A New Assessment of Bicycle Helmets: The Brain Injury Mitigation Effects of New Technologies in Oblique Impacts

Abstract

New helmet technologies have been developed to improve the mitigation of traumatic brain injury (TBI) in bicycle accidents. However, their effectiveness under oblique impacts, which produce more strains in the brain in comparison with vertical impacts adopted by helmet standards, is still unclear. Here we used a new method to assess the brain injury prevention effects of 27 bicycle helmets in oblique impacts, including helmets fitted with a friction-reducing layer (MIPS), a shearing pad (SPIN), a wavy cellular liner (WaveCel), an airbag helmet (Hövding) and a number of conventional helmets. We tested whether helmets fitted with the new technologies can provide better brain protection than conventional helmets. Each helmeted headform was dropped onto a 45° inclined anvil at 6.3 m/s at three locations, with each impact location producing a dominant head rotation about one anatomical axes of the head. A detailed computational model of TBI was used to determine strain distribution across the brain and in key anatomical regions, the corpus callosum and sulci. Our results show that, in comparison with conventional helmets, the majority of helmets incorporating new technologies significantly reduced peak rotational acceleration and velocity and maximal strain in corpus callosum and sulci. Only one helmet with MIPS significantly increased strain in the corpus collosum. The helmets fitted with MIPS and WaveCel were more effective in reducing strain in impacts producing sagittal rotations and a helmet fitted with SPIN in coronal rotations. The airbag helmet was effective in reducing brain strain in all impacts, however, peak rotational velocity and brain strain heavily depended on the analysis time. These results suggest that incorporating different impact locations in future oblique impact test methods and designing helmet technologies for the mitigation of head rotation in different planes are key to reducing brain injuries in bicycle accidents.

An Overview of the Effectiveness of Bicycle Helmet Designs in Impact Testing

“…The H€ ovding protective gear had a lower PLA, PRA, and GAMBIT as compared to the other helmets. The reasons for this performance stem from the helmet's large size and low stiffness (Kurt et al, 2017;Abayazid et al, 2021). Such properties result in an increased duration of the impact and significantly lower peak acceleration values (Kurt et al, 2017;Abayazid et al, 2021).…”

“…The reasons for this performance stem from the helmet's large size and low stiffness (Kurt et al, 2017;Abayazid et al, 2021). Such properties result in an increased duration of the impact and significantly lower peak acceleration values (Kurt et al, 2017;Abayazid et al, 2021). Despite the substantial mitigation of PLA and PRA, it should be noted that the prolonged duration of the impact could potentially result in a high PRV, which could carry increased injury risks (Ommaya and Hirsch, 1971;Margulies and Thibault, 1992;Rowson et al, 2012;Hernandez et al, 2015a;Abayazid et al, 2021).…”

“…Such properties result in an increased duration of the impact and significantly lower peak acceleration values (Kurt et al, 2017;Abayazid et al, 2021). Despite the substantial mitigation of PLA and PRA, it should be noted that the prolonged duration of the impact could potentially result in a high PRV, which could carry increased injury risks (Ommaya and Hirsch, 1971;Margulies and Thibault, 1992;Rowson et al, 2012;Hernandez et al, 2015a;Abayazid et al, 2021). Additionally, the H€ ovding's large size and its increased duration of the impact, could mean increased coupling of the neck and shoulder during real-life impacts (Abayazid et al, 2021).…”

“…SPIN is a technology that replaces comfort padding with silicone padding (Bottlang et al, 2020). These specially developed pads are placed in critical locations in the helmet under the EPS layer and can shear in any direction to produce the same effect as a moving slip liner (Bliven et al, 2019;Abayazid et al, 2021). ODS utilizes two EPS liners that are connected by an array of elastomeric dampers (Bottlang et al, 2020).…”

“…The collapsible structure mitigation systems we considered in this paper are WaveCel and Koroyd technologies. WaveCel is made from a cellular copolymer material that flexes and glides to absorb energy from impacts and redirect energy away from the head (Bliven et al, 2019;Abayazid et al, 2021). The V-shaped collapsible cellular structure is recessed within the helmet liners and provides rotational suspension (Bliven et al, 2019).…”