Effects of Differing Purification Methods on Properties of Keratose Biomaterials

Keratin is a natural polymer found in hair fibers, skin, and nails. It has been investigated as a biomaterial since the 1970s, and has more recently been shown to have applications in healthcare such as medical devices and tissue engineering. Keratins are one of few intermediate filament forming proteins and demonstrate a propensity to self-assemble. Keratins extracted and purified from natural sources such as human hair fibers and wool tend to have weak mechanical properties, but can be cross-linked to form more robust structures. When extracting and purifying keratin proteins from natural fibers, the method of extraction is paramount to obtaining materials that retain the ability to self-assemble and form network structures with appreciable mechanical strength. Here, we compare and contrast two methods for purifying keratin extracts-one in which conventional purification methods are used and a second in which solution aggregation is minimized to promote purification of the molecular entities with the highest propensity for self-assembly, dimers of type I and type II hard keratins. Material that underwent the latter, novel extraction method exhibited higher purity in the form of a lower peptide content. Moreover, hydrogels formed from this material were found to demonstrate greater resistance to shear, and interestingly, increased susceptibility to enzymatic degradation in comparison to hydrogels formed from conventionally extracted material. This novel keratin purification method allows for enrichment of compounds with increased self-assembly behavior, and has the potential to overcome limitations noted in other studies where biomaterials fabricated from purified keratins demonstrated inferior mechanical characteristics.