Stabilized polymeric micelles by electrostatic interactions for drug delivery system

Methoxy poly(ethylene glycol)-block-oligo(L-aspartic acid)-block-poly(epsilon-caprolactone) with four aspartic acid groups was synthesized with a molecular weight and M-w/M-n of 8930 and 1.22. Polymeric micelles were formed by dialysis and stabilized by electrostatic interactions between the carboxylic acid groups and Calcium cations. The critical micelle concentration of mPEG-Asp-PCL was determined to be 0.078 mg/mL. At 0.02 mg/mL, the dissociation of micelles without ionic stabilization formed an opaque, phase-separated solution, while the stabilized micelles under the same conditions showed structural stability through ionic stabilization. The paclitaxel-loading and efficiency were 8.7% and 47.6%, respectively, and the drug loading increased the mean diameter from 73.0 nm to 87 nm, which was increased further to 96 run after ionic fixation. Rapid releases of approximately 65% of the encapsulated paclitaxel from a non-stabilized micelle and 45% from a stabilized micelle were observed in the first 24 h at pH 7.4 in a PBS Solution containing 0.1 wt% Tween 80. The stabilized micelles then showed a sustained, slow release pattern over a couple of weeks, while the profile from the non-stabilized micelles reached a plateau at approximately 75% after 50 h. The enhanced micelle stability independent of concentration through ionic stabilization opens a way for preparing long circulating delivery systems encapsulating water-insoluble drugs. (C) 2009 Elsevier B.V. All rights reserved.