Towards a reliable characterisation of the mechanical behaviour of brain tissue: The effects of post-mortem time and sample preparation.

Since the early seventies, the material properties of brain tissue have been studied using a variety of testing techniques. However, data reported in literature show large discrepancies even in the linear viscoelastic regime. In the current study, the effect of the sample preparation procedure and of post-mortem time on the mechanical response of porcine brain tissue is examined. Samples from the thalamus region were prepared with different techniques and were tested for different loading histories. Each sample was tested in oscillatory shear tests (1% strain amplitude, 1-10 Hz frequencies) followed by sequences of 5% strain loading-unloading cycles. The stress response to the loading-unloading cycles showed a clear dependency on post-mortem time, becoming more stiff with increasing time. This dependency was affected by the mechanical history induced by the preparation procedure.