The material is a flexible, rubbery gel. The material, called a hydrogel, is about 80 percent water -- a composition very similar to human skin. The only other ingredient in the hydrogel is a polymer called polyvinyl alcohol, or PVA. A polymer is a large molecule made up of smaller molecules linked together in a chain.
Medicine, such as a healing agent, can be added to the material during the manufacturing process. In a clinical setting, a doctor would apply a "patch" of the drug-containing material to a wound, covering it with a bandage.
"One of the advantages to delivering drugs with a bioadhesive patch on the skin is that the patient gets a slow, constant dose over a longer period of time, perhaps a few days," Peppas says. "In most situations this will heal the wound faster than applying medication that acts locally for only a short time. Also, you do not have the inconvenience and cost of adding more medication each time you change a dressing."
Because the hydrogel is mostly water, when in use it needs to be in contact with a somewhat moist surface, such as a wound, and covered so that it will not dry out. It can be stored in water or dried to be stored and rehydrated for later use, Peppas says. He estimates the material can be stored for about six months.
What's new and improved about the material is not so much the way it delivers drugs, but its composition and the way it is made.
"Most biomaterials made out of polymers, such as artificial veins and other types of patches, need to have chemicals called crosslinking agents or curing agents added during their manufacture in order to hold them together so that the polymer does not dissolve into the body," Peppas says.
"All the unreacted chemicals must later be thoroughly washed out of the biomaterial, because if they leach out into the body, they can be toxic," he says. "While the current materials are certainly safe, we avoid any possibility of leaching impurities because we don't add potentially toxic materials in the first place."
The procedure Peppas developed to make the new bioadhesive relies on a simple freeze/thaw process. The polymer, which looks like powdered laundry detergent, is mixed with water, then poured into flat molds and frozen and thawed in several cycles. During this process, a certain amount of the polymer crystallizes, which allows the material to maintain its solidity while being flexible and elastic.
Peppas, who is a faculty member in Purdue's School of Chemical Engineering, presented information on the new material in November at a meeting of the American Institute of Chemical Engineers.
Peppas started developing the material at Purdue in 1990 and also worked with Japanese researchers at Hoshi University during a sabbatical leave in Japan.
"We were looking for an alternative way to prepare these solid materials without having to add chemical agents, which is known in the field as a benign manufacturing process," Peppas says. "We also knew we needed to have about 75 to 80 percent water, because we wanted to be able to put it in contact with the skin."
Peppas says the primary application of the Purdue bioadhesive is for delivering drugs to an external wound not associated with an operation, such as a knife gash or other nonsuperficial wound that would be treated by a doctor. Peppas is conducting animal tests with the material to determine its strength and effectiveness at drug delivery.
Because the material also sticks to mucous membranes, Peppas is looking into the possibility of applying it in the nose to deliver allergy medication, for example, or in the mouth to treat lesions in the mouth.
Peppas says the material's strength and elasticity are fairly constant in water from about 60 degrees Fahrenheit to about 122 degrees, but in water above 122 degrees the crystalline structure begins to break down and the gel dissolves.
"This should not be a problem when the material is used for the application of delivering drugs to an external wound," Peppas says. Most people do not bathe or shower in temperatures above or below these, and in cold weather, warmth and moisture from the skin will keep the material intact, he says.
Source: Nicholas Peppas, (765) 494-7944; e-mail, email@example.com
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Purdue biomedical engineer Nicholas Peppas has developed a new type of material that adheres to the skin and can be used to deliver drugs to wounds in a slow, controlled manner, speeding up the healing process. (Purdue News Service Photo by David Umberger)
Color photo, electronic transmission, and Web and ftp download available. Photo ID: Peppas/Bioadhesive
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