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.

Surface modification during hydroxyapatite powder mixed electric discharge machining of metallic biomaterials: a review

“…During EDM process the various intermetallic alloys, biocompatible oxides, and carbides are formed on the coating surface of metallic biomaterial, which [202] Pure graphite/hydrocarbon oil [203] Pure Ti/deionized water [204] Pure Ti/hydrocarbon oil [205] Pure Ti/deionized water [206] Pure Ti/deionized water [210] Pure Ti/deionized water × × √ √ √ × √ × × × Zr-based bulk metallic glass/HAp [212] Pure Ti/hydrocarbon fluid [213] Copper/EDM oil [220] Pure Ti (Grade 2)/deionized water [223] Pure titanium/mineral oil Cu 11 Ni 10 Ti 9 Be 3 /HAp [224] T i [226] Graphite, tungsten, tungsten + copper/deionized water…”

“…HAp lowers surface roughness by increasing flushing capacity and stabilizing the HAp-EDM process by expanding the machining gap [224]. Micro-HAP (MHAP) and nano-HAP (NHAp) applied to deionized water (DW) in EDM were explained by Yaşar and Ekmekci [220]. The deionized water-treated surface showed obvious crater voids, whereas the µHAp surface had a more combined surface with a cavity-cover layer.…”

“…The contact angles of the HAp-EDM specimens decrease over time as the spark energy and HAp quantity rise because of increased surface energy, nanopores, shallow craters, and oxide formation. The higher the surface hydrophilicity results, the smaller the surface contact angle [220]. Surface hydrophilicity improves cell response, such as osteoblastic cell attachment and proliferation, by increasing cell adhesion adsorption.…”

“…The substance is considered cytocompatible if the proportion of viable cells is equal to or higher than 70%. MTT is considered the 'gold standard' in cytotoxicity research, but it has numerous flaws [220]. As a result, cell culture conditions may influence the metabolism and rate of MTT reduction, and the interaction between the test substance and MTT may influence the results [227].…”

“…As a result, coated surface promotes bioactivity offering better biological fixation, cell proliferation, etc. Yaşar et al [220] examined the effect of mixing of micro and nano-HAp powder in dielectric during HAp-EDM of Ti alloy and observed the presence of oxides and carbide of Ti on the coated surface. Al-Amin et al [224] revealed the effect of mixing carbon nanotube (CNT) in dielectric during HAp-EDM of 316L SS and noticed the formation of Cr 2 C, Fe 14 Cr 2 C, Cr 7 C 3 , Fe 5 C 2 , and Fe 7 C 3 compounds due to decomposition of mixed CNT and mineral oil.…”