Many important drugs are like table salt; they crystallize easily. When they do, the crystals are stubbornly difficult to dissolve. They crystallize instead of remaining dispersed, whether in the pill or after release in the digestive tract. Many medicines locked into crystals don't dissolve fast enough to work properly. If that happens, they can't reach their target.
Polymers are introduced to interfere with crystallization. "But the polymers that are presently FDA approved are not effective in meeting all the challenges," said Edgar. "They may prevent a process called nucleation but not stop growth of the crystal if it gets started. Or they may not continue to work after a period of time or if conditions are too hot or too damp. We needed to design a better polymer."
Imagine sugar dissolved in water. If a bit of dust is introduced, it can lead to nucleation the sugar sticks to the dust and then crystal growth. In this example, the polymer would cover the dust mote and repel the sugar molecules, preventing nucleation.
"Stopping nucleation is relatively easy, like stopping a skier before he starts down the hill," said Edgar. "Stopping growth is harder, like trying to stop the skier once he is speeding down the slope. But our polymers can do both stop nucleation and growth."
Edgar and Taylor are working with natural cellulose to create derivatives known as cellulose esters. "They are the polymers used to create LCD screens, automotive paint, and cellophane tape," said Edgar. "Cellulose is an abundant, renewable, completely natural polymer used by nature as the 'steel reinforcing rod' of trees and a major component of all plants."
The Virginia Tech and Purdue groups have discovered that the effective design for pharmaceutical applications is cellulose omega-carboxyesters, which are cellulose esters that the researchers hav
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