Abstract: Objective To construct poly(lactic-co-glycolic acid)(PLGA) micro-spheres with adjustable acidic degradation properties for application as an injectable scaffold in tissue engineering and carriers of drug release.Methods Sodium tripolyphosphate(TPP) was encapsulated by using W/O/W double-emulsion solvent evaporation method into PLGA micro-spheres.Results When the mixing molar ratio of PLGA to TPP was 64:1,the pH value of the solution containing PLGA/TPP micro-spheres could be well maintained at a neutral condition during the degradation of PLGA.The pH value of the resulting solution after being degraded for 28 days was 6.93,significantly higher than that of the respective one containing the pristine PLGA micro-spheres under the same condition(P<0.05).The amount of TPP could render a dramatic effect on the degradation behaviors of PLGA.When the molar ratio of PLGA to TPP was increased into 12:1,the pH value of the solution containing those PLGA/TPP micro-spheres would decrease to 6.35 after being degraded for 28 days,significantly lower than that of the pristine PLGA micro-spheres at the same time point(pH=6.66)(P<0.05).Conclusion The addition of such kind of salt with strong buffering capacity can efficiently neutralize the acid produced from the degradation of PLGA micro-spheres so as to prohibit the decrease in the pH value of the surrounding environment.However,if too much salt were used,the degradation of PLGA micro-spheres would also be accelerated.

Key words: PLGA, Polyphosphate salt, Encapsulation, Degradation