Technical uses of keratin-based nanofibers

Keratin is a protein constituent of wool, hair, feathers, and horns that represent an important source of renewable raw materials. Keratin can be extracted and purified to maintain a high molecular weight (45–60 kDa) using green processes (e.g., sulfitolysis) from animal products like wool. It can be processed from water solutions to produce nanofiber coating for textiles suitable for technical uses such as filtration and protective clothing. Keratin has demonstrated good adsorption properties towards toxic substances like heavy metal ions, dyes, formaldehyde and other hazardous VOCs (volatile organic compounds). Its applications can also be foreseen in water purification and air cleaning. Therefore, when transformed into nanofibers, keratin can improve its properties as a component of advanced filter media for separation and filtration processes due to high porosity, small pore sizes, high permeability, and large specific surface area. The main challenge in using keratin as a coating layer of a textile filter material is to make water-insoluble nanofibers, ensuring satisfactory durability for a real application. We disclosed that heating treatments of keratin nanofibers can greatly improve their stability to water and moisture. Interestingly, the keratin nanofibers did not lose their nanofibrous shape at high temperatures. On the contrary, the nanofiber size can significantly decrease after the treatment. Even the chemical structure of the keratin was not altered after heating. IR spectral feature changes seem to show formations of inter-chain crosslinking amide bonds. In this way, it is possible to produce a keratin nanofiber layer on textiles for active highefficiency filters to be tested for heavy metals, dyes, and VOC removal. Moreover, stabilized keratin nanofibers are able to promote and guide fibroblast growth and exert antibacterial action if properly doped with antibacterial ions, demonstrating promising applications in the biomedical field (e.g., coatings, dressings). Acknowledgments. This work was carried out within the PROTECTED project (P2022XT785) financed by the European Union through the NextGenerationEU plan, Mission 4, Component C2, Investment 1.1. as a part of the PRIN 2022 PNRR Call (D.D.1409 of 14/09/2022) of the Italian Ministry of University and Research (MUR).