Highly hydrated deformable polyethylene glycol-tethered lipid bilayers.

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.

Aperiodic CrSc multilayer mirrors for attosecond water window pulses.

Extending single attosecond pulse technology from currently sub-200 eV to the so called 'water window' spectral range may enable for the first time the unique investigation of ultrafast electronic processes within the core states of bio-molecules as proteins or other organic materials. Aperiodic multilayer mirrors serve as key components to shape these attosecond pulses with a high degree of freedom and enable tailored short pulse pump-probe experiments. Here, we report on chirped CrSc multilayer mirrors, fabricated by ion beam deposition with sub-angstrom precision, designed for attosecond pulse shaping in the 'water window' spectral range.

Influence of ibuprofen on phospholipid membranes.

A basic understanding of biological membranes is of paramount importance as these membranes comprise the very building blocks of life itself. Cells depend in their function on a range of properties of the membrane, which are important for the stability and function of the cell, information and nutrient transport, waste disposal, and finally the admission of drugs into the cell and also the deflection of bacteria and viruses. We have investigated the influence of ibuprofen on the structure and dynamics of L-α-phosphatidylcholine (SoyPC) membranes by means of grazing incidence small-angle neutron scattering, neutron reflectometry, and grazing incidence neutron spin echo spectroscopy. From the results of these experiments, we were able to determine that ibuprofen induces a two-step structuring behavior in the SoyPC films, where the structure evolves from the purely lamellar phase for pure SoyPC over a superposition of two hexagonal phases to a purely hexagonal phase at high concentrations. A relaxation, which is visible when no ibuprofen is present in the membrane, vanishes upon addition of ibuprofen. This we attribute to a stiffening of the membrane. This behavior may be instrumental in explaining the toxic behavior of ibuprofen in long-term application.

Cell motility on polyethylene glycol block copolymers correlates to fibronectin surface adsorption.

Adhesion and motility of cells on polyethylene glycol (PEG) engineered surfaces are of fundamental interest for the development of biotechnological devices. Here, the structure of PEG block copolymers physisorbed to surfaces by polyLlysine (PLL) or polypropylene oxide (PPO) is studied. Cell behavior on such surfaces incubated with fibronectin (FN) is analyzed via time-lapse microscopy, the amount and the location of FN is determined via neutron reflectivity. While FN does not adsorb onto PPOPEG, 0.4-0.7 mg m(-2) of FN is found in the vicinity of the PLL moiety of PLLPEG. Cells exhibit 21% increased motility on PLLPEG (5 kDa PEG chains) compared to pure FN layers, and 12% decreased motility for PLLPEG (2 kDa PEG chains). These findings suggest that by design of PEGylated surfaces cell migration can be controlled.

Neural Stem Cell Spreading on Lipid Based Artificial Cell Surfaces, Characterized by Combined X-ray and Neutron Reflectometry.

We developed a bioadhesive coating based on a synthetic peptide-conjugate (AK-cyclo[RGDfC]) which contains multiples of the arginyl-glycyl-aspartic acid (RGD) amino acid sequence. Biotinylated AK-cyclo[RGDfC] is bound to a supported lipid bilayer via a streptavidin interlayer. Layering, hydration and packing of the coating is quantified by X-ray and neutron reflectometry experiments. AK-cyclo[RGDfC] binds to the streptavidin interlayer in a stretched-out on edge configuration. The highly packed configuration with only 12% water content maximizes the number of accessible adhesion sites. Enhanced cell spreading of neural stem cells was observed for AK-cyclo[RGDfC] functionalized bilayers. Due to the large variety of surfaces which can be coated by physisorption of lipid bilayers, this approach is of general interest for the fabrication of biocompatible surfaces.