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If
you throw a rubber balloon filled with water against a wall, it will
spread out and deform on impact, while the same balloon filled with
honey, which is more viscous, will deform much less. If the balloon’s
elastic rubber was stiffer, an even smaller change in shape would be
observed.
By
simply analyzing how much a balloon changes shape upon hitting a wall,
you can uncover information about its physical properties.
Although
cells are not simple sacks of fluid, they also contain viscous and
elastic properties related to the membranes that surround them; their
internal structural elements, such as organelles; and the packed DNA
arrangement in their nuclei. Because variations in these properties can
provide information about cells’ state of activity and can be indicative
of diseases such as cancer, they are important to measure.
UCLA
bioengineering researchers have taken advantage of cells’ physical
properties to develop a new instrument that slams cells against a wall
of fluid and quickly analyzes the physical response, allowing for the
identification of cancer and other cell states without expensive
chemical tags.
The
instrument, called a deformability cytometer, was developed by UCLA
biomedical engineering doctoral students Daniel Gossett and Henry Tse
and assistant professor of bioengineering Dino Di Carlo. It consists of a
miniaturized microfluidic chip that sequentially aligns cells so that
they hit a wall of fluid at rates of thousands of cells per second. A
specialized camera captures microscopic images of these cells at a rate
of 140,000 pictures per second, and these images are then automatically
analyzed by custom software to extract information about the cells’
physical properties.
Other
researchers had previously discovered that the physical properties of
cells could provide useful information about cell health, but previous
techniques had been confined to academic research labs because measuring
the cells of interest could take hours or even days. With the
deformability cytometer, the group can prepare samples and conduct an
analysis of tens of thousands of cells within 10 to 30 minutes.
“Our
system makes use of an approach that (U.S. Secretary of Energy) Steven
Chu used to stretch DNA to, instead, stretch cells,” Di Carlo said.
“This required us to engineer the fluid dynamics of the system such that
cells always entered the stretching flow in the same place, making use
of inertial focusing technology my group has been pioneering.”
With
a system in place to measure the physical properties of cells at much
higher rates, the bioengineers teamed up with collaborators across the
UCLA campus to measure various cell populations of interest to
biologists and doctors.
Along
with UCLA stem cell biologist Amander Clark, an assistant professor of
of molecular, cellular and developmental biology, Di Carlo’s team
confirmed that stem cells that have the capability to become any tissue
type stretch much less than their progeny, which are already in the
process of becoming a particular tissue.
In
collaboration with cytopathologist Dr. Jian Yu Rao, a professor of
pathlogy and laboratory medicine at the David Geffen School of Medicine
at UCLA, the team accurately detected cancer cells from pleural fluids
using the high-speed deformability cytometer. Pleural fluid, which
builds up around the lungs, is traditionally challenging to analyze
because it contains a mixture of cell types — including immune cells,
mesothelial cells from the chest wall lining and, potentially, low
concentrations of cancer cells.
“The
main problem for the diagnosis is that with cytomorphology alone, it
can be difficult to distinguish mon-malignant mesothelial cells that are
reactive to conditions such as inflammation, infection and injury from
metastatic cancer cells or malignant mesothelial cells,” Rao said. “So
this technique has tremendous clinical utility in that regard.”
With
Rao and Dr. Otto Yang, a professor in the infectious diseases division
at the Geffen School of Medicine and the department of microbiology,
immunology and molecular genetics, the researchers found that in
addition to identifying cancer, the technique was also sensitive to
states of acute and chronic inflammation in which populations of white
blood cells are primed to respond to infection. Measuring the state of
the immune system can aid in diagnosing immune disorders such as AIDS or
in evaluating patients’ rejection of transplants early on, allowing
doctors to modify anti-rejection therapies.
“The
applicability to infectious diseases and organ transplantation is still
theoretical,” said Yang, who is also a researcher with the UCLA AIDS
Institute. “Immune cells change physical characteristics as they are
activated, and so, in theory, this technology could be harnessed to
detect immune responses against infections or transplanted organs.”
“Working
with other folks across campus has been amazing,” Di Carlo said.
“Anytime we talked with Amander, Otto or Jian Yu, we learned something
new which helped us refine our system and the problems we chose to
address. We all live in slightly different worlds, and sometimes
communication is difficult, but bioengineering is great in that we can
communicate in different languages and bridge the engineering school to
medicine and biology much more effectively.”
The
results were reported online in the journal Proceedings of the National
Academy of Sciences of the USA and will be published in a forthcoming
print issue of the journal. More information can be found at Di Carlo’s laboratory website.
The
research was funded by a Young Faculty Award from the Defense Advanced
Research Projects Agency (DARPA) and a Packard Foundation Fellowship for
Science and Engineering.
Cytovale
Inc., a spin-off out of UCLA Engineering assisted by the school’s
Institute for Technology Advancement, is exploring first steps toward
commercialization of the instrument.
Hydrodynamic stretching of single cells for large population mechanical phenotyping
