2008.11.025

AN

O’Dea, R.D., Osborne, J.M., El Haj, a. J., Byrne, H.M., Waters, S.L., 2013. The interplay between tissue growth and scaffold degradation in engineered tissue constructs. J. Math. Biol. 67, 1199–1225. doi:10.1007/s00285-012-0587-9

M

Olde Riekerink, M.B., Claase, M.B., Engbers, G.H.M., Grijpma, D.W., Feijen, J., 2003. Gas plasma etching of PEO/PBT segmented block copolymer films. J. Biomed. Mater. Res. A 65, 417–428. doi:10.1002/jbm.a.10520

ED

Onodera, J., Saito, A., George, J., Iwasaki, T., Ito, H., Aso, Y., Hamano, T., Kanai, A., Miyata, T., Nagai, Y., 2002. Application of atelocollagen solution for lacrimal duct occlusion. Adv. Exp. Med. Biol. 506, 1277–1281.

PT

Ostuni, E., Chapman, R.G., Holmlin, R.E., Takayama, S., Whitesides, G.M., 2001. A survey of structureproperty relationships of surfaces that resist the adsorption of protein. Langmuir 17, 5605–5620. doi:10.1021/la010384m

CE

Panduranga Rao, K., 1996. Recent developments of collagen-based materials for medical applications and drug delivery systems. J. Biomater. Sci. Polym. Ed. 7, 623–645. doi:10.1163/156856295X00526 Pape, L.G., Balazs, E.A., 1980. The use of sodium hyaluronate (Healon) in human anterior segment surgery. Ophthalmology 87, 699–705.

AC

Park, J.B., Lakes, R.S., 1992. Biomaterials: An Introduction. Plenum Press, New York, New York. Park, K.Y., Kim, H.K., Kim, B.J., 2013. Comparative study of hyaluronic acid fillers by in vitro and in vivo testing. J. Eur. Acad. Dermatology Venereol. doi:10.1111/jdv.12135 Park, S.N., Park, J.C., Kim, H.O., Song, M.J., Suh, H., 2002. Characterization of porous collagen/hyaluronic acid scaffold modified by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide cross-linking. Biomaterials 23, 1205–1212. doi:10.1016/S0142-9612(01)00235-6 Park, Y.D., Tirelli, N., Hubbell, J.A., 2006. Photopolymerized hyaluronic acid-based hydrogels and interpenetrating networks, in: The Biomaterials: Silver Jubilee Compendium. pp. 203–210. doi:10.1016/B978-008045154-1.50023-X Peattie, R.A., Nayate, A.P., Firpo, M.A., Shelby, J., Fisher, R.J., Prestwich, G.D., 2004. Stimulation of in vivo angiogenesis by cytokine-loaded hyaluronic acid hydrogel implants. Biomaterials 25, 2789– 34

ACCEPTED MANUSCRIPT 2798. doi:10.1016/j.biomaterials.2003.09.054 Pitt, C.G., Gratzl, M.M., Kimmel, G.L., Surles, J., Schindler, A., 1981. Aliphatic polyesters II. The degradation of poly (DL-lactide), poly (epsilon-caprolactone), and their copolymers in vivo. Biomaterials 2, 215–220. doi:10.1016/0142-9612(81)90060-0 Plattt, V.M., Szoka, F.C., 2008. Anticancer therapeutics: Targeting macromolecules and nanocarriers to hyaluronan or CD44, a hyaluronan receptor, in: Molecular Pharmaceutics. pp. 474–486. doi:10.1021/mp800024g

IP

T

Popa, E.G., Carvalho, P.P., Dias, A.F., Santos, T.C., Santo, V.E., Marques, A.P., Viegas, C.A., Dias, I.R., Gomes, M.E., Reis, R.L., 2014. Evaluation of the in vitro and in vivo biocompatibility of carrageenan-based hydrogels. J. Biomed. Mater. Res. - Part A. doi:10.1002/jbm.a.35081

CR

Prestwich, G.D., Marecak, D.M., Marecek, J.F., Vercruysse, K.P., Ziebell, M.R., 1998. Controlled chemical modification of hyaluronic acid: Synthesis, applications, and biodegradation of hydrazide derivatives, in: Journal of Controlled Release. pp. 93–103. doi:10.1016/S0168-3659(97)00242-3

US

Ratanavaraporn, J., Furuya, H., Tabata, Y., 2012. Local suppression of pro-inflammatory cytokines and the effects in BMP-2-induced bone regeneration. Biomaterials 33, 304–316. doi:10.1016/j.biomaterials.2011.09.050 Ratner, B.D., 2016. A pore way to heal and regenerate: 21st century thinking on biocompatibility. Regen. Biomater. 3, rbw006. doi:10.1093/rb/rbw006

AN

Ratner, B.D. (Buddy D.., 2013. Biomaterials science : an introduction to materials in medicine. Academic Press.

