Hydrothermally synthesized HA-Cs-Pd multifunctional composite coatings on metastable β-Ti12Cr alloy for enhanced corrosion resistance, bioactivity, and antibacterial performance

Abstract

Advanced biomaterials are required for bone reconstruction to overcome the mechanical and biological limitations of conventional titanium alloys. In this study, hydroxyapatite-chitosan-palladium (HA-Cs-Pd) composite coatings were successfully synthesized on metastable beta-Ti12Cr alloy surfaces using a hydrothermal method. The coatings were characterized using X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy (FE-SEM/EDS), while their electrochemical, wettability, antibacterial, and cellular response properties were systematically evaluated. Potentiodynamic polarization measurements showed that chitosan (Cs) incorporation provided the most effective corrosion protection, with the HA-Cs coating exhibiting the lowest corrosion current density (icorr = 2.21 mu A/cm(2)), the highest polarization resistance (Rp = 22.6 k Omega cm(2)), and the lowest corrosion rate (0.010 mm/year) among all systems, compared to icorr = 3.04 mu A/cm(2) and Rp = 17.8 k Omega cm(2) for pure HA. Low-content Pd doping (1 wt%) increased the corrosion current to 10.00 mu A/cm(2) due to microgalvanic effects, whereas raising the Pd content to 2 wt% partially restored stability (icorr = 5.71 mu A/cm(2), Rp = 10.0 k Omega cm(2)). Contact angle measurements confirmed that all coatings remained hydrophilic (<90 degrees), ranging from 13 degrees +/- 1 degrees (HA-wt.%1Pd) to 37 degrees +/- 1 degrees (HA-Cs-wt.%2Pd). Pd addition enhanced antibacterial activity against Pseudomonas aeruginosa by suppressing bacterial adhesion and biofilm formation, while in vitro biological analyses demonstrated favorable cell viability and surface adhesion behavior on all coated samples. Among the investigated systems, the HA-Cs-wt.%2Pd coating exhibited the most balanced overall performance, combining improved surface homogeneity, antibacterial activity, hydrophilic behavior, and acceptable electrochemical stability. The findings suggest that HA-Cs-Pd composite coatings may provide an effective surface modification strategy for orthopedic and dental implant applications.