Kovacs-like memory effect in strain stiffening collagen networks

TL;DR

This study reveals a Kovacs-like memory effect in collagen networks, showing non-monotonic stress relaxation linked to strain stiffening and negative normal stresses, highlighting unique nonequilibrium mechanics.

Contribution

It demonstrates a novel memory effect in biopolymer networks, specifically collagen, occurring in the nonlinear strain-stiffening regime, expanding understanding of structural memory in biological materials.

Findings

Memory effect occurs only in nonlinear strain-stiffening regime

Strong correlation between memory response and negative normal stresses

Memory persists over a broad range of strain amplitudes

Abstract

Materials driven far from equilibrium can encode memories of past deformations through long-lived structural reorganisations. Such memory effects-reflecting parameters such as deformation direction, magnitude, and duration have been widely explored in soft amorphous solids. Here, we report a Kovacs-like memory effect manifested as a non-monotonic stress relaxation in vitro biopolymer networks formed by collagen, an essential component of the mammalian extracellular matrix. Using shear rheology combined with in-situ optical imaging, we find that this memory effect emerges exclusively in the nonlinear strain-stiffening regime, and persists over a much broader range of strain amplitudes than previously reported for other viscoelastic amorphous materials. Furthermore, we uncover a strong correlation between the memory response and the development of negative normal stresses and associated strain fields, highlighting the unique nonequilibrium mechanics underlying memory formation in biopolymer networks.