Creating conjugated hydrogel encapsulated membranes
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Creating Conjugated Hydrogel Encapsulated Membranes Tae-Joon Jeon, Noah Malmstadt, and Jacob Schmidt Department of Bioengineering, UCLA, 7523 Boelter Hall, 420 Westwood Plaza, Los Angeles, CA, 90095 ABSTRACT Device engineering for ion channel proteins requires developing systems that incorporate mechanically stable, long-lived lipid bilayer membranes. Building on our previous work, we have further increased lipid bilayer longevity through covalent conjugation of lipid molecules in the bilayer to an encapsulating hydrogel. This is accomplished by polymerizing the hydrogel in situ around a gigaohm-seal membrane containing vinyl-modified lipid head groups, forming a conjugated hydrogel encapsulated membrane (cgHEM). Membranes formed in this manner show remarkable stability, maintaining gigaohm-level resistance for over 270 hours, better than an order-of-magnitude improvement over the previous state of the art. They also demonstrate the capacity to support the incorporation and measurement of ion channel proteins at the singlemolecule level. INTRODUCTION There is much interest in developing devices that incorporate ion channel proteins, to serve both as nanoscale molecular sensing elements[1-3] and as the targets of screening assays for drug discovery.[4] In order to measure single-channel currents through ion channels, engineered devices must be capable of supporting high-quality lipid bilayer membranes characterized by gigaohm-level resistive seals. Unfortunately, conventional lipid bilayer membranes are short-lived and fragile, lasting less than 24 hours and requiring mechanical isolation. We have previously described a system for encapsulating lipid bilayer membranes in a hydrogel matrix: a technique that mechanically stabilizes these membranes and increases their lifetime nearly five-fold.[5] In this report, we describe an extension of this encapsulation system in which the hydrogel is covalently conjugated to the lipid bilayer, further improving the membrane’s stability and longevity. The idea of covalently conjugating a lipid bilayer membrane to a supporting substrate is not new: membranes formed by connecting lipids to solid surfaces via flexible tether molecules have been a subject of considerable research.[6] The formation of membranes on solid supports can stabilize pin-hole defects in the membranes during the process of bilayer assembly, limiting their resistance.[7] Tethered membranes also have a finite electrolyte reservoir between the planar electrode that underlies the membrane and the membrane itself, limiting the duration of single-channel DC conductance experiments that can be performed. While these shortcomings makes single-molecule conductance measurements in tethered membranes difficult, such membranes do gain significant increases in stability and longevity from attachment to a solid support.[8] In order to combine the advantages of tethered membranes with the high resistance and free electrolyte transport typical of freestanding planar lipid bilayers, we have developed a twostep meth
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