sealPurdue Science and Health Briefs
____

July 1998

New biomaterial has 'star' power

WEST LAFAYETTE, Ind. -- The next star in drug delivery and medical technology may be a new material developed by Purdue University researchers.

Kelley Keys, a chemical engineering graduate student, has made new gels from a material called a star polymer. The gels' potential applications include removing substances such as cholesterol from the blood and delivering high concentrations of drugs to specific areas in the body, such as tumors.

Keys, a Carmel, Ind., native, presented her research results June 24 at a meeting of the Controlled Release Society in Las Vegas.

Most polymers are large molecules made up of smaller molecules linked together in a chain, but a star polymer has a central core with many arms radiating out from it. The end of each arm can be very chemically reactive, and it can bind with materials such as cells, drugs, proteins and antibodies.

"The large number of arms in a very small volume would make these star polymers very useful in biological and pharmaceutical applications, such as delivering a high concentration of drugs throughout the body or to a specific target," Keys says.

The star polymer gels Keys developed are made from the polymer polyethylene glycol, or PEG, a nontoxic, noncarcinogenic substance used in many biomedical applications. A few of the up to 70-some arms on each star molecule are used to bind them together to form the gel, leaving the majority of the arms free to react. The average diameter of an individual PEG star molecule is less than 50 nanometers, 100 times smaller than a red blood cell.

An important new property of some of these gels is that they can recognize and remember specific substances through a process called molecular imprinting, a technique developed by other researchers over the past five years.

"During the preparation of the star polymer gels, we add molecules of a particular drug or protein," explains Nicholas Peppas, Keys' faculty adviser and the Showalter Distinguished Professor of Biomedical Engineering at Purdue. "The reactive ends of the star polymer's arms rearrange themselves around the molecule. When we leach out the drug or protein, the polymer remains in that configuration. Later, if we pass the same drug or protein over the gel, the polymer recognizes the molecule and binds to it."

In her experiments, Keys imprinted a gel with the drug proxyphylline, a bronchodilator used to increase the lungs' ability to take in air. Her results showed that the gel "remembers" the proxyphylline and rebinds to the drug at a very high rate. She also passed several other similar drugs through the imprinted gel, but they did not bind to it. The gel can be imprinted with a variety of substances, but once imprinted, it cannot be modified to recognize a substantially different molecule, Peppas says.

Peppas says one future use of the gel would be to imprint it to recognize low-density lipoproteins, or LDLs, which are linked to cholesterol formation in arteries. The gel then could absorb and remove these substances from the blood in a dialysis-type procedure, or perhaps work in the body to move these substances away from danger areas, such as the aorta.

Peppas says another future use for star polymer gels might be to deliver high concentrations of cancer-fighting drugs to a tumor.

"One could imprint a gel so that some of the arms recognize specific cancerous cells, while other arms in the same gel carry an anti-cancer drug," he says. "These gels also could be used as a surface coating, such as on an artificial organ, to provide additional binding sites for cells or antibodies."

Keys used gamma radiation to coax the star polymers into forming a gel, which is a new method of gel preparation. Her methods give the gels superior mechanical stability while maintaining a large number of active groups on the arms, Peppas says.

Keys' research is funded by the Showalter Foundation.

CONTACTS: Keys, (765) 494-3331; e-mail, keys@ecn.purdue.edu

Peppas, (765) 494-7944; e-mail, peppas@ecn.purdue.edu

Take precautions to keep cool when heat is on

WEST LAFAYETTE, Ind. -- When the mercury soars outside, using a little common sense and drinking lots of liquids can keep things from getting too hot to handle.

That's the advice from Olivia B. Wood, associate professor of foods and nutrition at Purdue University. Wood works with athletes and teaches them the effects of dehydration and nutrition on the body. A heat wave, with temperatures in the 90s and humidity to match, is cause for concern, she says.

"During a heat wave, it is important to be aware of the symptoms associated with dehydration and loss of body fluids." she says. "If you don't use common sense and prepare yourself, you could face some serious difficulties. Some of them could be fatal."

Wood says that when temperature and humidity are high, the body loses much of its cooling ability. "The body cools itself by the evaporation of sweat from the skin. In really hot and humid weather, sweat doesn't evaporate and the heat is trapped."

Be aware of signs of dehydration, she says. They include heat cramps, heat exhaustion and heat stroke. Heat cramps are signaled by thirst, chills, clammy skin, nausea and a throbbing heartbeat.

"If you experience these symptoms, immediately stop what you're doing and move to a cool location," Wood says. "Consume lots of water or some other cool liquid."

Paying attention to these early signs may prevent the onset of a much more serious condition, such as heat exhaustion or heat stroke, Wood says.

"Heat exhaustion is signaled by reduced sweating, shortness of breath, dryness of the mouth, a weak but rapid pulse, headache, dizziness and extreme fatigue," she says. "Again, drop everything and move to a cool location and consume cool liquids. Also, it is important to employ other methods to cool the body off. Take a cool shower or apply an ice pack to the forehead."

Wood says failure to pay attention to early warning signs may lead to the most serious type of heat stress -- heat stroke. At that point, immediate medical attention is required, because the person is in a life-threatening situation.

"Their temperature will increase dramatically," she says. "Because of severe dehydration, the body's circulatory system and kidneys can shut down."

Cool liquids, which can be easily absorbed from the stomach, are best for preventing and treating the early stages of dehydration, Wood says.

"Water, sodas without caffeine, sport drinks and fruit juices are all good choices," she says. "Plain water is the least expensive and most readily available."

Wood says to avoid concentrated beverages, as they may actually contribute to dehydration.

"Concentrated beverages are beverages that contain high levels of sugar, salt or potassium," she says. "These beverages stay in the stomach until sufficient fluids are drawn in to dilute them" she says. "Also, avoid alcohol and any kind of beverage with caffeine, because they act as diuretics, and increase the loss of fluid from the body."

How do you tell if you are getting enough liquid?

"Strong-colored, strong-smelling urine in small amounts indicates dehydration," she says. "Light-colored urine in normal amounts indicates normal hydration. The average amount of urine expelled per day varies among individuals, but it is usually about one and a half to two and a half quarts."

Wood says heat-related problems are preventable and fairly easy to avoid.

"When it gets hot outside, stay inside if at all possible," she says. "At the very least, stay in a cool place and drink lots of liquids. Use a little common sense, and you won't have a problem when mother nature turns up the heat."

CONTACT: Wood, (765) 494-8238; woodo@cfs.purdue.edu; http://www.cfs.purdue.edu/fdsnutr/people/wood.html

Compiled by Amanda Siegfried, (765) 494-4709; e-mail, amanda_siegfried@purdue.edu
Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu


* To the Purdue News and Photos Page