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Innovative coating could give medical implants a longer
life14 May 2005
By
mimicking an adhesive protein secreted by mussels and a
polymer that repels cells and proteins, researchers at
Northwestern University have designed a versatile new
two-sided coating that could breathe life into medical
implants.
Currently the longevity of certain medical
implants suffers because bacteria, cells and proteins in the
body gradually accumulate on the devices (known as fouling),
compromising their performance and threatening patients with
infections. Unfortunately, the polymers that studies have
shown to be effective at antifouling do not last long in-vivo,
falling prey to chemical degradation or to the body's enzymes.
In contrast, the molecular compound developed at
Northwestern, which sticks securely to a surface and prevents
cell and protein buildup, works for a long period of time. In
laboratory studies, the new coating provided effective fouling
resistance for more than five months, which Phillip B.
Messersmith, associate professor of biomedical engineering in
the McCormick School of Engineering and Applied Science and
lead investigator in the study, believes to be the longest
successful in-vitro antifouling demonstration.
The
findings are published online today (May 13) by the Journal of
the American Chemical Society, a peer-reviewed publication of
the American Chemical Society, the world's largest scientific
society.
While the coating has not been tested in
humans, it holds promise for use on a variety of medical
implants including urinary catheters, cardiac stents,
biosensors and dental implants and devices. The coating also
could be used to prevent the biofouling of water processing
equipment, ship hulls and other manmade structures in the
marine environment.
Looking for a solution to the
longevity problem in existing coatings, Messersmith teamed up
with Annelise Barron, associate professor of chemical and
biological engineering and an author on the paper. Barron is
an expert at creating peptoids -- synthetic molecules that are
closely related to the natural proteins or peptides they mimic
but don't degrade in the body.
Messersmith and Barron
wanted to use this durability of peptoids to the antifouling
coating's advantage. They proceeded to intelligently design a
new polymer made up of two parts, both playing a key role: a
short peptide that is the synthetic version of the sticky
dihydroxyphenylalanine (DOPA) molecule that gives mussels
their adhesive or anchoring strength and a longer peptoid
polymer resembling the structure of polyethylene glycol (PEG),
a widely studied antifouling polymer.
"We had a rich
chemistry available to us when designing this polymer," said
Messersmith. "The chemical characteristics of the antifouling
component are similar to polyethylene glycol but it lasts
longer because it is a peptoid and enzyme resistant. Plus, the
structure of the polymer's backbone, which is based on a
natural peptide, should make it very biocompatible and prevent
evoking an immune response in the body."
The
researchers tested their coating on titanium dioxide (a
material common in medical implants) in environments that
simulated physiologic conditions with fresh serum and cells.
The coating anchored itself firmly to the surface and
demonstrated excellent resistance to proteins and cells during
the five-month experiment. For the same reason the coating is
cell and protein resistant, it should also prove to be
bacteria resistant, Messersmith said.
Other authors on
the paper are lead author Andrea R. Statz, a graduate student
in biomedical engineering, and Robert J. Meagher, a graduate
student in chemical and biological engineering.
Contact: Megan
Fellman
fellman@northwestern.edu
847-491-3115
Northwestern
University
http://www.northwestern.edu/
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