In situ forming, mechanically resilient hydrogels prepared from 4a-[PEG-b-PTMC-Ac] and thiolated chondroitin sulfate for nucleus pulposus cell delivery.

Intervertebral disk degeneration (IVDD) is a common condition that causes severe back pain and affects patients' mobility and life quality considerably. IVDD originates within the central region of the disk called the nucleus pulposus (NP). Removing the damaged tissue and replacing it with NP cells (NPCs) delivered within an in situ forming hydrogel is a promising treatment approach. Herein we describe a hydrogel formulation based on 4-arm [poly(ethylene glycol)-b-poly(trimethylene carbonate)-acrylate] (4a[PEG-b-PTMC-Ac]) crosslinked with thiolated chondroitin sulfate via Michael-type reaction for this purpose. A library of hydrogels based on 15 kDa 4a-[PEG] with PTMC blocks of varying molecular weight were prepared and characterized. The instantaneous moduli of the hydrogels were adjustable from 24 to 150 kPa depending on the length of the PTMC block and the polymer volume fraction. The influence of each of these parameters was effectively explained using both scaling or mean field theories of polyelectrolyte hydrogels. The hydrogels were resistant to cyclic compressive loading and degraded gradually over 70 days in vitro. A hydrogel formulation with an instantaneous modulus at the high end of the range of values reported for human NP tissue was chosen to assess the ability of these hydrogels for delivering NPCs. The prepolymer solution was injectable and formed a hydrogel within 30 minutes at 37 °C. Bovine NPCs were encapsulated within this hydrogel with high viability and proliferated throughout a 28 day, hypoxic culture period. The encapsulated NPCs formed clusters and deposited collagen type II but no collagen type I within the hydrogels. Despite an initial gradual decrease, a steady-state modulus was reached at the end of the 28 day culture period that was within the range reported for healthy human NP tissue. This in situ forming hydrogel formulation is a promising approach and with further development could be a viable clinical treatment for IVDD.

Visible light degradable micelles for intraocular corticosteroid delivery.

Visible light responsive micellar drug delivery formulations are of notable interest for the treatment of ocular diseases, as their successful development would enable controlled drug release at the back of the eye, improving efficacy and reducing side-effects when compared to existing approaches. In this work, an aliphatic polycarbonate-based visible light responsive micelle formulation based on mPEG-b-poly(5-hydroxy-trimethylene carbonate) (PHTMC) was prepared wherein the pendant hydroxyl groups of the PHTMC repeating units were protected by blue light-labile [7-(diethylamino)coumarin-4-yl]methyl (DEACM). The photo-labile DEACM provided a photo-triggered release profile, as, upon the removal of these protecting groups by photo-irradiation, the micelles underwent structural disruption, leading to the release of the payload. The removal of DEACM also deprotected the pendant hydroxyl groups of PHTMC, leading to PHTMC backbone degradation via intramolecular cyclization.

In situ forming macroporous biohybrid hydrogel for nucleus pulposus cell delivery.

