Highly permeable polymeric membranes based on the incorporation of the functional water channel protein Aquaporin Z

TLDR

The study proposes that incorporating Aquaporin Z into amphiphilic polymer vesicles could yield more productive, sustainable water‑treatment membranes and offer tunable permeability for drug delivery. The authors investigated the permeability and solute‑transport characteristics of amphiphilic triblock‑polymer vesicles containing the bacterial water‑channel protein Aquaporin Z. The vesicles were fabricated from a symmetric block copolymer of poly‑(2‑methyloxazoline)–poly‑(dimethylsiloxane)–poly‑(2‑methyloxazoline) (PMOXA(15)–PDMS(110)–PMOXA(15)). Light‑scattering revealed that pure polymer vesicles were highly impermeable, yet AqpZ incorporation boosted water permeability by up to ~800‑fold, with an activation energy of 3.4 kcal/mol comparable to lipid‑membrane water channels, complete rejection of glucose, glycerol, salt, and urea, and productivity at least ten times higher than existing salt‑rejecting polymeric membranes.

Abstract

The permeability and solute transport characteristics of amphiphilic triblock-polymer vesicles containing the bacterial water-channel protein Aquaporin Z (AqpZ) were investigated. The vesicles were made of a block copolymer with symmetric poly-(2-methyloxazoline)-poly-(dimethylsiloxane)-poly-(2-methyloxazoline) (PMOXA(15)-PDMS(110)-PMOXA(15)) repeat units. Light-scattering measurements on pure polymer vesicles subject to an outwardly directed salt gradient in a stopped-flow apparatus indicated that the polymer vesicles were highly impermeable. However, a large enhancement in water productivity (permeability per unit driving force) of up to approximately 800 times that of pure polymer was observed when AqpZ was incorporated. The activation energy (E(a)) of water transport for the protein-polymer vesicles (3.4 kcal/mol) corresponded to that reported for water-channel-mediated water transport in lipid membranes. The solute reflection coefficients of glucose, glycerol, salt, and urea were also calculated, and indicated that these solutes are completely rejected. The productivity of AqpZ-incorporated polymer membranes was at least an order of magnitude larger than values for existing salt-rejecting polymeric membranes. The approach followed here may lead to more productive and sustainable water treatment membranes, whereas the variable levels of permeability obtained with different concentrations of AqpZ may provide a key property for drug delivery applications.