Additive manufacturing for orthopedic implants: morphological and material characterization of SLM thin Ti6Al4V samples

Abstract

In the last decades, the orthopedic industry has increasingly adopted Additive Manufacturing (AM) technologies, such as selective laser melting, to produce custom devices. Given their novelty with respect to discrete-size implants, New 2017/745 Medical Device Regulation introduced the need for safety and quality demonstration of such unique devices, a non-trivial task since no defined criteria state how to test them. In this scenario, numerical analyses can be a robust tool for the intended purposes as long as the reliability of the numerical models is verified in terms of geometry reconstruction and material assignment. The latter need has to deal with the peculiarities of AM in the production of lattice structures, distinctive features of this new generation of devices conceived to mimic bone morphology. Indeed, the struts of such structures have diameters of hundreds of microns, which approach AM accuracy limit. If, on the one hand, the issues related to AM production are well-known, on the other hand, it is not yet fully understood how to deal with them if thin struts are manufactured. Given the still questionable research area and starting from the few literature findings, this study aims to provide an exhaustive morphological and material characterization of Ti6Al4V thin struts produced by selective laser melting, supporting experimental activities with numerical analyses. The importance of investigating together their morphology and mechanical behavior will be highlighted: morphological analyses will constitute the first step to assess the quality of the manufactured samples and to correctly interpret the experimental results of static and fatigue tests. In this light, the differences with respect to the mechanical properties of both machined samples and thick AM samples will be outlined. The outcomes of this research will be fundamental for the development of reliable FE models of lattice-based devices.