20 | New Scientist | 20 February 2021Animal behaviourNow body heat could
power your gadgetsSELF-HEALING and eco-friendly
devices that generate electricity
from body heat could power
wearable gadgets.
Jianliang Xiao at the University
of Colorado, Boulder, and his team
used thermoelectric generators,
which convert heat into electricity.
The team embedded a number of
these in a thin film made from a
flexible polymer called polyimine
and wired them together with aTiny craft may soar
into forbidden zoneSUNLIGHT could be used to power
microfliers travelling above the
stratosphere in the mesosphere.
At present, the only vehicles
that can operate in this layer of
our atmosphere, between 50
and 80 kilometres up, are rockets
destined for space. The lower air
density doesn’t allow for sufficient
lift for aircraft, but it is too dense
for the safe passage of satellites.
Igor Bargatin at the University
of Pennsylvania and his team have
come up with a microflier that
might achieve sustained travel
through the mesosphere.
To do so, they exploited the
phenomenon of photophoresis.
This relies on the transfer of solar
energy – initially to an object such
as the new device, and then to air
molecules surrounding the object.
“When you expose [the craft] to
sunlight, the molecules that hit
the surfaces will absorb some ofFlight^ TechnologyA FEMALE vampire bat has adopted
an orphaned baby bat and begun
nursing it, after creating a close
social bond with the baby’s mother
before she died. This is unusual,
because while female bats live in
“maternity colonies”, they seem
to raise their young individually.
The observation was made
by Imran Razik at the Ohio State
University and his colleagues at
the Smithsonian Tropical Research
Institute in Panama while studying
the social behaviour of common
vampire bats (Desmodus rotundus).
They had captured 23 adult
female bats from three wild
colonies, then put them in a single
captive colony to see how they
developed relationships. Female
vampire bats can form social bonds
with other bats, grooming each
other and sharing food.One bat fell ill during the study
and died weeks after giving birth.
To the researchers’ surprise and
relief another bat adopted the
infant, says Razik. The team traced
the development of the relationship
between the sick mother bat (Lilith)
and the adoptive bat (BD), which
wasn’t pregnant or nursing. They
had initially shown a lot of mutual
grooming, suggesting they were
bonding, says Razik.
The healthy bat shared food much
more often than Lilith did, a trend
that increased as Lilith got sicker.
BD also helped take care of Lilith’s
baby, grooming it and even nursing
it, although she herself didn’t have a
baby. When Lilith died 19 days after
giving birth, BD fully adopted the
baby and raised it as her own (Royal
Society Open Science, doi.org/fvbf).
Christa Lesté-LasserreVampire bat shows soft side
by adopting orphaned baby
liquid gallium-indium alloy to
create stretchable bands that can
be worn on arms, legs and fingers
(pictured). The device costs less
than $10 to produce.
The team tested a wrist-worn
version with someone sitting and
walking. The increased body heat
during walking generated enough
power – 12.5 microwatts – to run
small sensors such as a heart
monitor or motion tracker.
The liquid metal and polyimine
make the device self-healing – the
team could cut it then place the
two halves next to each other, and
within a couple of hours it would
repair with no hit to performance.
This also means the device is
easy to recycle. Xiao’s team soaked
one in an alcohol-based solution to
break down the polyimine, freeing
the generators and liquid metal.
A new polyimine film was created
from the solution and recombined
with parts from the old device to
create a new one with comparable
performance (Science Advances,
doi.org/fvdv). Priti Parikhthe heat,” says Bargatin. “We
designed the [device] surfaces in
such a way that the top surface is
not very good at transferring heat
whereas the bottom surface is
very good at transferring heat
and as a result more molecules
will gain downward velocity
than upward velocity.”
This creates a lift force, he adds,
meaning that when the discs were
exposed to incident light intensity
of about 0.5 watts per square
centimetre at air pressures of
about 10 pascals they moved
through the air (Science
Advances, doi.org/fvqr).
The team believes that in the
future, versions of the microfliers
fitted with sensors could be used
to map wind and temperatures
in the mesosphere, which could
improve climate models.
Karen Aplin at the University of
Bristol, UK, wondered about some
practicalities of the fliers, such as
getting them to the mesosphere,
which would require a rocket.
Krista CharlesHE
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XIAO^ LABNews In brief