Nerve Repair from Crustacean Shell With Polyester Creates Mixed-fiber Material

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Crustacean Shell With Polyester Creates Mixed-fiber Material For Nerve Repair

In the clothing industry it's common to mix natural and synthetic fibers. Take

cotton and add polyester to make clothing that's soft, breathable and wrinkle

free.

http://www.sciencedaily.com/releases/2009/06/090616164002.htm

Now researchers at the University of Washington are using the same principle for

biomedical applications. Mixing chitosan, found in the shells of crabs and

shrimp, with an industrial polyester creates a promising new material for the

tiny tubes that support repair of a severed nerve, and could serve other medical

uses. The hybrid fiber combines the biologically favorable qualities of the

natural material with the mechanical strength of the synthetic polymer.

" A nerve guide requires very strict conditions. It needs to be biocompatible,

stable in solution, resistant to collapse and also pliable, so that surgeons can

suture it to the nerve, " said Miqin Zhang, a UW professor of material science

and engineering and lead author of a paper now available online in the journal

Advanced Materials. " This turns out to be very difficult. "

After an injury that severs a peripheral nerve, such as one in a finger, nerve

endings continue to grow. But to regain control of the nerve surgeons must join

the two fragments. For large gaps surgeons used to attempt a more difficult

nerve graft. Current surgical practice is to attach tiny tubes, called nerve

guides, that channel the two fragments toward each other.

Today's commercial nerve guides are made from collagen, a structural protein

derived from animal cells. But collagen is expensive, the protein tends to

trigger an immune response and the material is weak in wet environments, such as

those inside the body.

The strength of the nerve guide is important for budding nerve cells.

" This conduit serves as a guide to protect the neuron from injury, " Zhang said.

" If the tube is made of collagen, it's difficult to keep the conduit open

because any stress and it's going to collapse. "

Zhang and colleagues developed an alternative. The first component of their

material, polycaprolactone, is a strong, flexible, biodegradable polyester

commonly used in sutures. It is not suitable on its own for use as a nerve guide

because water-based cells don't like to grow on the polyester's water-repelling

surface.

The second component, chitosan, is found in the shells of crustaceans. It's

cheap, readily available, biodegradable and biocompatible, meaning that it won't

trigger an immune response. Chitosan has a rough surface similar to the surfaces

found inside the body that cells can attach to. The problem is chitosan swells

in water, making it weak in wet environments.

Researchers combined the fibers at the nanometer scale by first using a

technique called electrospinning to draw the materials into nanometer-scale

fibers, and then weaving the fibers together. The resulting material has a

texture similar to that of the nanosized fibers of the connective tissue that

surrrounds human cells.

The two materials are different and are difficult to blend, but proper mixing is

crucial because imperfectly blended fibers have weak points.

Zhang and colleagues built prototype nerve guides measuring 1.5 millimeters

(0.06 inches) in diameter, and between five and 15 centimeters (two to six

inches) long. They tested a guide made from the chitosan-polyester blend against

another biomaterial under study, polylacticcoglycolic acid, and a commercially

available collagen guide.

Of the three materials, the chitosan-polyester weave showed the most consistent

performance for strength, flexibility and resistance to compression under both

dry and wet conditions. Under wet conditions, which the researchers say best

mimics those in the body, the chitosan-polyester blend required twice as much

force to push the tube halfway shut as the other biomaterial, and eight times as

much force as the collagen tube.

The new material showed promise for nerve guides but would also work well for

wound dressings, heart grafts, tendons, ligament, cartilage, muscle repair and

other biomedical applications, Zhang said.

The research was funded by the National Science Foundation through a grant to

the UW's Engineered Biomaterials Research Center. Co-authors on the paper are

Ellenbogen, Narayan Bhattarai, Zhensheng Li, Gunn,

Leung, Ashleigh , Dennis Edmonson and Omid Veiseh of the UW; Ming-Hong

Chen of the National Yang-Ming University in Taiwan; and Yong Zhang of the

National University of Singapore.