Development and Validation of Mechanically Matched Skeletal Surrogates Through Simulation and Image Based Structural Optimization

Abstract

Mechanical surrogates for biomechanical testing have been crucial to the understanding of human injury mechanisms, risk mitigation, and biomedical device performance. Surrogates representing singular bones have been applied to understand fracture and long-term device behavior, while larger skeletal systems integrated into anthropometric test devices (ATDs) are used to understand human response to impact traumatic loading scenarios. However, a surrogate is only as useful as its biofidelity allows. Fabrication materials for these devices often pose a critical challenge between cost and biofidelic performance. Bone is a complex and structurally unique material with mechanical properties that no current manufacturing material can fully replicate. Structural optimization offers a potential solution by allowing for the manipulation of design geometry to create devices with programmable mechanical properties. Each study encompassed in this work explores the application of structural optimization in a unique scenario to create highly biofidelic mechanical surrogates for human skeletal structures. The first two studies aim to optimize the external geometry of two individual skeletal systems: (1) the cervical spine, and (2) the ribcage. Simulations of relevant loading patterns on the Global Human Body Models Consortium 50th percentile male pedestrian model were used to drive design response constraints of the optimizations before computational validation, prototype fabrication, and experimental validation occurred. In the final study, a pre-existing computational tool for optimizing the internal geometry of skeletal microstructures was evaluated to identify areas of improvement for translation to experimental use. The novel methodologies and devices described herein will lead to an improved understanding of bone mechanical behavior and enhanced safety engineering procedures for evaluating military personal protective equipment under explosive conditions.