Obstructed swelling and fracture of hydrogels

TL;DR

This study investigates how hydrogels swell around fixed obstacles, revealing that narrow, closely-spaced obstacles induce fracturing, and develops a theoretical framework to predict stress distributions and fracture conditions.

Contribution

The paper introduces an integrated experimental, simulation, and theoretical approach to understand obstructed swelling and fracture in hydrogels, highlighting the influence of obstacle geometry.

Findings

Hydrogels swell without fracture around large, spaced obstacles.

Narrow, closely-spaced obstacles cause hydrogels to fracture during swelling.

Finite element simulations map stress distributions, aiding fracture prediction.

Abstract

Obstructions influence the growth and expansion of bodies in a wide range of settings -- but isolating and understanding their impact can be difficult in complex environments. Here, we study obstructed growth/expansion in a model system accessible to experiments, simulations, and theory: hydrogels swelling around fixed cylindrical obstacles with varying geometries. When the obstacles are large and widely-spaced, hydrogels swell around them and remain intact. In contrast, our experiments reveal that when the obstacles are narrow and closely-spaced, hydrogels fracture as they swell. We use finite element simulations to map the magnitude and spatial distribution of stresses that build up during swelling at equilibrium in a 2D model, providing a route toward predicting when this phenomenon of self-fracturing is likely to arise. Applying lessons from indentation theory, poroelasticity, and nonlinear continuum mechanics, we also develop a theoretical framework for understanding how the maximum principal tensile and compressive stresses that develop during swelling are controlled by obstacle geometry and material parameters. These results thus help to shed light on the mechanical principles underlying growth/expansion in environments with obstructions.