Upcycling Wool and Feather Waste into Nanofibers via Eco-Friendly Hydrothermally Assisted Isolation of Keratin

Hydrothermal degradation processes are a particularly promising eco-friendly approach to keratin isolation from biomass. They, however, result in products with a broad molecular weight distribution, which can be particularly unfavorable for fiber production. In this study, we aimed to determine whether hydrothermally degraded feather and wool waste is suitable to produce nanofibers that retain the key functional properties of keratin, such as antioxidant activity and biocompatibility. Keratin/PEO blends were used for needleless electrospinning of nanofibers cross-linked with two different cross-linkers, ethylene glycol diglycidyl ether (EGDE) and pentaerythritol triacrylate (PETA), to improve their stability to water. The surface tension, pH, turbidity, zeta potential, and protein concentration of the keratin extract solutions were analyzed. The morphology of the produced nanofibers was analyzed using a scanning electron microscope, the surface chemical structure by attenuated total reflection–Fourier transform infrared spectroscopy (ATR-FTIR analysis), and the cross-linking success by water contact angle measurements. The antioxidant capacity and the biocompatibility of the nanofiber mats with skin cells were investigated using a 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assay and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) vitality test, respectively. The results showed that despite the unfavorable starting materials with a wide molecular mass range from 3 to 15 kDa and low average molecular weights keratin products obtained by a green hydrothermal extraction process can be used to produce nanofibers with excellent antioxidant properties and skin cell biocompatibility. The cross-linking of the nanofibers resulted in hydrophobic nanofiber surfaces; however, it impaired their biocompatibility with skin cells compared to noncross-linked nanofibers.