Silk fibroin coated TiO₂ nanotubes for improved osteogenic property of Ti6Al4V bone implants

Titanium and its alloys especially Ti6Al4V have long been used in biomedical implants. Although, Ti6Al4V is biocompatible, yet there has been consistent effort to improve its osteoconductive and osteogenic property to enhance the implant performance. In this regard, surface modification of Ti6Al4V implants with TiO₂ nanotubes and subsequent application of biopolymeric coating has started emerging as a promising approach. Keeping this perspective in mind, here we have coated nano TiO₂ modified Ti6Al4V surface with silk fibroin isolated from B. mori cocoons. The coating of silk fibroin was done on the implant using electrophoretic deposition technique at three different voltages. Topography analysis by AFM confirms the uniform coating of silk fibroin. A variation in contact angle from 89.7 ± 2° to 83.6 ± 2° was observed when tested for wettability using drop shape analyzer. The biocompatibility studies showed SF coated substrates support the adhesion of both MG63 bone cells and human mesenchymal stem cells (hMSCs). The formation of peripheral vinculin complexes on SF surface confirmed the adhesion through focal adhesion points. Consequently, SF coating improved the cellular expression of alkaline phosphatase by 1.1 times compared to the polished Ti6Al4V surface (PTi64). Increased expression of late osteogenic markers osterix and osteocalcin was also observed in hMSCs cultured on SF coated nanotubular surface compared to PTi64. These results together implied that coating of silk fibroin on TiO₂ modified Ti6Al4V surface improve the osteogenic potential of the implant.