Micropatterned solid-supported membranes formed by micromolding in capillaries

Abstract

The formation of individually addressable micropatterned solid-supported lipid bilayers has been accomplished by means of micromolding in capillaries. Small unilamellar vesicles were spread on glass slides to form planar supported membranes along microscopic capillaries molded as trenches into a polydimethylsiloxane (PDMS) elastomer. PDMS provides an elastic and transparent carrier for microcapillaries molded from silicon wafers displaying the desired inverse trenches. The so-called master structure has been conventionally etched into silicon by photolithography. The cured PDMS elastomer was briefly exposed to an oxygen plasma, rendering the surface hydrophilic, and subsequently attached to a glass surface in order to form hydrophilic capillaries equipped with flow-promoting pads on either side. One flowpad acts as a reservoir to be filled with the vesicle suspension, while the other one serves as a collector to ensure a sufficient capillary flow to cover the substrate completely. Formation of planar lipid bilayers on the glass slide along the capillaries was followed by imaging the flow and spreading of fluorescently labeled DMPC liposomes with confocal laser scanning microscopy. By means of scanning force microscopy in aqueous solution the formed lipid structures were identified and the height of the lipid bilayers was accurately determined. With both techniques, it was shown that the patterned bilayers remain separated and persist for several hours on the substrate in aqueous solution.

Melting and interdigitation of microstructured solid supported membranes quantified by imaging ellipsometry

“…Since lateral expansion of the membranes might be restricted or abolished in continuous supported lipid bilayers, microstructured membranes are particular useful to investigate phase changes in bilayers as a function of temperature or membrane active compounds. [27][28][29][30][31][32] Recently, we could show using noninvasive imaging ellipsometry of individually addressable microstructured lipid bilayers that the thermotropic phase behavior of bilayers formed from phosphatidylcholines and mixtures with cholesterol is similar to that obtained for multilamellar and vesicular systems. 33 We observed a substantial reduction in cooperativity of the main phase transition, specified by the number of simultaneously melting lipid molecules, and a shift in the main phase transition temperature to higher temperatures by 2 -6°C as a function of the pretreatment of the silicon surface.…”

“…[29][30][31][32] In brief, all preparation steps were carried out at 40°C, i.e., well above the main phase transition temperature of DMPC ͑23°C͒ and DiC 15 PC ͑33°C͒. The silicon wafers were cleaned with diluted aqueous HF solution ͑1% v/v͒ and activated in NH 4 OH / H 2 O 2 / H 2 O ͑1:1:5, v/v͒ at 75°C for 20 min.…”

“…By vesicle adsorption inducing rupture and spreading to form planar lipid bilayers confined to the capillary, membrane stripes consisting of various lipid compositions were obtained. 29,31 After 10 min, buffer was added to the PDMS channels on the silica surface to form a liquid film surrounding the stamp. Subsequently, the PDMS network was gently peeled off and the surface was extensively rinsed with buffer to remove remaining vesicles.…”

Thermal Expansion of Microstructured DMPC Bilayers Quantified by Temperature‐Controlled Atomic Force Microscopy

“…A microstructured 1,2-dimyristoyl-sn-glycero-3-phospocholine (DMPC) bilayer prepared by micromolding in capillaries [14,15] was imaged by means of temperature-controlled AFM while exposed to heating and cooling cycles. Figure 1 displays a set of AFM images of a microstructured DMPC bilayer taken at different temperatures, that is, heating the sample from 15.6 8C to 36.2 8C followed by cooling it from 32.1 8C to 16.6 8C.…”

Microstructuring of phospholipid bilayers on gold surfaces by micromolding in capillaries

“…Recently, we and others developed a general strategy for generating numerous selectively functionalized lipid membrane compartments using micromolding in capillaries [17][18][19]. This technique originates from the family of soft lithography and was first introduced by Whitesides and coworkers [20].…”