BACKGROUND: The active component in recombinant human bone morphogenetic protein-2/poly(lactide-co-glycolide) (rhBMP-2/PLGA) microsphere prone to be absorbed or lost during solution with physiological saline, and the setting time is uncontrollable using blood solution, so it is necessary to explore an sustained-release carrier that can control the setting time.OBJECTIVE: To construct an injectable BMP release system by combing rhBMP-2/PLGA microsphere with fibrin glue. DESIGN, TIME AND SETTING: An experimental comparative study was performed at the Department of Othopaedics, General Hospital of Chinese PLA from January 2005 to April 2008.MATERIALS: PLGA (polylactic acid/polyglycolic acid 75/25, M_r=3 000, with 0.025 L/g viscosity) was supplied by Shandong Institute of Medical Instruments; rhBMP-2 was offered by The Academy of Military Medical Sciences; and fibrin glue was supplied by Hangzhou Puji Medicine Technology Development Co., Ltd.METHODS:The rhBMP-2/PLGA microsphere was prepared using W/O/W solvent evaporation methods. rhBMP-2 loaded PLGA microsphere were incorporated in fibrin glue to establish injectable BMP release system.MAIN OUTCOME MEASURES: The setting time,release behaviors, electron spectroscopy for chemical analysis (ESCA) as well as pH values of composites were measured.RESULTS:①Compared with fibrin glue, the setting time of composites were slightly increased.②Initial burst release of the composites occurred, the drug release exceeded 16.76% within 2 days, and 76.75% of the drug was release within 42 days. ③ESCA showed that composites prolonged release times.④The PH value of composites was between microsphere and fibrin glue.CONCLUSION: RhBMP-2/PLGA microsphere/fibrin glue composite has satisfactory slow-release effect and syringeability, which not only degrade partial acid environment but also maintain the biological effect of higher density. Therefore, it forms a promising synthetic bone graft.