Substrate suppression of thermal roughness in stacked supported bilayers

Area of Science:

• Materials Science
• Biophysics
• Surface Science

Background:

• Lipid bilayers are fundamental to cell membranes.
• Understanding supported lipid bilayer behavior is crucial for biomaterials and drug delivery.
• Substrate interactions significantly influence bilayer properties.

Purpose of the Study:

• To investigate the structural properties of DPPE bilayers supported on a silicon substrate.
• To quantify the effects of substrate proximity on bilayer spacing and roughness.
• To elucidate the underlying physical mechanisms, including fluctuation suppression and Helfrich repulsion.

Main Methods:

• Fabrication of five 1,2-dipalmitoyl-sn-3-phosphatidylethanolamine (DPPE) bilayers.
• Support on a polished silicon substrate in excess water.
• Analysis of x-ray reflectivity to determine the density profile.

Main Results:

• Observed significantly smaller layer roughness and repeat spacing near the substrate compared to bulk systems.
• Demonstrated suppression of lateral fluctuations due to the flat substrate boundary.
• Quantified layer spacing decrease attributed to reduced Helfrich repulsion.

Conclusions:

• The substrate strongly influences supported lipid bilayer structure.
• Reduced spacing and roughness are direct consequences of substrate-induced fluctuation suppression.
• Helfrich repulsion plays a key role in determining spacing in supported lipid multilayer systems.