Balancing Permeability and Stability: A Study of Hybrid Membranes for Synthetic Cells Using Lipids and PBd-<i>b</i>-PEO Block Copolymers

We have synthesized hybrid membranes composed of amphiphilic block copolymers, polybutadiene-poly(ethylene oxide) [PBd-<i>b</i>-PEO], with different lengths [PBd₂₂-PEO₁₄ and PBd₁₁-PEO₈] and mixtures of phospholipids (DOPC:DOPG:DOPE 50:25:25 mol %) to combine the properties of both in terms of stability and fluidity of the membrane. The amphiphilic block copolymers increase the stability, whereas the lipids support the functionality of membrane proteins. The hybrid nature of the bilayers was studied by means of Cryo-TEM, Langmuir-Blodgett technique, atomic force microscopy (AFM), electrical measurements, and fluorescence-based stopped-flow assay to determine the permeability of the membrane for water and osmolytes. We observe that the structural, thermodynamic, and permeability properties of hybrid PBd₁₁-PEO₈ membranes are similar to their purely lipid counterparts, with the advantage of being more stable and resisting a higher transmembrane electrical potential. Hybrid membranes with the longer polymer, PBd₂₂-PEO₁₄, display more significant structural, thermodynamic, and permeability differences and show less favorable properties than hybrid-PBd₁₁-PEO₈ membranes.