Toward a biofidelic and repeatable physical head-brain model for application in blunt impact
Creators: Li, Yizhao
Publisher: name: University of Alberta Library
Year: 2023

<p>Headforms as a type of physical human head models are widely used in head injury research and for the design and assessment of safety gear. The mechanisms of head injury caused by blunt impact (a common loading scenario) are associated with global head kinematics and intracranial mechanics such as intracranial pressure (ICP). However, conventional headforms are limited to replicating only head kinematics. Although a few headforms have intracranial components to measure ICP including cerebrospinal fluid ICP (CSFP) and intraparenchymal ICP (IPP), such as the Blast Injury Protection Evaluation Device (BIPED) developed for blast scenarios, they lack the validation of biofidelity or cannot be used repeatedly in blunt impact. For modeling human mechanical responses, a headform should be biofidelic to provide realistic responses and repeatable to offer consistent measurements for the same loading conditions. This thesis aimed to characterize the impact responses and refine the design of the BIPED to contribute to the development of a biofidelic and repeatable headform capable of replicating both global head kinematics and ICP in blunt impact. Three studies were performed to achieve this aim. <br>
First, drop impact experiments were conducted to characterize the BIPED kinematic biofidelity and the repeatability of the BIPED linear acceleration and IPP. Results showed that the linear acceleration and IPP measures were repeatable with coefficients of variation (COVs) generally being less than 10%. While the BIPED acceleration peaks had no statistically significant difference with cadaveric data, the acceleration pulse durations were approximately 50% longer. CORrelation and Analysis (CORA) ratings that quantify the closeness between time histories of the headform and cadaver measurements ranged from 0.50 to 0.61 for the BIPED, compared to the range of 0.51–0.77 for the commonly used Hybrid III headform. The performed work quantitatively characterized the BIPED kinematic biofidelity and response repeatability, and the findings can inform the further improvement of the BIPED stiffness toward a biofidelic headform.<br>
The first study could not fully characterize the ICP biofidelity and the response repeatability. Therefore, the second study conducted pendulum impact experiments to further characterize the BIPED ICP biofidelity and the repeatability of BIPED kinematics and ICP. Sensors were added to the BIPED for measuring linear and angular kinematics along three axes and CSFPs at three locations, in addition to the IPP measurements. The head kinematics, CSFP, and IPP demonstrated acceptable repeatability with COVs generally being less than 10%. The BIPED front CSFP peaks and back negative peaks were within the range of the scaled cadaveric data, while side CSFP peaks were 30.9–92.1% greater than the cadaveric data. CORA ratings for the front CSFP (0.68–0.72) aligned with the reported rating (0.7) for good biofidelity. This study indicates that the BIPED could replicate human front CSFP in the frontal blunt impact, but further refinement of the intracranial components is required to improve the biofidelity of ICP at other locations.<br>
Based on the findings from the first two studies, one of the main limitations of the BIPED was its longer acceleration pulse durations compared to cadaveric data. Thus, the third study evaluated the refinement of the surrogate scalp material and thickness to improve the BIPED biofidelity. Drop impact tests were conducted with the BIPED skull and brain assembly attached to scalp pads of varied materials and thicknesses. While the selected materials exhibited a relatively minor effect on the linear acceleration and coup IPP, the scalp thickness showed a major effect. An optimal choice of scalp thickness and material was identified that could increase the acceleration CORA ratings by approximately 30% to approach the threshold of 0.7 for good biofidelity. <br>
In summary, the present thesis characterized the impact responses of the BIPED and improved its acceleration biofidelity to approach good biofidelity. This work is a significant step toward a validated comprehensive headform that can be a valuable tool to extend the depth of head injury research and advance the assessment methods of safety gear.</p>