Yuhang Hu1 Yang Lai1

1, University of Illinois at Urbana Champaign, Urbana, Illinois, United States

Gel is composed of cross-linked polymer network and solvent molecules. Gels have broad application in many engineering fields such as drug delivery, tissue scaffold, soft robots and so on. Mechanical characterization of soft gels has been challenging. Recently there is a growing interest in using indentation techniques on gels because of the practical easiness. While relaxation indentation has been developed in characterizing the poroelastic properties of gels, dynamic indentation has been found to provide more accurate measurements in small scale, in which the gel is under oscillatory loading. In this study, we use the characteristic phase lag between the applied indentation displacement and the force on the indenter due to the energy dissipation from solvent flow in the gel to characterize the poroelasticity of gels. We will show that the phase lag degree is a function of two parameters, Poisson’s ratio and normalized angular frequency. The solutions are derived for several shapes of indenters. The maximum value of the phase lag over a spectrum of actuation frequencies can be used to characterize the Poisson’s ratio of the gel, and the characteristic frequency corresponding to the maximum phase lag can be used to characterize its diffusivity.