TGF-β1 presenting enzymatically cross-linked injectable hydrogels for improved chondrogenesis

In this work, we developed a novel enzymatically cross-linked injectable hydrogel composed of carboxymethyl cellulose (CMC), sulfated carboxymethyl cellulose (sCMC) and gelatin for delivery of infrapatellar fat pad derived MSCs and articular chondrocytes to a cartilage defect site while enabling TGF-β1 mediated chondrogenesis. The sCMC component in the hydrogel served the purpose of mimicking heparan sulfate and thus enabled strong binding with TGF-β1 and its consequential long term presentation to the encapsulated cells. We demonstrated that amongst CMC/sCMC/gelatin hydrogels cross-linked with 1 and 2 mM H2O2, the latter demonstrated significantly higher compressive modulus and supported better in vitro cartilage formation. Thereafter, we explored the utility of this system to present TGF-β1 to encapsulated cells for prolonged time period. It was observed that these hydrogels could sequester >90% of encapsulated TGF-β1 for at least 4 weeks. The encapsulated TGF-β1 was shown to be bioactive and supported significantly better cell survival over control hydrogels. Further, the TGF loaded hydrogels demonstrated good sulfated GAG and collagen deposition which was higher than control hydrogels and comparable to those treated with soluble TGF-β1 through media. Interestingly, incorporation of TGF-β1 in hydrogels not only enhanced the expression and deposition of hyaline cartilage markers, but it also significantly reduced the deposition of fibrocartilage and hypertrophy markers. Overall, it was concluded that TGF-β1 immobilized CMC/sCMC/gelatin injectable hydrogels encapsulated with IFP MSCs and ACs present a promising, cost effective and easily translatable strategy for cartilage tissue engineering.