Biodegradable Wound Dressing, Potential for Improved Healing

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Sara Frisch [email protected]
or Tim Lucas [email protected]
News Services, 919/515-3470

FOR IMMEDIATE RELEASE Aug. 23, 1999

Biodegradable Wound Dressing Shows Potential for Improved Healing

NEW ORLEANS -- Scientists have developed a three-layered, biodegradable wound dressing that can improve the healing process of third- and fourth-degree burns.

The new dressing, created by North Carolina State University textile researchers, incorporates layers of chitosan -- a natural fiber extracted from crab shells -- and synthetic polymer compounds under a gauze layer. Preliminary in vivo and in vitro studies on pig skin showed that the composite wound dressing increased the healing rate and protected the wound from bacteria and other threats, as the two inner layers were absorbed into the skin.

The research team presented their findings at the 218th American Chemical Society national meeting on Monday, Aug. 23, in New Orleans.

An ideal wound dressing is lightweight, flexible, odor-free, impermeable to microorganisms, yet permeable for necessary water vapors and exudate (i.e. pus) leaving the wound. The new composite strives to meet these requirements, and has a distinct advantage over other dressings that need to be changed often and can be painful to remove. The inner layers of the composite dressing actually biodegrade and become part of the healed skin. Only the gauze outer layer must be removed and discarded, and that process doesn't disturb the wound.

Tests of the composite dressing showed that it was a viable option for solving some of the problems created by other dressings currently in use, says Allison London Brown, a former master's degree student at NC State and lead presenter of the study. She says re-application of dressings that disturb the wound can be uncomfortable for patients, especially when dressings attached to healing skin bring scabs off as they are removed. But the composite, London Brown says, can decrease the healing time, increase the healing rate, reduce the pain and produce less scarring. Most importantly, this biodegradable composite helps the skin grow back, she says.

NC State professor Dr. Sam Hudson, a collaborator on the research, says chitosan acts as a scaffolding by providing a cellulose-like base on which new skin cells can grow. "In a skin wound," he says, "cells are growing back over the injured area from the edges." Cells that erupt from underneath the wound can cause scarring. The chitosan layer forms a barrier, he says, that suppresses the undesired cell growth, encourages appropriate growth from the outer edges, and thus reduces scarring.

Chitosan, used in the layer closest to the wound, is known for its anti-fungal, anti-microbial, anti-viral and wound-healing properties. It is easily converted to a strong, flexible fiber, and the human body absorbs it easily. In the composite wound dressing, it protects the wound and helps the skin heal, while degrading and being absorbed by the healed skin.

For the second layer of the composite, the research team tested films made of two different biodegradable polymers. The second layer functioned to transport exudate, protect the wound, and prevent the outer gauze layer from adhering to the wound. It is the second line of defense against bacteria that may try to invade after the chitosan layer breaks down. This polymer film layer, about the consistency of cellophane paper, also degrades and becomes part of the healed skin.

The outermost layer, made of cotton or cotton-viscose, absorbs exudate and must be changed periodically. Because the wound is well-protected underneath, removing the gauze layer shouldn't hurt as much as removing traditional adhesive bandages.

The composite dressing has potential for widespread use, but further research is needed, London Brown says. In the in vivo study on living pigs, the wounds dried out too much. The composite dressing still needs the right balance of being moist enough to aid healing, but not too moist. Other areas for improvement, she says, are pinpointing the appropriate thickness of polymer films and ideal degradation times. And to make a commercial product, developers would need to combine the two inner layers into a single application.

Chitin, the base of chitosan, is the second-most abundant organic resource on the earth, says Hudson, one of the world's leading researchers on chitin and chitosan. In North Carolina, the annual harvest of 40 million pounds of crab produces 36 million pounds of waste, he says. From the shell waste, producers can harvest chitin and chitosan to make valuable products for the medical, food, fiber and textile industries.

"It's a natural resource that we're just beginning to tap into," London Brown says.

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NOTE TO EDITORS: For assistance reaching the research team, contact NC State News Services at 919/515-3470. Attached is the team's abstract from the meeting presentation.

"Biodegradable Composite Wound Dressing" Allison London Brown, master's degree recipient; Dr. Alan Tonelli, professor; Dr. Samuel Hudson, professor; Dr. Bhupender Gupta, professor; all of North Carolina State University College of Textiles

Abstract: Poly(lactic acid) (PLA), poly-epsilon-caprolactone (PCL), and chitosan (CH) are incorporated into a layered, biodegradable, bioabsorbable wound dressing. The CH layer rests directly on the wound and provides for accelerated healing of the wound. The next layer composed of either PLA or PCL provides protection for the wound from both microbes and further trauma and also permits transport of the wound exudate away from the wound and into the outer layer of the dressing, which is a simple gauze bandage. The gauze bandage may be changed without causing further trauma to the wound, and the contact CH layer and eventually the PLA or PCL layer will degrade and be bioabsorbed. Physical properties of the CH, PLA, and PCL films, including their morphology, water vapor permeability, degradation rates, bacterial permeability, and toxicity to human skin cells, were studied. An in vivo study performed on pigs gave preliminary results which indicated that the biodegradable/bioabsorbable, l