Design and Drug Carrier Application of a Photo-Responsive and pH-Sensitive Azobenzene Polymer Molecule

A series of amphiphilic block copolymers C₁₀-AZO-C₁₀-PDPA_n-PEG₄₅(C₁₀-azobenzene-C₁₀-poly2-(diisopropylamino)ethyl methacrylate-polyethylene glycol) (n=30,50,80) were designed and synthesized to improve stimuli-responsibility of pH/photo dual-responsive drug delivery system. In this paper, we used three steps to synthesize the copolymers. The data of proton nuclear magnetic resonance spectroscopy (¹H-NMR) and gel permeation chromatography (GPC) showed that copolymers were successfully synthesized. The florescence intensity ratio (I₃₇₃/I₃₈₄) of copolymeric micelles indicated that CMC (critical micelles concentrations) was negative correlation with PDPA polymerization degree. The image of transmission electron microscope showed that the copolymers were self-assembled to obtain uniform stable spherical micelle with particle size of 140—200 nm (0.3 mg/mL). Dynamic light scattering measurements were used to determine the diameters and Zeta potentials of the self-assembled copolymer micelles. Results showed that the copolymeric micelles were well dispersed in water. The structure of micelles was sensitively correlation with pH change. The pH-triggering points of copolymers were in the range of 6.3—7.2. And then, the reversible photo responsibility was investigated via UV-visible spectrophotometer. It was found that the absorption value of each copolymer micelle solution decreased at 350 nm (characteristic absorption peak of trans-AZO) and increased slightly at 440 nm (characteristic absorption peak of cis-AZO) when they were irradiated with 365 nm ultraviolet light, which indicated that the trans-structure was changed into cis-structure. After the solutions were irradiated with visible light of 470 nm, the cis-structures were found to convert into trans-structures again. Herein, we chose C₁₀-AZO-C₁₀-PDPA₃₀-PEG₄₅ for further experiment as its pH-triggering points fitted the pH environment of normal and cancer cells. In vitro release kinetics of copolymer micelles were studied using fluorescence spectrophotometer under different conditions. The cumulative drug release amount at pH 7.4 was apparently lower than those at pH 6.4 and 5.0. And the release amounts of micelles irradiated by ultraviolet rays were higher than those of non-irradiated samples. These results showed that the environmental stimuli responsibility of the copolymer micelles could control drug release by pH and light stimulations. Finally, we transfected the blank micelles to Hela cell. Cytotoxicity assay indicated that micelles had low cytotoxicity. Therefore, this copolymer-based drug carrier could be expected to achieve controllable drug release in response to different conditions.