Proof-of-Concept of an Adaptable Mechanical Metamaterial for Ice Hockey Helmet Liners

Ice hockey has one of the highest concussion rates in sports. A challenge in preventing concussions and developing helmets is the range of common head impacts. Currently, helmets provide increased protection during falls on the ice – what they are tested for in certification standards – but not during collisions between players that cause ~90% of concussions. Current helmet liners possess high stiffness to efficiently absorb impact energy during falls causing them to only partially compress during collisions. Hence, energy absorption is limited, leaving wearers susceptible to concussions. Reducing liner stiffness is not feasible, because protection during more severe impacts could be compromised. A helmet that can adapt its response to the occurring impact situation may enhance provided protection. A proof-of-concept study, to assess a mechanical metamaterial’s feasibility as an adaptive helmet liner, was undertaken. Compression tests of unit cells and cellular structures of the material at different strain rates (0.83, 8.3, and 83 s−1) suggest ~2.5-fold increased forces during compression and altered shapes of force vs. displacement traces. Such a switch in stiffness could facilitate helmet developments that maintain high protection levels during severe impacts while enhancing protection during impacts with more compliant bodies.