Influence of Ag-Cu nanoparticles on the microstructural and bactericidal properties of TiAlN(Ag,Cu) coatings for medical applications deposited by Direct Current (DC) magnetron sputtering

Most medical instrumentation is manufactured using AISI 420 martensitic stainless steel, due to its acceptable biocompatibility, good hardenability, adequate hardness and resistance to corrosion. However, this steel can be susceptible to contamination with bacteria, representing a potential risk to the patient's health. This research work focused on the development of titanium-aluminum-nitride coatings doped with silver and copper nanoparticles, TiAlN (Ag,Cu), with an appropriate bactericidal effect. TiAlN coatings doped with four different contents of Ag and Cu (11 at% to 20 at%) were deposited onto AISI 420 steel by means of DC unbalanced magnetron sputtering using two composite targets of Ti/Al and Ag/Cu. The diffusion of the Ag,Cu nanoparticles at the sample surface, as well as their quantity, size, shape and distribution, was controlled by appropriate adjustment of the power applied to the Ag/Cu- target, and the temperature and time of the deposition process. The mechanical, tribological and bactericidal properties of the compound depend on, among other factors, the above-mentioned characteristics of the nanoparticles. The microstructure, surface topography, and chemical and phase composition were analyzed by scanning and transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. To evaluate the bactericidal effect of the coatings, in vitro inhibition and adhesion tests were carried out using selected Staphylococcus aureus and Escherichia coll., two of the major pathogens associated with infections frequently found in hospital environments. The coating without doping presented a structure of columnar growth, which became densified with the increase in the Ag-Cu content and took on a glassy appearance, accompanied by an increased size of the Ag-Cu particles and consequently also in the surface roughness. TiAlN(Ag,Cu) with 17 and 20 at% Ag-Cu exhibited a higher bactericidal effect than TiAlN, showing high inhibition and less adhesion to both bacteria strains. Another series of techniques that comprehensively describe the relationship between external factors and the bactericidal response of the material were made. Based on the results obtained, the developed nanostructured coating system can be considered very promising for potential applications in surgical and dental instrumentation.