Head and brain injuries are commonly caused by head impacts in sport and recreational activities. Despite attempts to decrease head impact injury risk through mandated helmet use, mild brain injuries are still prevalent. Brain injury research and helmet assessment methods use surrogate models to acquire representative impact biomechanics. Current standardized mechanical surrogate neck models were developed for non-direct head impact applications and are too stiff in bending to produce realistic head rotations during direct-head impacts. Misrepresentation of head impact response behaviour restricts injury assessment effectiveness. To improve injury assessment capabilities and decrease the risk of mild brain injuries, new mechanical surrogate neck models must offer a more realistic head impact response.

The objective of this study was to refine the design and characterize the head impact response of a novel mechanical neck model. Design refinement methods addressed limitations of an existing mechanical neck prototype (the Phase I neck). Response during head impact experiments characterized the refined prototype (the Phase II neck) to evaluate repeatability, tunability, durability, and biofidelity. The overarching goal was to develop a neck model for use in head impact applications that exhibits humanlike responses.

The Phase II neck replicated the anthropometry of the 50th percentile male neck. The internal structure was composed of alternating rubber and aluminum elements, and three longitudinal steel cables to provide stabilization. Silicone rubber encased the internal structure to approximate viscoelastic tissue. A silicone flange at the base prevented neck hyperextension during head impact experiments. Compression springs were placed along the steel cables to tune head mechanics during head impact experiments.

The study used an instrumented head surrogate fixed to the neck prototype to acquire head mechanics. Head mechanics during head impact experiments at low (2 m/s) and high (6 m/s) impacts speeds, and at three locations (crown, back, and oblique-facemask) characterized the Phase II neck response. Quantified measures of neck response evaluated design refinements against the Phase I prototype, efficacy as a standardized model, and offered insight for future design iterations. The Phase II neck response compared to volunteer data available in literature provided a preliminary evaluation of its ability to produce humanlike head kinematics.

Overall, repeatability of impact mechanics exhibited an average coefficient of variation of 11%, which was an improvement compared to Phase I neck repeatability and satisfied requirements for standardized mechanical surrogates. By using different compression springs, the ability to tune head mechanics was demonstrated for back impacts. The ability to tune head mechanics during back impacts, but not during crown or facemask impacts, was explained by the cable and spring geometry. Minor design changes could produce tunable head mechanics for all impact directions. With the capacity to tune head mechanics, the Phase II neck can achieve a humanlike head impact response. A quantitative long-term repeatability study and a qualitative inspection demonstrated excellent durability compared to the Phase I prototype, as there were consistent response measures and no observed damage. Biofidelity of the Phase II neck was demonstrated by correlating time series head kinematics to those from human volunteer head impact experiments, with resulting CORAplus ratings greater than 0.75 (good curve correlation).

In summary, the Phase II neck was an improved model over the previous prototype regarding inter-test variance, durability, ability to tune head mechanics, and humanlike responses. Results suggest Phase II neck efficacy as a standardized model for use in head impact applications and the capability to replicate humanlike responses. A neck model that is repeatable, durable, and can be tuned to match the human head impact response could improve accuracy in acquiring mechanics associated with mild traumatic brain injuries.