Using powerful magnets to levitate fruit
flies can provide vital clues to how biological organisms are affected by
weightless conditions in space, researchers at The University of Nottingham
say.
The team of scientists has shown that
simulating weightlessness in fruit flies here on earth with the use of magnets
causes the flies to walk more quickly—the same effect observed during similar
experiments on the International Space Station.
Richard Hill, PhD, an EPSRC research fellow
in the University’s School
of Physics and Astronomy,
is one of the researchers involved in the study, which is published in Interface.
He said: “It is unfeasible to apply this
technique to investigating the effects of weightlessness on a human being
directly: no magnet exists that can do this. However, by studying the effects
on ‘model’ organisms such as the fruit fly, we can hope to obtain information
about the effects of weightlessness on particular biological mechanisms.
“It’s also important to remember that, in
our future endeavors to explore space, setting up permanent bases on our moon,
or Mars for example, or other planets, it will be crucial to understand the
effects of weightlessness on all living organisms: Our long-term survival will
of course require us to take with us many different biological organisms.”
The magnetic materials that we are most
familiar with are ferromagnetic materials such as iron, which are strongly
attracted to magnetic fields. However, most biological materials are affected
by a different type of magnetism called diamagnetism, in which objects are
weakly repelled from magnetic fields.
The team of scientists from Nottingham’s Schools of Physics and Astronomy and Biology
used the university’s powerful superconducting magnet to produce a very strong
magnetic field of around 16 T—approximately 350,000 times stronger than the
strength of the Earth’s field.
Inside the superconducting solenoid magnet,
the diamagnetic repulsive force on the flies can be large enough to just
balance the force of gravity so that they levitate with no support. This effect
was first demonstrated by Nobel Prize-winning physicist Andre Geim and
colleagues at the University
of Nijmegen in 1997 when
they used the same technique to levitate a live frog.
Hill added: “Crucially, as far as living
organisms are concerned, the levitation force balances the force of gravity
right down to the molecular level. This means we can compare the levitation
force, which balances the force of gravity in our magnet, with the centrifugal
force that balances the force of gravity on an astronaut in orbit around the
Earth.
“In orbit, aboard the International Space Station
for example, gravity is still present, but because an orbiting body is
effectively in ‘free-fall’, the centrifugal force on the astronauts (because
they’re going around the planet so quickly), is large enough to balance out the
force of gravity. Here, we’re using the diamagnetic force to balance gravity instead
of centrifugal force.”
The scientists need to be careful when
using a strong magnetic field as it can have other effects on living organisms.
However, they controlled for these effects by examining how the flies behaved
in different parts of the magnet: at the centre of their solenoid magnet, there
is a strong magnetic field but no diamagnetic force so the flies experienced
normal gravity. By comparing how flies in the centre of the magnet behaved with
flies outside the magnet, they could isolate the different effects of the
strong magnetic field.
Hill said: “What we showed was that the
flies in the magnet behaved in the same way that they behave in space. They walk
more quickly. Why they do this, we really don’t know yet. It may be because the
flies just find moving around in weightlessness easier on their joints and
muscles, or it could be that it’s some kind of response to their confusion
about which way is up and down when gravity is absent.”
Diamagnetic levitation doesn’t balance
gravity as perfectly as ‘real’ weightlessness does in space, but diamagnetic
levitation can be used to see which experiments are suitable and interesting to
perform in space before spending money on a space launch.
The advantage of doing these experiments on
the ground is that it’s a lot cheaper and much easier, and scientists do not
need to worry about the effects of high g-forces endured when launching the
flies into space on a rocket. It’s also very easy to do the comparison between
flies in weightlessness and flies in ordinary gravity: the scientists set up
the same experiment in different positions in the magnet and run the
experiments simultaneously. By moving the flies to different positions in the
magnetic field, they can simulate gravities between zero-g and 2g (twice the
Earth’s gravity conditions), enabling them to simulate the gravity on the moon
or Mars.