Abstract: BACKGROUND: Vancomycin is one of the first-choice antibiotics for osteomyelitis. Local administration can not only exert its antibacterial effect, but also greatly reduce systemic adverse reactions. 
OBJECTIVE: To optimize the preparation process of hydrochloric acid vancomycin-poly(propylene fumarate)/poly(lactic-co-glycolic acid) microspheres, and examine its in vitro release behavior and cytotoxicity. 
METHODS: The hydrochloric acid vancomycin-poly(propylene fumarate)/poly(lactic-co-glycolic acid) microspheres were prepared by the double emulsion solvent evaporation method (W1/O/W2). The encapsulation efficiency and drug loading capacity of microspheres were used as evaluation indicators. The effects of mass ratio of poly(propylene fumarate) and poly(lactic-co-glycolic acid), mass ratio of poly(propylene fumarate) and poly(lactic-co-glycolic acid) to vancomycin and dichloromethane concentration of oil phase poly(propylene fumarate) and poly(lactic-co-glycolic acid) on the preparation process were investigated by star point design-response surface method. The results were analyzed by multiple linear regression and binomial fitting. The effect surface method was used to optimize the optimal process conditions. The particle size of microspheres, the ζ potential, in vitro release behavior, and the cytotoxicity were measured. 
RESULTS AND CONCLUSION: (1) The hydrochloric acid vancomycin-poly(propylene fumarate)/poly(lactic-co-glycolic acid) microspheres were successfully prepared, and the optimal preparation process of the polymer microspheres was as follows: poly(propylene fumarate): poly(lactic-co-glycolic acid) mass ratio=2.41; poly(propylene fumarate)/poly(lactic-co-glycolic acid):pharmaceutical mass ratio=3.56; CH2Cl2 concentration of poly(propylene fumarate)/poly(lactic-co-glycolic acid)=129.73 g/L; the measured average encapsulation efficiency was 83.38%; deviation of 0.63% compared to predicted value; the measured average drug loading was 18.19%; deviation of 0.55% compared to predicted value. (2) The average particle size of the microspheres was 103.902 μm. The ζ potential was -21.5 mV. The cumulative release of the microspheres prepared with the optimal formulation was (22.90±0.55)% after 3 days, and the cumulative drug release reached (43.57±1.02)% after 28 days. After 28 days, the drug release of microspheres increased significantly, and the cumulative release amount was (97.89±1.39)% at 42 days. CTS classification was grade 1. (3) The microsphere preparation process optimized by the star point design-response surface method has good predictability. The optimized preparation process has good reproducibility, is simple and easy to implement, and the prepared microspheres have good in vitro sustained-release properties and biocompatibility. 

Key words: vacomycin, poly(lactic-co-glycolic acid), poly(propylene fumarate), microspheres, emulsion solvent evaporation method, star point design-response surface method, in vitro drug release, cytotoxicity