New biomaterial functionalized with natural antimicrobials to counteract microbial implant infections

Introduction. Mentha Piperita essential oil (EO) is a complex mixture of different natural biomolecules with proven antibacterial activity against Gram-positive and Gram-negative bacteria, fungi and viruses. Despite its increasing use in phytotherapy, application of Mentha Piperita EO in medicine is still quite scarce and almost no research work considers its application in combination with biomaterials. On the other hand, the possibility to employ the antibacterial properties of this EO together with its low resistance development risk and low toxicity is a challenging approach for the development of smart biomaterials for prosthetic applications. This work aimed to combine the antibacterial properties of Mentha Piperita EO with those of bioactive titanium alloy (Ti6Al4V) for medical applications in which good osteointegrability and antimicrobial effects are required. Materials and methods: Different concentrations of Mentha Piperita EO in ethanol were considered for the treatment of Ti6Al4V, made bioactive with a patented chemical treatment. The samples were characterized by means of X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), wettability and z potential analysis. Antibacterial tests were performed by assaying the Staphylococcus aureus adhesion on biomaterials through a sonication protocol, that allows to dislodge bacteria without altering their viability. Results: XPS analyses evidenced a significant increase in the carbon content for the modified Ti6Al4V alloy; FTIR analyses highlighted, on the modified samples, the presence of three peaks attributable to chelate compounds characteristic of the organic elements in EO. The wettability tests showed a reduction of the wettability after the modification with the EO and the z potential highlighted a shift of the isoelectric point to a less acidic value after the surface functionalization process. The antibacterial tests showed a significant (p<0.001) reduction of the adherent staphylococci on the modified surfaces after 24 h of incubation, with values of 1.71x108 CFU/ml for control samples and 6.80x107 CFU/ml for samples enriched with Mentha Piperita EO. Discussion and Conclusions: A multi-functional biomaterial for prosthetic implants that could enhance osteogenesis, and simultaneously prevent post-surgical infection and inflammation, is urgently needed. This research work shows the great potential of Mentha Piperita EO use for biomaterial surface functionalization with enhanced antibacterial properties. Furthermore, the use of Mentha Piperita oil of Pancalieri is consistent with the European policy of exploitation of the local regional natural resources (Piedmont).