Material properties and cytocompatibility of injectable MMP degradable poly(lactide ethylene oxide fumarate) hydrogel as a carrier for marrow stromal cells

Injectable in situ crosslinkable biomaterials seeded with multipotent progenitor cells and coupled with minimally invasive arthroscopic techniques are an attractive alternative for treating irregularly shaped osteochondral defects. An in situ crosslinkable poly(lactide-co-ethylene oxide-co-fumarate) (PLEOF) macromer has been developed with ultralow molecular weight poly(L-lactide) and poly(ethylene glycol) (PEG) units linked by fumaryl unit. The PLEOF macromer was crosslinked with the MMP-13 degradable peptide sequence QPQGLAK with acrylate end-groups or the methylene bisacrylamide (BISAM) crosslinker to form enzymatically or hydrolytically degradable hydrogels, respectively. Cell viability of the peptide crosslinker was significantly higher than that of BISAM. The relatively higher molecular weight peptide crosslinker significantly affected the water content and the rate of crosslinking (e.g., sol vs gel fraction). The addition of a small fraction of a highly reactive BISAM crosslinker to the PLEOF/peptide mixture reduced the gelation time and increased the elastic modulus while retaining enzymatic degradability of the hydrogel. Bone marrow stromal (BMS) cells were encapsulated in the peptide crosslinked PLEOF hydrogel; 84% of the encapsulated cells was viable after 1 week of incubation in osteogenic media. The encapsulated BMS cells differentiated to osteoblasts and produced a mineralized matrix, as measured by ALPase activity and calcium content. The degradation rate of the hydrogel depended on the ratio of the peptide to the BISAM crosslinker, MMP-13 concentration, and incubation time. The results demonstrate that the peptide crosslinked PLEOF hydrogel with tunable degradation characteristics is potentially useful as an injectable in situ crosslinkable carrier for bone marrow stromal cells.     

Structure-property evaluation of thermally and chemically gelling injectable hydrogels for tissue engineering

The impact of synthesis and solution formulation parameters on the swelling and mechanical properties of a novel class of thermally and chemically gelling hydrogels combining poly(N-isopropylacrylamide)-based thermogelling macromers containing pendant epoxy rings with polyamidoamine-based hydrophilic and degradable diamine cross-linking macromers was evaluated. Through variation of network hydrophilicity and capacity for chain rearrangement, the often problematic tendency of thermogelling hydrogels to undergo significant syneresis was addressed. The demonstrated ability to tune postformation dimensional stability easily at both the synthesis and formulation stages represents a significant novel contribution toward efforts to utilize poly(N-isopropylacrylamide)-based polymers as injectable biomaterials. Furthermore, the cytocompatibility of the hydrogel system under relevant conditions was established while demonstrating time- and dose-dependent cytotoxicity at high solution osmolality. Such injectable in situ forming degradable hydrogels with tunable water content are promising candidates for many tissue-engineering applications, particularly for cell delivery to promote rapid tissue regeneration in non-load-bearing defects.     

Biomimetic carbohydrate substrates of tunable properties using immobilized dextran hydrogels

Glycidylmethacrylate-modified dextran macromers (Dex-GMA) of different degrees of substitution (DS) were synthesized. The elastic modulus of the hydrogels produced using one-component and two-component macromer systems was measured using rheometry. When one macromer of DS 1/10 was used, a hydrogel modulus in the range of 0.2 Pa to 42 kPa was obtained by varying the Dex-GMA concentration from 80 to 200 mg/mL. When a mixture of two macromers of different DS (1/10 and 1/23) was used, a more uniform variation of modulus in the range of 0.4 Pa to 42 kPa was achieved by controlling the ratio of the two macromers. When dextran hydrogels were functionalized with fibronectin and immobilized onto glass substrates, the attachment, spreading, and growth of human aortic smooth muscle cells were modulated by the elastic properties of the dextran matrix. The dextran hydrogel system with tunable mechanical and biochemical properties appears promising for applications in cell culture and tissue engineering.     

