Biomedical Engineering Reference
In-Depth Information
Fig. 8.15 Bioinspired
self-pumping membrane
electrode
membrane
and buoyancy forces, can be tuned by the rotation frequency of the magnetic field.
Moreover, several artificial flagella swim in a swarm-like, coordinated fashion and
can be controlled as a single unit.
A bioinspired self-pumping membrane, which integrates a chemical-driven
electroosmotic pump into a synthetic track-etched polycarbonate membrane with
a pore diameter of 1m, has been described in Jun and Hess ( 2010 ). Such a
membrane mimics material exchange across biological membranes by specialized
channel proteins using ATP as fuel. As shown in Fig. 8.15 , Au and Pt electrodes
are deposited on opposite faces of the membrane and produce a transmembrane
potential due to the different abilities of the electrodes to catalyze the anodic and
cathodic reaction. When an electric field is applied across the pore, the counterions
attracted by the surface charges within the pore experience a force, while a plug-
like flow of the fluid at the channel wall is caused by the viscous drag between
fluid and counterions. Hydrogen peroxide acts as fuel for the electroosmotic flow,
its hydrolysis in aqueous environment generating an ionic current flow between
electrodes if they are short-circuited. More exactly, hydrogen peroxide transforms
into oxygen, electrons, and protons on the platinum electrode, the resulting electrons
passing into and closing the external electrical circuit, while the protons flow
through the membrane pore. The electrons and protons meet again at the gold
electrode, where they produce water after reacting with hydrogen peroxide. For
instance, in an aqueous solution, the current generated at an applied voltage of 1 V is
1:9A, the corresponding flow rate being 0:94 nL s 1 . The negative current and
flow rate values indicate that the current/flow direction is from the platinum to the
gold electrode. Pumping can occur when no external voltage is applied if hydrogen
peroxide is added to the solution at a 0.01 wt% concentration. In this case, at short
circuit, the flow across the membrane is directed from the platinum to the gold
electrode, no flow being observed when the external circuit is open. The current and
flow decrease in time from values of 0:26Aand0:9 nL s 1 if hydrogen peroxide
concentration, consumed at the electrodes, is not maintained at the same value.
Metabolic biological functions can also be mimicked with integrated nanode-
vices. For example, the response of beta cell at glucose can be reproduced with
ion-sensitive field-effect transistors ( Georgiou and Toumazou 2007 ). The beta cells
in pancreas sense the blood glucose originating from food intake and release the
insulin hormone, which helps glucose assimilation in cells and the subsequent
energy production. Faulty functioning of beta cells can lead to diabetes, which
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