Abstract
The concept of designing third-generation bioactive glasses for tissue engineering is based on the principle of providing a scaffold (i.e., structural support) and chemical conditions (i.e., ionic dissolution products) that initiate a synchronized sequence of cell level responses that result in the expression of genes required for living tissues regeneration. Realizing the goal of designing these glasses requires a thorough understanding of the complex sequence of reactions that control their rate of degradation (when in contact with physiological fluids) and the structural drivers that control them. While there is considerable amount of literature published on chemical dissolution behavior and apatite-forming ability of potentially bioactive glasses, the majority of data published to date has been produced using different experimental and measurement protocols. As a result, intercomparison of different datasets reveals inconsistencies between experimental groups. In this article, we have highlighted some major experimental challenges and choices that need to be carefully navigated in order to unearth the mechanisms governing the chemical dissolution behavior of bioactive glasses and to accurately understand the composition-structure-property relationships. Accordingly, a borosilicate based melt-quenched model bioactive glass system has been used to demonstrate the impact of thermal history on the structure and chemical dissolution behavior of glasses. The impact of thermal history on glass structure has been studied using 23Na, 11B, and 29Si magic angle spinning - nuclear magnetic resonance (MAS NMR) spectroscopy and fictive temperature measurements. The dissolution behavior of glasses in deionized water has been followed by inductively coupled plasma - optical emission spectroscopy (ICP-OES), X-ray diffraction and infrared spectroscopy. The dissolution experiments have been designed using surface area of glass powder - to - volume of solution (SA/V) approach instead of the ratio of mass of sample - to - volume of solution (typically used in bioactive glass studies). This approach not only allows us to draw a rigorous correlation between the molecular structure of glasses with their degradation behavior, but the data obtained using this approach can also be used to develop non-empirical predictive models for design of next generation bioactive glass compositions.
