Speaker
Description
Environmental conditions strongly influence the mechanical response of spider silk and therefore must be considered when interpreting experiments and designing silk-inspired materials [1, 2, 3]. In particular, variations in relative humidity can induce supercontraction together with a concomitant torsional response. However, these coupled effects have not yet been systematically investigated from either an experimental or a theoretical perspective. In particular, a macromolecular-scale interpretation of humidity-driven twist, and of its interaction with loading history, is still lacking. Here, we perform experiments under controlled environmental conditions to quantify the coupled evolution of axial deformation and torsion during humidity-driven supercontraction and mechanical loading. We then interpret the experimental results through a micromechanics-based model, inspired by the dual Poynting effect in fiber-reinforced cylinders [4], to relate humidity-induced axial shortening to the observed torsional response. In addition, cyclic tests reveal the onset of residual strain and its concomitant influence on torsion, indicating that loading history can alter the subsequent twist evolution during humidity cycles. The modeling framework is therefore extended to capture the coupling between residual deformation and torsional response. Overall, the combined experimental evidence and modeling provide a unified picture of how environment and loading history jointly govern spider-silk mechanics, and offer transferable tools for hygroscopically active fibers and bioinspired actuators.
References
[1] V. Fazio, D. De Tommasi, N. M. Pugno, G. Puglisi, J. Mech. Phys. Solids 164, 104857 (2022).
[2] V. Fazio, N. M. Pugno, G. Puglisi, Extreme Mech. Lett. 61, 102010 (2023).
[3] V. Fazio, A. D. Malay, K. Numata, N. M. Pugno, G. Puglisi, Adv. Funct. Mater. 35, 2420095 (2024).
[4] M. Fraldi, G. Puglisi, G. Saccomandi, Proc. R. Soc. A 481, 20240816 (2025).