Aquaporin-Containing Proteopolymersomes in Polyelectrolyte Multilayer Membranes

Abstract

The field of membranes saw huge developments in the last decades with the introduction of both polyelectrolyte multilayer (PEM)-based membranes and biomimetic membranes. In this work, we combine these two promising systems and demonstrate that proteopolymersomes (PP+) with the incorporated aquaporin protein can be distributed in a controlled fashion using PEMs, even on the inner surface of a hollow fiber membrane. In this way, various proteopolymersome multilayers (PPMs) are fabricated using PP+ as the positively charged species in combination with the polyanions poly(styrene 4-sulfonate) (PSS) and poly(acrylic acid) (PAA). It is shown by reflectometry through alternately adsorbing the polyanions and PP+ that, for both PAA and PSS, a good layer growth is possible. However, when the multilayers are imaged by SEM, the PAA-based PPMs show dewetting, whereas vesicular structures can only be clearly observed in and on the PSS-based PPMs. In addition, membrane permeability decreases upon coating the PPMs to 2.6 L∙m−2∙h−1∙bar−1 for PAA/PP+ and 7.7 L∙m−2∙h−1∙bar−1 for PSS/PP+. Salt retentions show that PAA/PP+ layers are defective (salt retentions <10% and high molecular weight cut-off (MWCO)), in line with the observed dewetting behavior, while PPMs based on PSS show 80% MgSO4 retention in combination with a low MWCO. The PSS/PP+ membranes show a Donnan-exclusion behavior with moderate MgCl2 retention (50%–55%) and high Na2SO4 retention (85%–90%) indicating a high amount of negative charge present within the PPMs. The corresponding PEMs, on the other hand, are predominately positively charged with MgCl2 retention of 97%–98% and Na2SO4 retention of 57%–80%. This means that the charge inside the multilayer and, thus, its separation behavior can be changed when PP+ is used instead of a polycation. When comparing the PPM membranes to the literature, similar performances are observed with other biomimetic membranes that are not based on interfacial polymerization, but these are the only ones prepared using a desired hollow fiber geometry. Combining PEMs and biomimetic approaches can, thus, lead to relevant membranes, especially adding to the versatility of both systems.

Aquaporin‐Based Biomimetic Membranes for Low Energy Water Desalination and Separation Applications

“…[125,126] In this context, a spacer linker, preferably charge-neutral hydrophilic polyethylene glycol (PEG), can be used to prevent the proximity between the protein-incorporated membrane layer and the surface. [125,126] Organic substrates also feature extensive choices of surface functionality (Figure 8), allowing the deposition and stabilization of biomimetic membrane layer with the substrate using ionic interaction, [80,86,127] hydrophobic interaction, [128] radical cross-linking, [103] thioester [129] and amide [93,105] bond formation, alkyne-azide cycloaddition via click chemistry, [130] silane coupling, [42] gold-thiol coupling, [43,128] glutaraldehydeamine cross-linking, [37] polydopamine (PDA) coating, [37,43] LbL deposition, [40,84,88,89,131,132] PAI-PEI cross-linking, [87] interfacial polymerization, [38,97,[133][134][135] and a combination of coupling techniques. [37,[41][42][43] The surface functionalization strategies are devised based on the intrinsic surface properties of the substrate, targeted interaction with the membrane layer, techniques to be used for membrane material deposition, and the post-deposition stabilization of the membrane layer.…”

Advances in Biohybridized Planar Polymer Membranes and Membrane‐Like Matrices

“…[64] In an example, a supporting structure made of a silicon wafer was coated through the adsorption of alternately-stacked, oppositely-charged polyelectrolytes, resulting in a polyelectrolyte multilayer (PEM)based membrane. [65] This membrane, containing hollow fibers derived from polyelectrolytes, served as a matrix to accommodate polymersomes. In this case, the charged interaction between polymer and polyelectrolyte can be tuned by reconstituting particular proteins in polymersomes that will alter their surface potential, making the membrane more robust and physically stable.…”

“…In an example, a supporting structure made of a silicon wafer was coated through the adsorption of alternately‐stacked, oppositely‐charged polyelectrolytes, resulting in a polyelectrolyte multilayer (PEM)‐based membrane [65] . This membrane, containing hollow fibers derived from polyelectrolytes, served as a matrix to accommodate polymersomes.…”

Amphiphilic Polyelectrolyte Complexes for Fouling-Resistant and Easily Tunable Membranes

“…The associative electrostatic interactions driving complex coacervation are similar to those driving the formation of LbL films . Recent advancements in LbL assembly on porous supports allowed the fabrication of NF membranes with somewhat tailored separation properties and functionalities (e.g., control over thickness, chemistry, and responsiveness), ,,− though it is not possible to tune parameters such as pore size and surface charge accurately or independently. LbL deposition requires complex and multistep fabrication processes, and results in a charged surface that can be prone to fouling when filtering solutes containing oppositely charged groups.…”