Researchers Forge New Material by Blending Chitosan and Polyester
June 22, 2009 – 3:01 pm
From the Wire: Researchers at the University of Washington have created a new medical material by blending chitosan with an industrial grade of polyester. Potentially suited for a number of medical applications, the hybrid fibre combines the excellent biocompatibility of chitosan with the mechanical strength of polyester.
The first application of the material will likely be in tiny tubes known as nerve guides that help severed nerves heal. To be suited for use in a nerve guide, a material must meet very strict requirements, according to Miqin Zhang, a professor of material science and engineering at the university.”It needs to be biocompatible, stable in solution, resistant to collapse and also pliable, so that surgeons can suture it to the nerve,” he explains. Meeting all of these requirements can be a tall order to fill.
The most commonly used material in nerve guides is collagen, a structural protein derived from animal cells. The material is expensive and tends to trigger an immune response. Collagen also has the drawback of being weak in wet environments such as those found inside the body. A nerve guide serves as a conduit to protect the neuron from injury, Zhang says. “If the tube is made of collagen, it’s difficult to keep the conduit open because [it can collapse under stress].”
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 readily 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. 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 fibres at the nanometer scale by first using electrospinning to draw the materials into nanosized fibres and then weaving the fibres together. The resulting material has a texture similar to that of the fibres of the connective tissue that surrounds human cells.
The two materials are different and are difficult to blend, but proper mixing is crucial because imperfectly blended fibres have weak points.
Zhang and colleagues built prototype nerve guides measuring 1.5 millimeters in diameter, and between five and 15 centimeters 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 says.
More information is available from the University of Washington.
Tags: chitosan, collagen, mixed-fibre, University of Washington
