www.advhealthmat.de www.MaterialsViews.com

PROGRESS REPORT

Biopolymer/Calcium Phosphate Scaffolds for Bone Tissue Engineering Jianhua Li, Bryan. A. Baker,* Xiaoning Mou, Na Ren, Jichuan Qiu, Robert I. Boughton, and Hong Liu* in this field. Autologous bone grafts stimulate little immune response, have osteoinductive and osteoconductive properties and integrate well with host bone. However, the limited supply of materials, need for further surgery, and high incidence of donor site morbidity associated with harvesting autologous bone grafts severely hinder its application.[5] Allografts and xenografts can be promising substitutes as an alternative treatment. Allografts and xenografts are not limited by availability and can provide large and variously shaped pieces of different bones. Additionally, there is no site-morbidity associated with graft harvesting for the patient, related medical expenses are reduced, and the grafts retain osteoinductive properties.[6] Despite these advantages, allografts and xenografts are known for their poor clinical performance with occurrences of infection and immunological rejection.[6,7] Finally, artificial implants, such as metallic and ceramic-based implants, may provide immediate support at the defect site, but experience material-related failure modes. For instance, metals integrate poorly with the surrounding tissue and are subject to corrosion or fatigue loading, while ceramic implants are brittle and have low tensile strengths, making them unsuitable for implantation in load-bearing sites. Motivated in part by some of the above limitations, the field of tissue engineering has arisen by integrating the principles of both engineering and life sciences to develop “biological substitutes that restore, maintain, or improve tissue function.”[8] One common tissue engineering strategy for the regeneration of bone is to use 3D porous scaffolds with bioactive molecules and living cells, or various combinations of the three to provide temporary support at the defect site and to guide cellular function.[9] In recent years, the development of new materials, designs, and synthesis methods for 3D scaffolds has become one of the main objectives in bone tissue engineering (BTE). Characteristics commonly considered advantageous for 3D scaffolds include 1) interconnected porous structures that facilitates cellular infiltration and mass transport; 2) adequate mechanical support; 3) controlled degradation; 4) surface chemistry that supports cellular adhesion, differentiation, and proliferation; 5) degradation products with no adverse response; and 6) component materials that can be processed into different shapes.[10,11] Two of these characteristics, the need for a porous structure and the need for adequate mechanical

With nearly 30 years of progress, tissue engineering has shown promise in developing solutions for tissue repair and regeneration. Scaffolds, together with cells and growth factors, are key components of this development. Recently, an increasing number of studies have reported on the design and fabrication of scaffolding materials. In particular, inspired by the nature of bone, polymer/ceramic composite scaffolds have been studied extensively. The purpose of this paper is to review the recent progress of the naturally derived biopolymers and the methods applied to generate biomimetic biopolymer/calcium phosphate composites as well as their biomedical applications in bone tissue engineering.

1. Introduction According to the AAOS (American Academy of Orthopedic Surgeons), there are about 6.3 million bone fractures each year in the United States, which are mainly caused by traumatic accidents, bone tumor removal, or severe nonunion fractures.[1,2] It is estimated that several hundred million individuals worldwide are suffering from bone diseases and injuries, and the number of bone failure patients due to traffic accidents has increased sharply with the increase of car ownership in developing countries. Current therapies for bone repair can be classified as autografts, allografts, xenografts, or artificial implants.[3,4] Transplanting autologous bone harvested from the patient, commonly from the iliac crest, is considered the gold standard

J. Li, Dr. N. Ren, J. Qiu, Prof. H. Liu State Key Lab of Crystal Materials Shandong University 27 Shandanan Road, Jinan, 250100, China E-mail: [email protected] Prof. B. A. Baker Biosystems and Biomaterials Division The National Institute of Standards and Technology MD 20899–8300, USA E-mail: [email protected] Dr. X. Mou, Prof. H. Liu Beijing Institute of Nanoenergy and Nanosystems Chinese Academy of Sciences Beijing, China Prof. R. I. Boughton Department of Physics and Astronomy Bowling Green State University Bowling Green, OH 43403, USA

DOI: 10.1002/adhm.201300562

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

wileyonlinelibrary.com

1

www.advhealthmat.de

PROGRESS REPORT

www.MaterialsViews.com

support, are often at odds with each other. The mechanical properties of scaffolds for bone regeneration should mimic the observed moduli for bone tissues, 10–1500 MPa, to avoid excessive deformation.[12] In comparison, traditional polymer processing techniques, such as porogen leaching or gas foaming, result in materials with a maximum compressive modulus of 0.4 MPa,[10] but have porous structures that facilitate cellular infiltration and mass transport. Balancing these material properties and considering the influence of scaffold microstructure on degradation are significant challenges to developing successful BTE scaffolds. In addition to the processing methods used to fabricate scaffolds, the component materials play an important role in determining scaffold properties. Ideally, the materials chosen for fabrication of BTE scaffolds should be osteoinductive and osteoconductive and promote osseointegration.[13] In fact, there is no material that currently matches all of these requirements. Numerous materials, including polymers, ceramics, and bioglasses have been studied and processed into scaffolds for BTE, each with its own advantages. For instance, polymers, including synthetic polymers and biopolymers, are widely used due to their biocompatibility, malleability into various structures and have tunable rates of degradation, mechanical, and chemical properties. Similarly, inorganic materials with compositions close to the mineral phase of bone (e.g., tricalcium phosphate, hydroxyapatite, and bioglasses) encourage osteogenesis and integrate well with the host bone.[14] However, each of these materials also has unique limitations. For example, synthetic polymers generally have low mechanical strength, poor shape retention, insufficient cell adhesion, and may release potentially toxic degradation products in vivo.[15] Biopolymers are difficult to handle, retain a potential risk of disease transmission depending on their source and purification, and also have weak mechanical properties. Finally, inorganic materials (e.g., ceramics and bioglasses) are known to be brittle, and, when cast in porous microstructures, exhibit low strength and toughness. Inspired by the nature of bone, researchers have combined organic polymers with inorganic materials, primarily calcium phosphate (CaP) to generate bioactive polymer/ceramic composite scaffolds. Importantly, these composites can be designed and tailored to meet many different requirements that single-component scaffolds cannot. Some of the general advantages of polymer–inorganic composites are discussed elsewhere.[16,17] In this paper, we focus on the recent progress made using naturally derived polymers in conjunction with nano-particulate calcium phosphate to fabricate composites, their potential application as delivery agents, and their interactions with stem cells.

2. Biopolymers for BTE Naturally derived biopolymers can be divided into three major classes according to their chemical structure: polysaccharides, proteins, and polyesters. Each is produced extensively by natural processes and can be extracted from bacteria, plants, and animals.[18–20] Biopolymers are uniquely similar to biological macromolecules and can be utilized to stimulate specific

2

wileyonlinelibrary.com

Jianhua Li obtained his B.Sc. from Shandong University in 2006. Currently, he is pursuing his Ph.D. degree under the supervision of Prof. Hong Liu in State Key Laboratory of Crystal Materials, Shandong University, China. His research interest in his Ph.D. study is mainly focused on biomaterials, cell–material interactions, and tissue engineering.

Prof. Bryan A. Baker obtained his M.Sc. in Physics at Furman University in 2003 and his Ph.D. degree in Materials Science and Engineering at Georgia Institute of Technology in 2010. His research interests are mainly focused on cell–material interactions, bio-inspired self-assembly of materials, soft materials, and biomaterials. Prof. Hong Liu received his B.Sc degree from Shandong Institute of Light Industry in 1985 and his Ph.D. degree from Shandong University in 2001. He is a professor in State Key Laboratory of Crystal Materials, Shandong University, China, and a joint professor at Beijing Institute of Nanoenergy and Nanosystems, CAS, China. His research interests are related to nanomaterials and nanodevices, tissue engineering, especially the interaction between stem cells and biomaterials.

cellular responses that synthetic polymers cannot. Moreover, biopolymers possess highly organized structures that contribute to cellular growth at various stages of development.[21] Though concerns exist over immunogenicity and potential disease transmission from animal sources, several biopolymer products have already received Food and Drug Administration (FDA) approval. In the following section, we summarize several of the more popular biopolymers (Table 1) and discuss their processing, antigenicity, and their in vitro apatite forming abilities.

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

www.advhealthmat.de www.MaterialsViews.com

PROGRESS REPORT

Table 1. Some common biopolymers applied in bone tissue engineering. Polymer Protein

Polysaccharides

Origin

Major antigenicity

Crosslinking agent

Dominating nucleation sites

Refs.