Degenerative intervertebral disc disease is a common source of chronic pain and reduced quality of life in people over the age of 40. While degeneration occurs throughout the disc, it most often initiates in the nucleus pulposus (NP). Minimally invasive delivery of NP cells within hydrogels that can restore and maintain the disc height while regenerating the damaged NP tissue is a promising treatment strategy for this condition. Towards this goal, a biohybrid ABA dimethacrylate triblock copolymer was synthesized, possessing a lower critical solution temperature below 37 °C and which contained as its central block an MMP-degradable peptide flanked by poly(trimethylene carbonate) blocks bearing pendant oligoethylene glycol groups. This triblock prepolymer was used to form macroporous NP cell-laden hydrogels via redox initiated (ammonium persulfate/sodium bisulfite) crosslinking, with or without the inclusion of thiolated chondroitin sulfate. The resulting macroporous hydrogels had water and mechanical properties similar to those of human NP tissue and were mechanically resilient. The hydrogels supported NP cell attachment and growth over 28 days in hypoxic culture. In hydrogels prepared with the triblock copolymer but without the chondroitin sulfate the NP cells were distributed homogeneously throughout in clusters and deposited collagen type II and sulfated glycosaminoglycans but not collagen type I. This hydrogel formulation warrants further investigation as a cell delivery vehicle to regenerate degenerated NP tissue. STATEMENT OF SIGNIFICANCE: The intervertebral disc between the vertebral bones of the spine consists of three regions: a gel-like central nucleus pulposus (NP) within the annulus fibrosis, and bony endplates. Degeneration of the intervertebral disc is a source of chronic pain in the elderly and most commonly initiates in the NP. Replacement of degenerated NP tissue with a NP cell-laden hydrogel is a promising treatment strategy. Herein we demonstrate that a crosslinkable polymer with a lower critical solution temperature below 37 °C can be used to form macroporous hydrogels for this purpose. The hydrogels are capable of supporting NP cells, which deposit collagen II and sulfated glycosaminoglycans, while also possessing mechanical properties matching those of human NP tissue.

Polymer micelles for the protection and delivery of specialized pro-resolving mediators.

Specialized pro-resolving mediators (SPMs) are being considered for the treatment of chronic inflammatory diseases. However, these polyunsaturated fatty acids are prone to oxidation and as a result have a short biological half-life. It was reasoned that a micelle formulation would provide sustained delivery of SPMs while providing protection from oxidation. Thus, micelle formulations were prepared with poly(ethylene glycol) (PEG) as the hydrophilic block and poly(trimethylene carbonate) (PT) containing unsaturated pendant groups, specifically benzyloxy (BT) and sorbate (ST) groups, as the hydrophobic block. The potential of these micelles was assessed using linoleic acid as a model SPM. Loading into a micelle core reduced the extent of oxidation of the model SPM and a sustained release of non-oxidized model drug was achieved for up to 20 days in vitro from the PEG-P(T-BT) micelles. These micelles were also non-cytotoxic over a wide concentration range, demonstrating the potential of this formulation for effective SPM release in vivo.

In Vivo Degradation Mechanism and Biocompatibility of a Biodegradable Aliphatic Polycarbonate: Poly(Trimethylene Carbonate-co-5-Hydroxy Trimethylene Carbonate).

A recently developed viscous liquid aliphatic polycarbonate, poly(trimethylene carbonate-co-5-hydroxy trimethylene carbonate), has advantageous properties for the delivery of acid-sensitive drugs such as proteins and peptides. This copolymer degrades in vitro via an alkaline-catalyzed intramolecular cyclization reaction yielding oligo (trimethylene carbonate), glycerol, and carbon dioxide, but its in vivo degradation mechanisms are presently unknown. The in vivo degradation mechanism and tissue response to this copolymer were investigated following subcutaneous implantation in Wistar rats. The molecular weight and composition of the copolymer varied in the same manner following subcutaneous implantation as observed in vitro. These findings suggest that the copolymer also degraded in vivo principally via intramolecular cyclization. The tissue response in terms of the inflammatory zone cell density, fibrous capsule thickness, and macrophage response was intermediate to that of two clinically used biodegradable sutures, Vicryl and Monocryl, indicating that the copolymer can be considered biotolerable. Collectively, the data show that further development of this copolymer as a drug delivery material is warranted.

Formulation parameters governing sustained protein delivery from degradable viscous liquid aliphatic polycarbonates.

Viscous liquid degradable polymers have advantages as drug depots for sustained protein delivery. We have created a new aliphatic polycarbonate for this purpose, poly(trimethylene carbonate-co-5-hydroxy trimethylene carbonate), which upon degradation retains a near neutral micro-environmental pH. As such, this copolymer is highly suited to the delivery of acid sensitive proteins. We show that the mechanism of protein release from this liquid copolymer is consistent with the formation of super-hydrated regions as a result of the osmotic activity of the solution formed upon distributed protein particle dissolution. Protein release can be manipulated by controlling polymer hydrophobicity which can be adjusted by molecular weight and choice of initiator. Moreover, protein release is highly dependent on protein solubility which impacts the osmotic activity of the solution formed upon dissolution of the protein particles while protein molecular size and isoelectric point are not as influential. As demonstrated by the release of highly bioactive vascular endothelial growth factor, formulations of this copolymer are suitable for prolonged delivery of protein therapeutics.

