John Woodward
Biotechnology Division, Chemical Sciences and Technology Laboratory
National Institute of Standards and Technology, Gaithersburg, MD 20899

       Hybrid bilayer membranes (HBM) are synthetic membrane mimics designed to form a biomimetic surface. The basic HBM system consists of a lipid monolayer adsorbed to an alkanethiol self-assembled monolayer. More advanced versions have used different thiolates in the base layer and cell membranes for the top layer. Atomic force microscopy has been used to probe the kinetics of how these layers form as well as assess the final structure. As a local probe of the surface the AFM provides information complementary to non-local probes such as IR spectroscopy, electrochemistry and small angle neutron scattering. By combining these techniques we are able to better understand HBM formation and exploit this knowledge to better engineer these surfaces for applications in tissue engineering and the study of membrane proteins.
       As an example the AFM image below shows a COS cell membrane hybrid with a mixed alkanethiol/lipid underlayer. The dark blue areas are low and the white areas are high. The AFM was used to make holes in the HBM . The hole on the left goes through the entire hybrid bilayer and is 5.3 nm deep while the one on the right only goes through on the top (COS cell membrane) layer and is 2.3 nm deep.