Plasma-electrolytic oxidation: A rapid single step post processing approach for additively manufactured biomedical implants

Laser-powder bed fusion (PBF-LB) has enabled production of customised skeletal implants that incorporate porous lattices structures to enable bone ingrowth. However, the inherent surface roughness of PBF-LB, characterised by partially adhered particles and undulating sub-topography, remains a barrier to adoption. As such PBF-LB surfaces require several time-consuming post-processing steps, nevertheless, conventional finishing techniques are often limited by geometrical part complexity, making them unsuitable for porous PBF-LB parts. Herein we explore the possibility to utilise plasma-electrolytic oxidation (PEO) as a rapid, single step surface finishing method not constrained by implant design. Specifically, PEO treatment was performed in a phosphate-based electrolyte on as-printed and polished Ti-6Al-4V PBF-LB samples with complete surface coverage and chemical functionalisation, as observed by optical profilometry, SEM-EDX, XRD and XRF, achieved after only 20 min. To test the lack of geometric constraints brought by PEO, clinically relevant BCC porous lattices were also successfully PEO treated accomplishing a coating that either masked or removed surface adhered particles throughout the structure. Promisingly for medical application, no cytotoxicity was noted for MC3T3-E1 murine osteoblasts over 7 days and significantly more ( p < 0.05) mineralisation was observed after 21 days compared with as-printed and polished PBF-LB controls. Still, an enhanced pro-inflammatory response, iNOS and TNF-α, was observed in murine RAW261 macrophages seeded on PEO surfaces, indicating further optimisation is required to guide the inflammatory process. Overall, these findings showcase the widespread opportunity to robustly ensure PBF-LB implant safety by using PEO to tackle partially adhered particles while also offering new avenues to enhance functionality through variations in coating chemistry. • PEO masked/removed adhered L-PBF particles and modified surface chemistry in 20 min. • As-printed and polished L-PBF PEO samples showed similar topology and composition. • Non-line-of-sign areas of relevant lattices were successfully coated with PEO. • Coated samples displayed a lack of cytotoxicity and enhanced mineralisation. • PEO as a L-PBF surface treatment unlimited by geometry and biologically functional.