Self-assembly, pH-responsibility and controlled release of doxorubicin of PDEAEMA-PEG-PDEAEMA triblock copolymers: effects of PEG length

Abstract

Effects of poly(ethylene glycol) (PEG) block length on the self-assembly of a series of pH-sensitive poly(N,N-diethylaminoethyl methacrylate)m-PEGn-poly(N,N-diethylaminoethyl methacrylate)m triblock copolymers (PDEAEMAm-PEGn-PDEAEMAm) have been studied. The synthesized triblock copolymers have an almost fixed PDEAEMA block length (m ≈ 65) and varying PEG block lengths (n = 11, 20, 89 or 134). The acid–base titration results show that the pKa value of the block copolymer shifts from 6.84 to 7.08 when the PEG block length increases from 11 to 134, indicating that the pH-sensitivity of the triblock copolymer can be adjusted through changing the PEG block length. With the increase of the hydrophilic PEG block length, the critical micelle concentration value of the triblock copolymer obtained from fluorescence spectroscopy changes from 5.50 × 10–3 to 13.23 × 10–3 mg mL−1. The block copolymers can self-assemble into the micelles in PBS solution at pH 7.4, and the average size of the self-assembly decreases from 178 nm to 45 nm with the increase of the PEG block length as determined by dynamic light scattering. The block copolymers show great biocompatibility in the cytotoxicity assay. Results from these triblock copolymers in the drug-controlled release indicate that the release rate of doxorubicin-loaded micelles at pH 5.0 is faster than that at pH 7.4, and the cumulative drug release in 48 h at pH 5.0 increases from 70.4% to 89.8% with the decrease of the PEG block length. Accordingly, this PDEAEMA65-PEGn-PDEAEMA65 copolymer is an excellent carrier for controllable drug delivery and release.