Design and Validation of a Stiffness-Matched Cervical Spine Surrogate.

Abstract

The purpose of this study was to develop a novel, low-cost, moldable cervical spine surrogate through topology optimization, using a validated human body model as ground truth to guide design and ensure biofidelity during multiplanar loading. The Global Human Body Models Consortium 50th percentile male pedestrian model (GHBMC M50) was used to establish multiplanar behavior by isolating the osteoligamentous cervical spine (OLS). Planar loading simulations in LS-Dyna were conducted to characterize the OLS response. These outputs served as target metrics for topology optimization to generate an anatomically inspired cervical spine surrogate. The optimization aimed to minimize volume fraction while constraining the design within volumetric bounds loosely defined by the GHBMC M50P OLS geometry and enforcing sagittal symmetry. Material properties of a two-part resin selected for fabrication were integrated into the optimization to ensure mechanical fidelity and enable a single-part, single-pour design. The final surrogate was fabricated using a custom two-part mold and tested under flexion, extension, and lateral bending using a six-degree-of-freedom robotic platform replicating the original simulation conditions. Trajectory-matched comparison of the GHBMC-M50 OLS and the novel surrogate yielded 1.5 N-m, 1.3 N-m, 0.1 N-m, and 0.2 N-m differences in moment required to traverse a physiologically relevant range of moment in flexion, extension, and left and right lateral bending respectively. Preliminary validation testing demonstrated that topology optimization enabled the creation of a monolithic, low-cost resin surrogate capable of replicating the biofidelic behavior of the GHBMC-M50P OLS.