Bio-inspired cotton fabrics treated with melanin/polydopamine nanocomposite: Synergistic photothermal, antibacterial, antioxidant, cytotoxic effect against cancer cells, and photocatalytic functionalities.

This study aimed to develop a sustainable, metal-free multifunctional finishing for cotton fabrics using naturally sourced melanin (M) recovered from pigmented wool waste and polydopamine (PDA), with particular emphasis on photothermal performance and multifunctional textile applications. A response surface methodology (RSM) design was used to optimize the M/PDA coating formulation. The treated fabrics were characterized by Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), and energy-dispersive X-ray spectroscopy (EDX). The optimized M/PDA-coated cotton exhibited temperature increases of 33 °C under sunlight and 32 °C under infrared irradiation, with only a 2 °C decrease after 10 washing cycles. The coating achieved 99.99% antibacterial efficiency against E. coli and S. aureus, up to 94% Cr(VI) removal, and photocatalytic degradation of methylene blue. The ΔE value after UV exposure decreased from 5.41 for raw cotton to 1.03 for M/PDA-treated cotton, indicating reduced UV-induced color change and enhanced photostability, and serving as an indirect indicator of UV-protection performance. The M/PDA coating also exhibited antioxidant activity and pronounced cytotoxicity against A375 melanoma cells, with approximately 14% cell viability, while maintaining 66% viability of L929 normal skin fibroblasts. The mechanical properties were maintained, while air permeability decreased by 12-18%. Overall, the M/PDA system integrates waste-derived melanin with PDA to enhance melanin adhesion and retention on cellulose, providing a metal-free platform for bio-derived protective and thermally responsive cotton.