Engineering Location and Shape on Stiffness-Matched Niti Mandibular Graft Fixation Plates

Graft fixation plates that ensure stability at the osteotomy site during healing are essential for skeletal reconstruction surgery aimed at repairing bone segmental defects caused by trauma or illness. However, in cases where graft fixation plate failure is common (e.g., large mandibular segmental defects), we hypothesize that a fixation method yielding an osteotomy site loading pattern that does not disrupt the normal loading of the healed bone will lead to reduced hardware and bone failures, thus minimizing the need for re-operation. The superelastic properties of nickel-titanium (NiTi) may facilitate better engagement of the entire fixation device compared to the current standard material, Ti6Al4V. Allowing the device to deform more during loading decreases the stiffness of the entire healing area, which helps prevent stress concentrations that could result in failure of the reconstructed device. In this study, we employ 4-point bending tests to evaluate the overall engagement (ductility) of straight NiTi plates based on varying pore geometries per the ASTM F382 standard. Results from 3D-printed, unbent NiTi mandibular fixation plates reveal no significant differences between the different pore geometries (i.e., orthogonal struts versus gyroid struts, both with 300 μm diameter and 300 μm pore size) under single-cycle failure testing. All pore geometries studied displayed an apparent elastic modulus ⟨E⟩ = 23.75 ± 3.33 GPa. While our aim in stiffness matching is regional, it is also beneficial for the plate to match the elasticity of cortical bone (E = 10-30 GPa), as this promotes engagement across the entire plate and the overall healing region. Tailoring the location and shape of the plate is also anticipated to aid in healing, subsequently restoring the normal stress-strain path in the bone post-healing. Current efforts are examining the relative risk of fatigue failure due to cyclic loading conditions in straight, 3D-printed NiTi mandibular fixation plates featuring the same two pore geometries.
 
Presentation Stage: Optimization — Maximizing Performance and Efficiency