Finite element modeling of the surrogate brain

Two-dimensional finite element models of the miniature pig brain were developed and used for the analysis of impulsive mechanical conditions thought to produce certain forms of brain injury. Existing brain injury experiments, conducted on the miniature pig, were analyzed using these models in an attempt to relate mechanical response to observed diffuse axonal injury (Gennarelli et Thibault, 1982; Margulies, 1990, and Meaney, 1993). An existing measure, referred to as the Cumulative Strain Damage Measure (CSDM), developed by Bandak (1995), was used to link the mechanical and injury responses of the brain to an external loading regime that is related to loadings typical of motor vehicle crash environments. The finite element models were sufficiently detailed to provisionally capture as realistic of a strain state as possible even disregarding the inherent anisotropies and inhomogeneities of the brain material. The first model (Model I) is a two-dimensional finite element plane strain representation of a physical model used in head loading experiments (Margulies, 1989) to explore the levels of loading that may be required to induce injury in the real pig brain. The physical model of the pig brain consisted of a silicone gel material, that crudely represents the real pig brain material, poured in a mid-coronally sliced skull of the pig brain to make a half-head model. The second model (Model II) is a two-dimensional plane strain finite element representation of a mid-coronal slice in the real pig brain. The material descriptions used in both models were obtained from the open literature. Material properties for Model II were approximated from those available for the human brain since no other reliable data is available. The work demonstrated the feasibility of new and innovative modeling techniques that provide approximations to essential mechanical behavior thought to be responsible for certain injury responses of the brain. These techniques are directly applicable to the development of advanced three dimensional models of the brain that can more accurately represent its response to mechanical loading.