Liquid Degradable Poly(trimethylene-carbonate-co-5-hydroxy-trimethylene carbonate): An Injectable Drug Delivery Vehicle for Acid-Sensitive Drugs.

Liquid, injectable hydrophobic polymers have advantages as degradable drug delivery vehicles; however, polymers examined for this purpose to date form acidic degradation products that may damage acid-sensitive drugs. Herein, we report on a new viscous liquid vehicle, poly(trimethylene carbonate-co-5-hydroxy-trimethylene carbonate), which degrades through intramolecular cyclization producing glycerol, carbon dioxide, and water-soluble trimethylene carbonate. Copolymer degradation durations from weeks to months were achieved with the 5-hydroxy-trimethylene carbonate (HTMC) content of the oligomer having the greatest impact on the degradation rate, with oligomers possessing a higher HTMC content degrading fastest. The degradation products were non-cytotoxic towards 3T3 fibroblasts and RAW 264.7 macrophages. These copolymers can be injected manually through standard gauge needles and, importantly, during in vitro degradation, the microenvironmental pH within the oligomers remained near neutral. Complete and sustained release of the acid-sensitive protein vascular endothelial growth factor was achieved, with the protein remaining highly bioactive throughout the release period. These copolymers represent a promising formulation for local and sustained release of acid sensitive drugs.

In vivo degradation behavior of enzyme-degradable poly(trimethylene carbonate)-based biohybrid networks of varying water content.

Polymeric biohybrid networks have significant potential as supportive materials for soft connective tissue regeneration. Their success in this regard is determined by their initial mechanical properties, which are dependent on their water content, as well as the rate at which these properties change with time due to cell mediated degradation. In this study the in vivo degradation and tissue response following implantation of matrix metalloproteinase (MMP)-degradable poly(trimethylene carbonate) (PTMC)-based biohybrid networks were assessed in a Wistar rat model. The networks examined varied in equilibrium water content from circa 20% to 70% w/w. The networks degraded through MMP secretion by inflammatory cells at the tissue-material interface, generating a mass loss profile consistent with surface erosion but modulus and sol content changes consistent with a bulk erosion process. This degradation profile was explained in terms of a population gradient in MMP concentration from the surface to the bulk of the networks due to diffusion restrictions. A histological analysis of the tissue surrounding the implants confirmed a moderate tissue response comparable to that observed towards a VicrylTM suture, suggesting that these new materials can be considered biocompatible.

In situ-forming, mechanically resilient hydrogels for cell delivery.

Injectable, in situ-forming hydrogels can improve cell delivery in tissue engineering applications by facilitating minimally invasive delivery to irregular defect sites and improving cell retention and survival. Tissues targeted for cell delivery often undergo diverse mechanical loading including high stress, high strain, and repetitive loading conditions. This review focuses on the development of hydrogel systems that meet the requirements of mechanical resiliency, cytocompatibility, and injectability for such applications. First, we describe the most important design considerations for maintaining the viability and function of encapsulated cells, for reproducing the target tissue morphology, and for achieving degradation profiles that facilitate tissue replacement. Models describing the relationships between hydrogel structure and mechanical properties are described, focusing on design principles necessary for producing mechanically resilient hydrogels. The advantages and limitations of current strategies for preparing cytocompatible, injectable, and mechanically resilient hydrogels are reviewed, including double networks, nanocomposites, and high molecular weight amphiphilic copolymer networks. Finally, challenges and opportunities are outlined to guide future research in this developing field.

