Additive manufactured porous biomaterials targeting orthopedic implants: a suitable combination of mechanical, physical and topological properties

Abstract

Orthopedic implants are under incessant advancement to improve their interactions with surrounding bone tissue aiming to ensure successful outcomes for patients. A successful biological interaction between implant and surrounding bone depends on the combination of mechanical, physical and topological properties. Hence, Ti6Al4V cellular structures appear as very promising solutions towards the improvement of conventional orthopedic implants. This work addresses a set of fundamental tools that allow improving the design of Ti6Al4V cellular structures produced by Selective Laser Melting (SLM). Three-point bending tests were carried out to estimate the elastic modulus of the produced structures. Morphological analysis allowed to evaluate the dimensional differences that were noticed between the model CAD and the SLM structures. Finite element models (adjusted CAD) were constructed with the experimentally obtained dimensions to replicate the mechanical response of the SLM structures. Linear correlations were systematically found for the dimensions of the SLM structures as a function of the designed model CAD dimensions. This has also been observed for the measured porosities as a function of the designed CAD models. This data can be used in further FE analyses as design guidelines to help engineers fabricating near-net-shape SLM Ti6Al4V cellular structures. Besides, polished and sandblasted surface treatments performed on the Ti6Al4V cellular structures allowed to obtain suitable properties regarding roughness and wettability when compared to as-produced surfaces. The capillarity tests showed that all the analyzed Ti6Al4V structures are able to transport fluid along its structure. The cell viability tests demonstrate Ti6Al4V cellular structures SLM produced did not release toxic substances to the medium, indicating that these structures can assure a suitable environment for cells to proliferate and attach. This study proposes a design methodology for Ti6Al4V cellular structures, that owe suitable mechanical properties but also provide a proper combination of porosity, roughness, wettability, capillarity and cell viability, all of them relevant for orthopedic applications. A Ti6Al4V cellular structured hip implant prototype gathering the suitable features addressed in this study was successfully SLM-produced.