Influence of Different Post-printing Treatments on the In-Vitro Bio-Compatibility of Three-dimensional Generated Titanium Plates

Aim: Patient-individual bone plates from titanium alloy (TiAl4V ELI) can be generated by 3D printing. Directly after printing, the samples have a very rough surface requiring further processing. The aim of the present study was to analyse the effect of different grinding and polishing procedures on sample surface and in vitro biocompatibility to make sure that the clinically approved material properties of the titanium alloy were not compromised by these treatments.
Materials and Method: Initial average surface roughness of 3D printed titanium discs (Ti6Al4V ELI) (d=5mm or 10 mm, h=2 mm), produced by selective laser melting (SLM; Ra=22.7 µm), was reduced by sandblasting followed by barrel finishing, electro-polishing, or plasma-polishing and was then evaluated using tactile surface quality measurement (DIN ISO EN 4288). Biocompatibility of the different sample groups (n=6-9 each) was assessed by quantification of metal-ion release, indirect cell viability and cytotoxicity tests as well as direct cell adhesion, analysed by fluorescence and scanning electron microscopy (SEM). Mouse fibroblasts (L929), osteosarcoma cells (Saos-2), human primary gingival fibroblast as well as human gingival epithelial cells were used in this study, respectively. Statistical evaluation was performed with the Kruskal Wallis test, followed by a posthoc Dunn's test to perform multiple comparisons.
Results: All tested treatments were suitable to obtain surface roughness values within the effective roughness spectrum (Ra 0.2 2 µm). Sandblasted, barrel finished, and electro-polished samples showed high cell viability in indirect tests, as well as good cell adhesion and proliferation when seeded directly with cells. In contrast, plasma-polished samples showed significantly reduced cell viability in indirect tests and very low attached cell numbers after direct colonization, probably caused by the high amount of vanadium ions, which could be found in the cell culture medium after metal-ion release from the plasma-polished samples.
Conclusions: Bone plates from titanium alloy generated by 3D printing are suitable for clinical use and are in line with the requirements for medical devices according to ISO 10993-5. However, relating to metal-ion release, post-printing treatment must be taken into consideration, critically.