Nano-Bio Integration - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 238

a b c

Fig. 9.3 Configurations of rotary motors driven by bacteria

Fig. 9.4 Hybrid
lipid-polymer container with
tunable permeability

lipid bilayer

pore

container

from chaotic dynamics of small molecules in a nonequilibrium state and in an
asymmetric environment is referred to as ratchet effect. A review on nanoscale
ratchets can be found in Hanggi and Marchesoni ( 2009 ), whereas a theoretical
approach to the rotary micromotor in a bacterial bath is presented in Angelani et al.
( 2009 ). The model supports the experimental finding that asymmetric objects can
spontaneously rotate into the desired direction if pushed by biological micromotors.
Bioinorganic hybrids, fabricated by randomly incorporating elastin-like polypep-
tides into silica membranes by sol-gel synthesis, can be used as smart membranes,
which exhibit molecular-level control of permeability in response to temperature
changes and act as molecular weight cutoff filters ( Rama Rao et al. 2002 ).
The porosity of the membrane depends on the hydrophilic or hydrophobic nature
of the polypeptides related to their conformations (the polypeptides are in a
collapsed state if hydrophobic), the transition between these two states in aqueous
environment taking place at the lower critical solution temperature (LCST). As a
consequence, above the LCST, the 2:5-m-thick hybrid membranes are permeable
only for molecules with weights less than 5,000 Da, whereas below LCST, the mem-
branes are completely impermeable. The LCST takes place at different temperatures
for different elastin-like polypeptides (e.g., at 34 ı C for ELP-60 and at 45 ı Cfor
ELP-13), and the permeation properties are fully reversible upon cyclic changes of
temperatures around the transition points.
A hybrid lipid-polymer nanocontainer with tunable permeability, illustrated in
Fig. 9.4 , has been reported in Dudia et al. ( 2008 ). It was fabricated by drilling holes
with a diameter of 1m in an impermeable 100-nm-thick polystyrene scaffold by
focused ion-beam lithography, sealing them with lipid bilayers and incorporating
into these bilayers pore-forming channel proteins that can be remotely controlled.