Effect of constant and alternating fluid flow conditions on the dissolution of bioactive glass S53P4

Fluid flow conditions strongly influence the dissolution behaviour of glasses by controlling mass transport and interfacial reactions. This study extends previous investigations under constant flow conditions by examining alternating flow rates and their influence on the dissolution behaviour of commercial S53P4 bioactive glass particles (500–800 µm) under physiologically relevant conditions. The dynamic dissolution was investigated in simulated body fluid using flow-through reactors under constant (0.04, 0.12, and 0.2 mL/min) and alternating-flow conditions (0.04 and 0.2 mL/min), where the flow rate was switched every 24 h, starting with either the lower or the higher flow rate. Solution pH and elemental concentrations were measured at selected time points during dissolution, and glass particles were characterised using SEM, FTIR, and XRD after 96 and 192 h. Cumulative silicon dissolution increased with increasing constant flow rate, reaching approximately 25%, 66%, and 72% after 192 h at flow rates of 0.04, 0.12, and 0.2 mL/min, respectively. Under alternating-flow conditions, cumulative dissolution depended strongly on the initial flow rate. When the experiment was initiated at the higher flow rate, cumulative silicon release reached approximately 50%, compared with 41% when initiated at the lower flow rate. These results indicate that transient periods of reduced flow slow subsequent glass dissolution, potentially through the formation of diffusion-limiting surface layers. Overall, the results highlight fluid flow rate and temporal variations in flow as key parameters governing bioactive glass dissolution and underscore their relevance for evaluating bioactive glass performance under physiological conditions.