Polymersomes are a class of synthetic vesicles composed of a polymer membrane surrounding an aqueous inner cavity. In addition to their overall size, the thickness and composition of polymersome membranes determine the range of potential applications in which they can be employed. While synthetic polymer chemists have made great strides in controlling polymersome membrane parameters, measurement of their permeability to various analytes including gases, ions, organic molecules, and macromolecules remains a significant challenge. In this Outlook, we compare the general methods that have been developed to quantify polymersome membrane permeability, focusing in particular on their capability to accurately measure analyte flux. In addition, we briefly highlight strategies to control membrane permeability. Based on these learnings, we propose a set of criteria for designing future methods of quantifying membrane permeability such that the passage of a variety of molecules into and out of their lumens can be better understood.

The contents of biological cells are retained within compartments formed of phospholipid membranes. The movement of material within and between cells is often mediated by the fusion of phospholipid membranes, which allows mixing of contents or excretion of material into the surrounding environment. Biological membrane fusion is a highly regulated process that is catalyzed by proteins and often triggered by cellular signaling. In contrast, the controlled fusion of polymer-based membranes is largely unexplored, despite the potential application of this process in nanomedicine, smart materials, and reagent trafficking. Here, we demonstrate triggered polymersome fusion. Out-of-equilibrium polymersomes were formed by ring-opening metathesis polymerization-induced self-assembly and persist until a specific chemical signal (pH change) triggers their fusion. Characterization of polymersomes was performed by a variety of techniques, including dynamic light scattering, dry-state/cryogenic-transmission electron microscopy, and small-angle X-ray scattering (SAXS). The fusion process was followed by time-resolved SAXS analysis. Developing elementary methods of communication between polymersomes, such as fusion, will prove essential for emulating life-like behaviors in synthetic nanotechnology.