In situ sprayed hydrogels containing resiquimod-loaded liposomes reduce chronic osteomyelitis recurrence by intracellular bacteria clearance.

At present, surgical debridement and systematic administration of antibiotics represent the mainstay of treatment for chronic osteomyelitis. However, it is now understood that Staphylococcus aureus (S. aureus) can survive within excessively polarized M2 macrophages and evade antibiotics, accounting for the high recurrence of chronic osteomyelitis. Effective treatments for intracellular infection have rarely been reported. Herein, we designed an in situ sprayed liposomes hydrogels spray with macrophage-targeted effects and the ability to reverse polarization and eradicate intracellular bacteria to reduce the recurrence of osteomyelitis. Resiquimod (R848)-loaded and phosphatidylserine (PS)-coating nanoliposomes were introduced into fibrinogen and thrombin to form the PSL-R848@Fibrin spray. Characterization and phagocytosis experiments were performed to confirm the successful preparation of the PSL-R848@Fibrin spray. Meanwhile, in vitro cell experiments validated its ability to eliminate intracellular S. aureus by reprogramming macrophages from the M2 to the M1 phenotype. Additionally, we established a chronic osteomyelitis rat model to simulate the treatment and recurrence process. Histological analysis demonstrated a significant increase in M1 macrophages and the elimination of intracellular bacteria. Imaging revealed a significant decrease in osteomyelitis recurrence. Overall, the liposome hydrogels could target macrophages to promote antibacterial properties against intracellular infection and reduce the recurrence of chronic osteomyelitis, providing the foothold for improving the outcomes of this patient population. STATEMENT OF SIGNIFICANCE: Chronic osteomyelitis remains a high recurrence although undergoing traditional treatment of debridement and antibiotics. S. aureus can survive within the excessively polarized M2 macrophages to evade the effects of antibiotics. However, few studies have sought to investigate effective intracellular bacteria eradication. Herein, we designed a macrophage-targeted R848-containing liposomes fibrin hydrogels spray (PSL-R848@Fibrin) that can reprogram polarization of macrophages and eradicate intracellular bacteria for osteomyelitis treatment. With great properties of rapid gelation, strong adhesion, high flexibility and fit-to-shape capacity, the facile-operated immunotherapeutic in-situ-spray fibrin hydrogels exhibited huge promise of reversing polarization and fighting intracellular infections. Importantly, we revealed a hitherto undocumented treatment strategy for reducing the recurrence of chronic osteomyelitis and potentially improving the prognosis of chronic osteomyelitis patients.