Porous Vesicles with Extrusion-Tunable Permeability and Pore Size from Mixed Solutions of PEO–PPO–PEO Triblock Copolymers

Block copolymer (BC) vesicles in aqueous solution can encapsulate hydrophilic molecules or nanoparticles for drug and gene delivery, enhanced imaging, microreactors, or sensors. Inexpensive, biocompatible poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymers (TBCs) would be ideal for these applications if they could form concentrated vesicle solutions to encapsulate such molecules with high efficiency. It is shown that solutions of two PEO–PPO–PEO TBCs (EO₅–PO₆₈–EO₅ and EO₁₀₀–PO₆₅–EO₁₀₀) form vesicles, that the vesicle membranes are permeable to low-molecular weight (MW) solutes, and that extrusion reduces the membrane permeability and MW cutoff. Osmotic permeabilities before and after extrusion are ≈1000 and ≈10 µm s⁻¹, respectively, while the MW cutoffs for solute rejection are ≈1000 and ≈400 g mol⁻¹. Therefore, it is hypothesized that the vesicles contain pores, and that extrusion reduces the pores' size and the membrane's porosity. These selectively permeable vesicles can function as microreactors or sensors encapsulating large solutes without the need to add channel molecules or proteins.