Effect of Sm³⁺ ions on structure and reactivity of S53P4 and 13-93 bioactive glasses

Bioactive glasses are widely recognized for their ability to bond with living tissues and stimulate regenerative processes, making them a cornerstone in the development of advanced biomaterials. Incorporating rare earth (RE) elements enables the integration of optical functionalities with biological activity while modifying network connectivity. However, previous studies have mainly focused on luminescent performance, and the structural mechanisms by which individual REE dopants influence dissolution kinetics and bioactivity remain insufficiently investigated. This study investigates the influence of samarium (Sm³⁺) doping on the structural and in vitro bioactive behavior of two Hench-type glasses, S53P4 and 13-93, containing 0.2 and 2 mol% Sm₂O₃. Structural characterization by MAS-NMR, FTIR, and Raman spectroscopy reveals that Sm³⁺ promotes silicate network depolymerization by generating non-bridging oxygens. Despite this depolymerization, Sm-doped glasses show reduced ion release (up to 20 % reduction in Ca and Si after 24 h), and lower pH changes (maximum pH 7.8 vs. 8.4 in the undoped glass), and a delayed hydroxycarbonate apatite (HCA) formation in simulated body fluid (SBF). These effects are attributed to strong SmO bonding and restricted ion mobility in the glass network. The findings indicate that Sm³⁺ modifies the glass network and influences dissolution kinetics, providing clearer insight into the structure-bioactivity relationship in REE-doped silicate glasses. This combined behavior may be used to guide the design of compositions with controlled degradation for regenerative applications.