When calculating the modified Head Impact Criteria (mHIC) (eq. 1, main text), the magnitude and duration of the acceleration between the time the falling ball first contacts the sample and the time when the sample rebounds to its initial position was considered. Analysis of the impact images shows that when the sample returns to its initial height the ball stops contacting the sample and is ejected. At the same time, the acceleration is equal to zero. This occurs between approximately 10 and 12 ms in experiments. Compared to the resin containing only 0.5% crosslinker (100% spacer monomer), the resin with sticker has a shorter gelation time and a higher modulus.