Kovacs-like memory effect in collagen networks and collagen-PNIPAM biocomposites

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.

In the last part of my talk, I shall also discuss the striking modifications in memory

formation in collagen networks seeded with thermoresponsive colloidal PNIPAM particles.