Thermoresponsive stiffening with microgel particles in a semiflexible fibrin network

TL;DR

This study demonstrates a temperature-responsive composite material where microgel particles induce a reversible 10-fold increase in stiffness of a fibrin network by contracting and adsorbing onto filaments, with models supporting the mechanism.

Contribution

It introduces a novel thermoresponsive stiffening mechanism in biopolymer composites using microgel particles that contract above LCST, supported by phenomenological models.

Findings

Composite stiffness increases up to 10-fold with temperature

Microgel particles contract and adsorb onto fibrin filaments

Models qualitatively match experimental data

Abstract

We report temperature-responsive soft composites of semiflexible biopolymer networks (fibrin) containing dispersed microgel colloidal particles of poly(N-isopropylacrylamide) (pNIPAM) that undergo a thermodynamically driven de-swelling transition above a Lower Critical Solution Temperature (LCST). Unlike standard polymer-particle composites, decreasing the inclusion volume of the particles (by increasing temperature)is concomitant with a striking increase of the overall elastic stiffness of the composite. We observe such a behavior over a wide composition space. The composite elastic shear modulus reversibly stiffens by up to 10-fold over a small change in temperature from 25-35{\deg}C. In isolation, the fibrin network and microgel suspension both soften with increased temperature, making the stiffening of the composites particularly significant. We hypothesize that stiffening is caused by contracting microgel particles adsorbing on the fibrin filaments and modifying the structure of the semiflexible network. We develop two phenomenological models that quantify this hypothesis in physically distinct manners, and the derived predictions are qualitatively consistent with our experimental data