M

Reagan, B.J., Madden, M.R., Huo, J., Mathwich, M., Staiano-Coico, L., 1997. Analysis of cellular and decellular allogeneic dermal grafts for the treatment of full-thickness wounds in a porcine model. J Trauma. doi:10.1097/00005373-199709000-00012

ED

Reeve, L., Baldrick, P., 2017. Biocompatibility assessments for medical devices – evolving regulatory considerations. Expert Rev. Med. Devices 14, 161–167. doi:10.1080/17434440.2017.1280392

PT

Rekha, M.R., Sharma, P.C., 2007. Pullulan as a promising biomaterial for biomedical applications: a perspective. Trends Biomater. Artif. Organs 20, 116–121.

CE

Rogers, C.M., Deehan, D.J., Knuth, C.A., Rose, F.R.A.J., Shakesheff, K.M., Oldershaw, R.A., 2013. Biocompatibility and enhanced osteogenic differentiation of human mesenchymal stem cells in response to surface engineered poly(d,l-lactic-co-glycolic acid) microparticles. J. Biomed. Mater. Res. - Part A. doi:10.1002/jbm.a.35063

AC

Rokkanen, P., Böstman, O., Vainionpää, S., Vihtonen, K., Törmälä, P., Laiho, J., Kilpikari, J., Tamminmäki, M., 1985. Biodegradable implants in fracture fixation: early results of treatment of fractures of the ankle. Lancet (London, England) 1, 1422–4. doi:10.1016/S0140-6736(85)91847-1 Russell, P.S., Monaco, A.P., 1964. The Biology of Tissue Transplantation. N. Engl. J. Med. 271, 610– 616. doi:10.1097/00006534-196603000-00012 Salem, A.K., Stevens, R., Pearson, R.G., Davies, M.C., Tendler, S.J.B., Roberts, C.J., Williams, P.M., Shakesheff, K.M., 2002. Interactions of 3T3 fibroblasts and endothelial cells with defined pore features. J. Biomed. Mater. Res. 61, 212–217. doi:10.1002/jbm.10195 Salgado, C.L., Sanchez, E.M.S., Zavaglia, C.A.C., Granja, P.L., 2012. Biocompatibility and biodegradation of polycaprolactone-sebacic acid blended gels. J. Biomed. Mater. Res. - Part A 100 A, 243–251. doi:10.1002/jbm.a.33272 Saraf, S., Alexander, A., Ajazuddin, Khan, J., Saraf, S., 2013. Poly(ethylene glycol)-poly(lactic-co35

ACCEPTED MANUSCRIPT glycolic acid) based thermosensitive injectable hydrogels for biomedical applications. J. Control. Release 172, 715–729. doi:10.1016/j.jconrel.2013.10.006 Sarazin, P., Roy, X., Favis, B.D., 2004. Controlled preparation and properties of porous poly(L-lactide) obtained from a co-continuous blend of two biodegradable polymers. Biomaterials 25, 5965–5978. doi:10.1016/j.biomaterials.2004.01.065 Schakenraad, J.M., Hardonk, M.J., Feijen, J., Molenaar, I., Nieuwenhuis, P., 1990. Enzymatic activity toward poly(L-lactic acid) implants. J. Biomed. Mater. Res. 24, 529–545. doi:10.1002/jbm.820240502

IP

T

Schwarzbauer, J., 1999. Basement membranes: Putting up the barriers. Curr. Biol. 9, R242–R244. doi:10.1016/S0960-9822(99)80153-5

CR

Schwarzbauer, J.E., 1991. Fibronectin: From gene to protein. Curr. Opin. Cell Biol. doi:10.1016/09550674(91)90051-Y Sela, M., Arnon, R., 1960. Studies on the chemical basis of the antigenicity of proteins. 1. Antigenicity of polypeptidyl gelatins. Biochem. J. 75, 91–102.