One-Pot Synthesis of Unsaturated Polyester Bioelastomer with Controllable Material Curing for Microscale Designs.

Synthetic polyester elastomeric constructs have become increasingly important for a range of healthcare applications, due to tunable soft elastic properties that mimic those of human tissues. A number of these constructs require intricate mechanical design to achieve a tunable material with controllable curing. Here, the synthesis and characterization of poly(itaconate-co-citrate-co-octanediol) (PICO) is presented, which exhibits tunable formation of elastomeric networks through radical crosslinking of itaconate in the polymer backbone of viscous polyester gels. Through variation of reaction times and monomer molar composition, materials with modulation of a wide range of elasticity (36-1476 kPa) are generated, indicating the tunability of materials to specific elastomeric constructs. This correlated with measured rapid and controllable gelation times. As a proof of principle, scaffold support for cardiac tissue patches is developed, which presents visible tissue organization and viability with appropriate elastomeric support from PICO materials. These formulations present potential application in a range of healthcare applications with requirement for elastomeric support with controllable, rapid gelation under mild conditions.

High modulus, enzyme-degradable poly(trimethylene carbonate)-peptide biohybrid networks formed from triblock prepolymers.

Biohybrid networks have the potential to have stiffnesses equivalent to that of native soft connective tissues as well as cell-mediated degradation behavior. Most strategies to generate such materials to date have utilized crosslinking of two separate and orthogonally functionalized polymers. Herein we describe a triblock prepolymer consisting of a central enzyme degradable peptide block flanked by two synthetic, hydrolysis resistant poly(trimethylene carbonate) blocks (PTMC) or poly(ethylene glycol)-PTMC blocks terminated in methacrylate groups. To form these prepolymers heterobifunctional PTMC and PEG-PTMC were prepared, possessing a vinyl sulfone terminus and a methacrylate terminus. These polymers were conjugated to a di-cysteine containing peptide through a Michael-type addition to form cross-linkable prepolymers. These prepolymers were then photo-cured to form enzyme degradable networks. The compressive moduli of the resulting water swollen networks was within the range of many soft connective tissues and was inversely proportional to the water solubility of the prepolymers. The prepolymer water solubility in turn could be tuned by adjusting PTMC molecular weight or by the addition of a PEG block. In vitro degradation only occurred in the presence of matrix metalloproteinases, and was fastest for networks prepared with prepolymers of higher water solubility.

Investigating the Effects of Tissue-Specific Extracellular Matrix on the Adipogenic and Osteogenic Differentiation of Human Adipose-Derived Stromal Cells Within Composite Hydrogel Scaffolds.

While it has been postulated that tissue-specific bioscaffolds derived from the extracellular matrix (ECM) can direct stem cell differentiation, systematic comparisons of multiple ECM sources are needed to more fully assess the benefits of incorporating tissue-specific ECM in stem cell culture and delivery platforms. To probe the effects of ECM sourced from decellularized adipose tissue (DAT) or decellularized trabecular bone (DTB) on the adipogenic and osteogenic differentiation of human adipose-derived stem/stromal cells (ASCs), a novel detergent-free decellularization protocol was developed for bovine trabecular bone that complemented our established detergent-free decellularization protocol for human adipose tissue and did not require specialized equipment or prolonged incubation times. Immunohistochemical and biochemical characterization revealed enhanced sulphated glycosaminoglycan content in the DTB, while the DAT contained higher levels of collagen IV, collagen VI and laminin. To generate platforms with similar structural and biomechanical properties to enable assessment of the compositional effects of the ECM on ASC differentiation, micronized DAT and DTB were encapsulated with human ASCs within methacrylated chondroitin sulfate (MCS) hydrogels through UV-initiated crosslinking. High ASC viability (>90%) was observed over 14 days in culture. Adipogenic differentiation was enhanced in the MCS+DAT composites relative to the MCS+DTB composites and MCS controls after 14 days of culture in adipogenic medium. Osteogenic differentiation studies revealed a peak in alkaline phosphatase (ALP) enzyme activity at 7 days in the MCS+DTB group cultured in osteogenic medium, suggesting that the DTB had bioactive effects on osteogenic protein expression. Overall, the current study suggests that tissue-specific ECM sourced from DAT or DTB can act synergistically with soluble differentiation factors to enhance the lineage-specific differentiation of human ASCs within 3-D hydrogel systems.

