| This work investigated an injectable, biodegradable hydrogel composite of oligo(poly(ethylene glycol) fumarate) (OPF) and gelatin microparticles (MPs) as a cell and growth factor carrier for osteochondral tissue engineering applications. An in vitro study first investigated chondrogenic differentiation of rabbit marrow mesenchymal stem cells (MSCs) encapsulated in single-layer hydrogel composites of different swelling ratios with or without transforming growth factor-beta1 (TGF-beta1). The results showed that hydrogel composites containing TGF-beta1-loaded MPs and of higher swelling ratios supported MSC chondrogenic differentiation. When implanted in a rabbit osteochondral defect, these hydrogel composites containing MSCs facilitated subchondral bone formation in the presence of TGF-beta1. However, the delivery of MSCs either with or without TGF-beta1 did not improve cartilage morphology. Accordingly, a bilayered OPF/MP hydrogel composite consisting of a chondrogenic layer and an osteogenic layer was fabricated. In vitro culture of the construct demonstrated that MSCs encapsulated in the chondrogenic layer differentiated into chondrocyte-like cells in the presence of TGF-beta1-loaded MPs. In the osteogenic layer, osteogenically precultured MSCs maintained their osteoblastic phenotype, and synergistically enhanced chondrogenic differentiation of the MSCs in the chondrogenic layer with TGF-beta1. In a following study investigating similar hydrogel composites, TGF-beta3-loaded MPs in the chondrogenic layer showed a more effectively stimulatory effect on MSC chondrogenic differentiation than TGF-beta1-loaded MPs. Furthermore, encapsulated cells of different degrees of osteogenic differentiation in the osteogenic layer were found to significantly influence the chondrogenic gene expression of co-cultured MSCs in both the presence and absence of TGF-beta3. Overall, this study demonstrated the fabrication of hydrogel composites that mimic the structure and function of osteochondral tissue, along with the application of these composites as cell and growth factor carriers for osteochondral tissue engineering. |
