Investigating the effect of germanium on the structure of SiO-ZnO-CaO-SrO-PO glasses and the subsequent influence on glass polyalkenoate cement formation, solubility and bioactivity.

A series of germanium (Ge)-containing glasses were synthesized based on a starting glass composition of SiO-ZnO-CaO-SrO-PO. Additions of GeO (6 and 12 mol%) were incorporated at the expense of SiO which retained the amorphous character, and each glass was processed to present similar particle size and surface area. Glass characterization using x-ray photoelectron spectroscopy (XPS) and magic angle spinning nuclear magnetic resonance (MAS-NMR) determined that the addition of GeO increased the fraction of lower Q-speciation and subsequently the concentration of non-bridging oxygens (NBO). Glass Polyalkenoate Cements (GPC) were formulated from each glass with 40, 50 and 60 wt% PAA, and presented time dependent solubility profiles (1, 10, 100, 1000 h) for the release of Si (4-140 mg/l), Ca (1-8 mg/l), Zn (<6 mg/l), Sr (2-37 mg/l), PO (2-43 mg/l) and Ge (20-911 mg/l) and attained pH values close to 7.5 after 1000 h. Ge-GPCs containing 40 wt% polyacrylic acid (PAA) presented appropriate working time (T) and setting times (T), and the corresponding compressive strengths ranged from (14-30 MPa). The Ge-GPCs (40, 50 wt%) presented a linear increase (R-0.99) with respect to time. Simulated Body Fluid (SBF) testing resulted in the Ge-GPCs encouraging the precipitation of crystalline hydroxyapatite on the GPC surface, more evidently after 100 and 1000 h incubation.