Rough-smooth-rough dynamic interface growth in supported lipid bilayers.

The role of lipid bilayer viscoelasticity and the substrate-bilayer interactions on the spreading behavior of supported phospholipid bilayer membranes is studied using fluorescence microscopy. Unlike the monotonic roughening observed on silica or in other dynamic interface growth systems, a unique rough-smooth-rough (RSR) interface transition occurred on chromium oxide with a roughness exponent of 0.45 ± 0.04. This RSR transition is attributed to the elasticity of the lipid bilayer which is initially under compression due to surface interactions, and is well approximated by adding an elastic term to the quenched noise Edwards-Wilkinson equation. A phase diagram depicting the conditions necessary to observe RSR transitions in dynamic interface systems is derived, revealing the classes of dynamically evolving systems is broader than previously thought, and the viscoelastic nature of the lipid bilayer may play a role in supported membrane behavior.

Exploring and exploiting chemistry at the cell surface.

Engineering the surface chemistry of a material so that it can interface with cells is an extraordinarily demanding task. The surface of a cell is composed of thousands of different lipids, proteins and carbohydrates, all intricately (and dynamically) arranged in three dimensions on multiple length scales. This complexity presents both a challenge and an opportunity to chemists working on bioactive interfaces. Here we discuss how some of these challenges can be met with interdisciplinary material synthesis. We also review the most popular classes of functional molecules grafted on engineered surfaces and explore some alternatives that may offer greater flexibility and specificity. Finally, we discuss the emerging field of dynamic surfaces capable of stimulating and responding to cellular activity in real time.

Formation and characterization of fluid lipid bilayers on alumina.

Fluid lipid bilayers were deposited on alumina substrates with the use of bubble collapse deposition (BCD). Previous studies using vesicle rupture have required the use of charged lipids or surface functionalization to induce bilayer formation on alumina, but these modifications are not necessary with BCD. Photobleaching experiments reveal that the diffusion coefficient of POPC on alumina is 0.6 microm (2)/s, which is much lower than the 1.4-2.0 microm (2)/s reported on silica. Systematically accounting for roughness, immobile regions and membrane viscosity shows that pinning sites account for about half of this drop in diffusivity. The remainder of the difference is attributed to a more tightly bound water state on the alumina surface, which induces a larger drag on the bilayer.

Lipid bilayer deposition and patterning via air bubble collapse.

We report a new method for forming patterned lipid bilayers on solid substrates. In bubble collapse deposition (BCD), an air bubble is first "inked" with a monolayer of phospholipid molecules and then touched to the surface of a thermally oxidized silicon wafer and the air is slowly withdrawn. As the bubble shrinks, the lipid monolayer pressure increases. Once the monolayer exceeds the collapse pressure, it folds back on itself, depositing a stable lipid bilayer on the surface. These bilayer disks have lateral diffusion coefficients consistent with high quality supported bilayers. By sequentially depositing bilayers in overlapping areas, fluid connections between bilayers of different compositions are formed. Performing vesicle rupture on the open substrate surrounding this bilayer patch results in a fluid but spatially isolated bilayer. Very little intermixing was observed between the vesicle rupture and bubble-deposited bilayers.