A new design of 3D-printed orthopedic bone plates with auxetic structures to mitigate stress shielding and improve intra-operative bending

Abstract

Orthopedic bone plates are most commonly used for bone fracture fixation for more than 100 years. The bone plate design had evolved over time overcoming many challenges such as insufficient strength and excessive plate–bone contact affecting the blood circulation. However, it is only made of two materials, either stainless steel (AISI 316L) or titanium (Ti–6Al–4V). There are two main limitations of metallic bone implants, namely stress shielding and the problem of malocclusion caused by the displacement of the fracture site during healing. To overcome the two problems, a new bone plate design with the incorporation of auxetic structures is proposed in this work. This study aims to use auxetic structure section in the bone plate that would decrease the stiffness of the region, thereby mitigating the stress-shielding effect and at the same time act as a deformable section to enable intra-operative bending for effective alignment while having enough bending strength and stiffness. Two different auxetic structures namely re-entrant honeycomb and missing rib structures were considered. The auxetic structure incorporated bone plates were designed, finite element analysis was done, fabricated using direct metal laser sintering technique, and tested. The results indicate that the re-entrant honeycomb structure incorporated bone plates serve as an effective bone design compared to the conventional bone plate design, in terms of stress shielding and intra-operative bending while offering similar mechanical and bending strength.