The synergistic effects of 3-D porous silk fibroin matrix scaffold properties and hydrodynamic environment in cartilage tissue regeneration
Autologous cell-based tissue engineering using three-dimensional porous scaffolds has provided a good option for the repair of cartilage defects. Silk fibroin-based scaffolds are naturally degradable materials with excellent biocompatibility and robust mechanical properties, indicating potential applications in cartilage tissue engineering. In this study, silk fibroin scaffolds prepared by freeze-drying (FD) and salt-leaching (SL300 and SL500) were fully characterized and used to study the effects of silk fibroin scaffold properties on chondrocyte attachment, proliferation and differentiation. The synergistic effects of scaffold properties and hydrodynamic environment generated by in vitro rocking culture were also investigated using static cultures as control. FD scaffolds with small pore size and lower porosity increased cell attachment but inhibited cell penetration and limited cell proliferation and differentiation. In contrast, SL scaffolds displaying a bigger pore size, higher porosity and crystallinity resulted in homogenous cell distribution, increasing cell proliferation and advanced chondrocyte differentiation in terms of their spherical morphology, predominant chondrogenic gene expression and abundant cartilaginous extracellular matrix production. A hydrodynamic environment was beneficial to chondrocyte proliferation, differentiation, and integrin gene expression in a pore size dependent manner with superior cartilage matrix production but limited hypertrophic differentiation obtained using chondrocyte-seeded SL500 scaffolds. Integrin alpha5beta1 might mediate these effects. Chondrocyte/SL500 silk fibroin constructs obtained under in vitro rocking culture might serve as an excellent implant for in vivo cartilage defect reparation.