Swelling-induced pattern transformations of periodic hydrogels -- from the wrinkling of internal surfaces to the buckling of thin films

TL;DR

This paper explores how swelling causes pattern transformations in periodic hydrogels, including wrinkling and buckling, and introduces new design possibilities for complex surface modes and internal surface micro-creases.

Contribution

It provides a comprehensive analysis of swelling-induced pattern transformations in various hydrogel structures, including novel internal surface wrinkling and micro-crease phenomena.

Findings

Single-phase structures match experimental results

Two-phase structures exhibit new wrinkling patterns

Reinforced hydrogels enable complex out-of-plane modes

Abstract

We investigate pattern transformations of periodic hydrogel systems that are triggered by swelling-induced structural instabilities. The types of microstructures considered in the present work include single-phase and two-phase voided hydrogel structures as well as reinforced hydrogel thin films. While the observed transformations of the single-phase structures show good agreement with experimental findings, the two-phase materials provide novel patterns associated with wrinkling of internal surfaces. Furthermore, an extensive parametric study on the reinforced hydrogel thin films reveals new opportunities for the design of complex out-of-plane surface modes caused by swelling-induced instabilities. Next to the mentioned buckling-type instabilities, we encountered the development of micro-creases at the internal surfaces of periodic media before the loss of strong ellipticity of effective moduli.