Investigation of Surface Functionalization and Coatings for Biomedical Applications by Zeta Potential and Adsorption Measurements on Solid Surfaces

Abstract

Even though zeta potential titration is widely employed for investigation of colloidal suspensions, it is still poorly applied to bulk solid surfaces. The measurement can be applied to surfaces in contact with water-based media, and it gives information about the isoelectric point of the surfaces, surface charge in function of pH, functional groups exposed on the surface, and adsorption/desorption processes at the solid-liquid interface. Zeta potential titration vs pH is useful for applications such as membranes, filters, biomaterials, semiconductors, textile fibres, cosmetic, detergents and minerals. In the present research, zeta potential of Ti6Al4V was measured using electro kinetic measurements (SurPASS, Anton Paar) after surface treatments, functionalization or coating. Zeta potential was measured, in function of pH, in a 0.001M KCl electrolyte solution; varying the solution of pH by addition of 0.05M HCl or NaOH through the instrument's automatic titration unit. Moreover, the effects of adsorption/desorption of ions and proteins after soaking in Simulated Body Fluid (SBF) and albumin (BSA) were tested. The tested Ti6Al4V samples were: 1) chemically treated samples finalized to better osseointegration through nanoscale surface topography, high hydroxylation degree and, eventually, an antibacterial action through silver nanoparticles; 2) surface functionalized samples with biomolecules for antibacterial and/or anti-inflammatory purposes (gallic acid as an example); 3) a coating of titanium boride finalized for better fretting, corrosion and wear resistance in artificial joints. The data will be compared and discussed. The technique is useful in order to compare exposed specific functional groups on the surface, and to measure the zeta potential at physiologic pH and the effects of ions adsorption on the surface charge, which is relevant for bioactive and antibacterial behaviour, as well as of protein adsorption which is also relevant for lubrication and wear in artificial joints.