Formation of Tethered Supported Bilayers by Vesicle Fusion onto Lipopolymer Monolayers Promoted by Osmotic Stress

Abstract

Lipid bilayer systems have been used extensively to study the structure and function of biomembranes including molecular recognition, permeation, adhesion, and fusion. 1-5 Further interest arises from their potential use as biosensors.6 , 7 While classical black lipid bilayer membranes are highly suitable as such model systems, they suffer from their limited long-term stability. 1 Additionally, to apply the broad range of surface sensitive experimental techniques developed in recent years for the characterization of ultrathin films, it is often necessary to immobilize lipid bilayers on solid supports. However, lateral fluidity of the lipid membrane is governed by the physical and chemical properties of the solid substrate. Thus, bilayer membranes prepared by the Langmuir-Blodgett (LB) technique or by vesicle fusion directly onto solid substrates are often polycrystalline or amorphous, and lateral lipid mobility within the membrane is restricted. While on hydrophilic oxidized silicon or glass a water layer (~1 nm thick) is formed which allows for free diffusion of phospholipid molecules (but not membrane-spanning proteins) within the bilayer,8 -10 on most other metals and metal oxides, lipid mobility is strongly suppressed.11 , 12 To preserve the membrane's natural properties, one promising approach is to rest it on a water-swellable (hydrophilic) polymer or polyelectrolyte cushion which can act as a deformable and mobile substrate6 , 13 , 14 like the cytoskeletal support in living cells. Such softly supported lipid bilayers can, in principle, exist in an entirely fluid state, nearly undisturbed by the presence of the supporting polymer gel which provides an aqueous compartment between the solid substrate and the membrane. In our recent work, we have studied DMPC bilayers on a highly branched cationic polymer (polyethylenimine, PEI). Important structural information about these polymer-supported bilayer systems formed by various preparation methods was provided by neutron scattering experiments.15 , 16 Furthermore, measuring the intermembrane interaction forces using the surface forces apparatus (SFA) technique has shown the effect of fluidity on membrane functionality.17These physisorbed, polymer-supported bilayers are only the first step in the approach of creating artificial biomembranes that more closely resemble living cells. To provide more biologically relevant architectures, molecular assemblies of increased complexity and longterm stability have been tested, including a partial chemical fixation of the membrane's lipids to the underlying polymeric substrate. 7,14,18,19 However, the construction of such "asymmetric" tethered supported membranes is not always straightforward, and each particular NIH Public Access Author ManuscriptLangmuir. Author manuscript; available in PMC 2010 October 13. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscript system needs to be optimized. The most versatile approach appears to be vesicle fusion onto polymer-supported lipid monolayers previously prep...

Ordering Transitions in Nematic Liquid Crystals Induced by Vesicles Captured through Ligand−Receptor Interactions

“…We interpret these results to indicate that exposure of the surface-immobilized vesicles to water resulted in the rupture of the vesicles and formation of bilayer assemblies spread on the surface (Figure 3b). 40,41 We also note that not all vesicles-like features on the surface disappeared on exposure to water (Figure 2b, arrow).…”

Solid supported lipid bilayers: From biophysical studies to sensor design

“…These include dextran [23], cellulose [119], chitosan [24], polyelectrolytes [21,[120][121][122], and lipopolymer tethers [19,22,26,27,30,31,123]. Two classes of polymer, polyelectrolytes and lipopolymers, are emerging as popular choices for cushion material.…”

“…Attachment of a lipopolymer to a substrate has been carried out via photoreactive coupling [22,23,28], sulfur-metal bond formation [27,29,30], epoxy group linkage [23], or silane bonding [123]. Some common polymer backbones used in the synthesis of lipopolymers are, acrylamide [19,27,30], ethyloxazoline [22,28], peptides [126] and ethyleneglycol [123]. It is important that the polymer cushion have the ability to swell in an aqueous environment and have minimal disruptive interactions with the bilayer and any other reconstituted membrane components [20].…”

“…It was found that thin polymer films could couple bilayers with a large variety of materials such as metal films, oxides, and semiconductor electrodes. Adding a polymer layer between an underlying substrate and the phospholipid bilayer can be achieved by the use of either a cushioning polymer film [20][21][22][23][24][25] or the direct tethering of the membrane to a lipid presenting polymer or peptide layer [26][27][28][29][30][31]. Other effective surface modification strategies include self-assembled monolayers (SAMs) [32,33] and the use of adsorbed or bound proteins as a cushioning layer [34][35][36][37][38][39].…”

Structural characterization of an elevated lipid bilayer obtained by stepwise functionalization of a self-assembled alkenyl silane film

“…20 One reported example is the synthesis of a terpolymer having an acrylamide backbone bearing a disulfide moiety for chemisorption onto gold substrates, lipid sidechains for membrane incorporation and amino-terminated triethylene glycol pendent groups as a hydrophilic cushion. 21 A more recent article reported the use of a synthetic thiohexa͑ethylene oxide͒ lipid for chemisorption onto gold surfaces. 22 Another approach uses a tripartite molecule consisting of a lipid attached to a poly͑ethylene glycol͒ molecule with a molecular weight of 3400 Dalton and a silane reactive group for substrate attachment by Langmuir-Blodgett ͑LB͒ transfer and thermal annealing.…”