Defect-free bioactive glass surfaces with a grooved microstructure at the low micrometer scale were achieved by a mold casting process. The process was applied to the well-known glass compositions 45S5 and 13-93. Such microstructured surfaces may exhibit especially favorable conditions for bone cell orientation and growth. The aim of the study was to assess the parameter range for a successful casting process and thus to produce samples suitable to investigate the interaction between structured surfaces and relevant cells. Viscous flow in its temperature dependence and thermal analysis were analyzed to identify a suitable process window and to design a manageable time-temperature process scheme. Counteracting effects such as formation of chill ripples, mold sticking and build-up of permanent thermal stress in the glass had to be overcome. A platinum gold alloy was chosen as mold material with the mold surface bearing the mother shape of the microstructure to be imprinted on the glass surface. First experiments studying the behavior of osteoblast-like cells, seeded on these microstructured glass surfaces revealed excellent viability and an orientation of the cells along the microgrooves. The presented results show that direct casting is a suitable process to produce defined microstructures on bioactive glass surfaces.

The interaction between bioactive glass and body fluid is crucial for the special properties of this material, therefore a large number of experimental data is available in literature. However, a frame for systematic interpretation of these results in terms of understanding the mechanisms at the interface between glass and body medium and the relation between glass composition and dissolution behavior is still missing. For two multicomponent bioactive glasses, 45S5 and 13-93, the Gibbs energies of the glassy material on one side and their aqueous system on the other side were calculated individually. The difference between solid material and aqueous system further constitutes the pH dependent Gibbs energy of hydration, ∆Ghydr. The impact of glass compositions and glassy or crystalline state on ∆Ghydr is demonstrated referring to chemical durability. Along considerations regarding the aqueous system, the thermodynamic calculations proof the precipitation of hydroxyapatite inwater and simulated body fluid for a systemcontaining P2O5 and Ca2+. In the course of deriving the Gibbs energies for bioactive glass compositions via constitutional compounds, bioactive behavior is discussed from the point of coexisting equilibrium phases in the system of Na2O-CaO-SiO2.

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