Liquid-Ordered/Liquid-Crystalline Phase Separation at a Lipid Bilayer Suspended over Microwells

The localization of liquid-ordered (L_o) and liquid-crystalline (L_α) phase domains on a silicon substrate with a microwell array is investigated. Although the phase separation of the L_o and L_α phases on both a giant unilamellar vesicle (GUV) and a supported membrane remains stable for a long time, the lateral diffusion of lipids across each domain boundary occurs quickly. Since the phase separation and domain arrangement are governed by the stiffness and lateral tension of the lipid membrane, the phase separation is rearranged on a micropatterned substrate. Similar phase separation of the L_o and L_α phases is observed at a lipid membrane suspended over a microwell. However, the L_α phase is preferred at a suspended membrane, and saturated lipids and cholesterol are excluded toward the supporting membrane on the periphery. Since the L_o domain area is reduced by anisotropic diffusion through the boundary between the suspended and supported membranes, a very slow reduction rate with a linear functional relation is observed. Finally, a localized L_α phase domain is observed at a membrane suspended over a microwell, which is surrounded by an L_o phase supported membrane.