Fabrication of a Hydroxyapatite coating reinforced with Functionalized graphene oxide deposited on a NiTi implant alloy: A bioactivity and electrochemical property analysis

The majority of the challenges within the broad application of titanium alloys used as biomedical implants are related to their interfacial properties; thus, surface modification represents a proper solution to overcome these issues. Surface functionalization by coating deposition is an appropriate choice for metallic implant surface modification [1]. In particular, inorganic ceramic coatings such as hydroxyapatite (HAp, Ca₁₀(PO₄)₆(OH)₂) have been widely employed to improve this incompatibility [2]. Nevertheless, the brittle nature and poor strength of HAp coatings are a problem, especially when the implant needs to work under load-bearing conditions. Therefore, the incorporation of nanoparticles as secondary bioactive fillers enhances their characteristics [3]. This work aims to investigate the effect of graphene oxide (GO) nanolayers functionalized with therapeutic cations as an active/passive filler to increase the bioactivity of an HAp coating and hinder the access of corrosive species to the metallic substrate. The release ability of functionalized graphene oxide (FGO) makes it a desirable candidate as a bioactive additive for bone regeneration. The flake morphology of these nanoparticles can enhance the barrier performance and the toughness of the HAp coating [4].

For this purpose, GO nanoparticles have been synthesized via the modified Hummer method and have been functionalized through absorption of strontium and gallium cations. Then, an HAp coating loaded with Sr/Ga-functionalized GO nanoparticles was deposited on nitinol samples. The effect of FGO incorporation on the anticorrosion behaviour of HAp-coated nitinol samples was studied via polarization and electrochemical impedance spectroscopy (EIS). Furthermore, the bioactivity and antibacterial performance of the composite coatings applied on implant samples have also been investigated.