nanotechnology
nano
bits
Joint Venture
Surgeons perform
more than 150,000 hip replacements a year, and many of those hips are
made of titanium. Little wonder: titanium is a wonderful metal—strong,
light, resistant to corrosives.
But artificial joints made of titanium are frequently rejected by the
body's immune system, leading to pain and the eventual need for
replacement.
Researchers at Purdue University in West Lafayette, Ind., have discovered
a way to coat exposed titanium so that medical implants made of it are
less irritating to the body. The key, it turns out, is to sheathe the
metal parts in a jacket of nanotubes.
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| Rosettes of DNA link up to form implant-protecting nanotubes. |
Experiments have shown that bone cells called osteoblasts attach readily
to artificial objects with surface features on the same scale as natural
tissues—some 100 nanometers across. These cells can form the base
for regenerated tissue around an artificial joint and protect it from
attack by immune cells.
Unfortunately, parts manufactured from titanium exhibit surface features
much larger, on the order of micrometers. Osteoblasts are one-third less
likely to form on such surfaces, and immune cells are better able to distinguish
such surfaces as being unnatural.
Chemist Hicham Fenniri and biomedical engineer Thomas Webster realized
they could protect titanium implants by encasing them in a coating with
fine surface features. Fenniri had just such a coating available: rod-like
tubes made from self-assembled rings of deoxyribonucleic acid. The rosette-shape
rings and nanotubes are composed of guanine and cytosine, two of the molecules
that are basic components of genes.
To determine what measure of protection the nanotubes could provide artificial
joints, the researchers coated titanium parts with the DNA coating and
submersed them a solution containing bone cells. After just a few hours,
nearly all the cells in the solution had glommed onto the coating.
Although other coating materials, such as ceramics, also attract osteoblasts,
the DNA-based nanotubes may have some advantages. The rods can form on
their own, meaning they may some day be produced in large quantities.
And the researchers say they may be able to design the rods to blend in
with specific parts of the body.
Conveyor Strand
The
holy grail of nanotechnology is the atomic-scale factory. Computer-controlled
nanorobots would assemble molecule-size parts to make all manner of miniature
products.
A sugar cube-size manufacturing plant is not close to being built, but
scientists at Lawrence Berkeley National Laboratory in California have
demonstrated one piece of a futuristic factory. By applying a small electric
current, they turned a carbon nanotube into an atomic conveyor belt.
Researchers have for a decade been able to move one atom at a time using
scanning tunneling microscopes. But the technique is too slow to be used
in mass production.
The new research points to a potentially faster way. Indium atoms were
deposited on a bundle of nanotubes, forming tiny crystals on the surface.
As a voltage is applied across the bundle, the indium crystals melt away
and reform farther down the bundle.
Over time, the crystals form and evaporate their way along the length
of the bundles until they pile up on the far end.
Lead researcher Chris Regan noted that not only are no atoms lost in the
process, but the process is reversible simply by changing the polarity
of the current.
Chemical Concern
Hoping to slow down
the headlong rush to developing nanoproducts, the British Royal Academy
of Engineering has called for tighter regulation of nanotechnology.
One particular point of concern was that nanoparticles, which are now
being introduced into consumer products such as cosmetics, need to be
better studied to determine if there are any long-term health risks. The
material ought to be treated more like a new chemical than a new technology,
the academy wrote in a report published in July.
European governments strictly regulate chemicals, but nanotechnology has
largely fallen through the regulatory cracks, the report said.
This section was written by Editor Jeffrey Winters.