Mechanical Behavior of Additively Manufactured Graded Auxetic Structure in Hip Implant

In the first part of this study, the mechanical properties of the uniform auxetic unit cell (negative Poisson’s ratio) have been investigated for application in the hip implant. We used auxetic cells to increase the contact surface between implant and bone under tensile loads. The elastic modulus of the uniform auxetic structure have been obtained by numerical, analytical and experimental methods in y direction. Comparing the elastic modulus in y direction of the analytical and numerical simulation with experimental tests showed there are a good agreement between the results. In the second part, the gradient structure has been used in order to reduce the stress shielding on the contact surface of the bone and implant, increase the efficiency of implant replacement and reduce infection. In the gradient structure, the elastic modulus in the contact surfaces is considered close to the elastic modulus of the bone, and gradually increases in the next layers. The elastic modulus of the gradient structure was calculated by two numerical and analytical methods. In the numerical method, the elastic modulus was obtained from Abaqus software and coding on MATLAB. The difference of the elastic modulus in these two methods was 4.8%, which shows that there is an acceptable agreement between the results.