T A Rector
Innovation
Birds inspire new
ultra-strong fastener
Galactic tussle will engulf Milky Way
An international team of astrophysicists has mapped the borders between two of our neighbouring galaxies
to reveal an ongoing galactic jostle that will eventually result in the formation of one super-galaxy
incorporating the Milky Way. The finding has been made by Alan McConnachie of the Herzberg Institute of
Astrophysics in Canada, together with colleagues in Australia, Europe and the US. Using the Canada-France-Hawaii Telescope (CFH T) in Hawaii, the researchers carried out the most extensive survey to date of
Andromeda – the closest large galaxy to the Milky Way – mapping stars over an area more than 100 times
larger than its well-photographed central disc. Next, the researchers turned their attention to one of
Andromeda’s smaller satellites, Triangulum – a densely packed galaxy about one-tenth the size of its spiral
neighbour. What they observed was an extended, stream-like structure protruding from Triangulum in the
direction of Andromeda. Using computer simulations (see image), the researchers have estimated that the
limb of stars was “ripped” from Triangulum roughly two billion years ago when the galaxies passed within
100 000 light-years of each other. The simulations predict that the next time that the two galaxies come
into close contact, within the next two billion years, Triangulum will be completely engulfed by its larger
neighbour. What is more, by the time Triangulum approaches Andromeda again, the Milky Way and
Andromeda will have moved much closer together, which will probably result in a three-way merger and the
formation of a new, larger galaxy (Nature 461 66).
Acoustic tweezers pinch living cells
Optical tweezers are a useful device for
manipulating tiny objects using the momentum of light. Now, physicists can also
add another set of tweezers to their toolkit –
“acoustic tweezers” that can manoeuvre
microscopic objects using sound.
The new device was developed by researchers at Pennsylvania State University
by combining two surface acoustic waves
(SAWs) on a chip. When a microscopic object is placed in the resulting standing wave,
it moves along a pressure gradient until it
reaches a node – that is, a point where the
two waves cancel – when the object then
comes to a complete standstill. By combining
several standing waves along the surface of
the piezoelectric chip, the researchers say
they can manoeuvre tiny objects by varying
the frequency of the sound.
To demonstrate their new acoustic tweez-
ers, the researchers arranged a series of
fluorescent polystyrene beads about 1 .9 µm
in diameter into a grid pattern. They then did
the same thing using the red blood cells of a
cow and the bacteria E. coli.
The researchers say that the new device
offers several advantages over optical tweezers. One is that the acoustic tweezers can be
used to manipulate living cells without damaging or killing them. Another potential advantage, according to the researchers, is that
the tweezers could cost just $20 per set, compared with $100 000 for optical tweezers.
The hope is that the optical tweezers can
be integrated into a single chip that can perform individual or multiple functions in a
so-called lab-on-a-chip. Such a device could
be used for medical applications, including
blood analysis, cell studies and tissue engineering (Lab on a Chip 10.1039/b910595f).
Now found in all manner of places from clothing to
industry, Velcro was invented in the 1940s by
Swiss inventor George de Mestral, who drew
inspiration from the difficulty he experienced
removing burrs from the fur of his dog. De Mestral
named his product Velcro from the French for
velvet (velours) and hook (crochet) on account of
its underlying mechanism – a piece of fabric
covered in tiny hooks fastening to a second piece
of fabric covered in tiny hairy loops.
The real beauty of this “wonder material”, writes
James Dacey, is that it can seal with a relatively
tight grip but still be released with minimal effort.
However, the drawback with these fasteners is that
their gripping mechanism tends to break down
when exposed to high temperatures, aggressive
cleaning chemicals, and harsh conditions.
Now, a team at the Technical University of
Munich led by Josef Mair, working with industrial
firms based in Germany, may have created a
product that overcomes this problem. “Metaklett”,
or “metal burr”, is a hook-and-loop fastener made
using steel, which is chosen for its high resistance
to mechanical loads and chemical corrosion. The
product is being developed with two separate hook
designs, both of which are resistant to chemicals
and remain fastened in temperatures of up to
800°C, the researchers claim.
The first hook mechanism is based on the
shape of a flamingo, and it has been chosen for its
strength. Depending on the direction of the
applied force, the fastener can withstand loads of
up to 35 tonnes per square metre. The second
type of hook, which resembles a “duck’s head”,
cannot support the same loads as the flamingo,
but it is more flexible because it can remain
fastened while subjected to stresses from a
variety of directions. Mair and his team are now
working on a third design – the “hybrid” model –
which combines the strength of the flamingo with
the flexibility of the duck.
The researchers have also been collaborating
with their industrial partners to create bespoke
metal fasteners for a range of applications. “I can
imagine Metaklett being used in hospitals – for
example as a means of fastening curtains that
does not get damaged when exposed to hospital
cleaning,” says Mair. He also told Physics World
that he can envisage his new metal fastener being
used both as a shield covering car exhaust pipes
and as a means of holding panels together in
planes. “A car parked in direct sunlight can reach
temperatures of 80°C, while temperatures of
several hundred degrees can arise around the
exhaust manifold,” he said.
