Aquaporin-Based Biomimetic Polymeric Membranes: Approaches and Challenges

In recent years, aquaporin biomimetic membranes (ABMs) for water separation have gained considerable interest. Although the first ABMs are commercially available, there are still many challenges associated with further ABM development. Here, we discuss the interplay of the main components of ABMs: aquaporin proteins (AQPs), block copolymers for AQP reconstitution, and polymer-based supporting structures. First, we briefly cover challenges and review recent developments in understanding the interplay between AQP and block copolymers. Second, we review some experimental characterization methods for investigating AQP incorporation including freeze-fracture transmission electron microscopy, fluorescence correlation spectroscopy, stopped-flow light scattering, and small-angle X-ray scattering. Third, we focus on recent efforts in embedding reconstituted AQPs in membrane designs that are based on conventional thin film interfacial polymerization techniques. Finally, we describe some new developments in interfacial polymerization using polyhedral oligomeric silsesquioxane cages for increasing the physical and chemical durability of thin film composite membranes

Selecting analytical tools for characterization of polymersomes in aqueous solution

Selecting the appropriate analytical methods for characterizing the assembly and morphology of polymer-based vesicles, or polymersomes are required to reach their full potential in biotechnology. This work presents and compares 17 different techniques for their ability to adequately report size, lamellarity, elastic properties, bilayer surface charge, thickness and polarity of polybutadiene-polyethylene oxide (PB-PEO) based polymersomes. The techniques used in this study are broadly divided into scattering techniques, visualization methods, physical and electromagnetical manipulation and sorting/purification. Of the analytical methods tested, Cryo-transmission electron microscopy and atomic force microscopy (AFM) turned out to be advantageous for polymersomes with smaller diameter than 200 nm, whereas confocal microscopy is ideal for diameters >400 nm. Polymersomes in the intermediate diameter range can be characterized using freeze fracture Cryo-scanning electron microscopy (FF-Cryo-SEM) and nanoparticle tracking analysis (NTA). Small angle X-ray scattering (SAXS) provides reliable data on bilayer thickness and internal structure, Cryo-TEM on multilamellarity. Taken together, these tools are valuable for characterizing polymersomes per se but the comparative overview is also intended to serve as a starting point for selecting methods for characterizing polymersomes with encapsulated compounds or polymersomes with incorporated biomolecules (e.g. membrane proteins)