Peptide-modified methacrylated glycol chitosan hydrogels as a cell-viability supporting pro-angiogenic cell delivery platform for human adipose-derived stem/stromal cells.

Cell-based therapies involving the injection of adipose-derived stem/stromal cells (ASCs) within rationally designed biomaterials are a promising approach for stimulating angiogenesis. With this focus, the current work explored the effects of incorporating integrin-binding RGD or IKVAV peptides within in situ-gelling N-methacrylate glycol chitosan (MGC) hydrogels on the response of encapsulated human ASCs. Initial studies focused on hydrogel characterization to validate that the MGC, MGC-RGD, and MGC-IKVAV hydrogels had similar biomechanical properties. ASC viability following encapsulation and culture under 2% O2 was significantly impaired in the MGC-IKVAV group relative to the MGC and MGC-RGD groups. In contrast, sustained viability, along with enhanced cell spreading and metabolic activity were observed in the MGC-RGD group. Investigation of angiogenic transcription suggested that the incorporation of the peptide groups did not substantially alter the pro-angiogenic gene expression profile of the encapsulated ASCs after 7 days of culture under 2% O2. Consistent with the in vitro findings, preliminary in vivo characterization following subcutaneous implantation into NOD/SCID mice showed that ASC retention was enhanced in the MGC-RGD hydrogels relative to the MGC-IKVAV group at 14 days. Further, the encapsulated ASCs in the MGC and MGC-RGD groups promoted murine CD31+ endothelial cell recruitment to the peri-implant region. Overall, the results indicate that the MGC-RGD and MGC hydrogels are promising platforms for ASC delivery, and suggest that strategies that support long-term ASC viability can augment in vivo angiogenesis through paracrine mechanisms. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 571-585, 2019.

Adipose-Derived Stem Cells in a Resilient In Situ Forming Hydrogel Modulate Macrophage Phenotype.

Injectable hydrogels have the potential to enhance stem cell-based therapies by improving cell localization, retention, and survival after transplantation. The inflammatory response to both the hydrogel and the encapsulated cells is a critical aspect of this strategy, with macrophages being highly involved in the process of hydrogel remodeling, angiogenesis, and tissue regeneration. As a step toward the development of a cell-based strategy for therapeutic angiogenesis, this work compared the intramuscular injection of allogeneic rat adipose-derived stem/stromal cells (rASCs) in an in situ gelling hydrogel with the injection of the hydrogel alone and rASCs in saline in an immunocompetent rat model by immunohistochemical analysis over 4 weeks. rASCs delivered in the hydrogel were retained intramuscularly at significantly higher densities as compared with cells delivered in saline. The encapsulated rASCs modulated the inflammatory response, promoting CD68+ macrophage recruitment, with the majority of infiltrating cells expressing the M1 marker CCR7, as well as a higher fraction of CD163+ M2c macrophages surrounding the hydrogel. Furthermore, rASCs reduced the initial expression of inducible nitric oxide synthase and promoted arginase-1 expression in the infiltrating macrophages over time, consistent with a shift toward a more proregenerative phenotype. Coincident with the enhanced macrophage infiltration, significantly more CD31+ lumens were observed surrounding and within the hydrogels with rASCs at 2 and 4 weeks as compared with the hydrogels alone. Overall, these results are a promising indication that encapsulated rASCs can have immunomodulatory effects and may enhance angiogenic processes after intramuscular injection, promoting a regenerative macrophage response and blood vessel formation.

Mechanically resilient injectable scaffolds for intramuscular stem cell delivery and cytokine release.

