Temporal zeta potential variations of 45S5 bioactive glass immersed in an electrolyte solution

45S5 bioactive glass (BG) is a bioactive material known to bond to bone in vivo through a surface calcium phosphate (Ca-P) layer. The goal of this stu dy was to address the importance of BG surface charge in the bioactive resp onse by examining the relationship between charge variations and the format ion of the surface Ca-P laver. The zeta potential of BG in an electrolyte s olution (TE) was measured by particle electrophoresis, and the formation of a Ca-P laver was characterized using SEM, EDXA, and FTIR. Si, Ca, and P so lution concentrations also were determined. The initial BG surface was nega tively charged, and two sign reversals were detected during 3 days of immer sion. The first, from negative to positive after 1 day, is attributed to th e adsorption of cations at the BG surface, and the second reversal was due to the precipitation of phosphate ions from solution. A strong correlation was found between the formation of a Ca-P layer and BG surface zeta potenti al variations. The dynamic shift in zeta potential from an initially negati ve surface to a positively charged surface directly corresponded with the f ormation of an amorphous Ca-P layer. In addition, when the glass surface ma tured into a crystalline Ca-P layer, it was associated with a reversal from a positive to a negative surface. Future work will focus on the effects of protein adsorption on BG surface charge and Ca-P laver formation kinetics as well as on cellular response to a changing BG surface. (C) 2000 John Wil ey & Sons, Inc. J Biomed Mater Res, 51, 80-87, 2000.