Comparison of innovated thermoplastic polyurethane and commercial helmet lining technology in mitigating concussions as measured by linear accelerations and risk of head injury during simulated horizontal impacts to the head

Abstract

Advances in helmet designs and technology have not completely eliminated the incidence of mild traumatic brain injuries (mTBI) in the sport of ice hockey. One issue that concerns researchers is that the vinyl nitrile (VN) and expanded polypropylenes (EPP) materials used to manufacture hockey helmets have remained the same since the implementation of mandatory helmets in the 1970s, due to the cost and capability of these materials to meet the aesthetic demands of the public. One potential avenue to address this concern is to use new thermoplastic polyurethane (TPU) lining materials in existing helmet shells to better mitigate impact forces while maintaining the aesthetic structure of the helmet. The TPU material has the desirable qualities of being tough, meaning that it is resistant to tearing. The TPU material also has highly elastic properties meaning that it can deform to absorb energy and quickly return to its original shape. Hence, the first purpose of this study was to compare the capability of the 3D printed TPU lining inserts to absorb energy during static loading to commercially available liners made from VN and EPP. The second purpose of this study was to determine the effectiveness of 3D printed TPU liners in reducing linear acceleration and risk of head injury from a simulated impact when compared to traditional liner materials during dynamic testing. The results from the static testing using a Chatillon TCD1100 Force Tester, indicated that the TPU liner absorbed 38.6% of the loading energy, which fell between the EPP (41.8%) and VN (15.8%) indicating that it performs approximately as well as, commercially available liners. The results from the simulated dynamic impacts to the head at five different locations, as defined by the NOCSAE protocol, revealed a significant interaction effect between impact location and liner type on measures of linear acceleration and risk of head injury. When examining the interaction effect, the results indicated that the EPP liner performed the best at the front and front boss locations, while the TPU liner performed the best at the side, rear boss, and rear locations. The primary implication of these results is that a hockey helmet lining material with multilayer characteristics composed of TPU and EPP structures would better mitigate impact forces from all locations to minimize the risk of concussions.