A promising strategy for treating peripheral ischemia involves the delivery of stem cells to promote angiogenesis through paracrine signaling. Treatment success depends on cell localization, retention, and survival within the mechanically dynamic intramuscular (IM) environment. Herein we describe an injectable, in situ-gelling hydrogel for the IM delivery of adipose-derived stem/stromal cells (ASCs), specifically designed to withstand the dynamic loading conditions of the lower limb and facilitate cytokine release from encapsulated cells. Copolymers of poly(trimethylene carbonate)-b-poly(ethylene glycol)-b-poly(trimethylene carbonate) diacrylate were used to modulate the properties of methacrylated glycol chitosan hydrogels crosslinked by thermally-initiated polymerization using ammonium persulfate and N,N,N',N'-tetramethylethylenediamine. The scaffolds had an ultimate compressive strain over 75% and maintained mechanical properties during compressive fatigue testing at physiological levels. Rapid crosslinking (<3 min) was achieved at low initiator concentration (5 mM). Following injection and crosslinking within the scaffolds, human ASCs demonstrated high viability (>90%) over two weeks in culture under both normoxia and hypoxia. Release of angiogenic and chemotactic cytokines was enhanced from encapsulated cells under sustained hypoxia, in comparison to normoxic and tissue culture polystyrene controls. When delivered by IM injection in a mouse model of hindlimb ischemia, human ASCs were well retained in the scaffold over 28 days and significantly increased the IM vascular density compared to untreated controls.

Composite Bioscaffolds Incorporating Decellularized ECM as a Cell-Instructive Component Within Hydrogels as In Vitro Models and Cell Delivery Systems.

Decellularized tissues represent promising biomaterials, which harness the innate capacity of the tissue-specific extracellular matrix (ECM) to direct cell functions including stem cell proliferation and lineage-specific differentiation. However, bioscaffolds derived exclusively from decellularized ECM offer limited versatility in terms of tuning biomechanical properties, as well as cell-cell and cell-ECM interactions that are important mediators of the cellular response. As an alternative approach, in the current chapter we describe methods for incorporating cryo-milled decellularized tissues as a cell-instructive component within a hydrogel carrier designed to crosslink under mild conditions. This composite strategy can enable in situ cell encapsulation with high cell viability, allowing efficient seeding with a homogeneous distribution of cells and ECM. Detailed protocols are provided for the effective decellularization of human adipose tissue and porcine auricular cartilage, as well as the cryo-milling process used to generate the ECM particles. Further, we describe methods for synthesizing methacrylated chondroitin sulphate (MCS) and for performing UV-initiated and thermally induced crosslinking to form hydrogel carriers for adipose and cartilage regeneration. The hydrogel composites offer great flexibility, and the hydrogel phase, ECM source, particle size, cell type(s) and seeding density can be tuned to promote the desired cellular response. Overall, these systems represent promising platforms for the development of tissue-specific 3-D in vitro cell culture models and in vivo cell delivery systems.

Highly Bioactive SDF-1α Delivery from Low-Melting-Point, Biodegradable Polymer Microspheres.

Aliphatic polyester biodegradable microspheres have been extensively studied for controlled and minimally invasive in situ protein delivery. However, they are commonly characterized by protein denaturation via acidic polyester degradation products, whereas their supraphysiologic modulus contributes to the inflammatory response upon implantation. To address these limitations, low-melting-point poly(ε-caprolactone-co-glycolide)-b-poly(ethylene glycol)-b-poly(ε-caprolactone-co-glycolide) (PEG-(PCG)2) copolymers were prepared and characterized for their ability to release bioactive stromal-derived factor-1α (SDF-1α) as a representative therapeutic protein. The PEG molecular weight was chosen such that it would be crystalline at room temperature to promote easy handling of the microspheres, whereas the molecular weight and composition of the hydrophobic PCG blocks were adjusted to ensure the polymer was a viscous amorphous liquid at 37 °C. Microspheres prepared from the triblock copolymers completely degraded within 8 weeks in vitro with a minor decrease in microenvironmental pH. A prolonged release of SDF-1α was observed with its bioactivity highly retained after encapsulation and release.

