Advances in drug delivery for articular cartilage

Repair of osteochondral defects with biodegradable hydrogel composites encapsulating marrow mesenchymal stem cells in a rabbit model

This work investigated the delivery of marrow mesenchymal stem cells (MSCs), with or without the growth factor transforming growth factor-beta1 (TGF-beta1), from biodegradable hydrogel composites on the repair of osteochondral defects in a rabbit model. Three formulations of oligo(poly(ethylene glycol) fumarate) (OPF) hydrogel composites containing gelatin microparticles (GMPs) and MSCs were implanted in osteochondral defects, including (i) OPF/GMP hydrogel composites; (ii) OPF/GMP hydrogel composites encapsulating MSCs; and (iii) OPF hydrogel composites containing TGF-beta1-loaded GMPs and MSCs. At 12weeks, the quality of new tissue formed in chondral and subchondral regions of defects was evaluated based on subjective and quantitative histological analysis. OPF hydrogel composites were partially degraded and the defects were filled with newly formed tissue at 12weeks with no sign of persistent inflammation. With the implantation of scaffolds alone, newly formed chondral tissue had an appearance of hyaline cartilage with zonal organization and intense staining for glycosaminoglycans, while in the subchondral region hypertrophic cartilage with some extent of bone formation was often observed. The addition of MSCs, especially with TGF-beta1-loaded GMPs, facilitated subchondral bone formation, as evidenced by more trabecular bone appearance. However, the delivery of MSCs with or without TGF-beta1 at the dosage investigated did not improve cartilage morphology. While OPF-based hydrogel composites supported osteochondral tissue generation, further investigations are necessary to elucidate the effects of MSC seeding density and differentiation stage on new tissue formation and regeneration.

Porcine gelatin microsphere/calcium phosphate cement composites: an in vitro degradation study

Scaffolds for bone tissue engineering preferably should be mechanically stable, osteoconductive, biodegradable and porous. To comply with these characteristics, calcium phosphate cements (CPCs) with porcine (type A) gelatin microspheres were formulated. In this experiment, in vitro degradation of 10 wt % gelatin type A microsphere CPCs (GELA CPCs) was followed for 12 weeks in proteolytic medium. Results showed a gradual decrease in mass, compression strength and E-modulus. Morphology investigation showed that degradation of the spheres started at the surface of the composite and gradually proceeded to the inner part. Overall, porcine gelatin microspheres can be used to generate in situ macroporosity into an injectable CPC.

Injectable biomaterials for regenerating complex craniofacial tissues

Engineering complex tissues requires a precisely formulated combination of cells, spatiotemporally released bioactive factors, and a specialized scaffold support system. Injectable materials, particularly those delivered in aqueous solution, are considered ideal delivery vehicles for cells and bioactive factors and can also be delivered through minimally invasive methods and fill complex 3D shapes. In this review, we examine injectable materials that form scaffolds or networks capable of both replacing tissue function early after delivery and supporting tissue regeneration over a time period of weeks to months. The use of these materials for tissue engineering within the craniofacial complex is challenging but ideal as many highly specialized and functional tissues reside within a small volume in the craniofacial structures and the need for minimally invasive interventions is desirable due to aesthetic considerations. Current biomaterials and strategies used to treat craniofacial defects are examined, followed by a review of craniofacial tissue engineering, and finally an examination of current technologies used for injectable scaffold development and drug and cell delivery using these materials.

Mesoporous calcium silicate for controlled release of bovine serum albumin protein

The purpose of this study is to synthesize mesoporous calcium silicate (CS or wollastonite, CaSiO(3)) and evaluate its possible application in protein/drug delivery. First, calcium silicate was synthesized by wet chemical method and then mesoporosity was created by acid modification of the synthesized CS particle using hydrochloric acid at pH 7, 4.5, and 0.5. The results showed that a hydrated silica gel with abundant Si-OH functional group formed on the surface of calcium silicate due to acid modification. This surface layer had mesoporous structure, with pore diameter between 4 and 5 nm. BET specific average surface area increased to 221, 333, and 356 m(2) g(-1) due to acid modification at pH 7, 4.5, and 0.5, respectively, whereas the surface area for unmodified CS particles was 65 m(2) g(-1). Protein adsorption studies indicated that mesoporous CS has higher ability to adsorb bovine serum albumin and lysozyme compared to unmodified particles. The release kinetics showed that proteins on mesoporous CS released sequentially over one week, whereas the proteins on unmodified particle followed burst release kinetics within a few hours. Human osteoblast cell-material interaction study showed that these materials were biocompatible and promoted excellent bone cell proliferation. In summary, this work has demonstrated the potential to produce mesoporous CS as a carrier for protein/drug delivery for bone regeneration and other biomedical applications.

