where 𝑡 1 =0 sec, 𝑡 2 is the time when the ball leaves the 3D structure (~10 ms), and 𝑎(𝑡) is the measured acceleration over time, as illustrated in Figure . The mHIC is normalized to the impact on the brain-like gel without any protection and the result, presented as a percentage, represents the relative reduction in severity of the impact the different protection structures provide. The bulk 0.5% crosslinker elastomer alone reduces the mHIC from 100% to (42.1±10.9)%, the magnitude of peak deceleration decreases from 68.5±8.5 g to 52.9±7.6 g, and the maximum voltage decreases from 0.73±0.35 V to 0.46±0.09 V (Figure and Table ). Note that we use voltage to characterize the relative change of the force during impact tests because piezoelectric sensors cannot reliably measure static force (see Materials and Methods). These results show that the inherent softness of the bulk elastomer helps reduce the severity of the impact.