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Shen and Pickard are probing the biomechanical properties of the
forisome, which, in a variety of plants, responds to injury by
swelling up in reaction to an increase of calcium. The swelling of the
proteins within transport cells protects the plant from hemorrhaging
nutrients. Once the danger passes, the forisomes go back to their
original shapes. The foursome's goal is to understand the system well
enough to enable future collaborators to develop a chemically stable
artificial forisome - a non-living system that can integrate functions
such as sensing, acting and logic in response to external stimuli.
Such a smart material would be biomimetic. One of the best examples of
a natural system whose behavior researchers would like to synthesize -
a biomimetic - is the famed Venus flytrap. Forisome is particularly
attractive as a biomimetic smart material because, unlike most protein
motors, it is not dependent on adenosine triphosphate (ATP) for its
activation, making it more flexible. Shen used a microfluidic device -
a soft lithography system of micro-channels embedded in fluids, so
small it fits in the palm of a hand - to see how the forisome proteins
would react to changes in calcium, pH and the hydrodynamic environment
itself.
Swell protein
Shen and her collaborators found that they could
induce swelling easily as well as reverse the swelling in the device,
rather more easily than other systems used previously to study the
proteins. "We're interested in the kinetics of the forisome proteins,"
Shen said. "We wanted to see how fast they change shape and also their
potential as a smart material. We intend to do other experiments that
might reveal the durability and actuation kinetics of forisomes." Shen
and her colleagues published their results in the July 2006 issue of
Smart Structures and Systems, An International Journal, Vo. 2, Number
3, 225-236. A separate paper also was published on the prospective
energy densities on forisome in 2006 in Materials Science and
Engineering: C Biomimetic and Supramolecular Systems, 26 (1), 104-112,
2006. Shen designs microfluidic devices to study a wide variety of
complex fluids and how they behave hydrodynamically on a very small
scale, anything" hard to see with the naked eye," she says. "The
devices are useful for lots of applications, for making novel
materials, drug delivery, and for studying the cellular and neuronal
growth. We're able to observe interfacial phenomena under a microscope."
Collaborations
Shen has performed research for Procter & Gamble,
for instance, to determine shelf life of shampoos and hair
conditioners. If the company wants to blend a certain type of shampoo
with a perfume, she can study the stability of the mixture inside a
microfluidic device under the microscope instantaneously. Shen is also
collaborating with Lars Angenent, Ph.D., Washington University
assistant professor of chemical engineering, on the behavior of
methanogens inside a microfluidic device, by imposing a concentration
gradient to see what’s the optimal pH level methanogens prefer to grow.
Their study can be applied in making microbial fuel cells and biofuel
cells.
Shen also is working with medical doctors in the
Washington University School of Medicine to see how cells and neurons
behave by guided channel design in the microfluidic environment.
She also is making monodispersed liquid crystals
droplets- which are the basis of computer and TV screens - and polymer
solutions (R. Sureshkumar, Ph.D., Washington University professor of
chemical engineering) inside the micro channels.
"In general, microfluidic devices are pretty
powerful," Shen said. "You can study anything from tiny droplets to
mixing of multiple fluids. What would take months or years for
macroscopic systems, can be done within seconds or minutes with
microfluidic devices. We often find in these environments that surface
properties and geometric confinement in liquid-liquid or liquid- gas
systems behave much differently than they do in beakers or tanks. "And
that’s very important in fabricating new materials for high tech
applications, making sleek shampoos, drug delivery systems, or just
improving the ice cream or ketch up texture. |
