Thermo-responsive organic–inorganic hybrid vesicles with tunable membrane permeability

Abstract

Herein, a series of crosslinked thermo-responsive organic–inorganic hybrid vesicles with different morphologies was prepared by the self-assembly of poly(ethylene oxide)-block-poly[N-isopropylacrylamide-random-3-(trimethoxysilyl)propyl methacrylate] [PEO-b-P(NIPAM-r-TMPM)] in DMF–water mixture. The copolymers were synthesized by reversible addition-fragmentation chain transfer (RAFT) mediated radical polymerization using a PEO macromolecular chain transfer agent. After self-assembly and gelation procedure in solution, porous vesicles and simple vesicles were obtained by tuning the solvent composition in the binary solvent mixture of water and DMF and the initial copolymer concentration (C_ini). The membranes of the as-formed vesicles were intact at C_ini = 10 mg mL⁻¹, 80 wt% H₂O, 28 °C; but, after gelation process, the pores of several tens of nanometers were generated within the membranes due to the crosslinking-induced tensile force. However, there was no morphology transition at low C_ini or low water content. The developments of vesicle size and the membrane permeability regarding change in temperature were studied by DLS analysis and Nile Red probe method. The cumulative release of a water-soluble model drug, hydroxychloroquine sulfate (HCQ), was used to determine the permeability of the gelated vesicles. While the gelated porous vesicles displayed no permeability dependence on temperature, the gelated simple vesicles exhibited enhanced permeability with temperature elevation. Also, with increase of the crosslinking density of membrane, numbers of TMPM units, the permeability of the simple vesicles was enhanced at 20 °C but remained unchanged at 45 °C.