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Subject: from the New Scientist Artificial cornea is both
strong and clear
TECHNOLOGY: FEATURE. p28
NS070825
#34 Artificial cornea is both strong and clear; Ten million
people worldwide suffer from corneal blindness, but
until now there has not been an artificial implant with
just the right combination of properties
Aria Pearson
AN ARTIFICIAL cornea has been created that is as strong and clear
as the real thing. It could allow millions of people with damaged
corneas to see.
Corneal blindness can be caused by disease, injury or infection of
the eye's clear surface. It can be cured with a transplant from a
human donor, but donors are scarce. The World Health Organization
estimates that 10 million people worldwide are blind because of
defective corneas, yet only 100,000 receive transplants each year.
Artificial corneas made from flexible hydrogels - polymers that
absorb water - are now available, but they are not permeable
enough to support epithelial cells on their surface. These cells
guard against bacteria and stop natural corneas becoming cloudy,
by preventing proteins from sticking to them. Adding more water
to the hydrogels allows glucose to diffuse through them and
nourish epithelial cells on the surface, but it also weakens
them. So there is a push to develop a synthetic cornea that is
both strong and permeable. "The long-term goal is an
off-the-shelf cornea that looks and acts like donor tissue," says
Heather Sheardown of McMaster University in Hamilton, Ontario.
Now Curtis Frank and colleagues at Stanford University in
California have done just that. They took polyacrylic acid, the
water-absorbing polymer found in diapers, and cross-linked it
with polyethylene glycol, which also absorbs water. The
cross-links mean that the resulting material is 20 times stronger
than either of the starting polymers on their own, and about the
same strength as a human cornea. Crucially it also has the same
water content as a real cornea, which greatly increases its
ability to transport nutrients to the epithelial cells.
After forming the material, which was presented at the American
Chemical Society meeting in Boston on 20 August, into a
6-millimetre-wide disc , the researchers implanted it in rabbits.
They found that glucose from the eye diffused through the
material and fed the epithelial cells growing on the surface,
which had been modified with collagen to promote cell growth.
Sheardown is also developing a cornea made from two intertwined
polymers. But it does not transport glucose as readily as Frank's
and she has not yet tested it on animals.
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Copyright 2007 Reed Business Information, UK, a division of Reed Elsevier
Inc.Al
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