Regulation of Hard Alpha-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 nails, 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. This mechanism ensures that even when immersed in water, the IFs remain dry and stiff. The study's results supported predictions that high matrix keratins swell less in water and have higher tensile modulus and yield stress, while disruption of the matrix leads to increased swelling and reduced mechanical properties. The findings highlighted the critical role of the keratin matrix in controlling IF hydration and the mechanical properties of keratins.