Chemical Post-Processing of SLM Ti6Al4V Structures Using HF with Propylene Glycol: Surface, Structural and Biological Evaluation of an Exploratory Post-Processing Strategy.

Selective Laser Melting (SLM) of Ti6Al4V produces implants with surface-adhered, weakly bonded powder particles that require post processing prior to biomedical use. Chemical etching with hydrofluoric acid (HF) is effective but often causes excessive material loss. In this study, SLM-fabricated Ti6Al4V samples were chemically etched using 1-3% HF solutions with and without the addition of propylene glycol. The influence of etching conditions on mass loss, surface morphology, roughness, wettability, chemical composition, internal porosity (using X-ray micro- computed tomography) and biological response was evaluated. The results indicted that increasing HF concentration increased material loss and powder removal efficiency. The addition of propylene glycol substantially reduced mass loss (up to 50%) while preserving effective powder removal and surface quality. Etched samples exhibited reduced roughness parameters and no cytotoxic effects toward Saos-2 cells. Moreover, selected etching conditions shifted the porous architecture toward pore-size distributions considered potentially more favorable for bone tissue ingrowth. These findings indicate that HF etching with propylene glycol is a promising post processing strategy for SLM Ti6Al4V implants, offering improved surface control with reduced material degradation.