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.

Virus retention filtration is a common step in modern biopharmaceutical manufacturing as it enables efficient removal of potential adventitious and endogenous viruses via size exclusion. Modern parvovirus retention filters have significantly improved fluxes and parvovirus retention in comparison to earlier versions of these filters. However, these filters may be more susceptible to premature fouling and require more effort for process optimization. Here, we demonstrate that polyamide‐6,6 (nylon‐6,6) membranes when used as prefilters can increase the capacity of these Parvovirus retentive filters that are less susceptible to premature fouling. We found that the mechanism of polyamide‐mediated filtration improvement can be explained by the binding of monoclonal antibody (mAb) aggregates with a diameter of 20–100 nm, and we show that this mechanism is shared by other types of adsorptive prefilters. Finally, by the combination of mobile phase screening, additive spiking, and molecular dynamics simulations, we show that polyamide‐6,6 removes mAb aggregates through hydrophobic interactions making its design space potentially complementary to other available prefilters. Our studies support the aggregate‐mediated mechanism of flux decay during viral filtration and suggest that polyamide‐6,6 could be considered as an alternative cost‐effective option to extend the capacity of viral filters.

Front Cover: A mixture of two poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) block copolymers, PEO100PPO68PEO100 and PEO5PPO68PEO5, forms vesicles in aqueous solution. The vesicle membranes are selectively permeable to small molecules, suggesting that they contain transmembrane pores. This size selectivity is extrusion‐tunable, and could allow the vesicles to serve as sensors or microreactors. Further details can be found in article number https://doi.org/10.1002/macp.201700620 by Manish Kumar and co‐workers.