US

Seliktar, D., Zisch, A.H., Lutolf, M.P., Wrana, J.L., Hubbell, J.A., 2004. MMP-2 sensitive, VEGFbearing bioactive hydrogels for promotion of vascular healing. J. Biomed. Mater. Res. A 68, 704– 716. doi:10.1002/jbm.a.20091

AN

Shalumon, K.T., Anulekha, K.H., Chennazhi, K.P., Tamura, H., Nair, S. V., Jayakumar, R., 2011. Fabrication of chitosan/poly(caprolactone) nanofibrous scaffold for bone and skin tissue engineering. Int. J. Biol. Macromol. 48, 571–576. doi:10.1016/j.ijbiomac.2011.01.020

ED

M

Sharaf, B., Faris, C.B., Abukawa, H., Susarla, S.M., Vacanti, J.P., Kaban, L.B., Troulis, M.J., 2012. Three-dimensionally printed polycaprolactone and beta-tricalcium phosphate scaffolds for bone tissue engineering: An in vitro study. J. Oral Maxillofac. Surg. 70, 647–656. doi:10.1016/j.joms.2011.07.029

PT

Sharma, B., Williams, C.G., Khan, M., Manson, P., Elisseeff, J.H., 2007. In vivo chondrogenesis of mesenchymal stem cells in a photopolymerized hydrogel. Plast. Reconstr. Surg. 119, 112–120. doi:10.1097/01.prs.0000236896.22479.52 Shin, H., Olsen, B.D., Khademhosseini, A., 2014. Gellan gum microgel-reinforced cell-laden gelatin hydrogels. J. Mater. Chem. B. Mater. Biol. Med. 2, 2508–2516. doi:10.1039/C3TB20984A

CE

Shin, H., Olsen, B.D., Khademhosseini, A., 2012. The mechanical properties and cytotoxicity of cellladen double-network hydrogels based on photocrosslinkable gelatin and gellan gum biomacromolecules. Biomaterials 33, 3143–3152. doi:10.1016/j.biomaterials.2011.12.050

AC

Shu, X.Z., Ahmad, S., Liu, Y., Prestwich, G.D., 2006. Synthesis and evaluation of injectable, in situ crosslinkable synthetic extracellular matrices for tissue engineering. J. Biomed. Mater. Res. - Part A 79, 902–912. doi:10.1002/jbm.a.30831 Shu, X.Z., Ghosh, K., Liu, Y., Palumbo, F.S., Luo, Y., Clark, R.A., Prestwich, G.D., 2004. Attachment and spreading of fibroblasts on an RGD peptide-modified injectable hyaluronan hydrogel. J. Biomed. Mater. Res. A 68, 365–375. doi:10.1002/jbm.a.20002 Silva-Correia, J., Zavan, B., Vindigni, V., Silva, T.H., Oliveira, J.M., Abatangelo, G., Reis, R.L., 2013. Biocompatibility evaluation of ionic- and photo-crosslinked methacrylated gellan gum hydrogels: In vitro and in vivo study. Adv. Healthc. Mater. 2, 568–575. doi:10.1002/adhm.201200256 Singh, S.R., 2009. Principles of Regenerative Medicine, Annals of Biomedical Engineering. doi:10.1007/s10439-009-9817-8 36

ACCEPTED MANUSCRIPT Slaughter, B. V, Khurshid, S.S., Fisher, O.Z., Khademhosseini, A., Peppas, N.A., 2009. Hydrogels in Regenerative Medicine. Adv. Mater. 21, 3307–3329. doi:10.1002/adma.200802106 Speer, D.P., Chvapil, M., Eskelson, C.D., Ulreich, J., 1980. Biological effects of residual glutaraldehyde in glutaraldehyde-tanned collagen biomaterials. J. Biomed. Mater. Res. 14, 753–764. doi:10.1002/jbm.820140607 Spenlehauer, G., Vert, M., Benoit, J.P., Boddaert, A., 1989. In vitro and in vivo degradation of poly(D,L lactide/glycolide) type microspheres made by solvent evaporation method. Biomaterials 10, 557– 563. doi:10.1016/0142-9612(89)90063-X