Articular cartilage tissue engineering

Articular cartilage repair remains a challenge to surgeons and basic scientists. The field of tissue engineering allows the simultaneous use of material scaffolds, cells and signalling molecules to attempt to modulate the regenerative tissue. This review summarises the research that has been undertaken to date using this approach, with a particular emphasis on those techniques that have been introduced into clinical practice, via in vitro and preclinical studies.

Toward the development of partially biodegradable and injectable thermoresponsive hydrogels for potential biomedical applications

A series of hydrogels containing a biodegradable dextran (Dex) chain grafted with a hydrophobic poly(-caprolactone)-2-hydroxylethyl methacrylate (PCL-HEMA) chain and a thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) chain were synthesized. The molecular weight of PCL-HEMA was determined by gel permeation chromatography, and the inner morphology of the hydrogel was observed by scanning electron microscopy. The release profiles from the hydrogels were investigated using bovine serum albumen as a model drug. It was found that the release behavior could be adjusted by varying the composition of the hydrogel. In vitro cytotoxicity studies of the hydrogels showed that the copolymer Dex-PCL-HEMA/PNIPAAm exhibited low cytotoxicity. The in vivo degradation and histological studies demonstrated that the hydrogels had good biocompatibility and were promising for use as an injectable polymeric scaffold for tissue engineering applications.

Intra-articular depot formulation principles: role in the management of postoperative pain and arthritic disorders

The joint cavity constitutes a discrete anatomical compartment that allows for local drug action after intra-articular injection. Drug delivery systems providing local prolonged drug action are warranted in the management of postoperative pain and not least arthritic disorders such as osteoarthritis. The present review surveys various themes related to the accomplishment of the correct timing of the events leading to optimal drug action in the joint space over a desired time period. This includes a brief account on (patho)physiological conditions and novel potential drug targets (and their location within the synovial space). Particular emphasis is paid to (i) the potential feasibility of various depot formulation principles for the intra-articular route of administration including their manufacture, drug release characteristics and in vivo fate, and (ii) how release, mass transfer and equilibrium processes may affect the intra-articular residence time and concentration of the active species at the ultimate receptor site.

In vitro and in vivo release of vascular endothelial growth factor from gelatin microparticles and biodegradable composite scaffolds

PURPOSE

This work evaluated gelatin microparticles and biodegradable composite scaffolds for the controlled release of vascular endothelial growth factor (VEGF) in vitro and in vivo.

METHODS

Gelatin crosslinking, VEGF dose, and buffer type were investigated for their effects on VEGF release. Release was also evaluated from microparticles confined within porous polymer scaffolds (composites). In vitro and in vivo studies were conducted using radiolabeled VEGF.

RESULTS

The effect of VEGF dose on its fractional release from gelatin microparticles in vitro was minimal, but the addition of collagenase to the buffer resulted in a higher cumulative release of VEGF. Gelatin crosslinking extent was a significant factor on release from both microparticles alone and composite scaffolds in vitro and in vivo. VEGF bioactivity from composite scaffolds in vitro was maintained above 90% of the expected bioactivity over 14 days.

CONCLUSIONS

VEGF release kinetics were dependent on the extent of gelatin crosslinking and were characteristic of the specific growth factor due to the effects of growth factor size, charge, and conformation on its complexation with gelatin. These studies demonstrate the utility of gelatin microparticles and their composite scaffolds as delivery vehicles for the controlled release of VEGF for tissue engineering applications.

