Optically transparent silver-loaded mesoporous thin film coating with long-lasting antibacterial activity

Abstract

Infectious diseases caused by microorganisms affect millions of people worldwide. In an effort to prevent infections induced by bacteria, a variety of antibacterial coatings have been designed. In this sense, the possibility to combine broad-range bactericidal agents such as silver and chemically and mechanically stable matrices such as mesoporous oxide thin films has been encouraging. In this study, titania–silica bilayer mesoporous thin film (MTF) coatings have been produced and loaded with silver species, and their bactericidal efficiency against Pseudomonas aeruginosa and Staphylococcus aureus was assessed over time. In this sense, coatings loaded with silver ions (MTF + Ag+) were analyzed in comparison with coatings confining silver nanoparticles (MTF + AgNP). EDS analysis revealed that both types of MTF coatings were loaded with high amounts of silver (MTF + Ag+ = 25%; MTF + AgNP = 34%). MTF + Ag+ showed extremely high bactericidal efficiency (percent reduction of 99.5 to >99.999) against both strains along 10 cycles of use, comparable to that observed with MTF + AgNP. Interestingly, silver release from both types of coatings was similar over the same testing period. However, contrary to MTF + AgNP, MTF + Ag+ have shown absolute optical transparency. This is relevant for any type of coating, as conservation of optical properties of the material surface where they are intended to be applied, is highly desirable. Moreover, the maximum silver ion sorption capacity of film coatings was 3 μg cm−2 and MTF + Ag+ were still loaded with silver after 10 cycles of use which indicates that the bactericidal effect could be extended beyond. These results spotlight the potentiality of MTF + Ag+ as antibacterial coatings for any ceramic and/or metallic surface with no alteration of optical and mechanical properties.