Evaluating mechanical response from kinetic threats in surrogate tissue materials and bone-tissue boundaries

Developing low-cost, practical human surrogates is essential for understanding the health effects of kinetic threats and improving protective equipment. Accurate characterization of energy propagation through tissue during kinetic events is important for refining surrogate models and experimental methodologies. Most data collection detailing surrogate tissue responses to kinetic threats has been qualitative, with few internal quantitative measurements obtained. To address this, this study evaluated four tissue surrogate materials with embedded pressure sensors and strain gauges. Two surrogate bone materials were used to assess various density-gradient bone-tissue interfaces, with each configuration exposed to low- and high-velocity kinetic stimuli. Inconsistent responses were observed among the trials performed, evidenced by poor agreement across the time-pressure histories. This mainly occurred at shallow depths, where tissue-bone interfaces heavily influence internal pressure dynamics for each material (x‾±33% kPa at 1 cm). However, depth-based effects later become dominant, as tighter intra-material agreement was observed (x‾±17% kPa at 5 cm). The tissue-bone boundaries yielded opposing results between the experimental setups, as low-density bone pairings produced the highest peak pressures during high-velocity testing. In contrast, high-density bone pairings had higher peak pressures throughout low-velocity testing. This was observed in all surrogate tissues except one, where its low shear modulus allowed the projectile to become permanently embedded, resulting in peak pressures with no-bone to be 10.2 kPa higher than with high-density bone. These results demonstrate the need for precise representation of bone-tissue interfaces to describe internal pressure dynamics from kinetic threats.