Antimicrobial Peptide Adsorption and Storage on Oxidized Metal Surfaces to Mitigate Bacterial Attachment

In the pursuit to create more natural, chemical-free antibacterial surfaces, fracture mechanics and the ability of laser-modified surfaces to store an antimicrobial agent have been investigated through the combination of scanning electron microscopy coupled with focused ion beam, infrared spectroscopy, bactericidal tests and a colorimetric method. It was found that the irradiation of a nanosecond pulsed laser on Ti-6Al-4V and 304L stainless steel surfaces creates colored oxide layers with 100-150 nm in thickness and, by using the adequate parameters, it is possible to obtain surfaces with cracks of 1-6 μm deep that not only penetrate the film but also the substrate. Physisorption was used to immobilize nisin, an antimicrobial agent, to the walls of those cracks. Antibacterial tests show that nisin-coated oxide layers exhibit antibacterial activity against Listeria monocytogenes even after immersion in water or the application of mechanical scrubbing, and release kinetics tests demonstrated that nisin desorption is promoted by acidic pH and that nisin is effectively stored into the cracks of stainless steel. The immobilization into the cracks of the titanium oxide layer seem to reveal that there is an excellent anchor between the peptide and the crack walls, but future research is still required.