Comparison among nanostructured biomaterials with different mechanisms and kinetics of bioactivity and antibacterial action

Evolution of biomaterials for implants progressively shifted the focus from adequate mechanical strength to improved biocompatibility and absence of toxicity and, finally, to fast tissue integration. Recently, new frontiers and challenges of titanium implants have been addressed with the focus on bioactivity and fighting bacterial infection and biofilm formation. This is closely related to the clinical demand of multifunctional implants able to simultaneously have a number of specific responses with respect to body fluids, cells and pathogenic agents. Nanotechnologies can have a substantial and effective impact in regulating the tissue-implant interface through controlled topography and surface functionalization at the nanoscale and some of them are here explored. Titanium and titanium alloys surface treated in order to be bioactive (induced precipitation of hydroxyapatite in contact with physiologic fluids) and antibacterial are here characterized and compared. They have in common surface topography at the nanoscale and functionalization with antibacterial metal ions or nanoparticles, but differ in surface reactivity in contact with the bodyfluids (simulated through SBF-Simulated Body Fluid, albumin and/or hydrogen peroxide complex solutions). The focus is on comparison of their mechanisms of action, kinetics of surface activity and biological response. A bioactive glass belonging to the system SiO2-Na2O-CaO-P2O5-B2O3-Al2O3 is used as reference for comparison with a classic bioactive material; the same glass doped with silver ions by ion exchange in aqueous solutions of silver nitrate was used as reference of antibacterial action through Ag ions release. Protocols of analysis suitable for evaluating and comparing the mechanisms of bioactivity and antibacterial action (FESEM, Raman, XPS, electrokinetic and electrophoretic zeta potential measurements), kinetics of surface reactivity (release of antibacterial agents, FTIR, cross section observation after soaking in SBF), biocompatibility (corrosion resistance and ion release in complex solutions) and biological response (biofilm formation, osteoblast adhesion and differentiation) of a wide range of inorganic biomaterials have been assessed and are here described and discussed.