IP

T

Sreejit, P., Verma, R.S., 2013. Natural ECM as Biomaterial for Scaffold Based Cardiac Regeneration Using Adult Bone Marrow Derived Stem Cells. Stem Cell Rev. Reports 9, 158–171. doi:10.1007/s12015-013-9427-6

CR

Stern, R., Asari, A.A., Sugahara, K.N., 2006. Hyaluronan fragments: An information-rich system. Eur. J. Cell Biol. 85, 699–715. doi:10.1016/j.ejcb.2006.05.009

US

Stevens, K.R., Einerson, N.J., Burmania, J.A., Kao, W.J., 2002. In vivo biocompatibility of gelatin-based hydrogels and interpenetrating networks. J. Biomater. Sci. Polym. Ed. 13, 1353–1366. doi:10.1163/15685620260449741

AN

Stevens, M.M., Marini, R.P., Schaefer, D., Aronson, J., Langer, R., Shastri, V.P., 2005. In vivo engineering of organs: the bone bioreactor. Proc. Natl. Acad. Sci. U. S. A. 102, 11450–11455. doi:10.1073/pnas.0504705102 Suganuma, J., Alexander, H., 1993. Biological response of intramedullary bone to poly-L-lactic acid. J. Appl. Biomater. 4, 13–27.

M

Sun, H., Mei, L., Song, C., Cui, X., Wang, P., 2006. The in vivo degradation, absorption and excretion of PCL-based implant. Biomaterials 27, 1735–1740. doi:10.1016/j.biomaterials.2005.09.019

ED

Tabata, Y., Hijikata, S., Ikada, Y., 1994. Enhanced vascularization and tissue granulation by basic fibroblast growth factor impregnated in gelatin hydrogels. J. Control. Release 31, 189–199. doi:10.1016/0168-3659(94)00035-2

PT

Tabata, Y., Ikada, Y., 1987. Macrophage activation through phagocytosis of muramyl dipeptide encapsulated in gelatin microspheres. J. Pharm. Pharmacol. 39, 698–704.

CE

Takechi, M., Ohta, K., Ninomiya, Y., Tada, M., Minami, M., Takamoto, M., Ohta, A., Nakagawa, T., Fukui, A., Miyamoto, Y., Kamata, N., 2012. 3-dimensional composite scaffolds consisting of apatite-PLGA-atelocollagen for bone tissue engineering. Dent. Mater. J. 31, 465–471. doi:10.4012/dmj.2011-182

AC

Tan, W., Krishnaraj, R., Desai, T.A., 2001. Evaluation of nanostructured composite collagen--chitosan matrices for tissue engineering. Tissue Eng. 7, 203–210. doi:10.1089/107632701300062831 Tang, S., Vickers, S.M., Hsu, H.P., Spector, M., 2007. Fabrication and characterization of porous hyaluronic acid-collagen composite scaffolds. J. Biomed. Mater. Res. - Part A 82, 323–335. doi:10.1002/jbm.a.30974 Tangsadthakun, C., Kanokpanont, S., Sanchavanakit, N., Banaprasert, T., Damrongsakkul, S., 2006. Properties of Collagen / Chitosan Scaffolds for Skin Tissue Engineering Fabrication of Collagen / Chitosan Scaffolds. J. Met. Mater. Miner. 16, 37–44. Taylor, P.M., Cass, A.E.G., Yacoub, M.H., 2006. Extracellular matrix scaffolds for tissue engineering heart valves. Prog. Pediatr. Cardiol. doi:10.1016/j.ppedcard.2005.11.010 Thacharodi, D., Panduranga Rao, K., 1996. Rate-controlling biopolymer membranes as transdermal 37

ACCEPTED MANUSCRIPT delivery systems for nifedipine: Development and in vitro evaluations. Biomaterials 17, 1307–1311. doi:10.1016/0142-9612(96)88676-5 Thébaud, N.-B., Pierron, D., Bareille, R., Le Visage, C., Letourneur, D., Bordenave, L., 2007. Human endothelial progenitor cell attachment to polysaccharide-based hydrogels: a pre-requisite for vascular tissue engineering. J. Mater. Sci. Mater. Med. 18, 339–345. doi:10.1007/s10856-006-06981 Tibbitt, M.W., Anseth, K.S., 2009. Hydrogels as extracellular matrix mimics for 3D cell culture. Biotechnol. Bioeng. doi:10.1002/bit.22361

IP

T

Tongers, J., Losordo, D.W., Landmesser, U., 2011. Stem and progenitor cell-based therapy in ischaemic heart disease: Promise, uncertainties, and challenges. Eur. Heart J. 32, 1197–1206. doi:10.1093/eurheartj/ehr018

CR

Toole, B.P., 2004. Hyaluronan: from extracellular glue to pericellular cue. Nat. Rev. Cancer 4, 528–539. doi:10.1038/nrc1391 Tronci, G., 2010. Synthesis , Characterization , and Biological Evaluation of Gelatin-based Scaffolds Dissertation.

