Towards Preliminary Surrogates To Biomechanically Model The Human Calvarium
Creators: Adanty, Kevin
Publisher: name: University of Alberta Library
Year: 2023

<p>Surrogate headforms are employed in injury biomechanics to reconstruct head impact scenarios and evaluate protective equipment. The development of human calvarium surrogates to mimic mechanical response at fracture would be an essential step forward in improving the biomechanical biofidelity of surrogate headforms. In order to develop and validate potential surrogates, it is important to gain knowledge of the physical properties and mechanical response of the calvarium. Therefore, the purpose of this dissertation was to determine the morphometry, geometry, and mechanical response of the human calvarium to guide the development of preliminary surrogate models of the calvarium with the intent to mimic mechanical response at fracture. To gain an appreciation for this body of work, it is important to accentuate the critical objectives concerning the characterization of morphometry, geometry, and the mechanical response of the human calvarium that were necessary to acquire before fabricating and evaluating the surrogate models. <br>
Human calvarium specimens of beam geometry were extracted from male and female donors in the frontal and parietal regions of the calvarium. The specimens were micro-computed tomography (CT) scanned followed by computer-based imaging analyses to quantify morphometric and geometrical properties. Statistically significant morphological distinctions at the levels of sex, location, and layers of the calvarium were established. Geometrical properties such as thickness, cortical and diploë layer thickness, and radius of curvature were also determined to physically construct the surrogates. The specimens were then mechanically characterized under 4-point quasi-static and dynamic impact bending to quantify their mechanical response. In quasi-static loading, it was found that the trabecular bone pattern factor of the diploë was a significant predictor of force and bending moment at fracture. The inner cortical layer had the greatest number of morphometric and geometric properties that were significant predictors of mechanical response including thickness, tissue mineral density, and porosity. In dynamic impact loading, it was found that the mechanical response between male and female calvaria was not significantly different. Overall, the average mechanical responses of the calvaria from both loading tests were required to evaluate how well they compared to the surrogate models.<br><br>
Three surrogate prototypes were constructed using readily available and cost-effective materials, specifically epoxy and chalk. The average geometry of the prototypes including thickness and radius of curvature was consistent with the beamed-shaped calvaria. The prototypes were tested under 4-point quasi-static and dynamic impact bending. The prototypes exhibited the most significant differences in mechanical response to calvaria under quasi-static loading compared to dynamic impact lading. In dynamic impact loading, where the loading and strain rate conditions are most relevant to real-world head impacts, it was determined that an epoxy-chalk layered surrogate was the best prototype for further development because its force at fracture, bending moment at fracture, tensile strain at fracture, tensile and compressive stress at fracture, tensile effective bending modulus, and tensile strain rate was not significantly different to calvaria. <br>
    The morphometry, geometry, and mechanical response of the human calvarium were characterized to guide the construction and evaluation of surrogate models of the calvarium using readily available and cost-effective materials. This dissertation may be a first step towards the development of a full-size surrogate model of the calvarium that may be employed to mimic fracture response when reconstructing head impact events and testing countermeasure equipment.</p>