Dissolution Kinetics of a Bioactive Glass by Continuous Measurement

Understanding the detailed dissolution behavior is of importance when novel glasses are designed for different clinical applications. The goal of this work was to develop a sensitive on-line analysis method to study the dissolution of bioactive glasses. An inductively coupled plasma optical emission spectrometer together with a flow-through microvolume pH electrode were utilized to continuously measure the concentration profile of the ions dissolving from glass particles into aqueous solutions. The method was tested with the bioactive glass 1-98 consisting of seven oxides: 6Na2O, 11K2O, 5MgO, 22CaO, 1B2O3, 2P2O5, and 53SiO2 (wt%). The influence of flow rate and temperature on the dissolution profile and kinetics of 1-98 was studied in ultrapure water. In addition, the influence of the solution composition was studied using ultrapure water and with tris(hydroxymethyl)aminomethane (TRIS) buffer. The strength of the method is that the initial dissolution can be accurately determined simultaneously both qualitatively and quantitatively. When using the highest flow rates, the dissolution rate changed from a diffusion-controlled toward a surface-controlled mechanism. As a result of the temperature increase, the overall dissolution increased according to Arrhenian behavior and led more rapidly to steady-state dissolution. The change of solution from unbuffered (ultrapure water) to TRIS changed the dissolution mechanism from uniform to preferential. In addition, higher concentrations of all ions were measured in TRIS than in pure water. The method develop is promising for fast screening of the dissolution mechanism of glasses in different experimental conditions.