Healing of articular cartilage defects treated with a novel drug-releasing rod-type implant after microfracture surgery

Microfracture therapy is a widely used technique for the repair of articular cartilage defects because it can be readily performed arthroscopically. However, the regenerated cartilage after microfracture surgery clearly differs from normal articular cartilage. This suggests that the clinical outcome of patients undergoing microfracture therapy could be improved. Dehydroepiandrosterone sulfate (DHEA-S) is known to protect against articular cartilage loss. Therefore, in an effort to achieve cartilage regeneration of high efficacy, we manufactured a DHEA-S-releasing rod-type implant for implantation into the holes produced by microfracture surgery. The polymeric rod-type implant was made of biodegradable poly (D, L-lactide-co-glycolide) (PLGA) and beta-tricalcium phosphate to enable controlled release of DHEA-S. The implant was dip-coated with a dilute PLGA solution to prevent the burst release of DHEA-S. The rod-type implant was sufficiently stiff to permit implantation into the holes made by microfracture. DHEA-S was released from the implant for more than four weeks. Furthermore, eight weeks after implantation into rabbit knees, the implants dramatically enhanced cartilage regeneration compared to control. Moreover, the degradation of the implant over the eight weeks from implantation into the knee did not induce any adverse effects. Therefore, this polymeric rod-type implant does not only provide an improvement in microfracture surgery, but also has great potential as a new formulation for drug delivery.

Chondrocyte signaling and artificial matrices for articular cartilage engineering

Chondrocytes depend on their environment to aid in their expression of appropriate proteins. It has been found that the interaction of integrin receptors with chondrocytes effects the production of extracellular molecules such as type II collagen and aggrecan. Additionally, the presence of growth factors such as IGF-1, TGF-beta1 and BMP-7 induce various signaling pathways that also aid in transducing phenotypic expressions by chondrocytes. Natural and synthetic polymers have been used to act as a scaffold for chondrocytes. The production of extracellular matrix proteins by chondrocytes has been studied. As tissue engineers, it is advantageous to explore the possibility of how altering biomaterial properties affect the signaling cascades by activation of receptors and transduction through the cytoplasm. This vital information will be able to aid in the future of engineering an appropriate biomaterial that can incorporate chondrocytes to act as a scaffold for articular cartilage.

Matrices and scaffolds for protein delivery in tissue engineering

The tissue engineering of functional tissues depends on the development of suitable scaffolds to support three dimensional cell growth. To improve the properties of the scaffolds, many cell carriers serve dual purposes; in addition to providing cell support, cutting-edge scaffolds biologically interact with adhering and invading cells and effectively guide cellular growth and development by releasing bioactive proteins like growth factors and cytokines. To design controlled release systems for certain applications, it is important to understand the basic principles of protein delivery as well as the stability of each applied biomolecule. To illustrate the enormous progress that has been achieved in the important field of controlled release, some of the recently developed cell carriers with controlled release capacity, including both solid scaffolds and hydrogel-derived scaffolds, are described and possible solutions for unresolved issues are illustrated.

Degradable hydrogel scaffolds for in vivo delivery of single and dual growth factors in cartilage repair

OBJECTIVE

As our population ages, treatment for joint pain associated with articular cartilage damage is becoming a prevalent challenge. Accordingly, this work investigates local delivery of two regulatory proteins - transforming growth factor-beta1 (TGF-beta1) and insulin-like growth factor-1 (IGF-1) - to cartilage defects from degradable scaffolds as a potential strategy for improving cartilage repair.

METHOD

The effects of TGF-beta1 and/or IGF-1 delivery on osteochondral repair in adult rabbits were examined through histomorphometric analysis of 11 markers of osteochondral repair.

RESULTS

Complete scaffold degradation occurred allowing for assessment of the healing response at 12 weeks post-surgery. When compared to untreated defects, higher scores were observed with IGF-1-treated defects for the six markers of neo-surface repair: neo-surface morphology, cartilage thickness, surface regularity, chondrocyte clustering, and the chondrocyte/glycosaminoglycan content of the neo-surface and the cartilage surrounding the defect. Surprisingly, the benefits of IGF-1 delivery were not maintained when this growth factor (GF) was co-delivered with TGF-beta1, despite numerous in vitro reports of the combinatory actions of these GFs.

CONCLUSIONS

While localized delivery of IGF-1 may be a promising repair strategy, further in vivo assessment is necessary, since fibrous tissue was commonly observed in the neo-surface of all treatment groups. More importantly, this study highlights the need to rigorously examine GF interactions in the wound healing environment and demonstrates that in vitro observations do not directly translate to the in vivo setting.

