High-performance biomimetic membranes made using genetically engineered aquaporins.

Aquaporins are membrane protein water channels present in cells, and they restrict the passage of contaminants including bacteria, viruses, minerals, proteins, DNA, dissolved gases, salts, detergents, and even protons without preventing the passage of water. Small molecules such as urea and boric acid, the removal of which is inefficient by conventional membranes are also rejected. Biomimetic membranes, an innovation in water filtration technology attempts to replicate a natural process occurring at the cell level; specifically, the highly-selective and efficient transport of different molecules across a cell membrane. Therefore, aquaporins have received worldwide attention because of their potential to form biomimetic membranes with high flux and selectivity for water treatment applications. However, challenges involved in the incorporation of aquaporin proteins in membranes limit their applicability. One of them is to attach aquaporins to the membranes without chemically altering or damaging the aquaporins during the binding to the membrane. The second challenge is to design and prepare an assembly that allows biomimetic membranes with aquaporins to sustain hydraulic water pressure gradients without losing their integrity and performance. Membranes modified with unaltered aquaporins displayed lower flux declines and higher flux recovery values after backwash as compared to unmodified PBI membranes. Also, modified membranes showed improved rejection values for both protein and salt solutions of different concentrations. However, a leakage of ions was observed between the channels of the modified membranes as aquaporins didn’t acquire the entire surface filtration area of the membrane for the feed to pass through. In order to make water flow occur through the channels to rejects protons, ions and other impurities more efficiently, the channels of the aquaporins need to be aligned with the direction of water flow. Therefore, aquaporin channels were aligned with the direction of flow. Functional groups were installed on AqpZ for covalent attachment to the polymer matrix so that the proteins could be immobilized to the membranes and aligned in the direction of the feed flow. Membranes modified with aligned aquaporins showed preliminary results with high initial flux, lower flux decline and higher flux recovery