(314b) Membrane Protein Nanosheet Based Membranes

Biological membranes containing membrane protein (MP) channels and MP-mimic functionalized materials have emerged as significant platforms to develop separation membranes with specific solute selectivity. Biomimetic membranes incorporating these pore structures are expected to exhibit high permeability and selectivity since they possess channels with well-defined pore geometry and functionality to exclude or pass specific solution components. Nevertheless, MP-based biomimetic membranes studied so far suffer from low protein insertion into biomimetic matrix and the use of vesicular morphologies of channel-incorporated liposomes. These challenges have resulted in much lower than anticipated improvements.

Passive β-barrel channel proteins can be regarded as ideal pore geometries since they have transport properties targeted towards specific small molecule separations necessary to maintain cellular functions. MPs in various organisms are used for exclusion of large molecules while allowing or inducing ion and small molecule passage. Additionally, the stability and mutation tolerance of these MPs make them ideal candidates for engineering channel based scalable membranes. The β-barrel structure is a robust scaffold with high thermodynamic stability and can be immobilized in an oriented and functionally-active form within amphiphilic polymers and lipid bilayers. These precisely-sized and stable MP channels were used in this work for constructing high performance biomimetic membranes.

In this presentation, we will present a comprehensive approach to construct scalable biomimetic membrane with rapid fabrication of highly porous β-barrel MP two-dimensional (2D) crystals and nanosheets. These highly packed crystalline structures and well-ordered nanosheets were fabricated by self-assembling MPs in a poly(butadiene)-b-poly (ethylene oxide) (PB-PEO) di-block copolymer matrix using an innovative solvent evaporation method that can be completed within 2-hours. The prepared 2D unique hybrid materials were deposited onto commercial porous substrates as high-performance and defect-free selective layers by a modified layer-by-layer approach. Three different pore-forming β-barrel MPs, outer membrane protein F (OmpF), a mutated version of a bacterial ferrichrome outer membrane transporter (designated FhuA ΔC/Δ4L), and channels formed from the Staphylococcus aureus toxin, alpha-hemolysin (αHL) were selected to demonstrate this approach. These proteins were chosen since they possess unique elliptical/cylindrical pore cross-section of 0.8×1.08 nm, 1.31×1.62 nm, and 1.50×1.50 nm for OmpF, FhuA ΔC/Δ4L, and αHL, respectively. Achieving high porosity, tuning such small pore sizes, as well as maintaining uniformity in pore sizes are quite difficult in current membrane models.

The three MP biomimetic membranes synthesized showed significant improvements in water permeability and maintained designed selectivity, as a result of high packing densities and unitary pore shapes of MP channels. These biomimetic membranes demonstrated 20-1000 times greater water permeability than commercial membranes with comparable molecular exclusion ratings. These water permeabilities were 293 ± 51 L m^-2 h^-1 bar^-1 (denoted as LMH bar^-1), 793 ± 226 LMH bar^-1, and 2,107 ± 235 LMH bar^-1 (all values mean ± s.d., n ≥ 3) for OmpF, FhuA ΔC/Δ4L, and αHL-based biomimetic membranes, respectively. In addition, these membranes demonstrated the molecular exclusion performance inferred from their barrier pore sizes with molecular weight cut-offs (MWCOs) of ~480, ~1,130, and ~930 Da for OmpF, FhuA ΔC/Δ4L, and αHL-based biomimetic membranes, respectively. These results exhibit the potential of utilizing β-barrel MPs to tailor membrane selectivity within a critical separation range, while enhancing water permeability.

In summary, we have fabricated densely packed MP-block copolymer based biomimetic membranes. The three MP-based membranes demonstrate greater water permeability while maintaining specific small solute selectivity than commercial membranes with similar separation ranges. This work presents a new class of materials combining high selectivity and permeability of MPs with block copolymers to synthesize stable membranes that could contribute to the energy reduction in chemical and biological separations.