Effect of thermal treatment on bioactive glass microstructure, corrosion behavior, zeta potential, and protein adsorption.

Bioactive glass ceramic is characterized by high mechanical strength and a slow rate of bone bonding. To understand the factors contributing to a decrease in the rate of bone bonding to bioactive glass ceramic, we evaluated the effect of different percentages of bioactive glass crystallization on corrosion behavior, zeta potential, and serum protein adsorption. X-ray diffraction analysis showed that heat treatment of bioactive glass in the temperature range 550 degrees -700 degrees C resulted in the precipitation of Na(2)Ca(2)Si(3)O(9) crystals in the glass matrix. The percentage of crystallization increased in the order: 5%, 8%, 45%, and 83% after thermal treatment at 550 degrees, 600 degrees, 650 degrees, and 700 degrees C/1 h, respectively. Scanning electron microscopic analyses of bioactive glass treated at 550 degrees C showed major glass in glass-phase separation. Moreover, energy-dispersive X-ray analyses indicated that during crystallization P is concentrated in the glassy phase. Induced-coupled plasma analyses showed that after 24 h immersion in simulated body fluid, the concentration of the released P ion increased as the crystallization percentage of bioactive glass increased. zeta potential of bioactive glass samples containing 5% crystallization had a statistically significant higher negative value than control untreated bioactive glass (p <.02). Control untreated bioactive glass adsorbed a statistically significant higher amount of serum protein than bioactive glass samples containing 5% crystallization (p <.02). Results of our study suggest that inhibition of protein adsorption might be responsible for the slow rate of bone bonding to bioactive glass ceramic. It is also possible that conformation changes inhibit the activity of the protein adsorbed onto thermally treated bioactive glass. Copyright 2001 John Wiley & Sons, Inc. J Biomed Mater Res 55: 387-395, 2001