Effects of ethylene oxide gas sterilization on physical properties of poly(L-lactide)-poly(ethylene glycol)-poly(L-lactide) microspheres

The aggregation of poly(ce-hydroxy acid) microspheres during ethylene oxide (EO) gas sterilization makes it difficult for the microspheres to be used in clinical applications. In this study, six kinds of PLLA-PEG-PLLA tribloc k copolymers (TriPLE) were synthesized with various composition ratios of P EG/PLLA in the range of 0.012 to 0.103. TriPLE microspheres were prepared b y the oil-in-water emulsion method. TriPLE microspheres were characterized by using H-1-NMR, get permeation chromatography (GPC), and differential sca nning calorimetry (DSC). After sterilization by EO gas at 55 degreesC, the microspheres were analyzed by scanning electron microscope (SEM), laser dif fractometry, standard sieves, X-ray diffraction (XRD), GPC, and DSC. When t he composition ratio of PEG/PLLA was above 0.02, the initial crystallinity of TriPLE in microspheres was as high as 50%, and the microspheres were sui table to be sterilized by EO gas. On the other hand, TriPLE microspheres, w hich had composition ratios of PEG/PLLA below 0.02, had low initial crystal linities of about 30%, and aggregated during EO gas sterilization. For thes e microspheres, crystallinity increased up to 50% during the sterilization, whereas other TriPLE microspheres did not show any changes in crystallinit y. Therefore, the aggregation of TriPLE microspheres during EO gas steriliz ation was markedly reduced as the initial crystallinity of TriPLE in the mi crospheres was increased.