US

van Blitterswijk, C.A., van der Brink, J., Leenders, H., Bakker, D., 1993. The effect of PEO ratio on degradation, calcification and bone bonding of PEO/PBT copolymer (Polyactive). Cells Mater. 3, 23–36.

AN

van der Rest, M., Garrone, R., 1991. Collagen family of proteins. FASEB J. 5, 2814–2823.

M

Van Dijkhuizen-Radersma, R., Péters, F.L.A.M.A., Stienstra, N.A., Grijpma, D.W., Feijen, J., De Groot, K., Bezemer, J.M., 2002. Control of vitamin B12 release from poly(ethylene glycol)/poly(butylene terephthalate) multiblock copolymers. Biomaterials 23, 1527–1536. doi:10.1016/S01429612(01)00286-1

ED

Van Vlierberghe, S., Dubruel, P., Schacht, E., 2011. Biopolymer-Based Hydrogels As Scaffolds for Tissue Engineering Applications: A Review. Biomacromolecules 12, 1387–1408. doi:10.1021/bm200083n

PT

Varghese, S., Hwang, N.S., Canver, A.C., Theprungsirikul, P., Lin, D.W., Elisseeff, J., 2008. Chondroitin sulfate based niches for chondrogenic differentiation of mesenchymal stem cells. Matrix Biol. 27, 12–21. doi:10.1016/j.matbio.2007.07.002

CE

Vercruysse, K.P., Marecak, D.M., Marecek, J.F., Prestwich, G.D., 1997. Synthesis and in vitro degradation of new polyvalent hydrazide cross-linked hydrogels of hyaluronic acid. Bioconjug. Chem. 8, 686–694. doi:10.1021/bc9701095

AC

Vert, M., Li, S.M., Spenlehauer, G., Guerin, P., 1992. Bioresorbability and biocompatibility of aliphatic polyesters. J. Mater. Sci. Mater. Med. 3, 432–446. doi:10.1007/BF00701240 Vert, M., Li, S.M., Spenlehauer, G., Guerin, P., 1992. Bioresorbability and biocompatibility of aliphatic polyesters. J. Mater. Sci. Mater. Med. 3, 432–446. doi:10.1007/BF00701240 Viola, J., Lal, B., Grad, O., 2003. The Emergence of Tissue Engineering as a Research Field. Natl. Sci. Found. A-07. Vizárová, K., Bako, D., Reháková, M., Macho, V., 1994. Modification of layered atelocollagen by ultraviolet irradiation and chemical cross-linking: Structure stability and mechanical properties. Biomaterials 15, 1082–1086. doi:10.1016/0142-9612(94)90094-9 Wang, P.Y., 1989. Compressed poly(vinyl alcohol)-polycaprolactone admixture as a model to evaluate erodible implants for sustained drug delivery. J. Biomed. Mater. Res. 23, 91–104. 38

ACCEPTED MANUSCRIPT Wang, Y.Y., Lü, L.X., Shi, J.C., Wang, H.F., Xiao, Z.D., Huang, N.P., 2011. Introducing RGD peptides on PHBV films through PEG-containing cross-linkers to improve the biocompatibility. Biomacromolecules 12, 551–559. doi:10.1021/bm100886w Weadock, K., Olson, R.M., Silver, F.H., n.d. Evaluation of collagen crosslinking techniques. Biomater. Med. Devices. Artif. Organs 11, 293–318. doi:10.3109/10731198309118815 Weadock, K.S., Miller, E.J., Bellincampi, L.D., Zawadsky, J.P., Dunn, M.G., 1995. Physical crosslinking of collagen fibers: Comparison of ultraviolet irradiation and dehydrothermal treatment, in: Journal of Biomedical Materials Research. pp. 1373–1379. doi:10.1002/jbm.820291108

