The Phenomenon of Biofilm Formation on Titanium Surfaces, Its Clinical Implications, and the Search for New Strategies in the Development of Functionalized Surfaces with Antibacterial Properties

The formation of a biofilm on the surface of the biomaterial is of key importance in the pathogenesis of infections. Biofilm is a dynamic multi-layer structure composed of, among others, bacterial cells and organic and inorganic substances secreted by microorganisms and eukaryotic cells. The process of biofilm formation accompanies chronic infections and consists of several stages. Bacterial cells produce an exopolysaccharide substance that surrounds microbes and at the same time allows for the formation of three-dimensional structures within which different degrees of metabolic activity of cells can be distinguished, giving them differentiated susceptibility to nutrient availability and survival periods of deficiency. The exopolysaccharide protects them from adverse environmental influences and, from a medical point of view, from the immune system and the antimicrobials used. The phenomenon of biofilm formation in the human body has intensified since medical technology has made it possible to implant various types of implants, which are made of biologically foreign materials, on a large scale. Their surfaces often turn out to be a convenient place for the formation of biofilms. Biofilm poses a high risk of spreading microbes to other parts of the body through the blood and causing difficult-to-treat and life-threatening infections, including sepsis. Biofilm is also related to the problem of acquiring multidrug resistance by microorganisms inhabiting its structure, which occurs through the horizontal transfer of resistance genes. To minimize the risk of biofilms forming on the surface of implants, scientists are looking for ways to modify the surface to make it more difficult or even impossible for microbial cells to colonize it. Titanium surfaces or surfaces functionalized with titanium dioxide, titanium ions, or titanium nanoparticles seem to be a promising way to reduce the possibility of biofilm formation. The TiO 2 main mechanism of antibacterial activity is the production of reactive oxygen species (ROS), which results in the killing effect on the biofilm. In this chapter, we present the process of biofilm generation and maturation, the medical risks associated with it, the main species of bacteria associated with biofilm formation (e.g., Staphylococcus aureus and Escherichia coli ), the opportunities offered by titanium implant surfaces as a way to counteract these processes, and the mechanisms of antimicrobial activities of TiO 2 -based materials.