Highly Hydrated Deformable Polyethylene Glycol-Tethered Lipid Bilayers

Abstract

The realization of a solid-supported lipid bilayer acting as a workbench for the study of membrane processes is a difficult task. For robustness, the bilayer has to be tethered to the substrate. At the same time, diffusion of the lipids and plastic deformations of the membrane should not be obstructed. Furthermore, a highly hydrated surrounding is mandatory. Here, we show that grafting of a polyethylene glycol-lipid construct (PEG2000-DSPE) to a silicon oxide surface via multiple-step silane chemistry and subsequent deposition of lipids by spin-coating result in a cushioned membrane that has the desired properties. Neutron and X-ray reflectometry measurements are combined to access thickness, density, and hydration of the bilayer and the PEG cushion. We observe a spacer of 55 Å thickness between lipid bilayer and silicon-oxide surface with a rather high hydration of up to 90 ± 3% water. While 11.5 ± 3% of the lipids are grafted to the surface, as determined from the neutron data, the diffusion constant of the lipids, as probed by diffusion of 0.5% Texas Red labeled lipids, remains rather large (D = 2.1 ± 0.1 μm(2)/s), which is a reduction of only 12% compared to a supported lipid bilayer reference without immobilized lipids. Finally, AFM indentation confirms the plastic behavior of the membrane against deformation. We show that rupture of the bilayer does not occur before the deformation exceeds 40 Å. Altogether, the presented PEG-tethered lipid bilayer mimics the deformability of natural cell membranes much better than standard solid-supported lipid bilayers.

Cell Motility on Polyethylene Glycol Block Copolymers Correlates to Fibronectin Surface Adsorption

“…In case of the PLL–PEG (2), the thickness of the PEG layer is 16% higher than predicted by the model. Nevertheless, the thickness of PEG is consistent with previous measurements of PEG cushions and PEG‐tethered lipid bilayers . In case of the PLL–PEG (5), the theoretical thickness of 116 Å is also in good agreement with the data fit, that produced a homogeneous layer of 68 Å and on top an exponential layer with a decay length of 33 Å.…”

“…Nevertheless, the thickness of PEG is [31] and PEG-tethered lipid bilayers. [32] In case of the PLL-PEG (5), the theoretical thickness of 116 Å is also in good agreement with the data fit, that produced a homogeneous layer of 68 Å and on top an exponential layer with a decay length of 33 Å . For the Pluronic film, the AdG model is not valid, as in that case the polymer extension is ruled by hydrophobic interaction with the surface.…”

Photosynthetic Proteins in Supported Lipid Bilayers: Towards a Biokleptic Approach for Energy Capture

“…[69b] Similarly, a versatile approach for the generation of polymer‐cushioned SLBs is the spin‐coating of membrane lipids onto PEG, followed by the incorporation of transmembrane proteins by the fusion of proteoliposomes. [5b], However, if the lipo‐PEG density were too high, there would be a large immobile fraction of lipids in the lower leaflet. Hence, a new approach using a multistep chemical process for the modification of silicon substrates with polymers of different molecular weights (lengths) was utilized to obtain a highly hydrated surface, which is helpful for the fabrication of SLBs with a uniform density of the polymer layer …”

“…[5b], However, if the lipo‐PEG density were too high, there would be a large immobile fraction of lipids in the lower leaflet. Hence, a new approach using a multistep chemical process for the modification of silicon substrates with polymers of different molecular weights (lengths) was utilized to obtain a highly hydrated surface, which is helpful for the fabrication of SLBs with a uniform density of the polymer layer …”

Biomembranes research using thermal and cold neutrons

“…Recent advances in the development of tethered bilayers on gold (Krueger, Meuse et al 2001) or silicon surfaces (Hughes, Howse et al 2008), or on nanostructured substrates (Hertrich, Stetter et al 2014), have enabled closer control of bilayer architecture and asymmetry that may better mimic the cellular environment and open the way to new classes of experiments. The development of magnetic contrast neutron reflectometry (MCNR), which uses a membrane supported on a magnetic substrate, and a magnetic field to modulate the SLD for spin polarized neutrons, has significantly improved the resolution and precision of the technique, allowing analysis of more complex lipid membrane systems (Le Brun, Holt et al 2008;Holt, Le Brun et al 2009).…”