Artemia swims while connected to a
cantilever. Credit: Sharadhi Nagaraja/Aalto University.
In physics, the mesoscale lies
between the microscopic and the macroscopic. It is not just the domain of tiny
living creatures like small larvae, shrimp, and jellyfish, but also where
physics equations become extreme. While the macroscopic realm is governed by
inertia and the microscopic by viscosity, the mesoscale is both and neither,
requiring a new set of physics to describe it.
Now, physicists at Aalto
University's Department of Applied Physics have discovered how organisms swim
in the mesoscale mix of viscosity and inertia. The study was recently published
in the journal Communications Physics.
Led by Assistant Professor Matilda
Backholm, the multidisciplinary team found the key to efficient swimming in
this realm is not just moving faster or growing bigger, but a phenomenon of
non-reciprocal motion known as time reversal symmetry breaking. The results
help fill a knowledge gap in fundamental physics and could pave the way for
applications such as mesorobotics; tiny robots injected inside a patient's body
for drug delivery or carrying out medical procedures.
Swim smarter, not harder
The team observed
Artemia—meso-organisms roughly 400–1,500 micrometers long—measuring the
physical forces at play when they swam in water while connected to a
cantilever.
"During swimming, Artemia
flexed a joint‑like part of its antenna, tracing a figure‑eight shape. We then
decided to quantify and measure this motion range," explained doctoral
researcher Sharadhi Nagaraja.
The figure‑eight motion added a
degree of freedom to Artemia's movement. It proved that the organism was
breaking time reversal symmetry—a physics concept governing motion in the
microscopic realm.
"Time reversal symmetry means
that if you film a movie of swimming bacteria, the bacteria's motion must look
different if you play the movie forward or in reverse. If this isn't the case,
then the swimmer cannot move forward. That's a fundamental requirement at this
highly viscous regime in fluid mechanics, but it's not a requirement anymore at
the mesoscale," Backholm explains.
At the mesoscale, Artemia do not
need to break time reversal symmetry to swim but they seem to do so anyway with
their antenna.
"We found that if Artemia
breaks time reversal symmetry more, they also swim better and they have a
higher propulsive force. This is something no one has been able to directly
measure for a living organism before," Nagaraja adds.
Backholm's team filmed countless
frames of Artemia's movement and used machine-learning to analyze them.
Handling the organisms themselves required the combined expertise of physicists
and biologists, along with a micropipette force sensor which Backholm has been
instrumental in developing.
"The micropipette force sensor technique is ideal for directly measuring
swimming forces of living meso-organisms, since it doesn't harm the swimmers
and allows us to image the swimming motion simultaneously as we measure the
time-resolved forces," postdoctoral researcher Rafael Ayala Lara explains.
From tiny organisms to tiny robots
Knowledge of mesoscale swimming
physics could help engineers build and program what Backholm calls mesorobots
for use in fields like medicine.
"The idea is to have very small robots that deliver medication to some specific
location in the body. For example, going directly into a tumor with the poison
instead of poisoning the entire body. Such mesorobots would be able to deliver
larger amounts of drugs than their microscopic counterparts," Backholm
says.
It's an avenue of research where
science is playing catch-up with nature, says Backholm.
"Nature has figured this out already: through evolution over millions of years, organisms have developed into the most efficient swimmers. Yet it's only now that engineers are starting to gain a deeper understanding."
Provided by Aalto University
Source: 'Mesoscale' swimmers could pave way for drug delivery robots inside the body
No comments:
Post a Comment