Medical device designers are always on the prowl for new materials that can perform a host of diagnostic and therapeutic tasks. Aiding them in their quest, researchers at the University of California, San Diego (UCSD) have conducted initial tests on the first practical smart material capable of interacting with low-power near-infrared (NIR) light. The material could eventually be suitable for use in medical diagnostic applications.

Current-generation smart materials are responsive to high-power NIR light, according to Adah Almutairi, director of the Laboratory of Bioresponsive Materials and UCSD assistant professor at the Skaggs School of Pharmacy and Pharmaceutical Sciences and the department of nanoengineering. However, high-power NIR light is ill suited for use in implantable medical device applications because it can damage cells and tissues. In contrast, because the UCSD researchers' material is sensitive to biologically benign levels of lower-power NIR light, it can potentially serve as an implantable vehicle for releasing drugs or imaging agents in the body.

"What's new about this material is that it breaks down into small molecules in response to low-power NIR light, which is safer than high-power NIR light and can penetrate deeper into the body than UV or visible light," Almutairi explains. Capable of forming large molecules similar in size to proteins, the polymer is uncharged. When a chemical group in the polymer absorbs two photons of NIR light, it is cleaved from the rest of the molecule. By designing the polymer piece by piece, the UCSD researchers can cause the cleaving process to trigger a chain of degradative reactions that induce the polymer to break apart into smaller, biologically benign molecules.

"No previous polymer was designed to break down into small molecules in response to low- power NIR," Almutairi adds. This process enables the polymer to encapsulate or enmesh drugs or other biologically active molecules and allows it to release them in response to NIR light. In the absence of NIR light, however, the polymer remains stable for several weeks.

"What's most exciting about NIR-triggered disassembly is the control it offers clinicians and biologists over bioactivity," Almutairi comments. "The applications for which it's most promising are those in which the delivery location of the material's contents is known."

Funded by a National Institutes of Health New Innovator Award and Saudi Arabia's King Abdulaziz City for Science and Technology, the UCSD smart polymer responds best to NIR light when it is relatively hydrated, making it best suited for formulating hydrogel delivery vehicles, Almutairi remarks. "Because they would enable controlled drug release to limited areas, hydrogels that release bound drugs on demand hold promise for treatments that have undesirable off-target effects." And while the researchers are careful not to predict a commercialization timeline, they are expanding their concept to create polymers with even greater sensitivity to NIR light and to develop polymers that feature different chemical properties.