Collagen

Animal tissue

Pathogen, terminal telopeptides

Dehydrothermal treatment, UV light; carbodiimide, aldehydes; transglutaminase, riboflavin

Charged amino acid

[22–30]

Silk fibroin

Silkworm, bombyx mori

Sericin

Glutaraldehyde, carbodiimide

Electronegative aminoacidic sequences

[31–34]

Chitosan

Crab shells, shrimps, fungal fermentation

Low toxicity

Glutaraldehyde, genipin, epoxy compound, sodium tripolyphosphate

Cationic amine groups

[35–41]

Starch

Plant

Nontoxicity

Sodium trimetaphosphate, malonic acid, formaldehyde, anhydride

OH− groups

[42–45]

Cellulose

Plant; bacteria

Low toxicity

Aldehydes, carbodiimides, carboxylic acids, irradiation

OH− groups

[46–49]

2.1. Collagen Collagens are the most abundant proteins, having 28 family members with at least one characteristic triple-helical domain and an affinity for several receptor families that participate in regulating cellular behaviors.[50] There is some concern about immunological responses or potential disease transmission (e.g., prions) from collagen as it is mainly derived from animal tissues.[51,52] Terminal telopeptides of collagen are believed to be a major cause of antigenicity for collagen.[22] Purification techniques using treatment with proteolytic enzymes like pepsin to remove the terminal telopeptides followed by precipitation and filtration can reduce or eliminate these concerns. Acid extraction methods are another possibility; however, the native structure of the collagen fibrils is likely to be destroyed.[53] When processed collagen is used for scaffolds, it is usually crosslinked to increase the mechanical properties and regulate cellular behavior.[54] Considerable effort has been devoted to the development of crosslinking treatments to tailor the mechanical and degradation properties of collagen-based scaffolds including physical,[23–25] chemical,[28] enzymatic,[29,30] and combination treatments. Popular chemical crosslinking methods involve the formation of either intramolecular or intermolecular ionic or covalent bonds between the amino acid residues of collagen. But chemicals like glutaraldehyde (GTA) are potentially toxic if residual molecules are released during degradation in vivo.[26] Physical crosslinking methods such as dehydrothermal treatment or exposure to ultraviolet light have been used, but with resulting insufficient crosslinking. Even with crosslinking, however collagen has a faster degradation rate than the rate of new bone formation. This rapid degradation occurs both in vitro and in vivo. Finding new crosslinking agents or other methods to improve the durability of the collagen scaffolds is a continuing challenge for its application in BTE. Finally, the intrinsic ability of collagen to mineralize has been well studied with numerous attempts to mimic the natural collagen-apatite structure. Simulated body fluid (SBF) is typically used to predict in vivo apatite formation.[55,56] When soaking in SBF, the charged residues of amino acids (carboxylate carbonyl groups) provide nucleation sites and subsequently induce nucleation of hydroxyapatite (HAp) crystals.[27,57,58] Further, the spatial arrangement of these charged groups or charged amino

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

Figure 1. Nudelman et al. have shown that collagen is an active scaffold for the formation of the oriented hydroxyapatite platelets, with domains of charged amino acids in both the gap zone and the overlap zone acting as nucleation sites for crystalline hydroxyapatite. Reproduced with permission.[108] Copyright 2010, Nature Publishing Group.

acids in the collagen fibril provides a structural nucleation template that controls the size and the 3D distribution of apatite (Figure 1).[59,60,108] 2.2. Chitosan Chitosan is a deacetylated derivative of chitin, which is the most abundant natural amino polysaccharide extracted from crab shells, shrimp, and fungal fermentation processes.[61] Chitosan

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

wileyonlinelibrary.com

3

www.advhealthmat.de

PROGRESS REPORT

www.MaterialsViews.com

Figure 2. Rusu et al. proposed a theoretical model of chitosan-controlled HAp formation and obtained the Cryo-TEM image of a chitosan/HAp composite. Reproduced with permission.[68] Copyright 2005, Elsevier.

can be easily processed into films, gels, as well as sponge-like scaffolds due to its solubility in dilute acids.[62] However, its poor solubility in water limits its application. Chitosan is characterized by its cationic chemical groups, which facilitate electrostatic interaction with anionic glycosaminoglycans (GAG) and proteoglycans. It also interacts with negatively charged microbial walls, which enables antibacterial applications. Chitosan possesses reactive functional groups that may be chemically modified. In vivo, degradation of chitosan is a hydrolytic process mediated primarily by lysozyme. The degradation rate is inversely related to the degree of crystallinity, which is a function of the extent of deacetylation.[38] Complete degradation of chitosan in vivo may last from several weeks to several months depending on the processing methods used. Degradation products of chitosan are nontoxic and chitosan-based scaffolds have been found to evoke a minimal foreign body reaction, with little or no fibrous encapsulation in vivo.[39] Previously, GTA was commonly used as a crosslinking agent for chitosan-based scaffolds. However, in more recent years, the nontoxic naturally derived crosslinker genipin has become a popular alternative for hydrogel,[63] film,[64] microsphere,[65] 3D framework,[66] and other chitosan applications.[67] In vivo research results indicate that genipin-crosslinked chitosan has a decreased inflammatory response and a slower degradation rate than GTA-crosslinked chitosan microspheres.[65] Addition-

4

wileyonlinelibrary.com

ally, genipin is fluorescent, which enables in situ visualization of genipin-crosslinked biomaterials. Finally, the inherent chemical properties of chitosan show some propensity to facilitate mineralization. Its majority cationic amine groups contribute to the adsorption of PO43− ions.[41] This adsorption coupled with the hydrophilic nature of chitosan favors apatite formation. Besides, according to Rusu’s study, the size distribution of HAp is dependent on the supramolecular structure of chitosan, which is sensitive to the pH (Figure 2).[68] 2.3. Silk Fibroin Silk fibroin, a naturally fibrous material produced by the silkworm and bombyx mori, has been used in sutures for centuries, and more modern applications have been FDA approved for soft tissue repair.[69] Like the collagen family, silks are fibrous proteins characterized by highly repetitive amino acid repeat units that selfassemble into anti-parallel β-sheet structures. These β-sheets are highly crystalline and essentially crosslink the protein through strong hydrogen bonds, as well as strong van der Waals interactions between stacked β-sheets, giving the material robust mechanical properties in some cases equivalent to man-made fibers. Virgin silk has two primary protein constituents, a structured fibrous protein known as fibroin and the glue-like protein

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

www.advhealthmat.de www.MaterialsViews.com

PROGRESS REPORT Figure 3. Marelli et al. have shown that only the hybrid sample containing the amorphous fragments of the silk fibroin (Cs group) demonstrated the formation of carbonated apatite (highlighted in red) when immersed in SBF. This figure presents SEM images and micro-CT 2D and 3D reconstructions of the sample. Reproduced with permission.[33] Copyright 2012, Elsevier.

sericin. Sericin is known as a sensitizer but can be completely removed to reduce antigenic effects. Silk purified in this way has been evaluated in both in vitro and in vivo testing as having good biocompatibility,[70,71] making it convenient in suture and ligament engineering applications. Despite these findings, silk retains some thrombogenic potential that is comparable to the most popular synthetic biomaterials currently used.[72] Though defined by the United States Pharmacopoeia as non-degradable, silk has been shown to resorb in vivo within 1 year.[72] The degradation rate of silk-based scaffolds can be tuned by changing the porosity, crystallinity, β-sheet structure, and molecular weight distribution in addition to using other processing methods.[73] Since it is more commonly used in the regenerated form, silk fibroin can be processed under aqueous conditions.[74] A direct comparison of processing methods found that silk scaffolds prepared from aqueous processes degraded in 6 months while those prepared from the organic solvent hexafluoroisopropanol persisted beyond 1 year in a rat intramuscular model.[73] Dissolution in aqueous solvents such as concentrated lithium bromide, lithium thioisocyanate, or a mixture containing CaCl2, water, and ethanol, can be processed into 3D porous matrices through freeze-drying, salt leaching, and gas foaming.[75] Other modifications associated with changes in surface chemistry can facilitate attachment of growth factors, cell binding domains like arginylglycylaspartic acid (RGD),[76,77] and even other polymers expanding the attainable range of cell and tissue engineering applications.[31] Fibroin mineralization has also been investigated. Previously, RGD-functionalized fibroin scaffolds were observed to preferentially mineralize compared to non-RGD functionalized scaffolds.[76,77] Investigations that separate the hydrophobic crystalline fractions and hydrophilic electronegative amorphous fractions of the silk fibroin have demonstrated that only the amorphous fractions formed carbonated apatite when immersed in SBF (Figure 3).[33] These findings support the conclusion that electronegative amino-acidic sequences direct silk fibroin mineralization.

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

2.4. Other Biopolymers In addition to collagen, chitosan, and silk, there are other naturally derived polymers used in BTE. Bacterial cellulose is an attractive biomaterial candidate because of its high tensile strength, aqueous absorption capacity, nanofibrous network, high crystallinity, and ability to be molded via accessible processing methods.[78]In vivo studies have shown good integration of cellulose into murine subcutaneous tissue with only mild chronic inflammation.[79] However, cellulose cannot bond directly to bone when implanted into the femur.[80] In vivo degradation of these implants is slow, as 60 weeks was necessary for complete dissolution of a cellulose sponge construct in murine subcutaneous tissue.[81] One of the most commonly used natural polymers is glycosaminoglycan hyaluronic acid (HA). HA is a major carbohydrate component of the extracellular matrix and is hydrophilic, nonimmunogenic, biodegradable and easy to produce and modify. It has been utilized extensively in cell encapsulation and drug delivery for BTE.[82,83] HA can also be modified and crosslinked for more stability. Patterson, et al. found that the rate of HA scaffold degradation influences the formation of mature bone by affecting the organization of the collagen matrix.[84] Despite these advantages, a key limitation of HA is its relatively poor mechanical properties. Another interesting polysaccharide for BTE is starch (mainly corn starch), which is usually used in blends with ethylene vinyl alcohol (SEVA-C),[85] polycaprolactone[86,87] or poly(llactic acid).[88] In a recent study, starch/β-polycaprolactone (SPCL) was used to compare the inflammatory response in two implantation rat models: subcutaneous and intramuscular.[86] Results suggested that the immune reaction induced by SPCL was slight but differential, with the intramuscular implantation resulting in a stronger inflammatory response than the subcutaneous implantation.[85] In vitro cytotoxicity evaluation of SEVA-C demonstrated that it was nontoxic, did not inhibit cell growth, and maintained cell viability after 4 weeks of culture. One of the advantages of starch-based scaffolds are their generally stiffer mechanical properties (a compressive modulus

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

wileyonlinelibrary.com

5

www.advhealthmat.de

PROGRESS REPORT

www.MaterialsViews.com

of the remaining ECM.[92,93] Acellular dermal matrices (ADM), which are derived from fullthickness skin treated to remove cells and cellular components but retain the native dermal structure, have already been utilized in biomedical applications such as wound healing and breast reconstruction.[94,95] Recently, porcine-derived ADM (PADM) has been studied as a potential tissue engineering scaffold for neovascularization, soft tissue repair, and bone regeneration.[53,96–98] In vitro culture of MC3T3-E1 pre-osteoblasts with this novel collagen-based scaffold showed good biocompatibility and supported cellular proliferation.[53] However, in vivo biocompatibility of these promising ECM scaffolds should be further evaluated.

