Surface modification of β-phase Ti implant by hydroaxyapatite mixed electric discharge machining to enhance the corrosion resistance and in-vitro bioactivity

The study presented an innovative method for surface modification of 3-phase titanium alloy using hydroxyapatite mixed electric discharge machining (HAM-EDM). The process enables one to deposit in-situ a biomimetic nano-porous HA-containing layer while shaping the base titanium, hence modifying the surface properties of the original substrate. A series of the dedicated HAM-EDM on titanium alloys have been conducted. Surface integrity, topography, and elemental composition of the modified surface were investigated by FE-SEM, EDS, XRD, and indentation techniques, while in vitro cell study was performed to evaluate biocompatibility and cell attachment of the treated surface. The morphology characterization results revealed that a natural bone-like nano-porous surface topography has been imparted on the beta-phae Ti implant surface using the HAM-EDM. The EDS and XRD examinations showed that the deposited layer comprised of Ti, Nb, Ta, Zr, O, Ca and 'P elements and formed biocompatible phases such as Ca-3(PO4)(2), CaZrO3, Nb8P5, CaO, TiP, Nb4O5, and TiO2, TiH on the beta-Ti implant surface, which improved the bioactivity of the alloy and beneficial for the promotion of osseointegration. The results revealed that a 18-20 pm thick recast layer containing biocompatible phases was generated, which has excellent metallurgical bonding with the base surface and offered mechanical interlocking to delamination. The HA deposited surface shows am improved hardness of 1275 HV which is 3-fold higher than the untreated surfaces; predominantly owing to the deposition of hard oxides on the modified surface. The HA-deposited bioceramic layer presented an excellent and higher corrosion resistance as compared to EDMed and un-treated specimens in simulated body fluid. The in-vitro bioactivity results confirmed that the nano-porous HA-containing layer exhibited the superior bioactivity and promotes adhesion, growth, proliferation, and differentiation of human osteoblastic MG-63 cells. (C) 2017 Elsevier B.V. All rights reserved.