CAN A SINGLE CONCENTRATION OF BIOACTIVE GLASS ACHIEVE BOTH OSTEOGENIC AND ANTIBACTERIAL EFFECTS?

Bioactive glass (BG) is well known for its osteoconductive, osteoinductive, and osteostimulatory properties, as well as its antibacterial activity, effects largely attributed to changes in pH and osmolarity during dissolution. Although BG demonstrates high clinical success rates (~90% in orthopaedic and dental applications) (Lindfors et al. 2017), reported failures are typically associated with inadequate debridement or postoperative complications (Steinhausen et al. 2021) rather than BG dosage. Most BG products used in orthopaedic surgery, such as S53P4 granules, are applied directly to fill defect sites, with dosage determined primarily by defect volume. If BG were to be used as a stand alone therapeutic agent, we hypothesize that a single dose cannot simultaneously optimize both osteogenic and antibacterial outcomes, regardless of composition. To simulate a clinically relevant scenario, we exposed Saos 2 osteoblast like cells and Staphylococcus aureus to the same BG concentration (25 mg/mL) at different BG compositions (45S5, S53P4, & 13-93) under direct contact conditions for 7 days. BG dissolution in DMEM and TSB media was characterized using ICP OES. Osteogenic effects were assessed via ALP activity, cell viability assay (Fluorescence microscopy, flow cytometry), and relative gene expression. Antibacterial effects were evaluated via colony forming units (CFU) and metabolic activity (XTT assay). Across BG types, we observed dose and time-dependent cytotoxicity in Saos 2 cells (~70% reduction in viability vs control), accompanied by a decline in ALP activity over time. No reduction in S. aureus growth occurred until later time points. Dissolution profiles showed similar pH increases and ion release patterns in both media. No hydroxyapatite (HA) formation was detected. A single BG concentration did not produce both the expected osteogenic and antibacterial effects. The tested dose was cytotoxic to Saos 2 cells yet insufficient to exert an early bactericidal effect on S. aureus. These findings suggest the need for dosage guidelines tailored to the intended clinical outcome for example, prioritizing bactericidal activity in osteomyelitis or optimizing osteogenesis when filling bone defects. Simply basing BG dosage on defect size may not be adequate for achieving dual therapeutic goals.