Structural changes of polylactic-acid (PLA) microspheres under hydrolytic degradation
✍ Scribed by M. F. Gonzalez; R. A. Ruseckaite; T. R. Cuadrado
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 241 KB
- Volume
- 71
- Category
- Article
- ISSN
- 0021-8995
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✦ Synopsis
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 smoothsurface microspheres were transformed to porous particles at the time of degradation at pH ϭ 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.