Preparation of pH-sensitive micelles from miktoarm star block copolymers by ATRP and their application as drug nanocarriers

In this study, novel pH-sensitive micelles were prepared from miktoarm star block copolymer, mPEG-b-P(MMA-co-MAA)2, by the atom transfer radical polymerization (ATRP) technique and dialysis method. Molecular structures and characteristics of the micelles were confirmed by 1H nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC), dynamic light scattering (DLS), and transmission electron microscopy (TEM). The self-assembled micelles have a very low critical micelle concentration, indicating a high colloidal stability in aqueous solution. Methotrexate (MTX) was selected as the model drug of poor solubility. A relatively high drug loading capacity was found, and the in vitro release studies revealed that about 26% of the drug was released in simulated gastric fluid (SGF, pH 1.2) over 48 h compared to the maximum drug release of about 98% in simulated intestinal fluid (SIF, pH 7.4). Thus, the pH-sensitive micelles might serve as promising carriers for oral drug delivery of hydrophobic drugs with controlled release behavior.