3. Scaffolds Incorporating Calcium Phosphate The ECM of native bone is composed primarily of hydroxyapatite (HAp) and fibrous collagen. To mimic this natural organic–inorganic composite, incorporation of calcium Figure 4. Schematic for general processing routes to produce biopolymer/calcium phosphate phosphate (CaP) into polymer matrices has composite scaffolds. A) Physical mixture of polymer solution and calcium phosphate particles become a popular method to fabricate scaffollowed by scaffold fabrication; B) Chemical deposition by alternatively exposure to Ca2+ and PO43- containing solutions; C) Introducing nucleation sites before incubating in SBF; D) Uti- folds for BTE. Currently, the most representalization of functional osteoblasts or osteo-induced stem cells to obtain a mineralized ECM tive calcium phosphate salt is HAp [Ca10(PO [99] followed by decellularization. CaP biomaterials are bioactive 4)6(OH)2]. and osteoconductive[100] and have the potential to be osteoinductive if fabricated with appropriate geometry of 117.5 ± 3.7 MPa for a reported SEVA-C sample).[85] Starch or topography.[101,102] When combined with a polymer matrix, is a mixture of linear and helical amylose and branched amy− normally as a nano-structured coating, CaP is able not only to lopectin with OH groups that provide the necessary binding improve the bone bonding behavior of polymeric materials, but at sites for Ca2+ ions in the SBF. This favors the binding of PO43− the same time play a positive role in enhancing cell adhesion and anions across uniformly distributed Ca2+ sites and the subseinducing the differentiation of osteoprogenitor cells. Below, the quent crystallization of hydroxyapatite.[45] incorporation methods applied to scaffold synthesis in order to produce natural biopolymer-based CaP composites are reviewed. 2.5. Extracellular Matrix Extracellular matrix (ECM) is a complex mixture of structural and functional glycosaminoglycans, glycoproteins, and small molecules arranged in a tissue-specific 3D architecture. Interest in developing a synthetic ECM that mimics properties of the native material stems from the vital role ECM plays in cellular behavior and phenotype. Alternatively, directly applying naturally occurring ECM scaffolds to regenerative medicine applications has seen increased attention.[53,89,90] This strategy generally involves transplanting the decellularized ECM from one tissue or species to another. ECM scaffolds can be obtained from a variety of tissues including dermis, small intestine, and urinary bladder from porcine, bovine, or human sources. The cellular and nuclear contents are believed to be the primary cause of host immune response to ECM from xenogeneic sources.[91] In order to address this challenge, several methods have been established to remove the cellular and nuclear contents from tissues or from whole organs while minimizing any adverse effect on the composition, biological activity, and mechanical integrity 6

wileyonlinelibrary.com

3.1. Physicochemical Process Using CaP nanoparticles is a simple route to introduce CaP into polymer-based scaffolds during synthesis. This physical mixing process (Figure 4A) is particularly suitable for polymers such as acid-soluble chitosan,[103] alginate,[104] and some soluble collagens. Alternatively, chemical deposition processes using calcium salts and phosphate or phosphoric acid can produce nano-featured CaP structures under controlled conditions. In these reactions, reagents are often added dropwise or the polymer matrix is exposed sequentially to reactants (Figure 4B). Flowing feed solution containing both calcium and phosphate ions has also been used to prepare collagen fibrils with CaP incorporated within the fibrils.[105] These and other techniques such as gas foaming, salt leaching, and freeze-drying take advantage of the ability to premix CaP components into the pre-formed polymer phase. The resulting scaffold can facilitate calcification via nucleation but does not necessarily guarantee a homogeneous distri-

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

www.advhealthmat.de www.MaterialsViews.com

PROGRESS REPORT

bution of the mineral phase, which may affect its interactions with cells. 3.2. Biomineralization Biomineralization has been widely used as an efficient process to form nano-featured constructs under mild conditions in vitro. Porous polymer scaffolds are generally immersed in SBF, which serves as a source of Ca2+ and PO43−. In vitro models of apatite formation on scaffolds in SBF are often used for predicting their bone forming potential in vivo. Though biopolymers tend to nucleate apatite due to their charged groups, mineralization is largely determined by the unique chemical properties of a given biopolymer. Methods to control the electrostatically induced mineralization process commonly use nucleation agents such as CaP crystals, anionic proteins, and the incorporation of negatively charged groups (Figure 4C). Kong et al. have incorporated HAp crystals into chitosan scaffolds in situ. Their results showed that the composite nucleated apatite more readily than pure chitosan.[56] Our group has synthesized a hydroxyapatite nanostructure layer-coated 3D porous chitosan-based scaffold by using HAp nanoparticles as nucleation sites for the growth of HAp nanostructures.[103] Besides this, an alternative to the introduction of CaP particles is pre-mineralization, which uses dipping the polymer scaffolds into alternate phosphorous and calcium solutions to form nucleation sites for apatite growth.[53,106] It should be noted that typical mineralization using SBF is performed in the absence of cells, since the hypertonic solutions do not provide the nutrients required for the maintenance of cell viability. Rao and co-workers used a modified culture medium to successfully achieve exogenous mineralization of cell-seeded collagen–chitosan hydrogels.[107] Figure 5. SEM images of samples at different stages of preparation for HAp-coated chitosan This method allows in vitro mineralization scaffold. a,b) Chitosan framework without the pre-addition of HAp mineralized in SBF for 8 d. of 3D protein constructs in the presence of Chitosan framework without the pre-addition of HAp mineralized in SBF for 2 (c,d), 4 (e,f), living cells for subsequent implantation in and 8 (g,h) days. Reproduced with permission.[103] Copyright 2011, American Chemical Society. vivo. Utilization of cells to directly mineralize polymer scaffolds is an alternative route. These mineralizing cells could be functional osteoblasts or facilitates binding of Ca2+. To mimic this charge attraction, stem cells induced by the osteogenic medium (Figure 4D). biopolymers have been synthesized with negatively charged Many scientists have tried to understand the mechanisms carboxylate and phosphate groups as a way to promote and conunderlying biomineralization, a topic which remains hotly trol the mineralization process.[113] Incorporation of negatively [ 108 ] debated. charged carboxymethyllysine groups resulted in the formation It is believed that matrix proteins (both collagenous of oriented crystals of octacalcium phosphate/hydroxyapatite and noncollagenous) play an essential role in biomineralizaphases in one such example.[114] Biopolymer/CaP composite tion.[109,110] Multiple anionic proteins that serve as nucleators and inhibitors control the deposition. Many of these mineraliscaffolds obtained through biomimetic mineralization possess zation-related proteins are acidic and phosphorylated, such as a two-level 3D structure with nanoscale apatite particles assembone sialoprotein and osteopontin.[110–112] These proteins are bled on the surface of microscale biopolymer pores as shown in Figure 5. Here, the morphology of hydroxyapatite coatings on characterized by high anionic glutamate (Glu) content, which Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

