The effect of micro and nano hydroxyapatite powder on biocompatibility and surface integrity of Ti6Al4V (ELI) in powder mixed electrical discharge machining

Abstract

The problem of achieving functional surface is receiving substantial attention with the demand for efficient medical devices in biomedical industry. To satisfy both mechanical and biomedical concerns, researchers try to develop appropriate commercial machining techniques. This study analyzes the micro and nano Hydroxyapatite (HAp) powder size effect on surface topography and biocompatibility of Ti-6Al-4V (ELI) biomaterial in Electrical Discharge Machining (EDM). We compare thoroughly the titanium surfaces that EDM’ed with three different HAp powder concentrations in Deionized Water (DW) (0 g l−1, 20 g l−1 Micro HAp, 20 g l−1 Nano HAp) and three pulse current levels (7 A, 12 A, 22 A). The roughness of surfaces varies between 0.38 μm and 6.61 μm. Using micro HAp powder in dielectric liquid lowered the surface roughness and enhanced the wettability whereas the nano HAp effect could be negligible. The Energy Dispersive x-ray Spectrometer results show the Ca and P ion migration from the HAp mixed dielectric to the workpiece surface during EDM. The x-ray Diffraction results affirmed the existence of HAp compounds and oxide phases in the surface structure. Biocompatibility tests employing MG63 osteoblast-like cells revealed that for 24 h culture period all EDM samples showed higher viability than the control in vitro. According to the statistical analyses ANOVA (Tukey), the MTT viability results showed a significant difference especially for those machined in micro HAp mixed DW dielectrics. On the other hand, for 72 h culture period, samples machined in DW with 7 and 12 A currents are more biocompatible and have a proliferative effect on MG63 cells. In conclusion, however the dependency on pulse current, powder additive, and topography of the surface exist; EDM can be employed as an effectual treatment to enhance the biocompatibility.