Cracking and self-healing in soft, shrinkable hydrogel packings

We aim to better understand cracking in granular, shrinkable packings. Such packings are relevant to agriculture and CO₂ sequestration; they also have potential uses in non-fouling films, biosensors, cosmetics, and drug delivery platforms. We use hydrogel particle packings as a model system and experimentally observed how these packings dry, shrink, and crack at an individual-particle level. Most remarkably, we observed a behavior where cracks can form but eventually self-heal. Furthermore, using discrete-element simulations that we developed, we found the precise range of individual-particle shrinkabilities, capillary forces, and contact forces needed to produce this self-healing behavior. Our results inform ways to control crack evolution, which could ultimately pave the way to engineering crack behavior for a wide variety of applications.