Genipin cross-linked PEG-block-poly(l-lysine)/disulfide-based polymer complex micelles as fluorescent probes and pH-/redox-responsive drug vehicles

We report the synthesis of genipin cross-linked polyionic complex (PIC) micelles by mixing a pH-sensitive/disulfide-based polymer, poly(DTPA-co-cysam), which was synthesized by copolymerization of diethylenetriaminepentaacetic (DTPA) dianhydride with cystamine, and a pH-sensitive copolymer, polyethylene glycol-block-poly(l-lysine) (PEG-b-PLL), with the aid of metal ion and subsequent cross-link. Their size and colloidal property were found to be determined by mixing weight percentage, polymer molecular weight, and metal ion. Upon genipin cross-link, the cross-linked compound not only stabilizes the assembled nanostructures but also induces red fluorescence, which is promising as a fluorescent probe for cell imaging. The experimental data suggested that the emission of red fluorescence may result from the presence of carboxyl group in the compact, cross-linked micelles. These genipin cross-linked PIC micelles were found to be biocompatible toward fibroblast 3T3 cells and exhibited noticeable pH-sensitive and glutathione-cleavable behavior based on doxorubicin (DOX) release experiments, suggesting that they are promising stimuli-responsive drug vehicles. The drug release behavior was found to depend on particle/membrane permeability and the percentage of amino group in the particles/membranes. This approach provides a simple and facile method to prepare multifunctional, cross-linked micelles by properly design of constituent homopolymer/copolymer for specific purpose.