Tuning the response of fluid filled hydrogel core–shell structures

Abstract

Hydrogels are hydrophilic polymer networks that swell upon submersion in water. Thanks to their bio-compatibility, compliance, and ability to undergo large deformations, hydrogels can be used in a wide variety of applications such as in situ sensors for measuring cell-generated forces and drug delivery vehicles. In this work we investigate the equilibrium mechanical responses that can be achieved with hydrogel-based shells filled with a liquid core. Two types of gel shell geometries are considered - a cylinder and a spherical shell. Each shell is filled with either water or oil and subjected to compressive loading. We illustrate the influence of the shell geometry and the core composition on the mechanical response of the structure. We find that all core–shell structures stiffen under increasing compressive loading due to the load-induced expulsion of water molecules from the hydrogel shell. Furthermore, we show that cylindrical core–shell configurations are stiffer then their spherical equivalents. Interestingly, we demonstrate that the compression of a core–shell structure with an aqueous core leads to the transportation of water molecules from the core into the hydrogel. These results will guide the design of novel core–shell structures with tunable properties and mechanical responses.