ANTIMICROBIAL PROPERTIES OF BIOACTIVE MATERIALS FUNCTIONALIZED WITH SILVER NANOPARTICLES AND PLANT DERIVED BIOMOLECULES TO MINIMIZE IMPLANT INFECTIONS

Background: titanium and its alloys have developed into key materials for biomedical applications owing to their biocompatibility with human tissues and excellent mechanical properties. Unmodified titanium is susceptible to microbial infections that might lead to implant failure and devastating complications with high morbidity and treatment costs. An effective approach to minimize microbial contamination on implant surfaces is to modify the biomaterial surface chemistry in order to reduce adhesion and biofilm development by microorganisms. The aim of this research was to evaluate the antibacterial activities of bioactive titanium alloy Ti6Al4V, functionalized with silver nanoparticles or the innovative Mentha piperita (MP) essential oil, both recognized for strong antimicrobial properties. Materials/methods: the titanium alloy Ti6Al4V substrate was made bioactive, by a patented chemical treatment and functionalized with silver nanoparticles or MP essential oil, directly grafted on the sample. The surface topography and chemical composition of functionalized surfaces were characterized by means of Field Emission Scanning Electron microscopy (FESEM), X-ray Photoelectron Spectroscopy and Fourier Transformed Infrared Spectroscopy. The modified surface antibacterial activity was assayed against Staphylococcus aureus ATCC 29213 by means of inhibition halo on agar medium and quantitative bacterial adhesion assays by using a sonication protocol to dislodge adherent bacteria. Results: the bioactivity test results showed the apatite like structure presence on the samples confirming thus their ability to form spontaneously apatite on their surfaces in physiological conditions. Ti6Al4V + Ag samples were able to produce a certain inhibition halo (Figure 1A, blue arrows), confirming the silver release detected in leaching tests; on the other hand no inhibition halo was detected for Ti6Al4V+MP (Figure 1A, red arrow), suggesting no release of mint oil. The evaluation of bacterial adhesion evidenced a significant reduction (p<0.05) in the amount of adherent bacteria for both Ti6Al4V+Ag and Ti6Al4V+MP(Figure 1B), suggesting a similar effect on adherent bacteria for both surfaces. These results suggest a different mechanism in the antibacterial action of the two materials which is actually under investigation. Conclusions: This study confirmed the antibacterial effects of Ag and increased the interest in the use of plant derivatives (in particular essential oils) as antimicrobials because of their relative safe status and their exploitation for multi-purpose functional uses. However, the most important activities of these compounds are as antiseptics and antimicrobials. The potential antibacterial action of the specimens, here confirmed by biological tests, suggest that the studied strategy could be a promising approach to create bio-inspired antibacterial surfaces, mainly for orthopaedic applications, to induce fast and physiological bone integration and reduce the incidence of prosthetic infections.