Stereocomplexes of Triblock Poly(lactide‐ PEG₂₀₀₀‐lactide) as Carrier of Drugs

Abstract

Triblock copolymers of poly(lactide)‐poly(ethylene‐glycol)‐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 acetonitrile 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.

Syntheses of polylactides by means of tin catalysts

“…109,110 Starting out from commercial PEGs, Zhu et al prepared A-B-A triblocks with amorphous poly(D,L-lactide) A-blocks and studied to what extent the crystallization of the PEG blocks depended on their length. [111][112][113] Other examples of such amorphous-amorphous triblocks were contributed by Deng et al 114 Triblock copolyesters based on a PEG B-block and crystalline PLLA A-blocks were first synthesized by Kricheldorf et al 115,116 A special working field which emerged around 1995 concerned the formation and characterization of stereocomplexes of PEG-based A-B-A block copolymers having PLLA or PDLA A-blocks. 110,[116][117][118][119][120] Kubies et al studied the microdomain structure of such triblock copolymers.…”

Stereocomplex Polylactide for Drug Delivery and Biomedical Applications: A Review

“…The stability of the self-assembly can be influenced by several environmental factors, including the pH, temperature, polymer concentration, and ionic strength [ 22 , 23 , 24 , 25 ]. Bishara et al synthesized stereocomplex particles composed of an enantiomeric triblock copolymer (PLA-PEG 2000 -PLA) by blending in acetonitrile solutions [ 26 ]. Figure 2 a shows that the stereocomplex nanoparticles have smooth surfaces resulting from PEG segments and sizes ranging from the nanometer to micrometer range.…”

“…Closed and open triangles depict specimens composed of PLLAx-PEG2000-PLLAy (x + y = 25) with D-PLA and PLLAx-PEG2000-PLLAy (x + y = 50) with D-PLA, respectively. This experiment was conducted in phosphate buffer (pH 7.4) at 37 °C [ 26 ], Copyright 2005. Reproduced with permission from WILEY-VCH Verlag GmbH & Co.…”

Synthesis and characterization of di‐polyester diamides

“…Among the most extensively studied degradable triblocks for biomedical applications, are those consisting of a central poly(ethylene glycol) (PEG) block and a poly(lactic acid) (PLA) block on each side of the central PEG block 1, 3, 4. In an earlier study,5 the synthesis and properties of a series of biomedical degradable poly(ester‐ether‐urethane)s, based on chain extended poly(caprolactone) (PCL)‐PEG‐(PCL) triblocks, was presented.…”