Direct chitosan-mediated gene delivery to the rabbit knee joints in vitro and in vivo

Chitosan vector system is expected to be useful for direct gene therapy for joint disease. This study first sought to confirm that foreign genes can be transferred to articular chondrocytes in primary culture. Next, chitosan-DNA nanoparticles containing IL-1Ra or IL-10 gene were injected directly into the knee joint cavities of osteoarthritis rabbits to clarify the in vivo transfer availability of the chitosan vectors. Clear expression of IL-1Ra was detected in the knee joint synovial fluid of the chitosan IL-1Ra-injected group. While no expression was detected in the chitosan IL-10-injected group, this demonstrates that the transfection efficiency of chitosan-DNA nanoparticles was closely related to the type of the gene product. A significant reduction was also noted in the severity of histologic cartilage lesions in the group that received the chitosan IL-1Ra injection. This avenue may therefore represent a promising future treatment for osteoarthritis.

Sustained release of TGFbeta3 from PLGA microspheres and its effect on early osteogenic differentiation of human mesenchymal stem cells

Despite the widespread role of transforming growth factor-beta3 (TGFbeta3) in wound healing and tissue regeneration, its long-term controlled release has not been demonstrated. Here, we report microencapsulation of TGFbeta3 in poly-d-l-lactic-co-glycolic acid (PLGA) microspheres and determine its bioactivity. The release profiles of PLGA-encapsulated TGFbeta3 with 50:50 and 75:25 PLA:PGA ratios differed throughout the experimental period. To compare sterilization modalities of microspheres, bFGF was encapsulated in 50:50 PLGA microspheres and subjected to ethylene oxide (EO) gas, radio-frequency glow discharge (RFGD), or ultraviolet (UV) light. The release of bFGF was significantly attenuated by UV light, but not significantly altered by either EO or RFGD. To verify its bioactivity, TGFbeta3 (1.35 ng/mL) was control-released to the culture of human mesenchymal stem cells (hMSC) under induced osteogenic differentiation. Alkaline phosphatase staining intensity was markedly reduced 1 week after exposing hMSC-derived osteogenic cells to TGFbeta3. This was confirmed by lower alkaline phosphatase activity (2.25 +/- 0.57 mU/mL/ng DNA) than controls (TGFbeta3- free) at 5.8 +/- 0.9 mU/mL/ng DNA (p < 0.05). Control-released TGFbeta3 bioactivity was further confirmed by lack of significant differences in alkaline phosphatase upon direct addition of 1.35 ng/mL TGFbeta3 to cell culture (p > 0.05). These findings provide baseline data for potential uses of microencapsulated TGFbeta3 in wound healing and tissue-engineering applications.

BMP signaling in the cartilage growth plate

Transforming growth factor-beta (TGF-beta) superfamily members play diverse roles in all aspects of cartilage development and maintenance. It is well established that TGF-betas and bone morphogenetic proteins (BMPs) play distinct roles in the growth plate. This chapter discusses key experiments and experimental approaches that have revealed these roles, and progress toward the identification of previously unsuspected roles. Current understanding of the mechanisms by which different TGF-beta and BMP pathways exert their functions is discussed. Finally attempts to utilize this information to promote cartilage regeneration, and important issues for future research, are outlined.

Tissue engineering osteochondral implants for temporomandibular joint repair

Tissue engineering has provided an alternative to traditional strategies to repair and regenerate temporomandibular joints (TMJ). A successful strategy to engineer osteochondral tissue, such as that found in the TMJ, will produce tissue that is both biologically and mechanically functional. Image-based design (IBD) and solid free-form (SFF) fabrication can be used to generate scaffolds that are load bearing and match patient and defect site geometry. The objective of this study was to demonstrate how scaffold design, materials, and biological factors can be used in an integrated approach to regenerate a multi-tissue interface. IBD and SFF were first used to create biomimetic scaffolds with appropriate bulk geometry and microarchitecture. Biphasic composite scaffolds were then manufactured with the same techniques and used to simultaneously generate bone and cartilage in discrete regions and provide for the development of a stable interface between cartilage and subchondral bone. Poly-l-lactic acid/hydroxyapatite composite scaffolds were differentially seeded with fibroblasts transduced with an adenovirus expressing bone morphogenetic protein-7 in the ceramic phase and fully differentiated chondrocytes in the polymeric phase, and were subcutaneously implanted into mice. Following implantation in the ectopic site, the biphasic scaffolds promoted the simultaneous growth of bone, cartilage, and a mineralized interface tissue. Within the ceramic phase, the pockets of tissue generated included blood vessels, marrow stroma, and adipose tissue. This combination of IBD and SFF-fabricated biphasic scaffolds with gene and cell therapy is a promising approach to regenerate osteochondral defects and, ultimately, the TMJ.