An approach to modulate degradation and mesenchymal stem cell behavior in poly(ethylene glycol) networks

A simple, sequential approach for creation of hydrolytically degradable poly(ethylene glycol) (PEG) hydrogels has been developed and characterized. The chemistry involves an initial step growth polymerization reaction between PEG-diacrylate and dithiothreitol (DTT) to form acrylate-terminated (-PEG-DTT-)n PEG chains, followed by photocross-linking to form a hydrogel network. Varying the extent of step growth polymerization prior to photocross-linking allowed for control over the equilibrium swelling ratio, degradation, and erosion of PEG hydrogels. Hydrogel degradability had a significant effect on behavior of human mesenchymal stem cells (hMSCs) encapsulated within PEG hydrogels, both in the presence and absence of an RGDSP cell adhesion ligand. In particular, enhanced network degradability resulted in enhanced hMSC viability and spreading during in vitro culture. Comparison of degradable and nondegradable hydrogels with similar physical properties (e.g., equilibrium swelling ratio) demonstrated that hMSC viability and spreading were dependent on network degradability. This study demonstrates that hydrolytically degradable PEG hydrogels can be formed via a sequential step growth polymerization and photocross-linking process and the resulting materials may serve as promising matrices for 3-dimensional stem cell culture and tissue engineering applications.     

Synthesis and characterization of radiopaque iodine-containing degradable PVA hydrogels

Poly (vinyl alcohol) (PVA) hydrogels are highly attractive for biomedical applications, especially for controlled release of drugs and proteins. Recently, degradable PVA hydrogels have been described, having the advantage that the material disappears over time from the implantation site. Herein, we report the synthesis of radiopaque degradable PVA, which gives a further advantage that the position of the hydrogel can precisely be determined by X-ray fluoroscopy. Radiopacity has been introduced by replacing 0.5% of the pendent alcohol groups on the PVA with 4-iodobenzoylchloride. This level of substitution rendered the polymer adequately radiopaque. The subsequent modification of 0.8% of the pendent hydroxyl groups with an ester acrylate functional group allowed for cross-linking of the macromers. The radiopaque hydrogels degraded over a time span of 140 days. Rheology data suggested that the macromer solutions were appropriate for injection.     

Synthesis and characterization of thermally and chemically gelling injectable hydrogels for tissue engineering

Novel, injectable hydrogels were developed that solidify through a physical and chemical dual-gelation mechanism upon preparation and elevation of temperature to 37 °C. A thermogelling, poly(N-isopropylacrylamide)-based macromer with pendant epoxy rings and a hydrolytically degradable polyamidoamine-based diamine cross-linker were synthesized, characterized, and combined to produce in situ forming hydrogel constructs. Network formation through the epoxy-amine reaction was shown to be rapid and facile, and the progressive incorporation of the hydrophilic polyamidoamine cross-linker into the hydrogel was shown to mitigate the often problematic tendency of thermogelling materials to undergo significant postformation gel syneresis. The results suggest that this novel class of injectable hydrogels may be attractive substrates for tissue engineering applications due to the synthetic versatility of the component materials and beneficial hydrogel gelation kinetics and stability.     

Facile synthesis and characterization of disulfide-cross-linked hyaluronic acid hydrogels for protein delivery and cell encapsulation

