Investigating the potential of auxetic structures in tibial insert toward multi-range load-carrying knee implant

The artificial tibial insert degrades within the human body over service time as a metallic femoral surface continues articulating against it. The degradation rate depends on gait patterns and mainly on the human body weight, as tibial inserts normally lack subject-specific customisation. This article investigates the feasibility of gyroid, square anti-chiral, and triangular auxetic structures for tibial insert applications. The mechanical performance of new tibial designs is compared against a conventional (bulk) tibial insert through computational and experimental studies. The preliminary stress-strain and deformation behaviours are studied with ANSYS Workbench. Whereas the Instron machine is used for experimental studies to test the 3D printed conventional and auxetic structure-based tibial inserts designed in this work. The experimental studies are performed under a wide range of quasi-static and cyclic loading conditions to understand their mechanistic performance and suitability for knee joint functionality. Among gyroid, square anti-chiral and triangular auxetic structures, the triangular design has demonstrated exceptional load-bearing capabilities up to 20 kN, an adequate deflection up to 2.3 mm, along with 34.8% reduction in component weight. The enhanced elastic recovery supported by auxetic structures can provide knee safety under impact loads. In addition, it is perceived that the auxetic structures-based tibial insert provides tunable effective stiffness, demonstrating the significance of auxetic lattice design and their suitability for a wider range of body weights to ensure mechanical stability, medical safety, and implant longevity.