wileyonlinelibrary.com

7

www.advhealthmat.de

PROGRESS REPORT

www.MaterialsViews.com

BMP-2 and BMP-7 are the most widely used growth factors, given their FDA approval for clinical use in the USA to repair bone injuries by mediating spinal fusion or fracture healing.[141] Commercially available BMP-2 uses a type I collagen scaffold as a carrier, but the release rate of BMP-2 is very fast, which may result in reduced bone formation efficacy.[142] Yang et al. found that an apatite coating of a collagen scaffold increases the release period as well as the osteogenic efficacy of BMP-2.[142] The 5× and 10× SBF apatite-coated collagen scaffolds released 91.8 ± 11.5% and 82.2 ± 13.1% Figure 6. A recent model of surface-directed mineralization of calcium phosphate from SBF at of their loaded BMP-2 over 13 d in vitro, 37 °C. Prenucleation clusters are formed in bulk solution (Stage 1) followed by their migration to the surface (Stage 2), then they transform into crystalline HAp (Stages 3, 4, and 5). Repro- respectively, whereas a bare collagen scaffold released 98.3 ± 2.2% over the initial day. duced with permission.[115] Copyright 2010, Nature Publishing Group. Consequently, BMP-2 delivery using apatitecoated collagen scaffolds resulted in 2.5-fold higher bone formation volume and 4.0-fold higher bone formachitosan scaffolds made with and without pre-addition of HAp tion area in mouse calvarial defect than BMP-2 delivery using crystals is shown.[103] noncoated collagen scaffolds.[142] In contrast to the classical view of crystallization pathways during biominerization, analytical studies on model systems Gene delivery via CaP-based biomaterials exhibits excellent of biomineralization have been proposed recently.[59,115] The performance, since CaP has binding affinity to DNA molecules, model proposed by Dey et al., for instance, provides us a new and CaP particles are also able to permeate the cell membrane vision to understand the biomineralization process and to and dissolve in the cell.[148,151] Keeney et al. utilized a collagen/ design appropriate surfaces to induce and control the nucleacalcium phosphate scaffold to deliver naked plasmid DNA tion of HAp (Figure 6). without the use of a gene vector. When the scaffold degrades, Table 2 summarizes the methods of construction of biopolthe plasmids release into the bony site followed by cell uptake ymer/CaP composites. in complex with CaP particles, thus achieving elevated levels of transfection and in vivo bone formation (Figure 7).[148] Results showed that the group containing scaffold+plasmids had a statistically higher bone volume in mouse femoral defects rela4. “Living” Scaffold: Delivery of Bioactive tive to the scaffold alone. Bone occupied ≈24% of the area of Molecules and Cells for Bone Regeneration interest in the scaffold+plasmids group in comparison to ≈10% in the controls after 4 week reparation in a mouse intra-femoral A current method in tissue engineering is to combine scaffolds with stem cells and in some cases bioactive molecules to create model (Figure 7B). a “living” scaffold. In these constructs, the scaffold provides Delivery of growth factors or their encoding genes via scafboth a growth environment for the cells and a delivery vector folds has been proved to effectively enhance bone regeneration. for cell-based therapies. However, the use of exogenous stimulation may influence the Bone repair and regeneration applications have explored balance of bone and vessel remodeling resulting in excessive using cell sources ranging from primary adult osteoblasts (bone bone formation or vascular leakage.[150] Lately, micro-RNA[150] cells) to bone marrow mesenchymal stem cells (BMSCs). Mesand antibodies[149] have been explored as osteogenic stimulaenchymal stem cells (MSCs) are the most commonly used cell tion factors encapsulated in a biopolymer scaffold to treat bone source and are derived from adult human tissues, including defects. Micro-RNAs function as repressors of gene expression bone marrow stroma and potentially other tissues as well.[135– at the post-transcriptional regulation level. Therefore, overex137] One of the critical functions of MSCs under physiological pression or inhibition of microRNAs can regulate bone regenconditions is to support the process of bone remodeling.[138] eration through the coordination of endogenous angiogenThe origin of cell-based therapeutics can influence their osteesis and osteogenesis processes.[150] The tethered anti-BMP2 ogenic potential. For example, adipose tissue-derived MSCs monoclonal antibodies (mAbs) can trap BMP ligands and thus have been suggested as inferior cell materials compared to provide BMP inductive signals for osteogenic differentiation BMSCs.[135,139] MSCs are thought to have the capacity to differand in vivo bone regeneration (Figure 8).[149] entiate into a number of cell types (including osteoblasts, chonIt is becoming better understood that not only bioactive drocytes, adipocytes etc.) in response to specific growth factors molecules regulate cell fate but also do the physical and chemand supplements, which include BMPs, TGF-β, IGF, FGF, and ical signals arising from their complex surrounding extracelVEGF.[136,140] Table 3 lists some of the biopolymer-based scaflular matrix (ECM).[152,153] Subsequently, engineering biomatefolds that have been used in conjunction with bioactive molrials to mimic the signaling of native ECM is a continuing goal ecules (i.e., growth factors, plasmid DNA, antibody, etc.) and for bone regeneration. Naturally derived biopolymers perform cellular components for bone tissue engineering. a diverse set of functions in their native microenvironment.

8

wileyonlinelibrary.com

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

www.advhealthmat.de www.MaterialsViews.com

PROGRESS REPORT

Table 2. Methods of construction of biopolymer/CaP composites. Incorporation methods

Polymer

CaP form

Scaffold structure

Brief protocol

Refs.

Physical mixture

Collagen

HAp

Porous

Freeze-drying followed by chemical crosslinking of collagen/HAp mixture

[116]

Hap nanorods

Nanofibrous

Electrospinning a mixture of polyvinyl alcohol–collagen–hydroxyapatite

[117]

Chitosan

Silk fibroin

Chemical deposition

Biomimetic mineralization

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

Naturally derived HAp

Porous

Freeze-drying the mixture

[118]

nHAp

Highly porous

Freezing and lyophilization of chitosan–nHAp dispersion

[119]

Bioactive glass ceramic nanoparticles

Macroporous

Lyophilization

[120]

Tuna bone HAp

Sponge

Lyophilization

[121]

HAp with low crystallinity Micro-porous mesh/sponge Knitted silk mesh was immersed in HAp/silk slurry and then freeze-dried to form scaffold.

[122]

HAp

Porous

Salt leaching

[123]

Alginate

HAp particle

Porous

Using calcium ions released from HAp to form gel followed by freeze-drying

[104]

Gelatin

α-tricalcium phosphate

Porous

Freeze-drying followed by crosslinking

[124]

Collagen

HAp

Sponge; fiberous

Simultaneous titration co-precipitation method

[125]

Chitosan

nHAp

Porous

Using double-diffusion technique to form nHAp and a thermally induced lyophilization technique to form scaffold

[126]

Silk fibroin

Calcium-deficient HAp

Particles

Loading on the surface of deprotonated silk fibroin particles with calcium and phosphate ions

[127]

Silk

HAp nanoparticles

Knitted scaffolds

The silk scaffold was alternatively immersed in CaCl2 and Na2HPO4 solution

[128]

Alginate

HAp with low crystallinity

Beads

Dripping the Na-alginate solution containing phosphate into the calcium containing gelling bath

[129]

Collagen

CaP

Hydrogels

Enzymatic mineralization by incorporation of alkaline phosphatase

[130]

Intra fibrillar nanoapatite

Fibrous

Carbonated HAp

Osteoid-like hydrogel

Incorporation of silk fibroin derived polypeptide to mimic the role of anionic non-collagenous proteins in biomineralization process

[33]

Carbonated HAp

A isotropic equiaxed or unidirectional lamellar structure

Scaffolds were precipitated from collagencontaining modified SBF by self-assembly and subjected to controllable freeze casting.

[132]

HAp

Native matrix

Premineralization with alternate exposure to CaCl2 and Na2HPO4solution before incubating in SBF

[53]

Biomimetic hierarchical nanoapatite assembly [131] using polyvinylphosphonic acid as a biomimetic analog of matrix phosphoproteins

Chitosan

HAp

Porous

Nanocrystal induced biomineralization

[103]

Silk fibroin

HAp

Film

Calcium ions were added into the silk fibroin film before incubation in 1.5×SBF

[133]

Bacterial cellulose

Calcium-deficient HAp

Pellicles/tubes

Negatively charged by the adsorption of carboxymethyl cellulose to initiate nucleation followed by SBF incubation

[78]

Alginate

HAp

Porous

Incubating in a modified SBF

[134]

Collagen/Chitosan

Calcium deposition

Hydrogel

Using a modified culture medium to achieve exogenous mineralization

[107]

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

wileyonlinelibrary.com

9

www.advhealthmat.de

PROGRESS REPORT

www.MaterialsViews.com Table 3. Bioactive molecules delivery via biopolymer scaffolds in bone tissue engineering. Biopolymer/scaffold structure Collagen-HAp/ porous

Bioactive molecules

Seeded cells for implantation [i] or in vitro cultured cells [c]

In vivo animal model

Refs.

BMP-2

Rat calvarial osteoblasts [c]

Mouse calvarial defect model

[142]

Collagen-HAp/ porous

NGFβ



Rat calvarial defect model

[143]

Gelatin/ hydrogel

BMP-2

Preosteoblast W20–17 cell line [c]

Sprague Dawley rats

[144]

BMP-2, BMP-7

rBMSCs [c]

(In vitro study)

[145] [146]

Chitosan /3D fiber mesh Silk fibroin-nHA/ fiber

BMP-2

hBMSCs [c]

(In vitro study)

Silk firoin-nHA/porous

BMP-2

Osteoblasts [c]

(In vitro study)

[32]

VEGF, BMP-2

hBMSCs [i]

Mouse segmental femur defect model

[147]

pDNA encoding BMP2

rBMSCs [c]

(In vitro study)

[116] [148]

Alginate/hydrogel Collagen nano-HAp/ porous

pDNA encoding VEGF165



Mouse intra-femoral model

Alginate/microspheres

anti-BMP2 monoclonal antibody

hBMSCs [i]

Calvarial defects in mice

[149]

HyStem-HP/hydrogel

MicroRNAs-26a

hBMSCs [i]

Mouse subcutaneous implant model and calvarial bone defect model

[150]

Collagen/CaP particles porous

BMP2, bone morphogenetic protein-2; TGF-β3, transforming growth factor-β3; VEGF, vascular endothelial growth factor; NGFβ, nerve growth factor β; hBMSCs, human bone marrow stem cells; rBMSCs, rat bone marrow stem cells; pDNA, plasmid-DNA; HyStem-HP, a combination of thiol-modified hyaluronan, and thiol-modified heparin.

