Water-Responsive Silk Fibers Enhanced by Feeding Silkworms with Multi-Wall Carbon Nanotubes or Graphene Oxide

Abstract

The natural functional silkworm silk fibers, known for their outstanding mechanical properties, biodegradability, and fabric comfort, have attracted significant research interest. In this work, we report the enhanced mechanical and thermal properties of silk fibers obtained by feeding silkworms with multi-walled carbon nanotubes (MWCNT) and graphene oxide (GO). The results indicate that carbon materials were successfully incorporated into the silk fibers, with minimal influence on their morphology. However, the presence of carbon nanomaterials hindered the structural transformation of silk molecules from random coils and α-helices to β-sheets, as evidenced by FTIR analysis. The mechanical properties of the silk fibers were also improved, with tensile strength of 0.77 GPa increasing by up to 54% for GO 1.0% feeding. The thermal properties of the feeding prepared silk fibers were significantly improved, with T_m increasing by 84.7 and 104.9 °C, and initial decomposition temperatures rising by 55 and 41.4 °C for MWCNT 1.0% and GO 1.0%, respectively. Furthermore, we report the water-driven tensile actuation of coiled silk fibers. The results indicate that the silk fibers with helical coils exhibit a contraction response to water stimulus. The maximum contraction of the modified silk fibers feeding with MWCNT and GO stroke reached 9.9 and 12.2%, respectively. The load-carrying capability of the muscle increased from 8.4 g of the control silk to 9.4 and 11.5 g of MWCNT and GO feeding silk, respectively, indicating the improvement of the contractile work capacity of silk fiber. Such actuation behavior originates from the giant volume expansion induced by water absorption. The novel MWCNT/GO modified silk fibers is expected to open up possibilities of the potential applications in smart textiles sensitive to water or humidity.