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 degreesC, 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 (theta = 26.6 +/- 2.0degrees) 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 pH(IEP)=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 pHsimilar to7 (-58.6+/-5.5mV) influenced albumin adsorption and mechanisms are discussed in terms of entropy and enthalpy gains from conformational unfolding and cations coadsorption. (C) 2002 Elsevier Science Ltd. All rights reserved.