Poroviscoelastic Cartilage Properties in the Mouse From Indentation

A method for fitting parameters in a poroviscoelastic (PVE) model of articular cartilage in the mouse is presented. Indentation is performed using two different sized indenters and then these data are fitted using a PVE finite element program and parameter extraction algorithm. Data from a smaller indenter, a $15μm$ diameter flat-ended $60deg$ cone, is first used to fit the viscoelastic (VE) parameters, on the basis that for this tip size the gel diffusion time (approximate time constant of the poroelastic (PE) response) is of the order of $0.1s$⁠, so that the PE response is negligible. These parameters are then used to fit the data from a second $170μm$ diameter flat-ended $60deg$ cone for the PE parameters, using the VE parameters extracted from the data from the $15μm$ tip. Data from tests on five different mouse tibial plateaus are presented and fitted. Parameter variation studies for the larger indenter show that for this case the VE and PE time responses overlap in time, necessitating the use of both models.