Figure 7. The ability of a collagen/calcium phosphate scaffold to act as its own vector for gene delivery and to promote bone formation. A) A collagen/calcium phosphate scaffold carrying naked plasmid can mediate transfection without the presence of a non-viral vector. B) In vivo bone formation was enhanced by using collagen/calcium phosphate gene delivery system. Reproduced with permission.[148] Copyright 2010, Elsevier.

Utilizing these polymers in CaP composites provides features mimicking the extracellular matrix and potentially may be adapted to both chemically and physically signal cell selfrenewal and osteogenic differentiation. A recent study has demonstrated that hydroxyapatite-coated chitosan scaffolds-

10

wileyonlinelibrary.com

altered cell shape and cytoskeletal organization of rat bone marrow-derived mesenchymal stem cells in vitro, as compared with the smooth surfaced chitosan framework. The results suggest that the nano-structured surface of the HAp acts as a critical signal cue promoting osteogenic differentiation in vitro.[66] Another report also showed that HAp coating on the silk scaffold resulted in an osteogenic differentiation of the seeded BMSCs in a normal culture medium, and this effect was further enhanced by culturing in osteogenic medium, indicating enhanced osteoinductivity of the HAp-coated silk scaffold.[128] Furthermore, recent in vivo studies also revealed the positive role of HAp incorporation in bone regeneration in defect models from small to large animals.[154,155] For instance, Liu et al. demonstrated that nanofibrous hydroxyapatite/ chitosan (nHAp/CTS) scaffolds can promote bone regeneration by supporting the adhesion, proliferation, and activating integrin-BMP/Smad signaling pathway of BMSCs, when compared with the CTS group without HAp.[155] The BMSCs exhibited higher ALP activity on nHAp/CTS than CTS group. In vivo, nHAp/CTS/BMSCs exhibited superior ability for bone reconstruction than other groups for cranial bone defects after 10 and 20 weeks of implantation (Figure 9).[155] On the other hand, native protein also plays an important role in the regulation cells and bone formation. For instance, Wagner-Ecker et al. found that the ectopic bone formation capacity of human BMSC populations depended strongly on the biomaterial and was promoted when collagen was preserved in biological bone substitutes.[156] In another study, collagen was found to be a far better substrate for regulating MSC osteoblastic differentiation in comparison with the synthetic polymer (PLGA).[157] Furthermore, in this study, the HAp-incorporated collagen group exhibited a straightforward intramembranous bone formation mode at ectopic sites, whereas the HAp-synthetic polymer group demonstrated an endochondral bone formation mode (Figure 10).[157] In conclusion, biopolymer/CaP, in particular collagen/HAp composite, has been shown to be an outstanding platform for

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

www.advhealthmat.de www.MaterialsViews.com

PROGRESS REPORT

ingenious designs mentioned in the previous section, the materials and designs used in clinical trials are very straightforward. CaP materials are the most frequently-used grafting material. In one case, a collagen/ hydroxyapatite biomaterial (Geistlich BioOss) is used to reconstruct the alveolar bone defect in cleft lip and palate patients using mesenchymal stem cells from deciduous dental pulp through prospective qualitative and quantitative analysis of bone neoformation. Other than this, there are no more studies using natural biopolymers as grafting materials in this table. There are also many human clinical studies, which have not obtained approval from institutions such as FDA or EMEA, published in the literature on bone tissue engineering. We conducted a literature review regarding the clinical application of natural biopolymers, using the search engine of Pubmed (the world’s largest biomedical publication database) for published clinical studies. Search terms were: “collagen,” “chitosan,” “starch,” “cellulose,” “silk,” or “gelatin” and “bone tissue engineering.” The filters were set as follows: Article types-Clinical trial; Species-Humans. The searching results (conducted on September 10, 2013) showed that 16 reports were related to collagen, 1 report to chitosan, 1 report to cellulose, and none for the others. Obviously, Figure 8. Co-encapsulation of anti-BMP2 monoclonal antibody (mAb) and mesenchymal stem collagen is the most important choice for cells in alginate microspheres for bone tissue engineering. A) The schematic of alginate beads- clinical studies, and there is much potential antibody delivery system and the release profile of the anti-BMP2 mAb. B) In vivo bone forfor other promising biopolymers. In a pilot mation was enhanced by using the co-encapsulation of anti-BMP2 monoclonal antibody and clinical trial, a gradient composite osteomesenchymal stem cells. Reproduced with permission.[149] Copyright 2013, Elsevier. chondral scaffold based on type I collagen– hydroxyapatite was used to treat osteochondral lesions involving the subchondral bone in 13 patients (15 delivering bioactive molecules, for guiding the osteogenic difdefect sites).[158] The scaffold has a porous tri-layer structure: ferentiation of stem cells and for consequently promoting bone the cartilaginous layer consists of type I collagen, the intermehealing process. diate layer consists of a combination of type I collagen (60%) and HAp (40%), whereas the lower layer consists of a mineralized blend of type I collagen (30%) and HAp (70%). The histo5. Clinical Studies logical analysis (performed in two cases at 6 months) revealed that the subchondral bone was perfectly formed and the scafUp to now, numerous animal models, such as mouse, rat, fold material was completely reabsorbed. However, such early rabbit, dog, sheep, and goat models have been used for bone clinical evaluation in this study cannot determine the success tissue engineering studies. All these efforts dedicated to bone rate of the procedure and the number of evaluated cases was regeneration using tissue engineering strategies provide scafrelatively low. folds with best performance in the animal model. Off-the-shelf Collagen also can assist the expansion of MSCs in vitro.[159,160] commercially available bone scaffolds for human use can be In clinical applications of regenerative therapies, human mesanticipated. Before the release of a tissue-engineered product, enchymal stem cells (hMSC) have been one of the most proman investigational new drug application should be submitted ising candidates, due to their multilineage differentiation potento FDA or the European Medicines Agency (EMEA) following tial and immunomodulatory properties. hMSC are normally completion of all phases of the clinical trials. A search conextracted from the patient’s own bone marrow aspirate, which ducted on September 10, 2013, on clinicaltrials.gov, a service has less than 0.01% MSCs.[136] This limited supply has motiof the U.S. National Institutes of Health, using “bone tissue vated efforts to use in vitro expansion of these valuable cells. engineering” as search terms, showed 33 results, of which six A challenge in this method continues to be the diminishing studies are relevant and listed in Table 4. Compared with the

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

wileyonlinelibrary.com

11

www.advhealthmat.de

PROGRESS REPORT

www.MaterialsViews.com

Figure 9. The promotion of bone regeneration by nanofibrous hydroxyapatite/chitosan scaffolds by regulating BMSCs. A) Morphology and proliferation of rat BMSCs on scaffolds. B) X-ray examination of the whole calvarias after 10 and 20 weeks implantation in vivo. Reproduced with permission.[155] Copyright 2013, Elsevier.

Figure 10. Biopolymer (collagen) and synthetic polymer (PLGA) differs in directing MSC differentiation and bone formation mode. Reproduced with permission.[157] Copyright 2013, Elsevier. Table 4. Clinical studies of BTE on clinicaltrials.gov. Cell resource

Condition

Intervention model

Phase

study status

Study start

Collagen and HAp (Geistlich Bio-Oss)

Materials

MSCs from deciduous tooth

Cleft lip and palate

Single group assignment



Recruiting

May 2013

β-TCP (Cerasorb)

Autologous bone repair cell

Tooth loss

Parallel assignment

I, II

Active, not recruiting

March 2010

Allogenic bone tissue

Autologous BMSCs

Lumbar Spondylolisthesis and/or degenerative discopathy

Parallel assignment

I, II

Recruiting

June 2012

Allogenic bone tissue

Autologous BMSCs

Avascular necrosis of Femur head

Parallel assignment

I, II

Recruiting

July 2012

Resorbable polymer/ ceramic

MSCs

Surgically-created resection cavity

Single group assignment

I

Recruiting

July 2013

Autologous bone marrow mononuclear cells

Pseudoarthrosis

Parallel assignment

II

Recruiting

April 2011

Porous matrix of calcium phosphate

12

wileyonlinelibrary.com

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

www.advhealthmat.de www.MaterialsViews.com

PROGRESS REPORT

Figure 11. Overview of biopolymer-based bone tissue engineering strategy.

ability of MSCs to differentiate into osteoblast-like cells during culture.[161] In vitro expansion of MSCs by conventional tissue culture methods may lead to the loss of both their proliferative and differentiation potential. Cultivation on various collagenous biomaterials has been used as a novel strategy to overcome these limitations. Mauney et al. have demonstrated that a denatured type I collagen matrix not only preserved MSC osteogenic differentiation capability during in vitro expansion, but also maintained the ability to mediate bone formation in vivo.[159] Katayama et al. used a radial-flow bioreactor (RFB) to induce 3D expansion of hMSCs on a type I collagen large scaffold, which enabled uniform expansion of hMSCs with no change in cellular characteristics.[160]

6. Summary Biopolymers have unique advantages over synthetic polymers owing primarily to their derivation from biological sources in which their chemistry and structural properties impart their functionality. Reproducing this functionality is a continuing goal in tissue engineering research. Composites from these naturally derived biopolymers, particularly nano-particulate CaP biocomposites can not only provide a mechanically enhanced microporous matrix, but also nano-featured structures that support cellular attachment, migration, proliferation, and differentiation. These scaffolds can also be adapted as delivery agents for bioactive molecules and stem cells. Challenges remain, however, that hinder their further clinical application. These challenges may include the variation between batches and the safety concerns presented by the use of animal-derived collagens. Despite this, the adaptation of biopolymers in conjunction with CaP composites represents a promising avenue for bone tissue engineering (Figure 11).

