Oct. 12, 2000 CHAMPAIGN, Ill. — Scientists at the University of Illinois have fabricated ultrathin organic films that can be stacked together and “erased” by environmental stimuli. The erasable polymer multilayers could have applications in many diverse fields ranging from medicine to materials science.
“We specifically designed this material so that when it is placed in the desired environment, it would readily dissolve and release embedded agents such as drugs,” said Steve Granick, a professor of materials science at the UI and a researcher at the Frederick Seitz Materials Research Laboratory on campus. “We can control the durability of the material through the application of external stimuli.” To make their erasable material, Granick and postdoctoral research associate Svetlana Sukhishvili build up, layer by layer, very thin films of alternating polymeric acids and bases on a germanium crystal. The films also could be deposited on other materials, such as glass, mica or Teflon. Foreign compounds can be added to the layers as they are formed.
“By adding additional layers, we not only increase the amount of the embedded compound, we also make the material more stable, robust and resistant to attack in unwanted environments,” Granick said. Assembly of the films is guided by hydrogen bonding. “One unique aspect of the assembly process is reversibility,” Granick said. “The resulting multilayers can be selectively destroyed after they are created.”
The controlled destruction of the material can be initiated by a change in pH (the degree of acidity or alkalinity of a solution), the application of an external electric field or by a change in a surrounding salt concentration (both of which break the material’s ionic bonds).
“The release of an embedded compound occurs when the multilayer films are exposed to appropriate environmental conditions that erase them,” Granick said. “A drug, for example, could be released in a patient’s stomach or at the site of a wound, depending on the desired pH.”
Similarly, an electronic sensor could immediately release an embedded agent by applying an electric field and dissolving the material. Although the work is still a long way from any practical application, “the concept can be used to design the deliberate and controlled release of foreign agents that have been embedded within the material,” Granick said.
The researchers demonstrated proof of principle by embedding molecules of the dye Rhodamine 6G in the multilayer films and then releasing them by erasing the films through appropriate stimuli.
Granick and Sukhishvili described their erasable polymer films in the Sept. 14 online version of the Journal of the American Chemical Society.
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