Available online 12 November 2025

Bioactive phosphosilicate glasses with high in vitro bioactivity and mechanical strength were developed by elucidating the roles of ZrO2 and P2O5 in governing structure, dissolution behavior, and bioactivity. In comparison to conventional bioactive glass such as 45S5, these glasses exhibit an intriguing phenomenon of slow initial dissolution rates yet overall high ion releases in long-term reactions. This is found to originate from the inhibited reorganization of silica gel layers influenced by Zr-O-Si cross-linkages, as previously observed in zirconia-containing nuclear waste glasses. The suppression effect is evidenced by the progressive increase in gel layer thickness, reaching its maximum at 4 mol% ZrO2 incorporation. Additionally, TEM observations reveal nanopores within the gel and a depletion zone between the pristine glass and Zr-O-Si gel, further highlighting the critical role of ZrO2 in modulating dissolution and enhancing bioactivity. Molecular dynamics simulations confirm a mixed network of sixfold-coordinated [ZrO6] and fourfold-coordinated [SiO4] units, with the porous gel model indicating interconnected porosity that facilitates solution diffusion and glass dissolution. This work identifies a new class of bioactive glasses and establishes a clear relationship between structure, dissolution behavior, and bioactivity, providing insights for the rational design of advanced bioactive materials.

Our findings show that ZrO2 containing bioactive glasses have unusual dissolution behaviors and high bioactivity. By using a range of characterization methods and molecular dynamics computer simulations, the short and medium range glass structure were revealed and their relation to the dissolution behavior and in vitro bioactivity were elucidated. We found that although zirconia decreases initial glass dissolution rate, it hinders the gel layer reorganization hence increases the overall dissolution and leaching of alkali and alkali earth ions that lead to improved bioactivity. This behavior increases the design space of bioactive glass compositions and enable design of glasses that have simultaneously high modulus, low thermal expansion, high thermal stability and high in vitro bioactivity.

Bioactive glass

Zirconia oxide

In vitro bioactivity

Dissolution

Structure Characterization

Molecular dynamics simulations

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