Effect of PEG chain length and hydrophilic weight fraction on polymersomes prepared from branched (PEG)3-PLA co-polymers

A series of monomethoxy-polyethylene glycol (mPEG)-based branched amphiphilic copolymers of poly(dl-lactic acid) (PLA) with varying hydrophilic fraction and mPEG chain length were synthesized and used for preparing polymersomes by emulsion-diffusion-evaporation method. Effect of mPEG chain length and hydrophilic weight fraction on polymersome's particle size, protein adsorption, degradation, drug loading, and release kinetics were studied. For degradation study, polymersomes were suspended in acidic buffer at 37 degrees C where they degraded by poration followed by fragmentation and were stable at 4 degrees C and pH 7.4. Polymersomes were relatively stable with increased mPEG chain length and hydrophilic weight fraction, maintaining vesicular integrities under conditions of study. Protein adsorption studies showed a decrease in protein adsorption with increasing mPEG chain length and hydrophilic weight fraction of the copolymer. Drug loading and drug release profile of polymersomes were carried out using hydrophobic and hydrophilic dyes. The copolymers with short hydrophobic block chain have shown lower hydrophobic dye loading, while copolymers with longer hydrophobic block have shown higher hydrophobic dye loading however such trend was not observed for hydrophilic dye. The results indicated that hydrophobic dye, localized in the membrane of polymersomes, released within 2 hr while hydrophilic dye showed 25% burst release followed by sustained release till 21 days that could be attributed to thick bilayer membrane. The findings of this study have suggested that polymersomes made from such copolymers would be potential carrier systems for hydrophobic and hydrophilic drugs and would be able to control and sustain the release of hydrophilic dye. Copyright (C) 2010 John Wiley & Sons, Ltd.