Analysis of corrosion behaviour and surface properties of plasma-sprayed composite coating of hydroxyapatite–tantalum on biodegradable Mg alloy ZK60

Abstract

Magnesium (Mg) and its alloys are promising candidates for biodegradable bio-implants. However, the excessive corrosion in the physiological environment and subsequent decline in the mechanical integrity of Mg and its alloys have limited their utility as biomaterials. In the present study, an attempt has been made to improve the corrosion resistance of Mg alloy ZK60 plasma sprayed with tantalum (Ta)-reinforced hydroxyapatite coating. The experiment was conducted with three varied levels, i.e. 10, 20 and 30 weight percent (wt%) of Ta-content in hydroxyapatite coating. The coatings were characterized and in vitro corrosion behaviour was investigated by electrochemical measurements in Ringer's solution along with the analysis of surface properties. The corrosion resistance of the Mg alloy increased with the incremental increase in Ta reinforcement in hydroxyapatite coating. An increase in the protection efficiency was analysed for the Ta-reinforced hydroxyapatite coatings (∼10%, 18% and 23% for hydroxyapatite-10Ta, hydroxyapatite-20Ta and hydroxyapatite-30Ta, respectively) as compared to the pure hydroxyapatite coating. The hydroxyapatite coating effectively increased the surface hardness of the Mg alloy and Ta reinforcement further enhanced it. Surface roughness decreased with the incremental increase in Ta-content in hydroxyapatite coating. Wettability analysis revealed the hydrophilic nature of pure hydroxyapatite and Ta-reinforced hydroxyapatite coatings. The results of the study suggest that the proposed Ta reinforcement in hydroxyapatite is potentially important for biodegradable Mg bio-implants.

Review of the Effect of Surface Coating Modification on Magnesium Alloy Biocompatibility

“…The corrosion rate of zinc was lower than that of magnesium, and zinc had a positive effect on bone mineralization and cell protein synthesis, thus improving the long-term viability and bone binding ability of the HA coating. Singh et al [84] successfully sprayed Ta/Ti coating on AZ31B magnesium alloy by the plasma spraying process, which has high hardness and reduced wear This behavior is attributed to the high passivation property of cold sprayed Ta/Ti coatings and the rough surface (island shape) of these coatings, which can provide proper nucleation sites for the formation and growth of calcium phosphate compounds in Hanks solution, and the dense structure of Ta layer hinders the penetration of corrosive solution. Mohajernia et al [85] prepared a hydroxyapatite coating containing multi-walled carbon nanotubes (MWCNTs).…”

Polymeric Coatings for Magnesium Alloys for Biodegradable Implant Application: A Review

“…Appropriate coating methodology is selected based on the coating material and the merits and demerits of the techniques, as elaborated in Table 2 . However, there are critical limitations on the coating chemistry because of the toxicity/biosafety concerns [ 15 , 16 , 17 ]; for example, Al coating is prohibited since it can cause Alzheimer’s and dementia, even though Al is known to improve corrosion resistance. Besides, any local disruptions in the metallic coating will cause severe galvanic corrosion to the underneath Mg alloy because of Mg’s highly electronegative/anodic nature [ 18 ].…”