Injectable hyaluronic acid (HA) hydrogels cross-linked via disulfide bond are synthesized using a thiol-disulfide exchange reaction. The production of small-molecule reaction product, pyridine-2-thione, allows the hydrogel formation process to be monitored quantitatively in real-time by UV spectroscopy. Rheological tests show that the hydrogels formed within minutes at 37 °C. Mechanical properties and equilibrium swelling degree of the hydrogels can be controlled by varying the ratio of HA pyridyl disulfide and macro-cross-linker PEG-dithiol. Degradation of the hydrogels was achieved both enzymatically and chemically by disulfide reduction with distinctly different kinetics and profiles. In the presence of hyaluronidase, hydrogel mass loss over time was linear and the degradation was faster at higher enzyme concentrations, suggesting surface-limited degradation. The kinetics of hydrogel erosion by glutathione was not linear, nor did the erosion rate correlate linearly with glutathione concentration, suggesting a bulk erosion mechanism. A cysteine-containing chemokine, stromal cell-derived factor 1α, was successfully encapsulated in the hydrogel and released in vitro without chemical alteration. Several different cell types, including fibroblasts, endothelial cells, and mesenchymal stem cells, were successfully encapsulated in the hydrogels with high cell viability during and after the encapsulation process. Substantial cell viability in the hydrogels was maintained up to 7 days in culture despite the lack of adhesion between the HA matrix and the cells. The facile synthesis of disulfide-cross-linked, dual-responsive degradable HA hydrogels may enable further development of bioactive matrices potentially suitable for tissue engineering and drug delivery applications.     

Cross-linking and degradation of step-growth hydrogels formed by thiol-ene photoclick chemistry

Thiol-ene photoclick hydrogels have been used for a variety of tissue engineering and controlled release applications. In this step-growth photopolymerization scheme, four-arm poly(ethylene glycol) norbornene (PEG4NB) was cross-linked with dithiol containing cross-linkers to form chemically cross-linked hydrogels. While the mechanism of thiol-ene gelation was well described in the literature, its network ideality and degradation behaviors are not well-characterized. Here, we compared the network cross-linking of thiol-ene hydrogels to Michael-type addition hydrogels and found thiol-ene hydrogels formed with faster gel points and higher degree of cross-linking. However, thiol-ene hydrogels still contained significant network nonideality, demonstrated by a high dependency of hydrogel swelling on macromer contents. In addition, the presence of ester bonds within the PEG-norbornene macromer rendered thiol-ene hydrogels hydrolytically degradable. Through validating model predictions with experimental results, we found that the hydrolytic degradation of thiol-ene hydrogels was not only governed by ester bond hydrolysis, but also affected by the degree of network cross-linking. In an attempt to manipulate network cross-linking and degradation of thiol-ene hydrogels, we incorporated peptide cross-linkers with different sequences and characterized the hydrolytic degradation of these PEG-peptide hydrogels. In addition, we incorporated a chymotrypsin-sensitive peptide as part of the cross-linkers to tune the mode of gel degradation from bulk degradation to surface erosion.     

Characterization of protein release from hydrolytically degradable poly(ethylene glycol) hydrogels

We present a novel fully hydrophilic, hydrolytically degradable poly(ethylene glycol) (PEG) hydrogel suitable for soft tissue engineering and delivery of protein drugs. The gels were designed to overcome drawbacks associated with current PEG hydrogels (i.e., reaction mechanisms or degradation products that compromise protein stability): the highly selective and mild cross‐linking reaction allowed for encapsulating proteins prior to gelation without altering their secondary structure as shown by circular dichroism experiments. Further, hydrogel degradation and structure, represented by mesh size, were correlated to protein release. It was determined that polymer density had the most profound effect on protein diffusivity, followed by the polymer molecular weight, and finally by the specific chemical structure of the cross‐linker. By examining the diffusion of several model proteins, we confirmed that the protein diffusivity was dependent on protein size as smaller proteins (e.g., lysozyme) diffused faster than larger proteins (e.g., Ig). Furthermore, we demonstrated that the protein physical state was preserved upon encapsulation and subsequent release from the PEG hydrogels and contained negligible aggregation or protein–polymer adducts. These initial studies indicate that the developed PEG hydrogels are suitable for release of stable proteins in drug delivery and tissue engineering applications. Biotechnol. Bioeng. 2011; 108:197–206. © 2010 Wiley Periodicals, Inc.     

