Robust Silk Fibroin Aerogel Fibers Designed by Dual Cross-Linking for Thermal Insulation.

Silk fibroin (SF) is ideal for aerogel fibers owing to its abundance, biodegradability, biocompatibility, and structural tunability, yet pristine SF aerogel fibers have insufficient performance for practical use. Here, a dual cross-linking strategy combining enzymatic cross-linking and Zn2+ coordination was used, leveraging their noncompetitive inhibition to produce SF aerogel fibers featuring low density, high strength, and outstanding thermal insulation. SF concentration governs the pore architecture formed by enzymatic cross-linking. Zn2+ ions complex with SF molecular chains, creating a more intricate three-dimensional network alongside the covalent bonds from enzymatic cross-linking. At 0.1 M Zn2+, the dual-cross-linked SF aerogel fibers achieve a maximum toughness of ∼0.31 MJ m-3 and optimal thermal insulation with ∼2.9 °C. Woven fabrics outperform commercial nylon, cotton and wool in thermal insulation. Superior performance arises from air-trapping pores suppressing conduction/convection and infrared-reflective pore walls reducing radiative loss. This work provides a guideline for designing biomass aerogel fibers.