Osteogenic enhancement of silk fibroin-based bone scaffolds by forming hybrid composites with bioactive glass through GPTMS during sol-gel process

Silk fibroin-based porous scaffolds have attracted many attentions as sustainable solutions for treatment of nonunion bone fracture due to their decent biocompatibility. However, the lack of intrinsic bioactivity and rapid enzymatic degradation are main complications that limit its use as bone scaffolds. Herein, we developed a simple way to enhance bone bonding as well as long-term stability under physiological condition by crosslinking silk fibroin polypeptides with bioactive glass through GPTMS during sol-gel process. GPTMS provided many benefits to the developed organic-inorganic hybrid scaffolds. First, it prevented silk fibroin polypeptides from being leached out. While the uncrosslinked hybrid scaffolds submerged in protease solution suffered from 50 % weight loss within one day, it took 28 days for the GPTMS-crosslinked hybrid scaffolds to experience similar degradation level. Second, GPTMS crosslinking induced the formation of silk crystalline ?-sheets and hence increased the compressive modulus of the hybrid scaffolds from 0.015 MPa to 3.122 MPa, which is close to that of the cancellous bone. Further, the hybrid scaffolds could induce crystallization of calcium phosphate under simulated body fluid, which resulted in greater SaOS-2 osteoblast proliferation on the hybrid scaffolds than silk fibroin or bioactive glass controls throughout 28-day cultivation. The cells on hybrid scaffolds also showed greater levels of osteogenic markers (alkaline phosphatase activity and calcium deposition) than those on silk fibroin scaffolds. This work therefore demonstrates that GPTMS crosslinking with bioactive glass during sol-gel process not only provided the hybrid scaffolds retarded enzymatic degradation and greater mechanical integrity. Bioactivity was also remarkably increased, enhancing the potential use of silk fibroin-based scaffolds for bone tissue engineering applications.