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

7. Disclosures Contribution of NIST, not subject to copyright in the United States. Certain equipment, instruments, or materials are identified in this paper in order to adequately specify the experimental details. Such identification does not imply recommendation by the NIST nor does it imply the materials are necessarily the best available for the purpose.

Acknowledgements The authors are thankful for funds from National Natural Science Foundation of China (Grant No. 51372142), National Science Fund for Distinguished Young Scholars (NSFDYS: 50925205), Innovation Research Group (IRG: 51021062) and the “100 Talents Program” of Chinese Academy of Sciences. Thanks for the support from the “thousands talents” program for pioneer researcher and his innovation team, China. Received: October 12, 2013 Revised: November 15, 2013 Published online:

[1] A. Greenwald, S. Boden, V. Goldberg, Y. Khan, C. Laurencin, R. Rosier, J. Bone Joint Surg. Am. 2001, 83, S98. [2] B. Stevens, Y. Yang, A. Mohandas, B. Stucker, K. T. Nguyen, J. Biomed. Mater. Res. B 2008, 85, 573. [3] A. Kolk, J. Handschel, W. Drescher, D. Rothamel, F. Kloss, M. Blessmann, M. Heiland, K.-D. Wolff, R. Smeets, J. Cranio-Maxillo-Fac. Surg. 2012, 40, 706. [4] R. Dimitriou, E. Jones, D. McGonagle, P. V. Giannoudis, BMC Med. 2011, 9, 66.

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

wileyonlinelibrary.com

13

www.advhealthmat.de

PROGRESS REPORT

www.MaterialsViews.com [5] H. Schaaf, S. Lendeckel, H.-P. Howaldt, P. Streckbein, Oral Surg. Oral Med. Oral Path. Oral Rad. Endodontol. 2010, 109, 52. [6] S. N. Khan, F. P. Cammisa Jr, H. S. Sandhu, A. D. Diwan, F. P. Girardi, J. M. Lane, J. Am. Acad. Orthop. Surg. 2005, 13, 77. [7] J. G. Pilitsis, D. R. Lucas, S. R. Rengachary, Neurosurg. Focus 2002, 13, 1. [8] R. Langer, J. Vacanti, Science 1993, 260, 920. [9] D. W. Hutmacher, J. T. Schantz, C. X. F. Lam, K. C. Tan, T. C. Lim, J. Tissue Eng. Regen. Med. 2007, 1, 245. [10] S. J. Hollister, Nat. Mater. 2005, 4, 518. [11] S. Bose, M. Roy, A. Bandyopadhyay, Trends Biotechnol. 2012, 30, 546. [12] R. W. Goulet, S. A. Goldstein, M. J. Ciarelli, J. L. Kuhn, M. Brown, L. Feldkamp, J. Biomech. 1994, 27, 375. [13] M. M. Stevens, Mater. Today 2008, 11, 18. [14] H. Zhou, J. Lee, Acta Biomater. 2011, 7, 2769. [15] E. L. Hedberg, H. C. Kroese-Deutman, C. K. Shih, R. S. Crowther, D. H. Carney, A. G. Mikos, J. A. Jansen, Biomaterials 2005, 26, 4616. [16] K. Rezwan, Q. Chen, J. Blaker, A. R. Boccaccini, Biomaterials 2006, 27, 3413. [17] M. Okamoto, B. John, Prog. Polym. Sci. 2013, 38, 1487. [18] B. H. Rehm, Nat. Rev. Microbiol. 2010, 8, 578. [19] C. Castro, R. Zuluaga, J.-L. Putaux, G. Caro, I. Mondragon, P. Gañán, Carbohydr. Polym. 2011, 84, 96. [20] G. Franz, W. Blaschek, Meth. Plant Biochem. 1990, 2, 291. [21] H. Y. Cheung, K. T. Lau, T. P. Lu, D. Hui, Compos. Part B-Eng. 2007, 38, 291. [22] A. Lynn, I. Yannas, W. Bonfield, J. Biomed. Mater. Res. B 2004, 71, 343. [23] M. G. Haugh, M. J. Jaasma, F. J. O’Brien, J. Biomed. Mater. Res. A 2009, 89, 363. [24] C. M. Tierney, M. G. Haugh, J. Liedl, F. Mulcahy, B. Hayes, F. J. O’Brien, J. Mech. Behav. Biomed. Mater. 2009, 2, 202. [25] J. W. Drexler, H. M. Powell, Tissue Eng. 2010, 17, 9. [26] L. Olde Damink, P. Dijkstra, M. Luyn, P. Wachem, P. Nieuwenhuis, J. Feijen, J. Mater. Sci. Mater. Med. 1995, 6, 460. [27] L. J. Zhang, X. S. Feng, H. G. Liu, D. J. Qian, L. Zhang, X. L. Yu, F. Z. Cui, Mater. Lett. 2004, 58, 719. [28] J. Li, N. Ren, J. Qiu, H. Jiang, H. Zhao, G. Wang, R. I. Boughton, Y. Wang, H. Liu, Int. J. Biol. Macromol. 2013, 61, 69. [29] S. Hayes, C. S. Kamma-Lorger, C. Boote, R. D. Young, A. J. Quantock, A. Rost, Y. Khatib, J. Harris, N. Yagi, N. Terrill, PLoS One 2013, 8, e52860. [30] R. N. Chen, H. O. Ho, M. T. Sheu, Biomaterials 2005, 26, 4229. [31] A. R. Murphy, D. L. Kaplan, J. Mater. Chem. 2009, 19, 6443. [32] Y. H. Zhang, L. J. Zhu, J. M. Yao, Adv. Mater. Res. 2011, 175, 253. [33] B. Marelli, C. E. Ghezzi, A. Alessandrino, J. E. Barralet, G. Freddi, S. N. Nazhat, Biomaterials 2012, 33, 102. [34] Y. Lin, X. Xia, K. Shang, R. Elia, W. Huang, P. Cebe, G. Leisk, F. G. Omenetto, D. L. Kaplan, Biomacromolecules 2013. [35] R. A. A. Muzzarelli, M. Mattioli-Belmonte, A. Pugnaloni, G. Biagini, Chitin Chitinases 1999, 87, 251. [36] C. T. Liao, M. H. Ho, Membranes 2010, 1, 3. [37] Y. Liu, W. Chen, H. I. Kim, J. Appl. Polym. Sci. 2012, 125, E290. [38] H. Zhang, S. H. Neau, Biomaterials 2001, 22, 1653. [39] A. K. Azab, B. Orkin, V. Doviner, A. Nissan, M. Klein, M. Srebnik, A. Rubinstein, J. Controlled Release 2006, 111, 281. [40] M. E. Frohbergh, A. Katsman, G. P. Botta, P. Lazarovici, C. L. Schauer, U. G. K. Wegst, P. I. Lelkes, Biomaterials 2012, 33, 9167. [41] D. Baskar, R. Balu, T. S. S. Kumar, Int. J. Biol. Macromol. 2011, 49, 385. [42] T. G. Dastidar, A. N. Netravali, Carbohydr. Polym. 2012, 90, 1620. [43] F. M. Carbinatto, A. G. de Castro, B. S. F. Cury, A. Magalhães, R. C. Evangelista, Int. J. Pharm. 2011, 423, 281.