Development of a biostable replacement for PEGDA hydrogels

The exceptional tunability of poly(ethylene glycol) (PEG) hydrogel chemical, mechanical, and biological properties enables their successful use in a wide range of biomedical applications. Although PEG diacrylate (PEGDA) hydrogels are often used as nondegradable controls in short-term in vitro studies, it is widely acknowledged that the hydrolytically labile esters formed upon acrylation of the PEG diol make them susceptible to slow degradation in vivo. A PEG hydrogel system that maintains the desirable properties of PEGDA while improving biostability would be valuable in preventing degradation-related failure of gel-based devices in long-term in vivo applications. To this end, PEG diacrylamide (PEGDAA) hydrogels were synthesized and characterized in quantitative comparison to traditional PEGDA hydrogels. It was found that PEGDAA hydrogel modulus and swelling can be tuned over a similar range and to comparable degrees as PEGDA hydrogels with changes in macromer molecular weight and concentration. Additionally, PEGDAA cytocompatibility, low cell adhesion, and capacity for incorporation of bioactivity were analogous to that of PEGDA. In vitro hydrolytic degradation studies showed that the amide-based PEGDAA had significantly increased biostability relative to PEGDA. Overall, these findings indicate that PEGDAA hydrogels are a suitable replacement for PEGDA hydrogels with enhanced hydrolytic resistance. In addition, these studies provide a quantitative measure of the hydrolytic degradation rate of PEGDA hydrogels which was previously lacking in the literature.     

Design of biomimetic cell-interactive substrates using hyaluronic acid hydrogels with tunable mechanical properties

Hyaluronic acid (HA) is a natural polysaccharide abundant in biological tissues with excellent potential for constructing synthetic extracellular matrix analogues. In this work, we established a simple and dependable approach to prepare hyaluronic acid-based hydrogels with controlled stiffness and cell recognition properties for use as cell-interactive substrates. This approach relied on a new procedure for the synthesis of methacrylate-modified HA macromers (HA-MA) and, on photorheometry allowing real time monitoring of gelation during photopolymerization. We showed in this way the ability to obtain gels that encompass the range of physiologically relevant elastic moduli while still maintaining the recognition properties of HA by specific cell surface receptors. These hydrogels were prepared from HA macromers having a degree of methacrylation <0.5, which allows to minimize compromising effects on the binding affinity of HA to its cell receptors due to high substitution on the one hand, and to achieve nearly 100% conversion of the methacrylate groups on the other. When the HA hydrogels were immobilized on glass substrates, it was observed that the attachment and the spreading of a variety of mammalian cells rely on CD44 and its coreceptor RHAMM. The attachment and spreading were also shown to be modulated by the elastic properties of the HA matrix. All together, these results highlight the biological potential of these HA hydrogel systems and the needs of controlling their chemical and physical properties for applications in cell culture and tissue engineering.     

Hydrolytically degradable poly(ethylene glycol) hydrogel scaffolds as a cell delivery vehicle: Characterization of PC12 cell response

The central nervous system (CNS) has a low intrinsic potential for regeneration following injury and disease, yet neural stem/progenitor cell (NPC) transplants show promise to provide a dynamic therapeutic in this complex tissue environment. Moreover, biomaterial scaffolds may improve the success of NPC‐based therapeutics by promoting cell viability and guiding cell response. We hypothesized that a hydrogel scaffold could provide a temporary neurogenic environment that supports cell survival during encapsulation, and degrades completely in a temporally controlled manner to allow progression of dynamic cellular processes such as neurite extension. We utilized PC12 cells as a model cell line with an inducible neuronal phenotype to define key properties of hydrolytically degradable poly(ethylene glycol) hydrogel scaffolds that impact cell viability and differentiation following release from the degraded hydrogel. Adhesive peptide ligands (RGDS, IKVAV, or YIGSR), were required to maintain cell viability during encapsulation; as compared to YIGSR, the RGDS, and IKVAV ligands were associated with a higher percentage of PC12 cells that differentiated to the neuronal phenotype following release from the hydrogel. Moreover, among the hydrogel properties examined (e.g., ligand type, concentration), total polymer density within the hydrogel had the most prominent effect on cell viability, with densities above 15% w/v leading to decreased cell viability likely due to a higher shear modulus. Thus, by identifying key properties of degradable hydrogels that affect cell viability and differentiation following release from the hydrogel, we lay the foundation for application of this system towards future applications of the scaffold as a neural cell delivery vehicle. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:1255–1264, 2013     

