Department of Mechanics: Seminar: Cohen 2025

From micro to macro: Unraveling the origin of the counterintuitive response in spider silk fibers

Noy Cohen

Technion, Haifa, Israel

Abstract: Spider silk is an extraordinary protein material characterized by high strength and toughness. Upon exposure to high humidity, silk fibers experience a reduction in stiffness of several orders of magnitude, supercontraction (i.e., a shortening of up to ~60% in length), and twist. These counterintuitive responses originate from a unique polymeric structure made of crystalline domains that are embedded in a highly aligned amorphous matrix. Broadly, high humidity leads to water uptake by the silk, which in turn motivates the dissociation of intermolecular hydrogen cross-linking bonds. In this talk, I will present energetically motivated models based on tools from statistical mechanics that shed light on the relations between the microstructure and the macroscopic behavior and capture the overall response of silk fibers. The models are validated through a comparison to experimental findings. The insights from these models provide a method to characterize the microstructural evolution of hydrogen-bond dominated networks and pave the way to the design of novel biomimetic fibers with non-trivial properties.