Scientists Discover Method
for Sculpting
How Chemicals Spread in Fluid Flows
How Chemicals Spread in Fluid Flows
Solely
adjusting the aspect ratio of a pipe – regardless of its shape – precisely
controls how medicine, pollutants, nutrients and chemicals travel down it and
hit their target
(Chapel Hill , N.C. University
of North Carolina at Chapel
Hill and their team have created art of their own: a method that precisely
sculpts how fluids spread chemicals as they travel to hit their target.
The work, to appear in the Nov.
17 advance online issue of Science, has profound implications in
fields such as medicine, chemistry and environmental management, for example,
where having the ability to precisely control how drugs, chemicals and
pollutants approach their destination is potentially critical for optimizing
their effect, potency and lifespan.
“You might want a chemical, for
example, to hit its target all at once or you might want it to build up
gradually,” said McLaughlin, chair of UNC-Chapel Hill’s department of
mathematics. “Until now, scientists had little control on the exact way for a
chemical to do that. This work gives them a simple method so that they can achieve
either of these goals — or anything in between.”
McLaughlin and his colleague,
Roberto Camassa, Kenan Distinguished Professor of Mathematics, revealed that
the secret to such control lies solely in the relative dimensions of the tube,
not the properties of the fluid or the chemical dissolved within it.
Specifically they showed that the relationship between a pipe’s width and
height — or aspect ratio — governs the shape of the chemical spread as it flows
with the fluid down the tube.
A circle and square are just as
wide as they are tall, while an ellipse and rectangle are wider in one
dimension than the other. By squishing the tube away from being a perfect
circle, the researchers showed that they can change the way that a solute
reaches its target: Solute traveling down a skinny pipe barrages its target
fast, but if the same solution travels down a fat pipe, the solute crawls
slowly upward to its target until the big punch hits at the end.
They found that precisely the
same effect occurs in rectangular ducts, such that in skinny ones, solute
arrives at the target strong, like a heavy punch; if you stretch the rectangle
into a square, the solute reverses its approach, arriving in a slow and gradual
upward swing.
“That was the big surprise,”
said Camassa. “We stumbled upon this incredible disconnect between two
different geometries. It’s one of nature’s universal principles governing the
shape of solute spreading and it can be used to optimize results in many
industries that deal with chemicals dissolved in fluid flows.”
The implications reach far and
wide, particularly in microfluidic devices, which contain miniaturized
components for routing and processing very small amounts of fluids. They are
used in health care for making small, biological test kits or for precisely
manufacturing drugs. This new work can be used to optimize microfluidic devices
for any particular goal. For example, researchers can potentially optimize the
delivery of cancer drugs or antibiotics to minimize damage to surrounding tissues
and thus minimize side effects.
Economics also play a big role,
explained McLaughlin and Camassa, who are both in UNC-Chapel Hill’s College of Arts
Precision elliptical pipes may
be difficult and expensive to manufacture. But the new work shows that
rectangular pipes, which are easier and cheaper to produce, can do the same
job, delivering a fluid with calculated precision given the right aspect ratio.
As a bonus, rectangular ducts stretch solute much less than ellipses, an effect
that can be important in delivering more highly concentrated substances,
another factor when considering cost and shape of a pipe.
The team, including graduate
students Manuchehr Aminian and Francesca Bernardi, and postdoctoral scholar
Daniel Harris, has revealed one of nature’s universal principles governing how
fluids spread solute in microfluidic environments.
“It’s sort of a slam dunk,
having analysis, computation and experiment, all these approaches confirming
each other, ” said McLaughlin. “It says that this phenomenon is really there
and can be used for far-reaching applications.”
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