The mechanisms behind the hydration-induced mechanical response of spider silk

Dr Noy Cohen (Technion - Israel Institute of Technology)

Thursday 17th November, 2022 14:00-15:00 Maths 311B / ZOOM (ID: 875 6661 5914)

Abstract

Spider silk is an extraordinary protein material that exhibits counterintuitive mechanical behaviors such as a reduction in stiffness of several orders of magnitude, supercontraction (i.e. a shortening of up to ~60% in length), and twist upon exposure to high humidity. These non-trivial 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, two model that explain the origin of supercontraction and twist in spider silk will be presented. Using tools from statistical mechanics, I will show that the dissociation of intermolecular bonds gives rise to a transition from a glassy to a rubbery phase, an increase in entropy, and a decrease in free energy. These factors shed light on the underlying mechanisms that govern supercontraction and agree with experimental findings. In addition, I will employ a continuum-based framework to show that the twist behavior originates from helical features that exist in a glassy spider silk fiber. The merit of these works is two-fold: (1) they account for the microstructural evolution of spider silk in response to water uptake and (2) they provide a method to characterize the microstructural evolution of hydrogen-bond dominated networks. The insights from the presented models pave the way to the design of novel biomimetic fibers with non-trivial properties.

 

1) N. Cohen and C.D. Eisenbach, “Humidity-Driven Supercontraction and Twist in Spider Silk”, Physical Review Letters, 128:098101, 2022.

2) N. Cohen, M. Levin, and C.D. Eisenbach, “On the origin of supercontraction in spider silk”, Biomacromolecules, 22:993-1000, 2021.

Add to your calendar

Download event information as iCalendar file (only this event)