Influence of hydrogel network microstructures on mesenchymal stem cell chondrogenesis in vitro and in vivo.

Hydrogels, which provide three-dimensional (3D) niches for encapsulating bone marrow mesenchymal stem cells (BMSCs), are becoming a promising tissue engineering solution for chondrogenic differentiation of BMSCs. However, it remains a challenge to design a hydrogel material for effective chondrogenesis of BMSCs because of the complexity of cartilage ECM and cell–matrix interactions. Thus far, various studies have shown the physical–chemical cues of hydrogel materials to impact BMSCs chondrogenesis, but the design of the 3D network microstructure of the hydrogel to induce BMSCs chondrogenesis is still far from optimized. In this study, we successfully prepared two types of collagen hydrogels, namely, the fibrous network and porous network, with the same chemical composition and similar mechanical strength but with two distinct network microstructures. The two different network microstructures significantly influenced mass transfer, protein adsorption, degradability, and contraction of the collagen hydrogels. Moreover, the cells presented distinct proliferation and morphology in the two hydrogels, which consequently modulated chondrogenic differentiation of BMSCs derived from rat. Collagen hydrogels with a fibrous network promoted more chondrogenic differentiation of BMSCs without additional growth factors in vitro and subcutaneous implantation in vivo than those with a porous network. Moreover, fibrous network resulted in less ECM calcification than porous network. However, the fibrous network could not prevent hypertrophy of the chondrogenic cells induced by BMSCs. Overall, these results revealed that the 3D network microstructure of a hydrogel was a key design parameter for the chondrogenic differentiation of BMSCs.