Self-Spreading of Phospholipid Bilayer in a Patterned Framework of Polymeric Bilayer

Abstract

Phospholipid bilayers spontaneously spread on a hydrophilic substrate such as glass in aqueous solution due to the energetic gain of surface wetting. This process (selfspreading) was utilized to form a patterned model biological membrane containing reconstituted membrane proteins. A mechanically stable framework of polymerized lipid bilayer was first generated by the lithographic polymerization of a diacetylene phospholipid. Then, natural lipid membranes (fluid bilayers) were introduced into the channels between polymeric bilayers by the self-spreading from a phospholipid reservoir. The spreading velocity could be fitted into a slope of-0.5 in a double logarithmic plot versus time, due to the balance between spreading force and resistive drag. The preformed polymeric bilayer accelerated the spreading by the energetic gain of covering hydrophobic edges with lipid bilayer. At the same time, the domains of polymeric bilayer obstructed spreading, and the spreading velocity linearly decreased with their fractional coverage. Above the critical coverage of ca. 50%, self-spreading was completely blocked (percolation threshold), and fluid bilayer was confined in the polymer-free regions. Nonspecific adsorption of lipids onto the surface of polymeric bilayers was negligible, which enabled a heightened signal-to-background ratio in the reconstitution and observation of membrane proteins. Self-spread bilayers had a higher density of lipids than those formed by the spontaneous rupture of vesicles (vesicle fusion), presumably due to the continual supply of lipid molecules from the reservoir. These features give the selfspreading important advantages for preparing patterned model membranes with reconstituted membrane proteins.

A Study of the Effects of Plasma Surface Treatment on Lipid Bilayers Self-Spreading on a Polydimethylsiloxane Substrate under Different Treatment Times

“…A pre-dried lipid source that adhered to a solid substrate is rehydrated, and the lipid bilayers self-spread on the supporting surface. Due to the continual supply of lipid molecules from the lipid source, self-spreading lipid bilayers have a high lipid packing density , and hence can be a useful platform to study functions of transmembrane proteins affected by membrane tension. Self-spreading has also been used to fabricate a lipid-flow chip , and a bilayer array .…”

Integrated model membrane for biophysical studies and biomedical applications

“…Natural lipid bilayers were incorporated into the patterned framework of polymeric bilayer by vesicle fusion or spontaneous spreading of phospholipids from lipid aggregates (self-spreading). 9,10) Membrane proteins were reconstituted into the patterned membrane either from purified/solubilized micelles or crude native membranes. The photoreceptor rhodopsin (Rh) was purified from the rod outer segments (ROS) of bullfrogs (Rana catesbeiana), and was reconstituted into a pre-formed SLB by the rapid dilution of solubilized Rh molecules.…”

“…5). 9,10) In vesicle fusion, lipid vesicles adsorb onto a hydrophilic surface, rupture, and lipid patches fuse with each other. Currently, SLBs are most commonly generated by vesicle fusion owing to its technical simplicity.…”

“…Formation of SLBs was accelerated in the presence of polymeric bilayers both for vesicle fusion and self-spreading, indicated that the hydrophobic edges of polymeric bilayer reduced the energetic barriers of SLB formation. 9,10) In the patterned hybrid membrane, polymeric and fluid lipid bilayers form a continuous membrane. A partially polymerized bilayer, in which nanoscopic polymeric bilayer domains only partially cover the substrate surface, can be generated by modulating the UV dose for polymerization [Figs.…”