Structural Changes of Polylactic-Acid (PLA) Microspheres under Hydrolytic Degradation

M.F.GONZÁLEZ; R.A.RUSECKAITE; T.R.CUADRADO

JOURNAL OF APPLIED POLYMER SCIENCE

Wiley & Sons

Año: 1999 vol. 71 p. 1223 - 1230

0021-8995

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 5 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