Regulation of hard α-keratin mechanics via control of intermediate filament hydration: matrix squeeze revisited

The study explored the mechanical properties of mammalian hard α-keratins, such as wool, hair, and nail, focusing on the role of intermediate filament (IF) hydration. It was found that while IFs are sensitive to hydration, hard α-keratins remain stiff in water due to the matrix squeeze hypothesis. This hypothesis proposed that during keratinization, IFs are stiffened and locked into a dehydrated state by the oxidation and cross-linking of the surrounding keratin matrix. The study's results supported this hypothesis, showing that high matrix keratins in water swelled less and had higher tensile modulus and yield stress. Disruption of the keratin matrix led to increased swelling and decreased mechanical properties, highlighting the matrix's critical role in controlling IF hydration and the mechanical behavior of keratins.