Osteochondral xenografts are potentially inexpensive, widely available alternatives to fresh allografts. However, antigen removal from xenogenic cartilage may damage the extracellular matrix and reduce compressive stiffness. Non‐crosslinked xenogenic cartilage may also undergo rapid enzymatic degradation in vivo. We hypothesized that natural crosslinking agents could be used in place of glutaraldehyde to improve the mechanical properties and enzymatic resistance of decellularized cartilage. This study compared the effects of genipin (GNP), proanthocyanidin (PA), and epigallocatechin gallate (EGCG), on the physical and mechanical properties of decellularized porcine cartilage. Glutaraldehyde (GA) served as a positive control. Porcine articular cartilage discs were decellularized in 2% sodium dodecyl sulfate and DNase I followed by fixation in 0.25% GNP, 0.25% PA, 0.25% EGCG, or 2.5% GA. Decellularization decreased DNA by 15% and GAG by 35%. For natural crosslinkers, the average degree of crosslinking ranged from approximately 50% (EGCG) to 78% (GNP), as compared to 83% for the GA control. Among the natural crosslinkers, only GNP significantly affected the disc diameter, and shrinkage was under 2%. GA fixation had no significant effect on disc diameter. Decellularization decreased aggregate modulus; GA and GNP, but not EGCG and PA, were able to restore it to its original level. GNP, PA, and GA conferred a similar, almost complete resistance to collagenase degradation. EGCG also conferred substantial resistance but to a lesser degree. Overall, the data support our hypothesis and suggest that natural crosslinkers may be suitable alternatives to glutaraldehyde for stabilization of decellularized cartilage. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1037–1046, 2016.

A scaffoldless or self-assembly approach to cartilage tissue engineering has been used to produce hyaline cartilage from bone marrow–derived mesenchymal stem cells (bMSCs), but the mechanical properties of such engineered cartilage and the effects the transforming growth factor (TGF) isoform have not been fully explored. This study employs a cell culture insert model to produce tissue-engineered cartilage using bMSCs. Neonatal pig bMSCs were isolated by plastic adherence and expanded in monolayer before being seeded into porous transwell inserts and cultured for 4 or 8 weeks in defined chondrogenic media containing either TGF-β1 or TGF-β3. Following biomechanical evaluation in confined compression, colorimetric dimethyl methylene blue and Sircol dye–binding assays were used to analyze glycosaminoglycan (GAG) and collagen contents, respectively. Histological sections were stained with toluidine blue for proteoglycans and with picrosirius red to reveal collagen orientation, and immunostained for detection of collagen types I and II. Neocartilage increased in thickness, collagen, and GAG content between 4 and 8 weeks. Proteoglycan concentration increased with depth from the top surface. The tissue contained much more collagen type II than type I, and there was a consistent pattern of collagen alignment. TGF-β1–treated and TGF-β3–treated constructs were similar at 4 weeks, but 8-week TGF-β1 constructs had a higher aggregate modulus and GAG content compared to TGF-β3. These results demonstrate that bMSCs can generate functional hyaline-like cartilage through a self-assembling process.

We speculate that an acellular osteochondral xenograft may be a good alternative to allografts for repair of focal articular cartilage lesions. In order to make a xenograft resistant to enzymatic degradation and to prevent a chronic immune response it may be beneficial to stabilize it through crosslinking. The concept is analogous to treatment of porcine bioprosthetic heart valves with glutaraldehyde. The purpose of this study was to evaluate genipin, a natural crosslinking agent with low cytotoxicity, for stabilization of decellularized cartilage. Porcine articular cartilage discs were decellularized in SDS and nucleases and then crosslinked in genipin. The utility of genipin was determined from its effects on degree of crosslinking, mechanical properties, dimensional stability, enzymatic resistance, and in vitro biocompatibility. Degree of crosslinking, compressive moduli, and collagenase resistance varied over a wide range depending on genipin concentration. The equilibrium compressive modulus could be increased from approximately 50% to more than 120% that of native cartilage, and the time to complete degradation by collagenase could be extended from less than 12 h to more than 15 days. Radial shrinkage of approximately 4% was observed at a genipin concentration of 0.1% wt/vol, and cartilage coefficient of friction against glass increased in a concentration-dependent manner. Autologous chondrocytes displayed little difference in viability or their ability to attach and spread over the surface of genipin-fixed cartilage compared to non-crosslinked cartilage during 6 weeks of culture. These results indicate that genipin may be efficacious for stabilization of a decellularized porcine osteochondral xenograft. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:1949–1957, 2017.

Platelet-rich plasma (PRP) may have the potential to enhance articular cartilage regeneration through release of growth factors including transforming growth factor isoforms. The purpose of this study was to investigate the potential for PRP to stimulate chondrogenic differentiation in three-dimensional PRP hydrogel constructs. Allogenic PRP was prepared using a double centrifugation protocol which resulted in a platelet concentration approximately 250% above baseline. Canine marrow stromal cells were encapsulated at 6.8×10⁶cells/ml in either 2% sodium alginate or in a 3:1 mixture of freshly prepared PRP and 2% alginate. PRP and alginate beads were cultured in chemically defined chondrogenic medium with and without 10 ng/ml TGF-β3. PRP cultures were additionally supplemented with frozen-thawed PRP. In the absence of TGF-β3, PRP had a mild stimulatory effect on cell proliferation. PRP did not stimulate cell proliferation in the presence of TGF-β3. Cells exposed to TGF-β3 accumulated significantly more GAG/DNA than those which were not, but there was not a statistically significant difference between alginate and PRP. Total collagen content was greater in PRP than in alginate, regardless of TGF-β3. Chondrogenesis in PRP was qualitatively and spatially different than that which occurred in conventional alginate beads and was characterized by isolated centers of intense chondrogenesis. Overall the results demonstrate that PRP alone weakly promotes chondroinduction of marrow stromal cells, and the effect is greatly augmented by TGF-β3.