New Generation of "Nanoporous" Polymers is Reported Major Impact Seen In Filtration, Clinical Assays And Biotechnology

PITTSBURGH -- The beauty and complexity of self-assembling, cubic-phase materials have aroused interest mainly at the level of basic science, but recent experimental and theoretical advances by University at Buffalo biomaterials scientists could thrust them onto a technological fast track.

The data were reported here today by the researchers at the annual meeting of the American Institute of Physics at the David L. Lawrence Convention Center.

The advances make it possible to control for the first time the chemistries of nanostructured polymers made from cubic-phase liquid crystals, as well as the sizes of their pores, which measure in the nanoscale range.

Cubic phases self-assemble when water and surfactant combine with oil in the proper concentrations, forming lyotropic (solvent-induced) liquid crystals. The liquid crystals then may be polymerized.

Potential applications for microporous materials developed in the cubic phase are broad, ranging from cell-like matrices for holding proteins in clinical assays like the HIV test, to purification materials for pharmaceutical production, to filters for catching contaminants in microelectronics production, to efficient separation materials for fields ranging from chromatography to the fuel and steel industries.

David M. Anderson, Ph.D., assistant professor of biomaterials at UB and principal investigator, noted that in each of these applications, the sizes of the pores are a critical characteristic. Microporous materials currently in use demonstrate variations in pore size within a single sample, making it difficult, if not impossible, to control which fluids flow through the material and which cannot.

"Here we are in 1994, with no high-permeability membrane materials that have a uniform pore-size at the nanometer level," Anderson noted.

He said that because his cubic-phase polymers could be designed to keep out specific molecules, while passing others through, they could help to reduce many of the most significant costs involved in industries, such as pharmaceuticals, where, he said, 50 percent of production costs are spent on purification.

Several companies are working with Anderson to use cubic-phase polymers to develop the next generation of membranes and to commercialize biomaterials applications, such as new high-permeability hydrogels for contact lenses. His work also is being funded by the Army Research Office.

Key to the group's recent discoveries was its establishment of accurate mathematical models for cubic phases.

"Much of the modeling of cubic phases tends to describe the materials in a general way," said Anderson. "But because I was interested in polymerizing the cubic-phase liquid crystals for specific applications, I needed mathematical models that could tell me the materials' precise specifications."

The researchers polymerized styrene, creating cubic-phase liquid crystals through which the polystyrene is threaded. Using various analytical techniques, they examined the samples and discovered a sequence of cubic-phase structures that had never been seen before.

"We found cubic-phase polymers the composition of which we could adjust from 9 percent water and a pore-size of 2 nanometers to 80 percent water and a pore-size of about 15 nanometers," he said.

With studies that showed such a clearly defined relationship between chemical composition and pore-size, Anderson said it was possible to draw a detailed, accurate map of how chemical composition would affect pore-size.

For example, he said, an artificial dialysis membrane might require pores of, say, exactly 3.5 nanometers so that waste products could pass through it, while important nutrients and proteins could not.

"With the results we now have, it should be possible to design a cubic-phase material with specifications this precise and with the optimal chemistry," said Anderson.

The group also made some theoretical advances that will help it to understand and optimize conditions for forming cubic phases.

"You need a theory to relate the chemical structure of the surfactant molecule to the micro-structure of the liquid crystals it forms," said Anderson. "We believe we have described a theory that takes a big step in that direction. If we know the chemical formulae for the surfactants or related copolymers, we can interpret and to some extent even predict, under what conditions cubic phases will form."

NOTE TO EDITORS: Color slides that illustrate the polymerized cubic phases may be obtained by contacting Ellen Goldbaum at the UB News Bureau, 716-645-2626.

Anderson's work, for which he was awarded two international patents in 1993, also has demonstrated that the cubic-phase structure is retained after controlled polymerization, a prerequisite for exploiting the versatile cubic structure in commercial applications.

He said that in biomedical applications, the cubic-phase polymers also appear to be optimal matrices, or supports, for proteins, such as those in enzyme assays that detect antigens involved in viral infections and other disease states.

"The cubic phase is by far the best-known matrix for proteins," he said. "In the cubic phase, the protein finds itself in a lipid bilayer environment that mimics its natural environment in the cell.

"Typically, when you bond a protein to some flat surface for a reaction, you can only use maybe a microgram of the protein," he said. "But with these materials, we can make a thin film of the cubic phase with the protein immobilized inside of it. This means you can have a thousand times more capacity for carrying out the reaction because you have so much more protein available."

Anderson said that in addition to the technological advances his work will permit, it also increases the fundamental understanding of cells, since the same forces that determine the formation of liquid crystal structures are also crucial in the morphology of living cells. He noted that phospholipids in the body assemble themselves into biomembrane systems that are very similar to cubic-phase materials, an observation that was made in the late 1960s.