Structural changes of polylactic‐acid (PLA) microspheres under hydrolytic degradation
Structural changes of polylactic‐acid (PLA) microspheres under hydrolytic degradation
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DOI：
10.1002/(sici)1097-4628(19990222)71:8
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发表时间：
1999-02
影响因子：
3
通讯作者：
M. Gonzalez;R. Ruseckaite;T. Cuadrado
中科院分区：
文献类型：
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作者：
M. Gonzalez;R. Ruseckaite;T. Cuadrado
以95%L和5%d-乳酸异构体为原料，在195℃下无催化剂直接缩聚，制得低相对分子质量的聚乳酸，并将其用于乳液-溶剂挥发法合成微球。采用凝胶渗透色谱(GPC)、X射线散射(XRD)、差示扫描量热法(DSC)和扫描电子显微镜(SEM)等技术，跟踪了微球在37℃下体外降解过程中的形态和结构变化。在潮湿环境中储存的样品在加热后结晶能力增加。初始光滑表面的微球在pH=7(37°C)下降解时转变为多孔粒子。质量损失-时间曲线的形状支持非均相整体降解过程的存在。水解后，残留粒子的相对分子质量降低，结晶度增加。90天后，结晶度达到53%。X-射线衍射谱表明形成了晶态低聚结构。低分子量物种的结晶将不能在药物输送系统中实现所需的聚乳酸吸收。©1999 John Wiley&Sons，Inc.J Appl Polym Sci 71：1223-1230,1999
Low molecular-weight polylactic acid (PLA) was obtained by direct polycondensation of a mixture of 95% l and 5% d-lactic acid isomers, without catalyst, at 195°C. This polymer was used for the synthesis of microspheres by emulsion–solvent evaporation method. Gel Permeation Chromatography (GPC), X-ray Scattering (XRD), Differential Scanning Calorimetry (DSC), and Scanning Electron Microscopy (SEM) techniques were applied to follow morphological and structural changes of particles along in vitro degradation at 37°C. The original microspheres were amorphous but could crystallize partially upon heating. Samples stored in a humid environment exhibited an increase in the crystallization capability upon heating. Initial smooth-surface microspheres were transformed to porous particles at the time of degradation at pH = 7 (37°C). The shape of mass loss vs. time curve supports the presence of a heterogeneous bulk degradation process. After hydrolytic degradation the residual particles showed a molecular weight decrease and a crystallinity increase. After 90 days the crystallinity attained a value of 53%. The X-ray diffraction spectrum indicated the formation of a crystalline oligomeric structure. Crystallization of low molecular weight species will not enable the desired PLA absorption in drug delivery systems. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1223–1230, 1999