Osteochondral repair in the rabbit model utilizing bilayered, degradable oligo(poly(ethylene glycol) fumarate) hydrogel scaffolds

Abstract

In this study, hydrogel scaffolds, based on the polymer oligo(poly(ethylene glycol) fumarate) (OPF), were implanted into osteochondral defects in the rabbit model. Scaffolds consisted of two layers-a bottom, bone forming layer and a top, cartilage forming layer. Three scaffold formulations were implanted to assess how material composition and transforming growth factor-beta1 (TGF-beta1) loading affected osteochondral repair. Critical histological evaluation and scoring of the quantity and quality of tissue in the chondral and subchondral regions of defects was performed at 4 and 14 weeks. At both time points, no evidence of prolonged inflammation was observed, and healthy tissue was seen to infiltrate the defect area. The quality of this tissue improved over time with hyaline cartilage filling the chondral region and a mixture of trabecular and compact bone filling the subchondral region at 14 weeks. A promising degree of Safranin O staining and chondrocyte organization was observed in the newly formed surface tissue, while the underlying subchondral bone was completely integrated with the surrounding bone at 14 weeks. Material composition within the bottom, bone-forming layer did not appear to affect the rate of scaffold degradation or tissue filling. However, no bone upgrowth into the chondral region was observed with any scaffold formulation. TGF-beta1 loading in the top layer of scaffolds appeared to exert some therapeutic affect on tissue quality, but further studies are necessary for scaffold optimization. Yet, the excellent tissue filling and integration resulting from osteochondral implantation of these OPF-based scaffolds demonstrates their potential in cartilage repair strategies.