Delivery of TGF-β1 and chondrocytes via injectable, biodegradable hydrogels for cartilage tissue engineering applications

In this work, novel hydrogel composites, based on the biodegradable polymer, oligo(poly(ethylene glycol) fumarate) (OPF) and gelatin microparticles (MPs) were utilized as injectable cell and growth factor carriers for cartilage tissue engineering applications. Specifically, bovine chondrocytes were embedded in composite hydrogels co-encapsulating gelatin MPs loaded with transforming growth factor-beta1 (TGF-beta1). Hydrogels with embedded cells co-encapsulating unloaded MPs and those with no MPs served as controls in order to assess the effects of MPs and TGF-beta1 on chondrocyte function. Samples were cultured up to 28 days in vitro. By 14 days, cell attachment to embedded gelatin MPs within the constructs was observed via light microscopy. Bioassay results showed that, over the 21 day period, there was a statistically significant increase in cellular proliferation for samples containing gelatin MPs, but no increase was exhibited in samples without MPs over the culture period. The release of TGF-beta1 further increased cell construct cellularity. Over the same time period, glycosaminoglycan content per cell remained constant for all formulations, suggesting that the dramatic increase in cell number for samples with TGF-beta1-loaded MPs was accompanied by maintenance of the cell phenotype. Overall, these data indicate the potential of OPF hydrogel composites containing embedded chondrocytes and TGF-beta1-loaded gelatin MPs as a novel strategy for cartilage tissue engineering.

A silanized hydroxypropyl methylcellulose hydrogel for the three-dimensional culture of chondrocytes

Articular cartilage has limited intrinsic repair capacity. In order to promote cartilage repair, the amplification and transfer of autologous chondrocytes using three-dimensional scaffolds have been proposed. We have developed an injectable and self-setting hydrogel consisting of hydroxypropyl methylcellulose grafted with silanol groups (Si-HPMC). The aim of the present work is to assess both the in vitro cytocompatibility of this hydrogel and its ability to maintain a chondrocyte-specific phenotype. Primary chondrocytes isolated from rabbit articular cartilage (RAC) and two human chondrocytic cell lines (SW1353 and C28/I2) were cultured into the hydrogel. Methyl tetrazolium salt (MTS) assay and cell counting indicated that Si-HPMC hydrogel did not affect respectively chondrocyte viability and proliferation. Fluorescent microscopic observations of RAC and C28/I2 chondrocytes double-labeled with cell tracker green and ethidium homodimer-1 revealed that chondrocytes proliferated within Si-HPMC. Phenotypic analysis (RT-PCR and Alcian blue staining) indicates that chondrocytes, when three-dimensionnally cultured within Si-HPMC, expressed transcripts encoding type II collagen and aggrecan and produced sulfated glycosaminoglycans. These results show that Si-HPMC allows the growth of differentiated chondrocytes. Si-HPMC therefore appears as a potential scaffold for three-dimensional amplification and transfer of chondrocytes in cartilage tissue engineering.

Dual growth factor delivery from degradable oligo(poly(ethylene glycol) fumarate) hydrogel scaffolds for cartilage tissue engineering