Biodegradable thermoresponsive hydrogels for aqueous encapsulation and controlled release of hydrophilic model drugs

A series of hydrogels with both thermoresponsive and completely biodegradable properties was developed for aqueous encapsulation and controlled release of hydrophilic drugs in response to temperature change. The hydrogels were prepared in phosphate-buffered saline (pH 7.4) through free radical polymerization of N-isopropylacrylamide (NIPAAm) monomer and a dextran macromer containing multiple hydrolytically degradable oligolactate-2-hydroxyethyl methacrylate units (Dex-lactateHEMA). Swelling measurement results demonstrated that four gels with feeding weight ratios of NIPAAm:Dex-lactateHEMA = 7:2, 6:3, 5:4, and 4:5 (w/w) were thermoresponsive by showing a lower critical solution temperature at approximately 32 degrees C. The swelling and degradation of the hydrogels strongly depended on temperature and hydrogel composition. An empirical mathematical model was established to describe the fast water absorption at the early stage and deswelling at the late stage of the hydrogels at 37 degrees C. Two hydrophilic model drugs, methylene blue and bovine serum albumin, were loaded into the hydrogels during the synthesis process. The molecular size of the drugs, the hydrophilicity and degradation of the hydrogels, and temperature played important roles in controlling the drug release.     

Functional nucleus pulposus-like matrix assembly by human mesenchymal stromal cells is directed by macromer concentration in photocrosslinked carboxymethylcellulose hydrogels

Intervertebral disc (IVD) degeneration is associated with several pathophysiologic changes of the IVD, including dehydration of the nucleus pulposus (NP). Tissue engineering strategies may be used to restore both biological and mechanical function of the IVD following removal of NP tissue during surgical intervention. Recently, photocrosslinked carboxymethylcellulose (CMC) hydrogels were shown to support chondrogenic, NP-like extracellular matrix (ECM) elaboration by human mesenchymal stromal cells (hMSCs) when supplemented with TGF-β3; however, mechanical properties of these constructs did not reach native values. Fabrication parameters (i.e., composition, crosslinking density) can influence the bulk mechanical properties of hydrogel scaffolds, as well as cellular behavior and differentiation patterns. The objective of this study was to evaluate the influence of CMC macromer concentration (1.5, 2.5 and 3.5 % weight/volume) on bulk hydrogel properties and NP-like matrix elaboration by hMSCs. The lowest macromer concentration of 1.5 % exhibited the highest gene expression levels of aggrecan and collagen II at day 7, corresponding with the largest accumulation of glycosaminoglycans and collagen II by day 42. The ECM elaboration in the 1.5 % constructs was more homogeneously distributed compared to primarily pericellular localization in 3.5 % gels. The 1.5 % gels also displayed significant improvements in mechanical functionality by day 42 compared to earlier time points, which was not seen in the other groups. The effects of macromer concentration on matrix accumulation and organization are likely attributed to quantifiable differences in polymer crosslinking density and diffusive properties between the various hydrogel formulations. Taken together, these results demonstrate that macromer concentration of CMC hydrogels can direct hMSC matrix elaboration, such that a lower polymer concentration allows for greater NP-like ECM assembly and improvement of mechanical properties over time.     

