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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.
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