Spherical indentation testing of poroelastic relaxations in thin hydrogel layers

In this work, we present the Poroelastic Relaxation Indentation (PRI) testing approach for quantifying the mechanical and transport properties of thin layers of poly(ethylene glycol) hydrogels with thicknesses on the order of 200 μm. Specifically, PRI characterizes poroelastic relaxation in hydrogels by indenting the material at fixed depth and measuring the contact area-dependent load relaxation process as a function of time. With the aid of a linear poroelastic theory developed for thin or geometrically confined swollen polymer networks, we demonstrate that PRI can quantify the water diffusion coefficient, shear modulus and average pore size of the hydrogel layer. This approach provides a simple methodology to quantify the material properties of thin swollen polymer networks relevant to transport phenomena.