Multi-modal imageability and degradation characteristics of high-borate glass systems for transient embolization

Two glass series were developed based on the substitution of a monovalent glass modifier for a di- or trivalent ion in a high borate glass system. The BRS series consists of compositions 0.70 B ₂ O ₃ –0.30-X Rb ₂ O – X SrO, and the BRG series consists of compositions 0.70 B ₂ O ₃ –0.30-X Rb ₂ O – X Ga ₂ O ₃ , where 0.00 ≤ X ≤ 0.10 in increments of 0.2. All glasses were characterized in order to examine their composition-structure-property relationships, and to assess their potential for use as degradable, radiopaque embolic agents. Glasses were melt quenched, and evaluated in terms of structural changes ( ¹¹ B MAS-NMR, density, and glass transition temperature), changes in radiopacity (both CT and MRI), and changes in degradation timeframes under simulated physiological conditions. Structural analysis determined there was no change in the B4% of the BRS series, despite a linear increase in density and Tg. The strontium acts as a crosslinker, creating a more hydrolytically stable network, which leads to longer dissolution times. Conversely, the BRG series displayed a linear decrease in the B4%, a decrease in density (Tg data not available), yet a slight increase in hydrolytic stability is also observed. Gallium most likely acts more as a glass former than a glass modifier, thereby sequestering oxygens from the tetrahedral boron centers, creating trigonal B3 centers and tetrahedral gallium. All glasses were found to be imageable on CT (intensity > 3200 HU at 120 kVp), and invisible on clinical MR imaging modalities.