Enhancing auxetic gradient structures for hip joint implants to optimize stress shielding reduction

Abstract This study investigates the design and optimization of a porous hip implant to mitigate stress shielding. Initially, the focus was on determining the elastic modulus of a three-dimensional auxetic structure, primarily in the y-direction. Various methods—numerical, analytical, and experimental—were used to assess the elastic properties. Additive manufacturing was employed to create samples, which were then tested for their elastic properties through compression testing. The results revealed a strong correlation between the elastic modulus values obtained from simulations and experimental tests in the y-direction. To further enhance the implant’s performance and reduce stress shielding at the implant-bone interface, a gradient structure was introduced. This gradient design progressively increases the elastic modulus away from the bone contact surfaces, aligning closely with the bone’s modulus at the interface. The elastic modulus of this gradient structure was computed using Abaqus software and validated through analytical methods in MATLAB, with a minimal 4.8% difference between the two approaches, demonstrating high agreement. The application of a genetic algorithm enabled the creation of a porous hip implant tailored to minimize stress shielding throughout its structure. This innovative approach, integrating numerical, analytical, and experimental techniques with gradient structures, holds promise for improving hip implant performance and enhancing patient outcomes by reducing stress-shielding complications.