Tough, Semisynthetic Hydrogels for Adipose Derived Stem Cell Delivery for Chondral Defect Repair.

Cell-based therapies have great potential to regenerate and repair injured articular cartilage, and a range of synthetic and natural polymer-based hydrogels have been used in combination with stem cells and growth factors for this purpose. Although the hydrogel scaffolds developed to date possess many favorable characteristics, achieving the required mechanical properties has remained a challenge. A hydrogel system with tunable mechanical properties, composed of a mixture of natural and synthetic polymers, and its use for the encapsulation of adipose derived stem/stromal cells (ASCs) is described. Solutions of methacrylated chondroitin sulfate (MCS) are mixed with solutions of acrylate-poly(trimethylene carbonate)-b-poly(ethylene glycol)-b-poly(trimethylene carbonate)-acrylate (PEG-(PTMC-A)2 ) in phosphate buffered saline and crosslinked via thermally initiated free radical polymerization. The hydrogel compressive equilibrium moduli and toughness are readily tailored by varying the concentration of the pre-polymers, as well as the molecular weight of the PEG used to prepare the PEG-(PTMC-A)2 . Two peptide sequences, GVOGEA and GGGGRGDS, are individually conjugated to the MCS to facilitate cell binding. The presence of the peptide ligands yields high ASC viability and long term metabolic activity following encapsulation in hydrogels prepared using the thermal initiator system. Overall, these hydrogels show promise as a minimally invasive ASC delivery strategy for chondral defect repair.

Long-Term Sustained Release from a Biodegradable Photo-Cross-Linked Network for Intraocular Corticosteroid Delivery.

Intravitreal sustained delivery of corticosteroids such as dexamethasone is an effective means of treating a number of ocular diseases, including diabetic retinopathy, uveitis, and age-related or diabetic macular edema. There are currently marketed devices for this purpose, yet only one, Ozurdex, is degradable. In vitro release of dexamethasone from the Ozurdex device is limited to approximately 30 days, however. It was the objective of this study to examine the potential for prolonged and sustained release of a corticosteroid in vitro from a degradable polymer prepared from terminally acrylated star co- and ter-prepolymers composed of d,l-lactide, ε-caprolactone, and trimethylene carbonate co-photo-cross-linked with poly(ethylene glycol) diacrylate. Through manipulation of the network polymer glass transition temperature and degradation rate, a sustained release of triamcinolone was achieved, with an estimated release duration greater than twice that of the Ozurdex system. Moreover, a period of nearly constant release was obtained using a network prepared from 5000 Da star-poly(trimethylene carbonate-co-d,l-lactide) triacrylate (3:1 trimethylene carbonate:d,l-lactide) co-cross-linked with 700 Da poly(ethylene glycol diacrylate). These formulations show promise as implantable, intravitreal corticosteroid delivery devices.

Chondrocyte Generation of Cartilage-Like Tissue Following Photoencapsulation in Methacrylated Polysaccharide Solution Blends.

Chondrocyte-seeded, photo-cross-linked hydrogels prepared from solutions containing 50% mass fractions of methacrylated glycol chitosan or methacrylated hyaluronic acid (MHA) with methacrylated chondroitin sulfate (MCS) are cultured in vitro under static conditions over 35 d to assess their suitability for load-bearing soft tissue repair. The photo-cross-linked hydrogels have initial equilibrium moduli between 100 and 300 kPa, but only the MHAMCS hydrogels retain an approximately constant modulus (264 ± 5 kPa) throughout the culture period. Visually, the seeded chondrocytes in the MHAMCS hydrogels are well distributed with an apparent constant viability in culture. Multicellular aggregates are surrounded by cartilaginous matrix, which contain aggrecan and collagen II. Thus, co-cross-linked MCS and MHA hydrogels may be suited for use in an articular cartilage or nucleus pulposus repair applications.