14

wileyonlinelibrary.com

[44] F. G. Torres, A. R. Boccaccini, O. P. Troncoso, J. Appl. Polym. Sci. 2007, 103, 1332. [45] M. Sadjadi, M. Meskinfam, B. Sadeghi, H. Jazdarreh, K. Zare, Mater. Chem. Phys. 2010, 124, 217. [46] Y. Chen, J. Bioact. Compatible Polym. 2009, 24, 137. [47] A. Sannino, C. Demitri, M. Madaghiele, Materials 2009, 2, 353. [48] S. Shi, S. Chen, X. Zhang, W. Shen, X. Li, W. Hu, H. Wang, J. Chem. Technol. Biotechnol. 2009, 84, 285. [49] C. Chang, L. Zhang, Carbohydr. Polym. 2011, 84, 40. [50] S. Ricard-Blum, Cold Spring Harbor Perspect. Biol. 2010. [51] Y. Kim, H. Nowzari, S. K. Rich, Clin. Implant Dent. Relat. Res. 2012, 15, 645. [52] R. J. Mullins, C. Richards, T. Walker, Aust. N. Z. J. Ophthalmol. 1996, 24, 257. [53] H. Zhao, G. Wang, S. Hu, J. Cui, N. Ren, D. Liu, H. Liu, C. Cao, J. Wang, Z. Wang, Tissue Eng. 2010, 17, 5–6, 765. [54] M. G. Haugh, C. M. Murphy, R. C. McKiernan, C. Altenbuchner, F. J. O’Brien, Tissue Eng. 2011, 17, 1201. [55] T. Kokubo, H. Takadama, Biomaterials 2006, 27, 2907. [56] L. Kong, Y. Gao, G. Lu, Y. Gong, N. Zhao, X. Zhang, Eur. Polym. J. 2006, 42, 3171. [57] W. Zhang, Z. L. Huang, S. S. Liao, F. Z. Cui, J. Am. Ceram. Soc. 2003, 86, 1052. [58] N. Almora-Barrios, N. H. De Leeuw, Cryst. Growth Des. 2011, 12, 756. [59] F. Nudelman, K. Pieterse, A. George, P. H. Bomans, H. Friedrich, L. J. Brylka, P. A. Hilbers, N. A. Sommerdijk, Nat. Mater. 2010, 9, 1004. [60] Y. Wang, T. Azaïs, M. Robin, A. Vallée, C. Catania, P. Legriel, G. Pehau-Arnaudet, F. Babonneau, M.-M. Giraud-Guille, N. Nassif, Nat. Mater. 2012, 11, 724. [61] M. Rinaudo, Prog. Polym. Sci. 2006, 31, 603. [62] C. Heinemann, S. Heinemann, A. Lode, A. Bernhardt, H. Worch, T. Hanke, Biomacromolecules 2009, 10, 1305. [63] F. Mwale, M. Iordanova, C. N. Demers, T. Steffen, P. Roughley, J. Antoniou, Tissue Eng. 2005, 11, 130. [64] J. Jin, M. Song, D. Hourston, Biomacromolecules 2004, 5, 162. [65] F. L. Mi, Y. C. Tan, H. F. Liang, H. W. Sung, Biomaterials 2002, 23, 181. [66] G. Wang, L. Zheng, H. Zhao, J. Miao, C. Sun, N. Ren, J. Wang, H. Liu, X. Tao, Tissue Eng. 2011, 17, 1. [67] R. A. A. Muzzarelli, Carbohydr. Polym. 2009, 77, 1. [68] V. M. Rusu, C.-H. Ng, M. Wilke, B. Tiersch, P. Fratzl, M. G. Peter, Biomaterials 2005, 26, 5414. [69] Serica Technologies I. Serica Technologies Receives FDA 510(k) Clearance for SeriScaffold Technology for Soft Tissue Repair. Available at: http://www.sericainc.com/en-us/news/ 2009. [70] L. Meinel, S. Hofmann, V. Karageorgiou, C. Kirker-Head, J. McCool, G. Gronowicz, L. Zichner, R. Langer, G. Vunjak-Novakovic, D. L. Kaplan, Biomaterials 2005, 26, 147. [71] M. Santin, A. Motta, G. Freddi, M. Cannas, J. Biomed. Mater. Res. 1999, 46, 382. [72] G. H. Altman, F. Diaz, C. Jakuba, T. Calabro, R. L. Horan, J. Chen, H. Lu, J. Richmond, D. L. Kaplan, Biomaterials 2003, 24, 401. [73] Y. Wang, D. D. Rudym, A. Walsh, L. Abrahamsen, H. J. Kim, H. S. Kim, C. Kirker-Head, D. L. Kaplan, Biomaterials 2008, 29, 3415. [74] U. J. Kim, J. Park, H. Joo Kim, M. Wada, D. L. Kaplan, Biomaterials 2005, 26, 2775. [75] R. Nazarov, H.-J. Jin, D. L. Kaplan, Biomacromolecules 2004, 5, 718. [76] L. Meinel, V. Karageorgiou, S. Hofmann, R. Fajardo, B. Snyder, C. Li, L. Zichner, R. Langer, G. Vunjak-Novakovic, D. L. Kaplan, J. Biomed. Mater. Res. A 2004, 71, 25. [77] S. Sofia, M. B. McCarthy, G. Gronowicz, D. L. Kaplan, J. Biomed. Mater. Res. 2001, 54, 139.

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

www.advhealthmat.de www.MaterialsViews.com

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

PROGRESS REPORT

[78] K. A. Zimmermann, J. M. LeBlanc, K. T. Sheets, R. W. Fox, P. Gatenholm, Mater. Sci. Eng. C 2009, 31, 43. [79] G. Helenius, H. B ckdahl, A. Bodin, U. Nannmark, P. Gatenholm, B. Risberg, J. Biomed. Mater. Res. A 2006, 76, 431. [80] M. M rtson, J. Viljanto, T. Hurme, P. Saukko, Eur. Surg. Res. 2000, 30, 426. [81] M. M rtson, J. Viljanto, T. Hurme, P. Laippala, P. Saukko, Biomaterials 1999, 20, 1989. [82] G. Bhakta, B. Rai, Z. X. Lim, J. H. Hui, G. S. Stein, A. J. van Wijnen, V. Nurcombe, G. D. Prestwich, S. M. Cool, Biomaterials 2012, 33, 6113. [83] M. N. Collins , C. Birkinshaw, Carbohydr. Polym. 2012 , 92 , 1262 . [84] J. Patterson, R. Siew, S. W. Herring, A. S. P. Lin, R. Guldberg, P. S. Stayton, Biomaterials 2010, 31, 6772. [85] A. Salgado, O. Coutinho, R. Reis, Tissue Eng. 2004, 10, 465. [86] T. Santos, A. Marques, B. Horing, A. Martins, K. Tuzlakoglu, A. Castro, M. van Griensven, R. Reis, Acta Biomater. 2010, 6, 4314. [87] A. M. Martins, A. Saraf, R. A. Sousa, C. M. Alves, A. G. Mikos, F. K. Kasper, R. L. Reis, J. Biomed. Mater. Res. A 2010, 94, 1061. [88] A. R. C. Duarte, J. F. Mano, R. L. Reis, J. Supercrit. Fluid. 2009, 49, 279. [89] H. C. Ott, T. S. Matthiesen, S. K. Goh, L. D. Black, S. M. Kren, T. I. Netoff, D. A. Taylor, Nat. Med. 2008, 14, 213. [90] B. E. Uygun, A. Soto-Gutierrez, H. Yagi, M. L. Izamis, M. A. Guzzardi, C. Shulman, J. Milwid, N. Kobayashi, A. Tilles, F. Berthiaume, Nat. Med. 2010, 16, 814. [91] M. Zheng, J. Chen, Y. Kirilak, C. Willers, J. Xu, D. Wood, J. Biomed. Mater. Res. B 2005, 73, 61. [92] P. M. Crapo, T. W. Gilbert, S. F. Badylak, Biomaterials 2011, 32, 3233. [93] T. W. Gilbert, T. L. Sellaro, S. F. Badylak, Biomaterials 2006, 27, 3675. [94] T. L. Carlson, K. W. Lee, L. M. Pierce, Plast. Reconstr. Surg. 2013, 131, 697. [95] M. L. Venturi, A. N. Mesbahi, J. H. Boehmler IV, A. J. Marrogi, Plast. Reconstr. Surg. 2013, 131, 9e. [96] D. M. Hoganson, E. M. O’Doherty, G. E. Owens, D. O. Harilal, S. M. Goldman, C. M. Bowley, C. M. Neville, R. T. Kronengold, J. P. Vacanti, Biomaterials 2010, 31, 6730. [97] H. Xu, H. Wan, W. Zuo, W. Sun, R. T. Owens, J. R. Harper, D. L. Ayares, D. J. McQuillan, Tissue Eng. 2009, 15, 1807. [98] X. Zhang, J. Yang, Y. Li, S. Liu, K. Long, Q. Zhao, Y. Zhang, Z. Deng, Y. Jin, Tissue Eng. 2010, 17, 423. [99] K. Bleek, A. Taubert, Acta Biomater. 2013, 9, 6283. [100] B. D. Boyan, Z. Schwartz, Nat. Rev. Rheumatol. 2011, 7, 8. [101] R. Z. LeGeros, Chem. Rev. 2008, 108, 4742. [102] H. Yuan, H. Fernandes, P. Habibovic, J. de Boer, A. M. C. Barradas, A. de Ruiter, W. R. Walsh, C. A. van Blitterswijk, J. G. de Bruijn, Proc. Natl. Acad. Sci. 2010, 107, 13614. [103] G. Wang, L. Zheng, H. Zhao, J. Miao, C. Sun, H. Liu, Z. Huang, X. Yu, J. Wang, X. Tao, ACS Appl. Mater. Inter. 2011, 3, 1692. [104] G. Turco, E. Marsich, F. Bellomo, S. Semeraro, I. Donati, F. Brun, M. Grandolfo, A. Accardo, S. Paoletti, Biomacromolecules 2009, 10, 1575. [105] M. Maas, P. Guo, M. Keeney, F. Yang, T. M. Hsu, G. G. Fuller, C. R. Martin, R. N. Zare, Nano Lett. 2011, 11, 1383. [106] H. J. Kim, U. J. Kim, H. S. Kim, C. Li, Bone 2008, 42, 1226. [107] R. R. Rao, A. Jiao, D. H. Kohn, J. P. Stegemann, Acta Biomater. 2012, 8, 1560. [108] H. Cölfen, Nat. Mater. 2010, 9, 960. [109] A. L. Boskey, Connect. Tissue Res. 1996, 35, 357. [110] A. George, A. Veis, Chem. Rev. 2008, 108, 4670.

