The influence of the manufacturing process conditions on the in-vitro bio-performance of Titanium alloys

The prolonged hospitalization due to the premature failure of the implant is one of the key aspect to be addressed by the new category of prosthetic devices, which must ensure a perfect fit with the surrounding bones and a good and fast healing process. Such strict requirements can be satisfied by processing Titanium (Ti) alloys using innovative manufacturing processes, like the SuperPlastic Forming (SPF) and the Single Point Incremental Forming (SPIF). Nevertheless, even if the biocompatibility of the Ti alloys is quite well assessed, the manufacturing conditions might affect the final characteristics of the implant. In fact, the adoption of lubricants used to reduce friction between the blank and the rotating tool (SPIF) or the graphite-based sprays to avoid sticking between the blank and the tools (SPF) should change into cytotoxic the produced prosthesis. In addition, the adoption of working temperatures higher than the room one, especially in the case of the SPF, represents a possible critical aspect due to the high reactivity of Ti alloys. In this work, some results of the Proof-of-Concept (P.o.C.) project FORMAE-BIO are presented. In particular, the biocompatibility and cytotoxicity performance of prosthetic devices produced via SPF and SPIF were investigated: a benchmark geometry (truncated pyramid) was manufactured via both the abovementioned processes, so that square samples could be extracted from specific regions of interest and subjected to in-vitro tests: results, gathered from different time points, showed that if the surfaces are not properly cleaned after the manufacturing, residuals of lubricants may gradually be released making the material cytotoxic or, alternatively, remaining adherent to the surface and hindering the cells' viability.