Diffusio-phoretic fast swelling of chemically responsive hydrogels

TL;DR

This paper introduces a continuum poroelastic model explaining rapid, acid-triggered swelling in hydrogels through a novel diffusio-phoresis mechanism, with implications for drug delivery and soft robotics.

Contribution

It develops a quantitative theory of gel diffusio-phoresis, revealing how ion release induces fast swelling beyond traditional solvent absorption rates.

Findings

Experimental validation of the diffusio-phoresis mechanism

Quantitative agreement between theory and experiments

Potential for designing stimuli-responsive hydrogels

Abstract

Acid-induced release of stored ions from polyacrylic acid hydrogels (with a free surface fully permeable to the ion and acid flux) was observed to increase the gel osmotic pressure that leads to rapid, temporary swelling faster than the characteristic solvent absorption rate of the gel. Here we develop a continuum poroelastic theory that quantitatively explains the experiments by introducing a "gel diffusio-phoresis" mechanism: Steric repulsion between the gel polymers and released ions can induce a diffusio-osmotic solvent intake counteracted by the diffusio-phoretic expansion of the gel network. For applications ranging from drug delivery to soft robotics, engineering the gel diffusio-phoresis may enable stimuli-responsive hydrogels with amplified strain rates and power output.