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Titanium surface modification by the Hydroxyapatite (HA) mixed Electrical Discharge Machining (EDM) is an alternative and promising technique to enhance the biocompatibility and to promote the biological performance in bone, which is dependent on surface properties, such as surface roughness, chemistry, and wettability. HA powder is used for the first time with electrical discharge machining to improve osteoblastic cell activity on the developed surfaces for Ti6Al4V. Different HA concentrations in deionized water were tested as an experimental variable during EDM. Abrasive polishing and electrical discharge machined control surfaces without powder addition also analyzed to compare the results. The surface characteristics of analyzed samples were evaluated by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffractometry (XRD), white light interferometry, and contact angle measurements. The wettability tests suggest that the hydroxyapatite powder mixed EDM'ed surfaces shows highly hydrophilic characteristics compared the other surfaces, abrasive polished and EDM'ed without powder addition in the dielectric. The results from the MTT assay revealed that those surfaces modified using HA powder addition in distilled water dielectric liquid promoted the most significant cell attachment/growth. The results indicate that HA powder mixed EDM offers a promising method for the surface modification of biomaterials such as titanium alloys.
Added powders in a dielectric medium substantially influence the features of electrical discharges due to altered interelectrode conditions during the electrical discharge machining (EDM) process. The main discharge channel is disturbed due to the added powders in dielectric liquid and leads formations of secondary discharges. Such altered discharge conditions generate a unique topography on the machined surface and consequent subsurface microstructure beneath it. Ti6Al4V work material machined using SiC powder mixing in de-ionized water for an extensive set of pulse-on duration and pulse currents. Then, different forms of secondary discharges were identified from the resultant surface features and corresponding subsurface microstructures. The results pointed out that generation of unevenly separated secondary discharges increased the material transfer rate from the powder mixed dielectric liquid to the machined surface by means of the decomposed ions in the plasma channel. Complete separation of the main discharge channel into evenly distributed secondary discharges is possible under specific machining conditions that suggested minimal deformation of the machined surface regarding microcracks, roughness, and heat affected layer thickness. Under such machining conditions, another means of material transfer mechanism is activated that lead a powder particle build-up process on the machined surface. Consequently, five different discharge forms were proposed to describe the resultant surface topographies and subsurface microstructures. The material migration phenomena and the mechanisms are discussed in relation to the pulse-on time and pulse current.
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.
The discharge gap phenomena in powder-mixed electrical discharge machining are examined using SiC powder mixing in water dielectric liquid. Surface modifications on machined work materials are investigated by means of optical, scanning electron microscopy and energy-dispersive spectroscopy. The experimental studies revealed that the surface morphology drastically affected the additives as means of secondary discharges and particle migration from dielectric liquid. Such mechanisms do not occur randomly and indicate a robust dependency with respect to powder suspension concentration, pulse on duration and current. The influence on discharge transitivity with respect to suspended particle concentration is noted with pock shape development due to secondary discharges followed by an intermediate stage signifying a sudden increase in particle migration from the dielectric liquid. The particles decomposed on the surface at specific operational conditions demonstrating the possibility of methodical surface alloying using the process. Finally, the mechanisms involved were elaborated with respect to operational parameters and discussed based on the experimental results.
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