Dissolution of Bioactive Glass S53P4 in Continuous Flows of Tris Buffer and Lactic Acid

Abstract

In vitro dynamic dissolution of bioactive glass S53P4 particles was studied in a cascade of three reactors. Tris buffer (pH 7.40) and lactic acid (pH 2.00) with flow rates of 0.2 and 0.04 ml/min were fed through the reactors for 24 h. The increased ion concentrations in Tris inflows to the second and third reactors decreased the dissolution of the particles. However, the normalised surface-specific mass loss rate decreased from the first to the third reactor and with decreasing flow rate. No distinct differences were observed in the reaction layers on the particles in the three consecutive reactors. This implied that the ions released in the previous reactors contributed to the reaction layers formed in the following reactors. Highly incongruent dissolution with similar dissolution rates of sodium, calcium, and phosphorus occurred with the two flow rates in lactic acid. Although a thick silica-rich layer formed on the particles, the low pH prevented calcium phosphate layer precipitation. The results imply that S53P4 particles in an implant react at different rates depending on their location but form similar reaction layer morphologies independent of their location in physiological solutions (pH 7.4). On the other hand, S53P4 particles exposed to acidic solutions with a pH < 5 likely dissolve incongruently, leaving a slowly dissolving Si-rich layer. In such an environment, the dissolution rates of Na, Ca, and P are independent of the location of the S53P4 particle in the implant. Thus, the pH and fluid flow are critical factors for the dissolution of S53P4 bioactive glass particles.