New Materials Show Promise For Coatings, Membranes, Drug Delivery

The materials are called co-polymer networks, which are "built" from intersecting chains of small molecules linked together to form a larger, mesh-like structure. The two molecular "building blocks," or monomers, used in the new materials are acrylic acid and a derivative of oligoethylene glycol. The properties of an individual material in the class can be varied depending on the relative amounts of the monomers used to prepare it.

"Because these materials are co-polymers, we can control their properties more precisely and over a wider range than we could if they were made of a single type of monomer," says Robert Scott, a Ph.D. candidate at Purdue who helped develop the material. "This level of versatility and control allows for a number of applications."

The new class of materials is unique in that it is the first time materials with such a wide variety of properties have been derived from a combination of these two monomers, says Scott's adviser Nicholas Peppas, the Showalter Distinguished Professor at Purdue. Peppas has conducted research in polymers for more than 26 years and has developed new materials and polymers for applications that include biomedical applications.

"The most exciting thing about this research is that we've not only developed a class of materials with diverse properties, but we've also come to understand fundamentally, on a molecular level, the basis for those properties," Scott says.

Scott will present information on the new materials in two talks March 16 at the annual meeting of the American Physical Society in Los Angeles. His research has been funded by the National Science Foundation and the National Institutes of Health.

The new materials, which were developed over the past four years with the help of lab assistant Atsmon Shahar, are particularly suited for separations applications, such as filtering mechanisms used in wastewater treatment, where only certain substances are allowed to pass through the mesh created by the interlacing polymers.

"As we increase the acrylic acid content of the materials, the oligoethylene glycol chains that make up the network move further apart, increasing the mesh size, which in turn determines what substances can pass through," Scott explains. "By varying the acrylic acid content, as well as other parameters, we can precisely control the size of the molecules we allow through."

Another application Scott has investigated in his lab is the controlled release of substances.

"We've made systems that contain a model drug, and we're studying how the rate of diffusion of that drug out of this polymer varies as we vary the polymer structure," Scott says. "Using the material as a membrane for drug delivery is a particularly appealing application because we have very fine control over what drugs could be released through it and under what conditions."

In addition, the acrylic acid in the materials makes them sensitive to the acidity, or pH, of their environment. The mesh size and diffusive properties vary depending on the pH of the environment -- an important consideration for drug delivery applications, since different parts of the body exhibit different pH levels. For example, a capsule incorporating this material and containing a particular drug might remain "closed" in the mouth and "open" in the stomach to release a drug.

One type of the material also can be made to have a very dense network of molecular chains, which would make it very resistant to liquids, Scott says. "In that case it might make an ideal coating for applications that require a very low permeability to moisture," he says. "We can also modify the properties so that it will absorb various amounts of liquid. We're looking very closely at how we can control its affinity for water." Depending on its affinity for water, the material might also find applications in the cosmetics industry in moisturizers, Peppas says.

Peppas says further studies of the materials will be needed before they are ready for industrial or medical use.