Medication On Demand

Over the past decade, scientists have devised several miniature controlled-release devices that respond to external stimuli such as a change in pH or exposure to light. Now, researchers have created the first such system that can be controlled with an electric field (J. Am. Chem. Soc., DOI: 10.1021/ja907560y). The new device could be used for in vivo treatment of tumors, among other applications.

Yingchun Zhu, a professor at China’s Shanghai Institute of Ceramics, and his colleagues constructed the system by fastening one end of dipolar 4-(3-cyanophenyl)butylene molecules to the inner walls of nanoscale silica pores. The researchers then loaded the pores of the derivatized silica with ibuprofen molecules and submerged the material in simulated extracellular fluid. When they placed the system in an alternating electric field, the tethered dipolar molecules swept back and forth like windshield wipers. This motion pushed the ibuprofen out of the pores and into the fluid at a rate controlled by the frequency of the alternating field.

Such a system could be particularly useful for organic compounds that won’t diffuse without assistance because of poor solubility in body fluids, Zhu says. For example, porous silica loaded with a chemotherapeutic agent could be incorporated in a microchip and implanted in a tumor, he notes. The chip would release the agent in response to an external field or, if the chip had its own tiny power supply, a local field controlled by the chip’s programming.

“Releasing cargos from mesoporous silica in response to an electric field is both neat and clever,” says J. Fraser Stoddart, a Northwestern University chemistry professor known for his work with nanomachines, including controlled-release devices. “I am sure that the idea has passed through quite a few minds in the drug-delivery field. It’s implementing it that matters, however, and Dr. Zhu and his collaborators have done just that both convincingly and elegantly.”