IP

T

West, J.L., Hubbell, J.A., 1996. Separation of the arterial wall from blood contact using hydrogel barriers reduces intimal thickening after balloon injury in the rat: The roles of medial and luminal factors in arterial healing. Proc. Natl. Acad. Sci. 93, 13188–13193. doi:10.1073/pnas.93.23.13188

CR

West, J.L., Hubbell, J. a., 1999. Polymeric biomaterials with degradation sites for proteases involved in cell migration. Macromolecules 32, 241–244. doi:10.1021/ma981296k Wichterle, O., Lim, D., 1960. Hydrophilic Gels for Biological Use. Nature 185, 117–118. doi:10.1038/185117a0

US

Willers, C., Chen, J., Wood, D., Xu, J., Zheng, M.H., 2005. Autologous chondrocyte implantation with collagen bioscaffold for the treatment of osteochondral defects in rabbits. Tissue Eng. 11, 1065– 1076. doi:10.1089/ten.2005.11.1065

AN

Williams, C.G., Kim, T.K., Taboas, A., Malik, A., Manson, P., Elisseeff, J., 2003. In vitro chondrogenesis of bone marrow-derived mesenchymal stem cells in a photopolymerizing hydrogel. Tissue Eng. 9, 679–688. doi:10.1089/107632703768247377

M

Williams, D.F., 2009. On the Nature of Biomaterials. Biomaterials 30, 5897–5909. doi:10.1016/j.biomaterials.2009.07.027

ED

Williams, D.F., 2008a. On the mechanisms of biocompatibility. Biomaterials 29, 2941–2953. doi:10.1016/j.biomaterials.2008.04.023 Williams, D.F., 2008b. Biocompatibility, in: Tissue Engineering. Elsevier, pp. 255–278.

PT

Williams, D.F., 2006. Enzymic hydrolysis of polylactic acid. Arch. Eng. Med. 1971-1988 (vols 1-17) 10, 5–7. doi:10.1243/EMED_JOUR_1981_010_004_02

CE

Williams, D.F., 1986. Definitions in Biomaterials, 4th ed. Proceedings of a Consensus Conference of the European Society for Biomaterials, Chester, England.

AC

Williams, D.F., Mort, E., 1977. Enzyme-accelerated hydrolysis of polyglycolic acid. J. Bioeng. 1, 231– 238. Wilson, S.L., Sidney, L.E., Dunphy, S.E., Rose, J.B., Hopkinson, A., 2013. Keeping an eye on decellularized corneas: a review of methods, characterization and applications. J. Funct. Biomater. 4, 114–61. doi:10.3390/jfb4030114 Wong, V.W., Rustad, K.C., Glotzbach, J.P., Sorkin, M., Inayathullah, M., Major, M.R., Longaker, M.T., Rajadas, J., Gurtner, G.C., 2011. Pullulan Hydrogels Improve Mesenchymal Stem Cell Delivery into High-Oxidative-Stress Wounds. Macromol. Biosci. n/a-n/a. doi:10.1002/mabi.201100180 Woodward, S.C., Brewer, P.S., Moatamed, F., Schindler, A., Pitt, C.G., 1985. The intracellular degradation of poly(epsilon-caprolactone). J. Biomed. Mater. Res. 19, 437–444. doi:10.1002/jbm.820190408 Yamamoto, S., Yoshimine, T., Fujita, T., Kuroda, R., Irie, T., Fujioka, K., Hayakawa, T., 1992. Protective effect of NGF atelocollagen mini-pellet on the hippocampal delayed neuronal death in gerbils. 39

ACCEPTED MANUSCRIPT Neurosci. Lett. 141, 161–165. doi:10.1016/0304-3940(92)90885-B Yan, L.P., Wang, Y.J., Ren, L., Wu, G., Caridade, S.G., Fan, J.B., Wang, L.Y., Ji, P.H., Oliveira, J.M., Oliveira, J.T., Mano, J.F., Reis, R.L., 2010. Genipin-cross-linked collagen/chitosan biomimetic scaffolds for articular cartilage tissue engineering applications. J. Biomed. Mater. Res. - Part A 95 A, 465–475. doi:10.1002/jbm.a.32869 Yang, F., Williams, C.G., Wang, D.A., Lee, H., Manson, P.N., Elisseeff, J., 2005. The effect of incorporating RGD adhesive peptide in polyethylene glycol diacrylate hydrogel on osteogenesis of bone marrow stromal cells. Biomaterials 26, 5991–5998. doi:10.1016/j.biomaterials.2005.03.018

