Significance of strain rate-dependence in modelling of organic materials

This paper explores the significance of the inherent strain rate-dependence of many biological materials. Such characteristics are pertinent to computational modelling of these materials for the purposes of surgical robotics and simulation. A pair of 2-dimensional finite element models of the human brain/ventricle system are developed and used to analyse the brain structural disease, hydrocephalus. The models are geometrically identical, and both incorporate a linear biphasic material model for the brain parenchyma. Model 1 is assigned a Young modulus value, E₀ = 3156 Pa, based on the instantaneous elastic response derived from a hyperviscoelastic model. Model 2 accounts for the extremely slow loading characteristic of the disease and a revised modulus value of E_∞ = 584.4 Pa is assigned. This significant variation in stiffness generates similar differences in the simulation results. The conclusion is that consideration of the intrinsic strain rate-dependence of organic materials is vital to the satisfactory modelling of such materials, and hence significant to surgical robot performance.