This work describes the development of a non-invasive means of simultaneously delivering insulin-like growth factor-1 (IGF-1) and transforming growth factor-beta1 (TGF-beta1) to injured cartilage tissue in a controlled manner. This novel delivery technology employs the water-soluble polymer, oligo(poly(ethylene glycol) fumarate) (OPF), in the fabrication of biodegradable hydrogels which encapsulate gelatin microparticles. Release studies first examined the effect of gelatin isoelectric point (IEP) and crosslinking extent on IGF-1 release from these microparticles. In the presence of collagenase, highly crosslinked, acidic gelatin (IEP=5.0) provided sustained release of IGF-1, 95.2+/-2.9% cumulative release at day 28, while less crosslinked microparticles and microparticles of alternate IEP exhibited similar release values after only 6 days. Encapsulation of these highly crosslinked microparticles in a network of OPF provided a means to further control release, reducing final cumulative release to 70.2+/-4.7% in collagenase-containing PBS. Final release values from OPF-gelatin microparticle composites could be altered by incorporating less crosslinked, non-loaded microparticles within these constructs. Finally, this technology was extended to the dual delivery of IGF-1 and TGF-beta1 by loading these growth factors into either the OPF hydrogel phase or gelatin microparticle phase of composites. Release profiles were successfully manipulated by altering the phase of growth factor loading and microparticle crosslinking extent. For instance, by loading TGF-beta1 into the gelatin microparticle phase, a burst release of 10.8+/-0.7% was achieved, while loading this growth factor into the OPF hydrogel phase resulted in a burst release of 25.2+/-1.5%. With either system, simultaneous, slow release of IGF-1 over a 4-week period was accomplished by selectively loading this protein into highly crosslinked, encapsulated microparticles. These results demonstrate the utility of these systems in future studies to assess the interplay and time course of multiple growth factors in cartilage repair.

Engineered osteochondral grafts using biphasic composite solid free-form fabricated scaffolds

Tissue engineering has provided an alternative to traditional strategies to repair cartilage damaged by injury or degenerative disease. A successful strategy to engineer osteochondral tissue will mimic the natural contour of the articulating surface, achieve native mechanical properties and functional load-bearing ability, and lead to integration with host cartilage and underlying subchondral bone. Image-based design (IBD) and solid free-form (SFF) fabrication can be used to generate scaffolds that are load bearing and match articular geometry. The objective of this study was to utilize materials and biological factors in an integrated approach to regenerate a multitissue interface. Biphasic composite scaffolds manufactured by IBD and SFF fabrication were used to simultaneously generate bone and cartilage in discrete regions and provide for the development of a stable interface between cartilage and subchondral bone. Poly-L-lactic acid/hydroxyapatite composite scaffolds were differentially seeded with fibroblasts transduced with an adenovirus expressing bone morphogenetic protein 7 (BMP-7) in the ceramic phase and fully differentiated chondrocytes in the polymeric phase. After subcutaneous implantation into mice, the biphasic scaffolds promoted the simultaneous growth of bone, cartilage, and a mineralized interface tissue. Within the ceramic phase, the pockets of tissue generated included blood vessels, marrow stroma, and adipose tissue. This combination of IBD and SFF-fabricated biphasic scaffolds with gene and cell therapy is a promising approach to regenerate osteochondral defects.

Transforming growth factor-β1 release from oligo(poly(ethylene glycol) fumarate) hydrogels in conditions that model the cartilage wound healing environment

This research demonstrates that controlled material degradation and transforming growth factor-beta1 (TGF-beta1) release can be achieved by encapsulation of TGF-beta1-loaded gelatin microparticles within the biodegradable polymer oligo(poly(ethylene glycol) fumarate) (OPF), so that these microparticles function as both a digestible porogen and a delivery vehicle. Release studies performed with non-encapsulated microparticles confirmed that at normal physiological pH, TGF-beta1 complexes with acidic gelatin, resulting in slow release rates. At pH 4.0, this complexation no longer persists, and TGF-beta1 release is enhanced. However, by encapsulating TGF-beta1-loaded microparticles in a network of OPF, release at either pH can be diffusionally controlled. For instance, after 28 days of incubation at pH 4.0, final cumulative release from non-encapsulated microparticles crosslinked in 10 and 40 mM glutaraldehyde (GA) was 75.4+/-1.6% and 76.6+/-1.1%, respectively. However, when either microparticle formulation was encapsulated in an OPF hydrogel (noted as OPF-10 mM and OPF-40 mM, respectively), these values were reduced to 44.7+/-14.6% and 47.4+/-4.7%. More interestingly, release studies, in conditions that model the expected collagenase concentration of injured cartilage, demonstrated that by altering the microparticle crosslinking extent and loading within OPF hydrogels, TGF-beta1 release, composite swelling, and polymer loss could be systematically altered. Composites encapsulating less crosslinked microparticles (OPF-10 mM) exhibited 100% release after only 18 days and were completely degraded by day 24 in collagenase-containing phosphate-buffered saline (PBS). Hydrogels encapsulating 40 mM GA microparticles did not exhibit 100% release or polymer loss until day 28. Hydrogels with no microparticle component demonstrated only 79.3+/-9.2% release and 89.2+/-3.4% polymer loss after 28 days in enzyme-containing PBS. Accordingly, these studies confirm that the rate of TGF-beta1 release and material degradation can be controlled by altering key parameters of these novel, in situ crosslinkable biomaterials, so that TGF-beta1 release and scaffold degradation may be tailored to optimize cartilage repair.

