“Active” surfaces control what’s on them
Researchers at MIT and in Saudi Arabia have developed a new way of making surfaces that can actively control how fluids or particles move across them. The work might enable new kinds of biomedical or microfluidic devices, or solar panels that could automatically clean themselves of dust and grit. “Most surfaces are passive,” says Kripa Varanasi, an associate professor of mechanical engineering at MIT, and senior author of a paper describing the new system in the journal Applied Physics Letters. “They rely on gravity, or other forces, to move fluids or particles.” Varanasi’s team decided to use external fields, such as magnetic fields, to make surfaces active, exerting precise control over the behavior of particles or droplets moving over them. The system makes use of a microtextured surface, with bumps or ridges just a few micrometers across, that is then impregnated with a fluid that can be manipulated — for example, an oil...