Creasing of hydrogels under compression: Harnessing an elastic instability to create active surfaces


Jungwook Kim1, Veronica Trujillo1, Anesia Burns1, and Ryan C. Hayward, rhayward@mail.pse.umass.edu2. (1) Polymer Science & Engineering, University of Massachusetts, Amherst, 120 Governors Drive, Amherst, MA 01003, (2) Department of Polymer Science and Engineering, University of Massachusetts, Conte Research Center, 120 Governors Drive, Amherst, MA 01003
Coating a substrate with a thin hydrogel layer provides a convenient means to tune properties such as biocompatibility, adhesion, and tribology. However, upon hydration of the gel, the constraint imposed by the substrate can generate large in-plane compressive stresses, in some cases leading to a creasing instability of the gel surface. While this instability has been known in practice for well over a century, it remains poorly understood. Using model polyacrylamide hydrogel systems, we have studied the onset of creasing as a function of material properties and gel thickness, and addressed basic questions regarding crease morphologies and growth mechanisms. Using the understanding gained from these studies, we are developing this instability as a route to create active surfaces, where we can exercise control over surface topography and chemical patterns in both space and time.