Wettability and surface charge of Si3N4–bioglass composites in contact with simulated physiological liquids

Wettability and surface charge studies were performed on a novel Si3N4–30 wt% bioglass biocomposite. Contact angle and surface tension variation with time were determined at 25°C, respectively, by the sessile and pendant drop techniques, for distinct testing liquids: water, diiodomethane, simulated body fluid (SBF) and bovine serum albumin (BSA) dissolved in SBF solution. This biocomposite revealed a hydrophilic character (θ=26.6±2.0°) and a surface tension value (66.6 mJ m−2) comparatively higher than those of the most common bioceramics. An important characteristic is the high work of adhesion towards SBF+BSA (96.4±0.2 mJ m−2) that was measured. The Si3N4–bioglass material is negatively surface charged above the pHIEP=2.5 in aqueous SBF+BSA solution, as a result of the presence at the surface of unsaturated Si–O bonds and Si–OH groups. The very high negative zeta potential at pH 7 (−58.6±5.5 mV) influenced albumin adsorption and mechanisms are discussed in terms of entropy and enthalpy gains from conformational unfolding and cations coadsorption.