“Breathing” Vesicles

Abstract

A vesicle system is described that possesses a pH-induced "breathing" feature and consists of a three-layered wall structure. The "breathing" feature consists of a highly reversible vesicle volume change by a factor of ca. 7, accompanied by diffusion of species into and out of the vesicles with a relaxation time of ca. 1 min. The triblock copolymer poly(ethylene oxide)(45)-block-polystyrene(130)-block-poly(2-diethylaminoethyl methacrylate)(120) (PEO(45)-b-PS(130)-b-PDEA(120)) was synthesized via ATRP. Self-assembly into vesicles was carried out at a pH of ca.10.4. The vesicle wall was shown by cryo-TEM to consist of a sandwich of two external ca. 4 nm thick continuous PS layers and one ca. 17 nm thick PDEA layer in the middle. As the pH decreases, both the vesicle size and the thickness of all three layers increase. The increase of the thickness of the intermediate PDEA layer arises from the protonation and hydration, but the swelling is constrained by the PS layers. The increase of the thickness of the two PS layers is a result of an increasing incompatibility and an accompanying sharpening of the interface between the PS layers and the PDEA layer. Starting at a pH slightly below 6, progressive swelling of the PDEA layer with decreasing pH induces a cracking of the two PS layers and also a sharp increase of the vesicle size and the wall thickness. By pH 3.4, the vesicle size has increased by a factor of approximately 1.9 and the wall shows a cracked surface. These changes between pH 10.4 and 3.4 are highly reversible with the relaxation time of ca. 1 min and can be performed repeatedly. The change in the wall structure not only increases dramatically the wall permeability to water but also greatly expands the rate of proton diffusion from practically zero to extremely rapid.

Polymeric Microtubules That Breathe: CO2‐Driven Polymer Controlled‐Self‐Assembly and Shape Transformation

“…The entire transformation is manipulated by CO 2 , which is in many ways reminiscent of a breathing deformable motion. [16] The tubular and micellar morphology can be identified as the beginning and end of this breathing motion.…”

Recent trends in the tuning of polymersomes’ membrane properties

“…Recently, Eisenberg et al have found an elegant way to control the size and permeability of polymersomes, using asymmetric triblock copolymer poly(ethylene oxide) 45 -block -polystyrene 130 -block -poly(2-diethylaminoethylmethacrylate) 120 (PEO 45 -b-PS 130 -b-PDEA 120 ) self-assembled into vesicles at pH 10.4, where PDEA is hydrophobic [85]. They clearly demonstrated that the membrane was made of 5 layers in the following order: PEO-PS-PDEA/PDEA-PS-PEO.…”

Spontaneous Vesicles Modulated by Polymers

“…The majority of processing methods for unilamellar vesicles production use an input of energy, ultrasonic treatment, elevated temperature or pressure [1] to disperse surfactants as a vesicle phase that in most cases is unstable and highly polydisperse. However, spontaneous formation of vesicles has been reported either by mixing surfactants with oppositely charged head groups [2][3][4][5][6] or with double-tailed surfactants [7][8][9] and with block-copolymer systems [10][11][12][13].…”