Electrochemistry of Biomimetic Membranes - Applications of Electrochemistry and Nanotechnology in Biology and Medicine - page 148

With only a few exceptions, biomimetic membranes consist of
a more or less complex architecture that includes a lipid bilayer. In
order of increasing complexity, they can be classified into: black
lipid membranes (BLMs), solid-supported bilayer lipid membranes
(sBLMs), tethered bilayer lipid membranes (tBLMs), polymer-
cushioned bilayer lipid membranes (pBLMs), S-layer stabilized
bilayer lipid membranes (ssBLMs), and protein-tethered bilayer
lipid membranes (ptBLMs). Mercury-supported lipid monolayers
and alkanethiol/lipid hybrid bilayers are particular biomimetic
membranes that contain a single lipid monolayer.
The possibility of self-assembling monolayers and bilayers on
metals with formation of rugged functionalized electrodes has
stimulated a research aiming at exploiting self-assembly for the
realization of biomembrane models capable of incorporating inte-
gral proteins in a functionally active state. To achieve this goal,
biomembrane models consisting of lipid bilayers should meet a
number of requirements:
(i) they should be robust enough for long-term stability, and be
easily and reproducibly prepared;
(ii) they should have the lipid bilayer in the liquid crystalline
state, and such as to allow lateral mobility;
(iii) they should have water (or, at least, a highly hydrated hy-
drophilic region) on both sides of the lipid bilayer;
(iv) they should be sufficiently free from pinholes and other de-
fects that might provide preferential pathways for electron
and ion transport across the lipid bilayer.
Requirements (ii) and (iii) are necessary for the incorporation of
integral proteins into the lipid bilayer in a functionally active state.
In fact, integral proteins have a hydrophobic domain buried inside
the biomimetic membrane, which must be sufficiently fluid to ac-
commodate this domain. Often, they also have hydrophilic do-
mains protruding by over 6 nm outside the lipid bilayer. To avoid
their denaturation and to promote their function, incorporation of
integral proteins into biomimetic membranes must ensure that their
extramembrane hydrophilic domains are accommodated in a hy-
drophilic medium on both sides of the lipid bilayer. Moreover, the
transport of hydrophilic ions across a solid-supported lipid bilayer
via ion channels or ion pumps is only possible if an aqueous or
hydrophilic layer is interposed between the bilayer and the sup-