In vitro release of transforming growth factor-beta 1 from gelatin microparticles encapsulated in biodegradable, injectable oligo(poly(ethylene glycol) fumarate) hydrogels

This research investigates the in vitro release of transforming growth factor-beta1 (TGF-beta1) from novel, injectable hydrogels based on the polymer oligo(poly(ethylene glycol) fumarate) (OPF). These hydrogels can be used to encapsulate TGF-beta1-loaded-gelatin microparticles and can be crosslinked at physiological conditions within a clinically relevant time period. Experiments revealed that OPF formulation and crosslinking time may be adjusted to influence the equilibrium swelling ratio, elastic modulus, strain at fracture, and mesh size of these hydrogels. Studies with OPF-gelatin microparticle composites revealed that OPF formulation and crosslinking time, as well as microparticle loading and crosslinking extent, influence composite swelling. In vitro TGF-beta1 release studies demonstrated that burst release from OPF hydrogels with a mesh size of 136 A was approximately 53%, while burst release from hydrogels with a mesh size of 93 A was only 34%. For hydrogels with a large mesh size (136 A), encapsulation of loaded gelatin microparticles allowed burst release to be reduced to 29-32%, depending on microparticle loading. Likewise, final cumulative release after 28 days was reduced from 71% to 48-66% by encapsulation of loaded microparticles. However, inclusion of gelatin microparticles within OPF hydrogels of smaller mesh size (93 A) was seen to increase TGF-beta1 release rates. The equilibrium swelling ratio of the microparticle component of these composites was shown to be greater than the equilibrium swelling ratio of the OPF component. Therefore, increased release rates are the result of disruption of the polymer network during swelling. These combined results indicate that the kinetics of TGF-beta1 release can be controlled by adjusting OPF formulation and microparticle loading, factors affecting the swelling behavior these composites. By systematically altering these parameters, in vitro release rates from hydrogels and composites loaded with TGF-beta1 at concentrations of 200 ng/ml can be varied from 13 to 170 pg TGF-beta1/day for days 1-3 and from 7 to 47 pg TGF-beta1/day for days 6-21. Therefore, these studies demonstrate the potential of these novel hydrogels and composites in the sustained delivery of low dosages of TGF-beta1 to articular cartilage defects.

Porous chitosan scaffold containing microspheres loaded with transforming growth factor-beta1: implications for cartilage tissue engineering

Damaged articular cartilage, caused by traumatic injury or degenerative diseases, has a limited regenerative capacity and frequently leads to the onset of osteoarthritis. As a promising strategy for the successful regeneration of long-lasting hyaline cartilage, tissue engineering has received increasing recognition. In this study, we attempted to design a novel type of porous chitosan scaffold, containing transforming growth factor-beta1 (TGF-beta1), to enhance chondrogenesis. First, to achieve a sustained release of TGF-beta1, chitosan microspheres loaded with TGF-beta1 (MS-TGFs) were prepared by the emulsion method, in the presence of tripolyphosphate; with an identical manner, microspheres loaded with BSA, a model protein, were also prepared. Both microspheres containing TGF-beta1 and BSA had spherical shapes with a size ranging from 0.2 to 1.5 microm. From the release experiments, it was found that both proteins were slowly released from the microspheres over 5 days in a PBS solution (pH 7.4), in which the release rate of TGF-beta1 was much lower than that of BSA. Second, MS-TGFs were seeded onto the porous chitosan scaffold, prepared by the freeze-drying method, to observe the effect on the proliferation and differentiation of chondrocytes. It was obviously demonstrated from in vitro tests that, compared to the scaffold without MS-TGF, the scaffold containing MS-TGF significantly augments the cell proliferation and production of extracellular matrix, indicating the role of TGF-beta1 released from the microspheres. These results suggest that the chitosan scaffold containing MS-TGF possesses a promising potential as an implant to treat cartilage defects.