Polymersome Membrane Permeability and Ionic Transport Properties in the Presence of Sub-2nm Carbon Nanotube Porins

Abstract

Synthetic diblock and triblock copolymer membranes are semi-permeable barriers that are capable of self-assembly into tunable membranes, which have contrasting mechanical properties from biologically derived and synthetic lipid bilayers. These thick and “robust” polymer membranes are typically thicker and have significantly reduced water permeability compared to lipid bilayers. These properties make them valuable alternative membranes for applications requiring exposure to physical stresses such as biosensors, drug delivery, and filtration. Previous attempts to engineer the permeability of these membranes included insertion of protein channels to improve permeably, (eg. Aquaporins), changing the polymer constituent to an inherently leaky polymer (eg. polystyrene-b-polyisocyanoalanine(2-thiophene-3-yl-ethyl)amide (PS-PIAT)), and removal of lipids from a mixed lipid-polymer vesicle following cross-linking and hydrolysis. We report a new strategy for improving permeability of polymer-membranes, based on incorporation of carbon nanotube porins into the polymer matrix. These short CNT pores exhibit the excellent transport properties inherent to carbon nanotubes, but are small enough that they can be easily incorporated into the membrane essentially acting as protein channel mimics. Here, we examine the permeability of diblock co-polymer membranes with and without these CNT pores and report the enhancement of permeability and ion transport characteristics of these novel membrane constructs.