Innovative Coating Could Give Medical Implants A Longer
Life
EVANSTON, Ill. --- 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.
This story has been adapted from a news release issued by
Northwestern University.
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