Production of a bio-compatible metallic implant via electropolymetrization method by coating a synthetic hydrogel on a titanium alloy

Abstract

Recently, titanium implants are used to solve many different health problems. Features of titanium, such as lightness, strength, high corrosion resistance and bio-compatibility have increased the usage of titanium in bio-materials. Titanium plates take an important role, especially in integrating bone fractures. Although titanium implants are essential materials for this purpose, to minimize the risks during healing period, bio-active titanium surfaces are desired. The aim of this study is to coat titanium alloy (Ti–6Al–4V) which is used as an implant material with a synthetic bio-compatible hydrogel, poly(HEMA–GDMA), by electropolymerization method in order to develop the functionality and the bio-compatibility of the material. In order to improve the adhesion of the coatings to the metal surface, first titanium working electrodes, were encapsulated in bakelite as circular plates and polished flat to a 3 μm finish. Then, each electrode was cleaned in an ultrasonic bath using ethanol for 10 min, rinsed with water and dried. All potentiostatic coating experiments were carried out using a potentiostat–galvanostat and an H-type glass cell. In the cell, (NH 4 ) 2 S 2 O 8 and H 2 SO 4 were used as the initiators of the electropolymerization where HEMA was the monomer and GDMA was the crosslinker. Na 2 SO 4 was also added to increase the conductivity of the solution as well as the thickness of the coatings. Titanium alloy (Ti 6 Al 4 V), reticulated vitreous carbon electrode (RVC) and saturated calomel electrode (SCE) were chosen as working electrode, counter electrode, and reference electrode, respectively. The electrochemical cell was purged with nitrogen for 30 min before any potential was applied. Then potential was ramped at 1 mV/s from 0 V (vs. SCE) to the desired potential and held for 30 min. During the electropolymerization, nitrogen purging was continued. First optimum coating conditions were determined in terms of applied potential, initiators, monomer and cross-linker concentrations. Then the surface morphologies of the coatings were examined by optical microscope and scanning electron microscope (SEM), the chemical characterizations were done using Fourier Transform Infrared Spectroscopy (FT-IR). Surface roughness and thickness of the coatings were obtained by the surface profilometer device. As a result, white and opaque coatings of poly(HEMA–GDMA) were produced uniformly on Ti 6 Al 4 V cathodes via electropolymerization method. Hazy surfaces of the coatings indicate the diffusion of light on reflectance as a result of rough surface morphology. Na 2 SO 4 addition is important as it increases the conductivity leading to thicker coatings.