Biomedical Engineering Reference
In-Depth Information
Fig. 4
Porous-anodized aluminum with neighboring cells of aluminum oxide merges together to
form the matrix supporting the aligned nanopores.
Left
, scheme;
center
, top view transmission EM;
right
, side view SEM (Reproduced from Asoh et al.
2001
with permission from The Electrochemical
Society, Inc.)
growth of CNTs or other nanomaterials or as substrate for several different
applications, like corrosion prevention for automobile and aerospace structures or
electrical insulation.
The anodization process takes place in a processing cell containing a cathode and
an anode. Usually, the metallic sample of choice functions as the anode, and it is
connected to the positive terminal of a DC power supply. A different conductive
material, inert in the anodizing bath, functions as the cathode (some example mate-
rials used as cathodes are carbon, lead, nickel, or stainless steel), and it is connected
to the negative terminal of the supply. When this circuit is closed, electrons are
allowed to move, being attracted by the positive terminal, and permit the reaction
between the ions present on the surface of the metal with the water molecules that
forms the oxide layer.
1.2
Nanofabrication by Bottom-Up Methods
With the fi rst decades of the new millennium, standard top-down techniques for
nanomanufacturing have approached a critical limit in the ability to miniaturize
components. Further size reduction has required innovative chemical routes.
Eric Drexler, a pioneer in nanotechnology, in 1986 said, “our ability to arrange
atoms lies at the foundation of technology.” From this point on, several bottom-up
approaches have blossomed, trying to build nanostructures one atom at a time, in the
most effi cient and precise way possible. On this aspect, nature is well-ahead of
human engineering: proteins build structures quickly and effectively mastering the
self-assembly of molecules as the basic building blocks of life. Nanoengineering is
today putting a lot of effort in combining old, well-known chemical methods with
new systems, even looking for inspiration from nature in bio-inspired structures and
bio-assisted synthesis of nanodevices (Madou
2002
) .
