Gel rupture and surface instabilities during dynamic swelling

Hydrogels have had a profound impact in the fields of tissue engineering, drug delivery, and materials science. Due to the network architecture and hydrophilic character of these materials, imbibement with water often results in uniform swelling and isotropic expansion which scales with the degree of cross-linking. However, the development of internal stresses during swelling can have dramatic consequences including transient surface instabilities as well as rupture or failure events. Historically, imbibement with water has been probed by characterizing hydrogels in two distinct states: (1) unswollen, or (2) in an equilibrium swelling state. However, to fully characterize and leverage these instabilities and rupture events, this dynamic process must be investigated directly. To address this gap, our ongoing work focuses on rupture events in poly(ethylene glycol)-based networks that occur in response to swelling with water. In homogeneous samples, we find that rupture events follow a three-stage process that can be described based on changes in the material properties during swelling. We also highlight unique failure events that occur in macroscopically patterned hydrogels, where distinct variations in network rigidity are engineered. With these patterned samples, complex surface instabilities arise during swelling, and we discuss how this dynamic behavior can be leveraged to improve surface and bulk material performance.