Recombinant Keratins Coating for Enhanced Skin-Implant Interface

Percutaneous osseointegrated prosthetics (POP), composed of metallic implants that penetrate bone and skin, are an alternative to socket-limb connection. Although POP devices have advantages for clinical usage, device failures can occur for long-term usage due to the decrease of epithelial cell attachment, epidermal down growth, inflammation, and avulsion at the skin-implant interface. To enhance the soft tissue-hard implant interface, surface modifications of the device have been conducted using morphological, physicochemical, and biochemical methods. Inspired by the skin-fingernail interface, we have investigated improving the promotion and maintenance of epidermal cell-to-device adhesion by using keratin coatings on the device. Nails, consisting of keratin, form a stable interface with mechanically mismatched skin without mechanical tearing or infection. In addition, keratins extracted from hair, wool, and feather have already been used in various biomaterials, due to its biological and mechanical durability, low immune responses, and cell adhesion properties. In our previous study, we identified that the keratin coating on metallic biomaterials facilitated the attachment of epidermal cells through focal adhesions that promoted a mature phenotype. These in vitro findings translated to an animal model where the results demonstrated reduced epidermal downgrowth. However, the work showed that the keratin coating degraded sooner than desired for the application of interest. This could be caused by various keratin nanostructures from extracted keratins that include various keratin types and contaminants due to a limitation in current keratin extraction techniques. In this study, we biosynthesized recombinant keratin to elucidate their self-assembly behaviors, depending on keratin types and explored the relationship between the self-assembled keratin nanostructures on the surface of metallic biomaterials and epidermal cell adhesion. Throughout the investigation, we examined the possibility to use recombinant keratin materials for enhanced soft tissue-metallic implant interface.