The high strain-rate behaviour of selected tissue analogues.

The high strain-rate response of four readily available tissue simulants has been investigated via plate-impact experiments. Comparison of the shock response of gelatin, ballistic soap (both sub-dermal tissue simulants), lard (adipose layers) and Sylgard(®) (a potential brain simulant) allowed interrogation of the applicability of such monolithic tissue surrogates in the ballistic regime. The gelatin and lard exhibited classic linear Hugoniot equations-of-state in the US-uP plane; while for the ballistic soap and Sylgard(®) a polymer-like non-linear response was observed. In the P/σX-v/v0 plane there was evidence of separation of the simulant materials into distinct groups, suggesting that a single tissue simulant is inadequate to ensure a high-fidelity description of the high strain-rate response of complex mammalian tissue. Gelatin appeared to behave broadly hydrodynamically, while soap, lard and Sylgard(®) were observed to strengthen in a material-dependent manner under specific loading conditions at elevated shock loading pressures/stresses. This strengthening behaviour was tentatively attributed to a further polymeric-like response in the form of a re-arrangement of the molecular chains under loading (a steric effect). In addition, investigation of lateral stress data from the literature showed evidence of operation of a material-independent strengthening mechanism when these materials were stressed above 2.5-3.0GPa, tentatively linked to the generically polymeric-like underlying microstructure of the simulants under consideration.