Development of a Silver-Doped High-Entropy Nitride Coating: Bactericidal and Antiviral Evaluation for Biomedical Applications

AISI 420 martensitic stainless steel is used for the manufacture of surgical and dental instruments, among others, whose surfaces can be colonized by bacteria and/or viruses that negatively affect the health of patients. The use of binary and ternary nitride coatings doped with different metallic nanoparticles has contributed to reducing the problems of infection with bacteria. However, there are few reports and studies on the biocidal and virucidal effect of high-entropy nitride coatings doped with silver nanoparticles, which could be an important alternative for antibacterial applications, also considering other advantages such as their excellent mechanical and tribological properties. In this work, a high-entropy nitride of (TiTaZrNbN)Agx doped with silver particles (Ag) was synthesized on AISI 420 stainless steel substrates via the magnetron sputtering technique. An attempt was made to elucidate the relationship between the microstructure and surface properties of the coatings with their potential activity against the selected bacteria and viruses. The Ag content in the coatings varied between 15.4 and 26.8 atom % by increasing the power supplied to the silver target between 50 and 110 W. The bactericidal effect of the synthesized nitride compound was studied via inhibition and adhesion tests against the bacteria Pseudomonas aeruginosa and Staphylococcus aureus . Moreover, the SARS-CoV-2 virus was selected to determine its virucidal effect. The deposited coatings exhibited columnar growth, and both the metal nitride matrix and the silver particles presented a NaCl-type cubic structure with preferential growth in the (111) and (200) planes. All of the coatings had a columnar structure whose width, surface roughness, and grain size increased with increasing silver content. Furthermore, the coatings present a hydrophobic behavior (increasing contact angle with increasing silver content) and decreasing surface energy. All of the coated steel samples strongly inhibited P. aeruginosa bacteria, and only sample RN-50W, with the lowest silver content, presented low adhesion of this bacteria. None of the coatings inhibited the S. aureus bacteria, and all of the coatings highly colonized the S. aureus bacteria in the adhesion test. The coatings deposited with powers of 50 and 90 W supplied to the silver target presented an average virucidal potential of 50% against the SARS-CoV-2 virus.