Functional Hybrid Chitosan Coatings With Cu Nanoparticles on the Shape Memory NiTi Enabling Bactericidal Activity

In this study, we introduce a hybrid approach for fabricating multifunctional coatings composed of chitosan and copper nanoparticles (CuNPs) on NiTi substrates. The fabrication process combines the immersion technique for chitosan layer deposition with inert gas condensation (IGC) based on magnetron sputtering for the generation of CuNPs. This method enables precise control over nanoparticle size and concentration, allowing for their uniform incorporation into a biopolymer matrix. The resulting CS/CuNPs/CS multilayers exhibit excellent surface coverage, nanoscale roughness (R_a of 30-65 nm), and moderately hydrophilic character (contact angle of 30°-35°), which collectively support cell adhesion and proliferation. Surface characterization confirmed the stability and durability of the coatings, which can be attributed to prior substrate activation using Piranha solution and plasma treatment. Electrochemical tests demonstrated enhanced corrosion resistance of the CS/CuNPs/CS layers, with a reduced current density (4.10 × 10^-4 mA/cm²) and good temporal stability. In vitro studies using the MG-63 osteoblast-like cell line indicated non-cytotoxicity response of the coatings, confirming their plausible applicability in tissue engineering. Antibacterial assays revealed effective inhibition of Staphylococcus aureus growth and complete elimination of Escherichia coli, highlighting the strong bactericidal potential of the developed system. Moreover, Cu ion release within the surface layer profiles obtained in Ringer's solution over a 7-day period showed a predominantly linear release of copper ions, indicating a controlled and sustained antimicrobial effect. The ability to modulate chitosan layer thickness and nanoparticle loading during sequential deposition steps enables the customization of the coating properties to meet specific therapeutic requirements while minimizing nanoparticle usage. This strategy offers a promising platform for developing safe, effective, and tunable antibacterial coatings for biomedical implants.