Synthesis and characterization of photo-cross-linked hydrogels based on biodegradable polyphosphoesters and poly(ethylene glycol) copolymers

Novel biodegradable hydrogels by photo-cross-linking macromers based on polyphosphoesters and poly(ethylene glycol) (PEG) are reported. Photo-cross-linkable macromers were synthesized by ring-opening polymerization of the cyclic phosphoester monomer 2-(2-oxo-1,3,2-dioxaphospholoyloxy) ethyl methacrylate (OPEMA) using PEG as the initiator and stannous octoate as the catalyst. The macromers were characterized by 1H NMR, Fourier transform infrared spectroscopy, and gel permeation chromatography measurements. The content of polyphosphoester in the macromer was controlled by varying the feed ratio of OPEMA to PEG. Hydrogels were fabricated by exposing aqueous solutions of macromers with 0.05% (w/w) photoinitiator to UV light irradiation, and their swelling kinetics as well as degradation behaviors were evaluated. The results demonstrated that cross-linking density and pH values strongly affected the degradation rates. The macromers was compatible to osteoblast cells, not exhibiting significant cytotoxicity up to 0.5 mg/mL. "Live/dead" cell staining assay also demonstrated that a large majority of the osteoblast cells remained viable after encapsulation into the hydrogel constructs, showing their potential as tissue engineering scaffolds.     

Gelation characteristics and osteogenic differentiation of stromal cells in inert hydrolytically degradable micellar polyethylene glycol hydrogels

The use of poly(ethylene glycol) (PEG) hydrogels in tissue engineering is limited by their persistence in the site of regeneration. In an attempt to produce inert hydrolytically degradable PEG-based hydrogels, star (SPELA) poly(ethylene glycol-co-lactide) acrylate macromonomers with short lactide segments (<15 lactides per macromonomer) were synthesized. The SPELA hydrogel was characterized with respect to gelation time, modulus, water content, sol fraction, degradation, and osteogenic differentiation of encapsulated marrow stromal cells (MSCs). The properties of SPELA hydrogel were compared with those of the linear poly(ethylene glycol-co-lactide) acrylate (LPELA). The SPELA hydrogel had higher modulus, lower water content, and lower sol fraction than the LPELA. The shear modulus of SPELA hydrogel was 2.2 times higher than LPELA, whereas the sol fraction of SPELA hydrogel was 5 times lower than LPELA. The degradation of SPELA hydrogel depended strongly on the number of lactide monomers per macromonomer (nL) and showed a biphasic behavior. For example, as nL increased from 0 to 3.4, 6.4, 11.6, and 14.8, mass loss increased from 7 to 37, 80, 100% and then deceased to 87%, respectively, after 6 weeks of incubation. The addition of 3.4 lactides per macromonomer (<10 wt % dry macromonomer or <2 wt % swollen hydrogel) increased mass loss to 50% after 6 weeks. Molecular dynamic simulations demonstrated that the biphasic degradation behavior was related to aggregation and micelle formation of lactide monomers in the macromonomer in aqueous solution. MSCs encapsulated in SPELA hydrogel expressed osteogenic markers Dlx5, Runx2, osteopontin, and osteocalcin and formed a mineralized matrix. The expression of osteogenic markers and extent of mineralization was significantly higher when MSCs were encapsulated in SPELA hydrogel with the addition of bone morphogenetic protein-2 (BMP2). Results demonstrate that hydrolytically degradable PEG-based hydrogels are potentially useful as a delivery matrix for stem cells in regenerative medicine.     

Photocrosslinked hyaluronic acid hydrogels: natural,biodegradable tissue engineering scaffolds

Ideally, rationally designed tissue engineering scaffolds promote natural wound healing and regeneration. Therefore, we sought to synthesize a biomimetic hydrogel specifically designed to promote tissue repair and chose hyaluronic acid (HA; also called hyaluronan) as our initial material. Hyaluronic acid is a naturally occurring polymer associated with various cellular processes involved in wound healing, such as angiogenesis. Hyaluronic acid also presents unique advantages: it is easy to produce and modify, hydrophilic and nonadhesive, and naturally biodegradable. We prepared a range of glycidyl methacrylate-HA (GMHA) conjugates, which were subsequently photopolymerized to form crosslinked GMHA hydrogels. A range of hydrogel degradation rates was achieved as well as a corresponding, modest range of material properties (e.g., swelling, mesh size). Increased amounts of conjugated methacrylate groups corresponded with increased crosslink densities and decreased degradation rates and yet had an insignificant effect on human aortic endothelial cell cytocompatibility and proliferation. Rat subcutaneous implants of the GMHA hydrogels showed good biocompatibility, little inflammatory response, and similar levels of vascularization at the implant edge compared with those of fibrin positive controls. Therefore, these novel GMHA hydrogels are suitable for modification with adhesive peptide sequences (e.g., RGD) and use in a variety of wound-healing applications.     