IP

T

Yang, K.C., Wu, C.C., Cheng, Y.H., Kuo, T.F., Lin, F.H., 2008. Chitosan/Gelatin Hydrogel Prolonged the Function of Insulinoma/Agarose Microspheres In Vivo During Xenogenic Transplantation. Transplant. Proc. 40, 3623–3626. doi:10.1016/j.transproceed.2008.06.092

CR

Yao, H., Miyamoto, T., Mukai, S., Yamamura, M., Tanaka, H., Nakagawa, T., Ryomoto, M., Inai, Y., Yoshioka, Y., Kaji, M., 2003. Long-term results of mitral valve replacement: Biological xenograft versus mechanical valves. J. Artif. Organs 6, 30–36. doi:10.1007/s100470300005

US

Yim, E.K.F., Liao, I.-C., Leong, K.W., 2007. Tissue compatibility of interfacial polyelectrolyte complexation fibrous scaffold: evaluation of blood compatibility and biocompatibility. Tissue Eng. 13, 423–433. doi:10.1089/ten.2007.13.ft-323

AN

Yu, H., Jia, Y., Yao, C., Lu, Y., 2014. PCL/PEG core/sheath fibers with controlled drug release rate fabricated on the basis of a novel combined technique. Int. J. Pharm. 469, 17–22. doi:10.1016/j.ijpharm.2014.04.045

M

Zamiri, P., Kuang, Y., Sharma, U., Ng, T.F., Busold, R.H., Rago, A.P., Core, L.A., Palasis, M., 2010. The biocompatibility of rapidly degrading polymeric stents in porcine carotid arteries. Biomaterials 31, 7847–7855. doi:10.1016/j.biomaterials.2010.06.057

ED

Zhang, F., Li, J., Zhu, T., Zhang, S., Kundu, S.C., Lu, S., 2015. Potential of biocompatible regenerated silk fibroin/sodium N-lauroyl sarcosinate hydrogels. J. Biomater. Sci. Polym. Ed. 26, 780–795. doi:10.1080/09205063.2015.1058576

PT

Zhao, X.F., Li, X.D., Kang, Y.Q., Yuan, Q., 2011. Improved biocompatibility of novel poly(L-lactic acid)/β-tricalcium phosphate scaffolds prepared by an organic solvent-free method. Int. J. Nanomedicine 6, 1385–1390. doi:10.2147/IJN.S20743

CE

Zhu, B., Li, W., Lewis, R. V, Segre, C.U., Wang, R., 2015. E-Spun Composite Fibers of Collagen and Dragline Silk Protein: Fiber Mechanics, Biocompatibility, and Application in Stem Cell Differentiation. Biomacromolecules 16, 202–213. doi:10.1021/bm501403f

AC

Zhu, J., 2010. Bioactive modification of poly(ethylene glycol) hydrogels for tissue engineering. Biomaterials. doi:10.1016/j.biomaterials.2010.02.044 Zhu, J., Marchant, R.E., 2011. Design properties of hydrogel tissue-engineering scaffolds. Expert Rev. Med. Devices 8, 607–626. doi:10.1586/erd.11.27 Ziats, N.P., Miller, K.M., Anderson, J.M., 1988. In vitro and in vivo interactions of cells with biomaterials. Biomaterials 9, 5–13. doi:10.1016/0142-9612(88)90063-4 Zisch, A.H., Lutolf, M.P., Ehrbar, M., Raeber, G.P., Rizzi, S.C., Davies, N., Schmökel, H., Bezuidenhout, D., Djonov, V., Zilla, P., Hubbell, J.A., 2003. Cell-demanded release of VEGF from synthetic, biointeractive cell ingrowth matrices for vascularized tissue growth. FASEB J. 17, 2260–2262. doi:10.1096/fj.02-1041fje Zong, C., Qian, X., Tang, Z., Hu, Q., Chen, J., Gao, C., Tang, R., Tong, X., Wang, J., 2014. Biocompatibility and bone-repairing effects: Comparison between porous poly-lactic-Co-glycolic 40

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