Design and fabrication of personalized knee prostheses by laser-based powder bed fusion: Influence of manufacturing process on geometric accuracy

Abstract

The manufacture of metal prostheses by a laser-based powder bed fusion process allows the definition of more effective customized prostheses, increasing the functionality of the operated joint, reducing the risk of implant failure, and increasing the time before revision. For this personalization to be successful, a high accuracy is required when fabricating the prosthesis surfaces. Aiming to understand the performance of this manufacturing process, this article reports the results in terms of geometrical accuracy of a cobalt-chrome alloy knee prosthesis at different process and postprocess conditions. The prosthesis was designed based on experimental data of a real subject. Starting from medical images, a personalized mathematical model of the knee featuring ligament and contact constraints was defined and used to determine the shape of the implant. The process and post-treatment parameters were defined to limit the residual stress of the component after the support removal, in order to minimize geometrical deformations. The optimal process parameters were obtained by experimental tests in combination with a simulation software for the prediction of thermomechanical deformation. The overall manufacturing procedure was validated by comparing the designed and obtained geometry, measured through an optoelectronic system and a laser scanner. Also, the properties of the components in terms of density, hardness, and roughness were verified. The results show that the proposed design procedure is feasible and accurate, reaching an average deviation between the theoretical and obtained surface of −0.02 ± 0.18 mm. The overall procedure also increased the hardness of the prosthesis.