Polymersomes with a smectic liquid crystal structure and AIE fluorescence

Abstract

A series of amphiphilic diblock copolymers PEG-TPE-b-PAChol containing a cholesterol-based smectic liquid crystal block PAChol and a tetraphenylethene (TPE) AIEgen situated between hydrophilic PEG and hydrophobic PAChol blocks were prepared by RAFT polymerization. The liquid crystal properties of the block copolymers were first characterized. One of the copolymers, PEG₄₅-TPE-b-PAChol₁₆, with a hydrophilic weight ratio of 18% was chosen for the self-assembly study using the nanoprecipitation method in dioxane/water and THF/water systems. The co-solvent (THF or dioxane) had a significant effect on its self-assembly behaviors. Characterization by cryo-EM showed that elongated ellipsoidal or tubular polymersomes with smectic ordering in the membrane were formed in the dioxane/water system. In contrast, spherical solid nanoparticles were obtained in the THF/water system as observed by SEM. All polymersomes and nanoparticles showed AIE fluorescence. The present work shows the possibility to obtain elongated polymersomes with both smectic LC orders and AIE fluorescence. By replacing the prototypical TPE with AIEgens that can be excited at longer wavelengths than UV, these cholesterol-based polymersomes and nanoparticles can be designed as fluorescent carriers of drugs for possible theranostic applications.