Switchable Surfaces

MIT researchers have developed a surface whose properties can be changed-from water repelling to water loving, for example-with the flip of a switch. This novel trick could be used to create faster, more efficient microscopic systems for drug delivery and manufacturing.

Led by Robert Langer, ScD '74, a professor of chemical and biomedical engineering, the research team has created a "forest" of special molecules on the surface of a gold electrode. The tips of the molecules are hydrophilic, or water loving, while their bases are hydrophobic, or water repelling. When an electric current is sent through the electrode, the attractive force causes the molecules to bend, exposing their hydrophobic bases. This changes the surface from its normal state, in which it attracts water, to a water-repellent state.
Although the concept seems simple, the working system took four years to construct.

A big challenge was finding the right tools for the job, according to medical engineering and medical physics doctoral candidate Thanh-Nga Tran of the Harvard-MIT Division of Health Sciences and Technology. Tran says it was difficult, for example, to locate instruments that could detect the nanoscopic molecules on the electrode's surface.

The team's next step will be tailoring the system to amplify the effect. Then, using different molecules, the group will begin to build surfaces with other changeable properties, such as adhesiveness and friction.