Osteogenic and antibacterial effects of double antibiotic-loaded microspheres

Infected bone defects present a significant clinical challenge, and the limitations of systemic antibiotic therapy necessitate a method for localized drug delivery to treat such wounds. In this study, vancomycin (Van)- and rifampin (Rif)-loaded poly(lactic-co-glycolic acid) (PLGA)/poly-l-lactic acid (PLLA) core-shell microspheres were prepared using coaxial electrospray technology for sequential release of the two antibiotics. Two formulations were fabricated with the drugs distributed in either the core or shell (Van/Rif and Rif/Van microspheres). Comprehensive microsphere characterization included evaluation of their morphology, drug encapsulation efficiency, and in vitro release kinetics. Biocompatibility was evaluated using MC3T3-E1 osteoblasts through adhesion, proliferation, and osteogenic differentiation assays. Antibacterial efficacy was assessed against Staphylococcus aureus in both planktonic and biofilm states in vitro and in a rat subcutaneous infection model in vivo. The results showed that uniformly sized, smooth-surfaced core-shell microspheres were successfully prepared. The Van/Rif microspheres (vancomycin in shell, rifampin in core) demonstrated superior synchronous release kinetics compared with the Rif/Van microspheres. Both formulations exhibited excellent biocompatibility, with no adverse effects on osteoblast viability, adhesion, proliferation, or differentiation. In vitro, both formulations achieved a high antibacterial rate (> 95%) against planktonic S. aureus and prevented biofilm formation. In vivo, both microsphere formulations significantly promoted wound healing, reduced bacterial load and neutrophil infiltration, and maintained high local antibiotic concentrations without systemic drug detection. In conclusion, coaxial electrospray-fabricated, dual antibiotic-loaded, core-shell microspheres provided controlled sequential drug release, excellent osteocompatibility, and potent localized antibacterial activity, representing a highly promising strategy for the treatment of bone infections.