Cathodic electrodeposition of zinc–zinc phosphate–calcium phosphate composite coatings on pure iron for biodegradable implant applications

Abstract

Faster degradation of iron based degradable implants in physiological media, particularly during the initial stages of implantation, poses difficulties in directly using them for clinical applications. The present study aims to deposit a zinc–zinc phosphate–calcium phosphate composite coating on pure iron by cathodic electrodeposition under varying current densities (2 to 5 mA cm⁻²) at 27 °C for 30 min to overcome the above mentioned limitation. The composite coating was characterized for the amount of coating deposited, surface morphology, elemental composition, nature of functional groups and phase contents. The corrosion behavior of composite coated pure iron in Hanks’ balanced salt solution was determined by potentiodynamic polarization, electrochemical impedance and immersion studies. The bioactivity of the composite coated iron was evaluated by immersing it in simulated body fluid. The changes in the morphological features, elemental composition and nature of functional groups present on the surface layer were used to understand the extent of corrosion attack and mineralization. The findings of the study reveal that cathodic electrodeposition enables the deposition of a uniform, highly crystalline zinc–zinc phosphate–calcium phosphate composite coating on pure iron with a plate-like morphology. X-ray diffraction measurements confirm the presence of zinc, zinc phosphate and calcium phosphate phases. The zinc–zinc phosphate–calcium phosphate composite coated pure iron offered a better corrosion resistance than the uncoated one in Hanks’ solution. The composite coating also exhibits good bioactivity in simulated body fluid. The study concludes that deposition of zinc–zinc phosphate–calcium phosphate composite coatings on pure iron will be useful to overcome the existing limitation of the higher rate of corrosion of pure iron during the initial stages of implantation.