Biomolecular hydrogels formed and degraded via site-specific enzymatic reactions

We present polymeric hydrogel biomaterials that are biomimetic both in their synthesis and degradation. The design of oligopeptide building blocks with dual enzymatic responsiveness allows us to create polymer networks that are formed and functionalized via enzymatic reactions and are degradable via other enzymatic reactions, both occurring under physiological conditions. The activated transglutaminase enzyme factor XIIIa was utilized for site-specific coupling of prototypical cell adhesion ligands and for simultaneous cross-linking of hydrogel networks from factor XIIIa substrate-modified multiarm poly(ethylene glycol) macromers. Ligand incorporation is nearly quantitative and thus controllable, and does not alter the network's macroscopic properties over a concentration range that elicits specific cell adhesion. Living mammalian cells can be encapsulated in the gels without any noticeable decrease in viability. The degradation of gels can be engineered to occur, for example, via cell-secreted matrix metalloproteinases, thus rendering these gels interesting for biomedical applications such as drug delivery systems or smart implants for in situ tissue engineering.     

基于天然水凝胶的生物材料在骨组织工程中的应用*

天然水凝胶是指原材料来自于天然生物材料的水凝胶。由于这种天然的聚合物含有构成生物体的天然成分,与天然组织具有生物学和化学相似性,而受到特别关注。天然水凝胶由于其与细胞外基质高度的相似性被认为是骨组织工程中优良的仿生基质材料。而针对天然水凝胶机械性能差、成骨诱导性能弱等缺陷,通常需要对天然水凝胶进行改性、引入其他材料或生物活性因子,以此来获得更适用于骨组织工程支架材料。对近年来基于天然水凝胶的生物材料在骨组织工程的应用,与其不同的应用形式(可注射水凝胶、多孔水凝胶支架、3D生物打印水凝胶支架等)进行了概述,以期对这类基于天然水凝胶的生物材料在未来骨组织工程中的应用提供参考。     

Characterization of photo-cross-linked oligo[poly(ethylene glycol) fumarate] hydrogels for cartilage tissue engineering

Photo-cross-linkable oligo[poly(ethylene glycol) fumarate] (OPF) hydrogels have been developed for use in tissue engineering applications. We demonstrated that compressive modulus of these hydrogels increased with increasing polymer concentration, and hydrogels with different mechanical properties were formed by altering the ratio of cross-linker/polymer in precursor solution. Conversely, swelling of hydrogels decreased with increasing polymer concentration and cross-linker/polymer ratio. These hydrogels are degradable and degradation rates vary with the change in cross-linking level. Chondrocyte attachment was quantified as a method for evaluating adhesion of cells to the hydrogels. These data revealed that cross-linking density affects cell behavior on the hydrogel surfaces. Cell attachment was greater on the samples with increased cross-linking density. Chondrocytes on these samples exhibited spread morphology with distinct actin stress fibers, whereas they maintained their rounded morphology on the samples with lower cross-linking density. Moreover, chondrocytes were photoencapsulated within various hydrogel networks. Our results revealed that cells encapsulated within 2-mm thick OPF hydrogel disks remained viable throughout the 3-week culture period, with no difference in viability across the thickness of hydrogels. Photoencapsulated chondrocytes expressed the mRNA of type II collagen and produced cartilaginous matrix within the hydrogel constructs after three weeks. These findings suggest that photo-cross-linkable OPF hydrogels may be useful for cartilage tissue engineering and cell delivery applications.