Fabrication, Characterization and Cellular Interactions of Keratin Nanomaterial Coatings for Implantable Percutaneous Prosthetics
Implantable medical devices face numerous complications when interfacing with soft tissue, and are plagued by negative responses from host tissue. One such class devices are percutaneous osseointegrated prosthetics (POP). POP consist of a bone anchored titanium post that extrudes through the skin and attaches to an external prosthetic. Compared to the traditional socket interface, POPs offer better stability, limb functionality, and osseoperception for both upper and lower prosthetic limbs. Although the POP surgery technique is well established, the main disadvantage to this technology remains the titanium (Ti) - skin interface. Some of the complications that can arise include epithelial downgrowth, mechanical tearing, and infection. Various types of coatings, surface structure, and antibiotic release technologies have been used to coat Ti in an effort to mitigate POP's associated obstacles, but these methods have failed to translate into published clinical studies and mainstream medical use.
One potential solution may be to mimic an interface already found in the human body, the fingernail-skin interface, which is infection-free and mechanically stable. The same keratins that make up the cortex of human hair fibers are found in the fingernail. These cortical human hair keratins can be extracted and purified, and fingernail-specific dimeric complexes coated onto Ti surfaces using silane coupling chemistry. Keratin has been used in other studies for its cell adhesion and differentiation properties, and it has been suggested that the Leu-Asp-Val (LDV) amino acid motif is the primary site responsible for cellular attachment.
In the present work, keratins extracted from human hair fibers and recombinant keratin nanomaterials (KN) were used to create biomimetic coatings on silanized Ti surfaces. These coatings were characterized and investigated for surface topography, elemental composition, cell adhesion motifs, and cell adhesion. Both keratin substrates showed the ability to create uniform coatings that retain a protein conformation that exhibits cell adhesion motifs. The coatings exhibit the ability to support cell adhesion of both epithelial and connective tissue cells. Application of fluid shear stress was used to test the mechanical adhesion strength of cells on keratin coatings. The structure, biochemical stability and sustained cellular adhesion of these coatings support keratin's capacity to provide a stable interface between POPs and skin. Side-by-side studies of extracted and recombinant keratins reveals that the recombinant form of these materials may provide distinct advantages for their use in POP devices.
Overall, this study confirmed that a uniform, silane-coupled keratin coating was feasible. We demonstrated the substrates contain a biological function in terms of cellular adhesion and phenotypic changes in skin-relevant cells. These results support the biomimetic function of keratin on silanized Ti, which may provide a suitable coating to translate percutaneous medical device coating applications toward clinical use.