Solvent control of crack dynamics in a reversible hydrogel

TL;DR

This study systematically investigates how solvent viscosity and environment influence crack dynamics in reversible gelatin hydrogels, revealing that increased viscosity slows crack propagation and affects gel fragility through diffusive processes.

Contribution

It introduces the first detailed analysis of solvent and environment effects on crack behavior in reversible hydrogels, highlighting the role of viscoplastic chain pull-out.

Findings

Increasing solvent viscosity slows crack propagation.

Soaking with solvent increases gel fragility.

Environmental viscosity affects crack dynamics via diffusive invasion.

Abstract

The resistance to fracture of reversible biopolymer hydrogels is an important control factor of the cutting/slicing and eating characteristics of food gels. It is also critical for their utilization in tissue engineering, for which mechanical protection of encapsulated components is needed. Its dependence on loading rate and, recently, on the density and strength of cross-links has been investigated. But no attention was paid so far to solvent nor to environment effects. Here we report a systematic study of crack dynamics in gels of gelatin in water/glycerol mixtures. We show on this model system that: (i) increasing solvent viscosity slows down cracks; (ii) soaking with solvent increases markedly gel fragility; (iii) tuning the viscosity of the (miscible) environmental liquid affects crack propagation via diffusive invasion of the crack tip vicinity. The results point toward the fact that fracture occurs by viscoplastic chain pull-out. This mechanism, as well as the related phenomenology, should be common to all reversibly cross-linked (physical) gels.