[111] G. K. Hunter, P. V. Hauschka, A. R. Poole, L. C. Rosenberg, H. A. Goldberg, Biochem. J 1996, 317, 59. [112] Y. Yang, Q. Cui, N. Sahai, Langmuir 2010, 26, 9848. [113] K. Rodríguez, S. Renneckar, P. Gatenholm, ACS Appl. Mater. Inter. 2011, 3, 681. [114] H. Ehrlich, T. Hanke, R. Born, C. Fischer, A. Frolov, T. Langrock, R. Hoffmann, U. Schwarzenbolz, T. Henle, P. Simon, J. Membr. Sci. 2009, 326, 254. [115] A. Dey, P. H. Bomans, F. A. Müller, J. Will, P. M. Frederik, N. A. Sommerdijk, Nat. Mater. 2010, 9, 1010. [116] C. M. Curtin, G. M. Cunniffe, F. G. Lyons, K. Bessho, G. R. Dickson, G. P. Duffy, F. J. O’Brien, Adv. Mater. 2012, 24, 749. [117] A. S. Asran, S. Henning, G. H. Michler, Polymer 2010, 51, 868. [118] J. Venkatesan, Z. J. Qian, B. M. Ryu, N. Ashok Kumar, S. K. Kim, Carbohydr. Polym. 2011, 83, 569. [119] W. Thein-Han, R. Misra, Acta Biomater. 2009, 5, 1182. [120] M. Peter, N. Binulal, S. Soumya, S. Nair, T. Furuike, H. Tamura, R. Jayakumar, Carbohydr. Polym. 2010, 79, 284. [121] R. Pallela, J. Venkatesan, V. R. Janapala, S.-K. Kim, J. Biomed. Mater. Res. A 2012, 100A, 486. [122] P. Shi, T. K. H. Teh, S. L. Toh, J. C. H. Goh, Biomaterials 2013, 34, 5947. [123] S. Bhumiratana, W. L. Grayson, A. Castaneda, D. N. Rockwood, E. S. Gil, D. L. Kaplan, G. Vunjak-Novakovic, Biomaterials 2011, 32, 2812. [124] S. Panzavolta, M. Fini, A. Nicoletti, B. Bracci, K. Rubini, R. Giardino, A. Bigi, Acta Biomater. 2009, 5, 636. [125] T. Yoshida, M. Kikuchi, Y. Koyama, K. Takakuda, J. Mater. Sci., Mater. Med. 2010, 21, 1263. [126] I. Manjubala, S. Scheler, J. Bossert, K. D. Jandt, Acta Biomater. 2006, 2, 75. [127] Y. Choi, S. Y. Cho, D. J. Park, H. H. Park, S. Heo, H. J. Jin, J. Biomed. Mater. Res. B 2012. [128] P. He, S. Sahoo, K. S. Ng, K. Chen, S. L. Toh, J. C. H. Goh, J. Biomed. Mater. Res. A 2013, 101A, 555. [129] M. Xie, M.Ø. Olderøy, J.-P. Andreassen, S. M. Selbach, B. L. Strand, P. Sikorski, Acta Biomater. 2010, 6, 3665. [130] T. E. L. Douglas, P. B. Messersmith, S. Chasan, A. G. Mikos, E. L. W. de Mulder, G. Dickson, D. Schaubroeck, L. Balcaen, F. Vanhaecke, P. Dubruel, J. A. Jansen, S. C. Leeuwenburgh, Macromol. Biosci. 2012, 12, 1077. [131] Y. Liu, N. Li, Y. Qi, L. Dai, T. E. Bryan, J. Mao, D. H. Pashley, F. R. Tay, Adv. Mater. 2011, 23, 975. [132] Z. Xia, X. Yu, X. Jiang, H. D. Brody, D. W. Rowe, M. Wei, Acta Biomater. 2013, 9, 7308. [133] R. Kino, T. Ikoma, A. Monkawa, S. Yunoki, M. Munekata, J. Tanaka, T. Asakura, J. Appl. Polym. Sci. 2006, 99, 2822. [134] D. Suárez-González, K. Barnhart, E. Saito, R. Vanderby Jr., S. J. Hollister, W. L. Murphy, J. Biomed. Mater. Res. A 2010, 95, 222. [135] P. Niemeyer, K. Fechner, S. Milz, W. Richter, N. P. Suedkamp, A. T. Mehlhorn, S. Pearce, P. Kasten, Biomaterials 2010, 31, 3572. [136] M. F. Pittenger, A. M. Mackay, S. C. Beck, R. K. Jaiswal, R. Douglas, J. D. Mosca, M. A. Moorman, D. W. Simonetti, S. Craig, D. R. Marshak, Science 1999, 284, 143. [137] J. S. Sun, S. Y. H. Wu, F. H. Lin, Biomaterials 2005, 26, 3953. [138] H. Kagami, H. Agata, A. Tojo, Int. J. Biochem. Cell Biol. 2010, 43, 286. [139] G. I. I. Im, Y. W. Shin, K. B. Lee, Osteoarthr. Cartilage 2005, 13, 845. [140] S. X. Hsiong, D. J. Mooney, Periodontol. 2000 2006, 41, 109. [141] P. C. Bessa, M. Casal, R. L. Reis, J. Tissue Eng. Regen. Med. 2008, 2, 1. [142] H. S. Yang, W. G. La, S. H. Bhang, T. J. Lee, M. Lee, B. S. Kim, Tissue Eng. 2011, 17, 2153.

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

wileyonlinelibrary.com

15

www.advhealthmat.de

PROGRESS REPORT

www.MaterialsViews.com [143] A. Letic-Gavrilovic, A. Piattelli, K. Abe, J. Mater. Sci. Mater. Med. 2003, 14, 95. [144] D. H. R. Kempen, L. Lu, T. E. Hefferan, L. B. Creemers, A. Maran, K. L. Classic, W. J. A. Dhert, M. J. Yaszemski, Biomaterials 2008, 29, 3245. [145] P. Yilgor, K. Tuzlakoglu, R. L. Reis, N. Hasirci, V. Hasirci, Biomaterials 2009, 30, 3551. [146] C. Li, C. Vepari, H. J. Jin, H. J. Kim, D. L. Kaplan, Biomaterials 2006, 27, 3115. [147] J. M. Kanczler, P. J. Ginty, L. White, N. M. P. Clarke, S. M. Howdle, K. M. Shakesheff, R. O. C. Oreffo, Biomaterials 2010, 31, 1242. [148] M. Keeney, J. J. J. P. van den Beucken, P. M. van der Kraan, J. A. Jansen, A. Pandit, Biomaterials 2010, 31, 2893. [149] A. Moshaverinia, S. Ansari, C. Chen, X. Xu, K. Akiyama, M. L. Snead, H. H. Zadeh, S. Shi, Biomaterials 2013, 34, 6572. [150] Y. Li, L. Fan, S. Liu, W. Liu, H. Zhang, T. Zhou, D. Wu, P. Yang, L. Shen, J. Chen, Y. Jin, Biomaterials 2013, 34, 5048. [151] V. Uskokovic´, D. P. Uskokovic´, J. Biomed. Mater. Res. B 2011, 96B, 152. [152] M. M. Stevens, J. H. George, Science 2005, 310, 1135.

16

wileyonlinelibrary.com

[153] C. Cha, W. B. Liechty, A. Khademhosseini, N. A. Peppas, ACS Nano 2012, 6, 9353. [154] J. C. Fricain, S. Schlaubitz, C. Le Visage, I. Arnault, S. M. Derkaoui, R. Siadous, S. Catros, C. Lalande, R. Bareille, M. Renard, T. Fabre, S. Cornet, M. Durand, A. Léonard, N. Sahraoui, D. Letourneur, J. Amédée, Biomaterials 2013, 34, 2947. [155] H. Liu, H. Peng, Y. Wu, C. Zhang, Y. Cai, G. Xu, Q. Li, X. Chen, J. Ji, Y. Zhang, H. W. OuYang, Biomaterials 2013, 34, 4404. [156] M. Wagner-Ecker, P. Voltz, M. Egermann, W. Richter, Acta Biomater. 2013, 9, 7298. [157] J. He, B. Jiang, Y. Dai, J. Hao, Z. Zhou, Z. Tian, F. Wu, Z. Gu, Biomaterials 2013, 34, 6580. [158] E. Kon, M. Delcogliano, G. Filardo, D. Pressato, M. Busacca, B. Grigolo, G. Desando, M. Marcacci, Injury 2010, 41, 693. [159] J. R. Mauney, D. L. Kaplan, V. Volloch, Biomaterials 2004, 25, 3233. [160] A. Katayama, T. Arano, T. Sato, Y. Ikada, M. Yoshinari, Tissue Eng. 2012, 19, 109. [161] H. Agata, I. Asahina, N. Watanabe, Y. Ishii, N. Kubo, S. Ohshima, M. Yamazaki, A. Tojo, H. Kagami, Tissue Eng. 2009, 16, 663.

© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Adv. Healthcare Mater. 2013, DOI: 10.1002/adhm.201300562

Calcium phosphate scaffolds for bone tissue engineering.

With nearly 30 years of progress, tissue engineering has shown promise in developing solutions for tissue repair and regeneration. Scaffolds, together...
11MB Sizes 0 Downloads 0 Views