A auxetic metamaterial structure: analysis of shear and bending, mechanical characterization

Purpose The purpose of this study is to investigate the potential of auxetic metamaterials, specifically Re-entrant and Re-entrant Triangular unit cell designs, in enhancing the performance of bone screws used in orthopedic surgeries. By leveraging their negative Poisson's ratio properties, these auxetic designs aim to improve screw-bone interfacial stability, reduce loosening and increase load-bearing capacity under shear and bending stresses. Through high-resolution 3D printing and mechanical testing, the study evaluates the effectiveness of auxetic bone screws compared to conventional designs, with the goal of advancing patient-specific, reliable orthopedic implants that enhance clinical outcomes and reduce long-term healthcare costs. Design/methodology/approach Auxetic bone screws were designed by integrating Re-entrant and Re-entrant Triangular unit cell geometries into the screw body to exploit negative Poisson's ratio behavior. High-resolution 3D printing was employed to fabricate the screws with precise geometrical accuracy, enabling reliable replication of complex auxetic structures. Mechanical performance was evaluated through shear and three-point bending tests, with conventional bone screws serving as controls. Comparative analysis focused on load-bearing capacity, deformation resistance and the influence of auxetic unit cell arrangement. This approach enabled systematic evaluation of auxetic design advantages for improving screw-bone fixation and orthopedic implant reliability. Findings The results demonstrated that auxetic bone screws, particularly those with Re-entrant Triangular unit cells, exhibited superior mechanical performance compared to conventional screws. They showed higher load-bearing capacity, enhanced deformation resistance and improved screw-bone interfacial stability under shear and bending loads. The auxetic structures' lateral expansion during loading increased contact with the surrounding bone, effectively reducing the likelihood of screw loosening. Additionally, the arrangement and geometry of unit cells significantly influenced performance, with optimized designs achieving the best outcomes. Originality/value This study is among the first to apply auxetic metamaterial concepts to bone screw design, offering a novel strategy to overcome the persistent problem of screw loosening in orthopedic implants. By integrating Re-entrant and Re-entrant Triangular auxetic unit cells, the research introduces designs that leverage negative Poisson's ratio behavior to actively improve screw-bone fixation under mechanical loading. The combination of high-resolution 3D printing with experimental mechanical testing provides new insights into how auxetic geometries influence implant stability. This original approach highlights the potential for patient-specific, mechanically superior and sustainable orthopedic implants beyond traditional screw designs.