New Lab-on-a-chip Measures Mechanics Of
of Article: http://www.sciencedaily.com/releases/2009/06/090630163113.htm
(June 30, 2009)
— Researchers at the University of Michigan have devised a microscale tool
to help them understand the mechanical behavior of biofilms, slimy colonies
of bacteria involved in most human infectious diseases.
Most bacteria in nature
take the form of biofilms. Bacteria are single-celled organisms, but they
rarely live alone, said John Younger, associate chair for research in the
Department of Emergency Medicine at the U-M Health System. Younger is a
co-author of a paper about the research that will be the cover story of the
July 7 edition of Langmuir.
The new tool is a
microfluidic device, also known as a "lab-on-a-chip."
Representing a new application of microfluidics, the device measures
biofilms' resistance to pressure. Biofilms experience various kinds of pressure
in nature and in the body as they squeeze through capillaries and adhere to
the surfaces of medical devices, for example.
"If you want to
understand biofilms and their life cycle, you need to consider their
genetics, but also their mechanical properties. You need to think of
biofilms as materials that respond to forces, because how they live in the
environment depends on that response," said Mike Solomon, associate
professor of chemical engineering and macromolecular science and
engineering, who is senior author of the paper.
Mechanical forces are at
play when our bodies defend against these bacterial colonies as well,
"We think a lot of
host defense boils down to doing some kind of physical work on these
materials, from commonplace events like hand-washing and coughing to more
mysterious processes like removing them out of the bloodstream during a
serious infection," he said. "You can study gene expression
patterns as much as you want, but until you know when the materials will
bend or break, you don't really know what the immune system has to do from
a physical perspective to fight this opponent."
studied these properties yet because there hasn't been a good way to
examine biofilms at the appropriate scale.
The U-M microfluidic
device provides the right scale. The channel-etched chip, made from a
flexible polymer, allows researchers to study minute samples of between 50
and 500 bacterial cells that form biofilms of 10-50 microns in size. A
micron is one-millionth of a meter. A human hair is about 100 microns wide.
Such small samples behave
in the device as they do in the body. Tools that require larger samples
don't always give an accurate picture of how a particular substance behaves
on the smallest scales.
The researchers found
that the biofilms they studied had a greater elasticity than previous
methods had measured. They also discovered a "strain hardening
response," which means that the more pressure they applied to the
biofilms, the more resistance the materials put forth.
If doctors and engineers
can gain a greater understanding of how biofilms behave, they could perhaps
design medical equipment that is more difficult for the bacteria to adhere
to, Younger said.
The experiments were
performed on colonies of Staphylococcus epidermidis and Klebsiella
pneumoniae, which are known to cause infections in hospitals.
The new microfluidic
device could also be used to measure the resistance of various other
soft-solid materials in the consumer products, food science, biomaterials
and pharmaceutical fields.
The paper is called,
"Flexible Microfluidic Device for Mechanical Property Characterization
of Soft Viscoelastic Solids Such as Bacterial Biofilms." The first
author is Danial Hohne, a recently-graduated Ph.D. student in the Department
of Chemical Engineering.
The research is funded by
the National Institutes of Health, the National Institute of General
Medical Sciences, the U-M Center for Computational Medicine and Biology and
the Department of Emergency Medicine.
Adapted from materials provided by University of