Improvement in bioactivity, hardness and friction resistance of 3 % manganese-doped hydroxyapatite coated on alumina using radio frequency magnetron sputtering

Abstract

Hydroxyapatite (HAP) is a common hard tissue implant material known for its superior biocompatibility and osteoconductivity. However, its poor mechanical strength, brittleness and slow degradation limit the applications. This study explores the enhancement of HAP mechanical properties and bioactivity by coating 3 wt% manganese-doped HAP (Mn-HAP) on another inert biomaterial alumina (Mn-HAP/Al₂O₃) substrates using the RF magnetron sputtering technique. Characterization of these samples was performed using Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Spectroscopy (EDS), Grazing Incidence X-ray Diffraction (GIXRD), Fourier Transform Infrared Spectroscopy (FTIR) and Brunauer-Emmett-Teller (BET) techniques. Mechanical property was assessed through Vicker's hardness and adhesion of the film was studied by scratch testing. Corrosion resistance was evaluated using Tafel plots in Ringer's solution by Electrochemical analyser (ECA), and dielectric properties were measured using Impedance analyser. Biocompatibility was examined by wettability tests, thrombogenicity, antioxidant test, antimicrobial investigation and MTT [3-(4, 5-dimethythiazol-2-yl)-2, 5-diphenyl tetrazolium bromide] assay. The results show that Mn-HAP/Al₂O₃ coatings exhibit superior properties as compared to pure HAP, alumina, and HAP/Al₂O₃. Mn-HAP showed enhanced crystallinity and grain refinement, leading to improved hardness of 1198 HV for Mn-HAP/Al₂O₃ as compared to 39.84 HV for pure HAP and 1028 HV for HAP/Al₂O₃. The friction coefficient was found to be best in the Mn-HAP/Al₂O₃ sample. Corrosion rate significantly decreases in Mn-HAP/Al₂O₃ (1.63 $\pm$ 0.28) mmpy after coating on alumina. In vitro studies demonstrated enhanced cell attachment, proliferation, and differentiation after Mn-HAP coating on alumina. Antimicrobial tests revealed improved resistance against E. coli and S. aureus, with Mn-HAP/Al₂O₃ showing a larger zone of inhibition. The study concludes that 3 wt% Mn-HAP coatings deposited by RF magnetron sputtering hold great promise for enhancing the performance and longevity of hard tissue implants, paving the way for advanced biomedical applications.