Stereocomplexes of triblock poly(lactide- PEG₂₀₀₀-lactide) as carrier of drugs

Triblock copolymers of poly(lactide)-poly(ethylene-grycol)-poly(lactide) {PLA-PEG₂₀₀₀-PLA) were synthesized by ring-opening polymerization of lactide and PEG₂₀₀₀ diol as co-catalyst. Stereocomplexes with particle sizes ranging from nanometers to microns were obtained by mixing acetonitrite solutions of pairs of enantiomeric homopoly(lactide) and the triblock copolymers. The stereocomplexes exhibited higher crystalline melting temperatures than the optically pure polymers. The ratio of PLA terminals in the copolymers had a significant effect on their stereocomplex degradation and drug release. These stereocomplexes were used for the encapsulation of dexamethasone for controlled release applications. Dexamethasone phosphate loading capacity, in vitro release, degradation and stability of polymers and formulation were investigated for one month. An increase in the dexamethsone phosphate content in the stereocomplex or a decrease in the PLA ratio in the copolymer resulted in a faster release of drug and polymer degradation.