Investigating patterned hydrogel matrix instabilities during swelling

The flexible, cross-linked nature of hydrogels affords tunable water sorption, a trait crucial in designing drug delivery systems and other dynamic soft matter systems. The imbibement or uptake of water into a hydrogel usually leads to uniform swelling, however when hydrogel materials are macroscopically patterned with distinct domains of different cross-link density, the stresses induced by swelling can lead to rupture and failure events. Our ongoing work reveals that if this rupture can be delayed or avoided by material design, such as tuning cross-link density gradient across the domain interface, unique surface features during swelling arise that ultimately change interfacial behavior. These features represent complex surface instabilities that arise from a material that does not achieve an equilibrium swelling state.  In this work, we present new methods of investigating these instabilities to better understand dynamic rupture and failure. This includes experimental approaches to estimate the compressive stress that causes surface buckling and the osmotic force associated with swelling of patterned domains. We discuss how understanding these dynamic processes will allow for more fine-tuned engineering of dynamic soft material systems and can inform material design.