New generation hopeite coating on Ti6Al4V (TC4) by radio frequency magnetron sputtering for prosthetic-orthopaedic implant applications: synthesis and characterisation

ABSTRACT

Bioceramic coatings with multifunctionality have emerged as an effective alternative to conventional coatings, owing to their combination of various properties that are essential for bio-implants, such as osseointegration and antibacterial character. In the present study, thin hopeite coatings were synthesised by radio frequency magnetron sputtering on TC4 substrates. The obtained hopeite coatings were thermally treated at 500°C in ambient air and characterised in terms of surface morphology, phase composition, surface roughness, adhesion strength, antibacterial efficacy, apatite forming ability, surface wettability and corrosion resistance by Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), Atomic Force Microscopy(AFM), Tensometer, Fluorescence-Activated Cell Sorting (FACS), Simulated Body Fluid (SBF) immersion, Contact Angle Goniometer and potentiostatic polarisation respectively. It was observed that the post-deposition annealing increases the crystallinity of the synthesised hopeite coatings. SEM analysis showed deposited particles are spherical in shape and small in dimensions (<1?μm in diameter). XRD results confirm the deposited coating is crystalline in nature. AFM analysis reveals deposited hopeite coating has an average surface roughness value of 8.66?nm. Tensile pullout experiments indicated that the adhesive strength of the hopeite coating is 21.75?±?2.1?MPa. FACS study confirms the deposited hopeite coating possesses antibacterial character. SBF immersion experiments clearly demonstrate apatite growth on the surface of the deposited hopeite coating. The surface wettability test showed that the deposited coatings are hydrophobic in character having an average contact angle value of 136.65°. Potentiodynamic polarisation experiments in SBF showed a significant improvement in corrosion resistance (R_p?=?7945.87?Ω?cm²) of hopeite coated samples. In summary, it can be concluded that the new generation multifunctional hopeite coating synthesised by an alternative new process route of radio frequency magnetron sputtering on TC4 substrates is an effective alternative to conventional coatings. This is largely attributed to the strong osseointegration and antibacterial character of deposited hopeite coating ensuring the overall stability of metallic orthopaedic implants.