Cilia are a scientific marvel, but they have been hard to copy in engineering, especially on a small scale. Researchers at Cornell University have now made a micro-sized artificial ciliary system with parts made of platinum that can control how fluids move on such a small scale. The technology could be used to make low-cost, portable diagnostic tools that can test blood samples, move cells around or help with microfabrication.

The paper, Cilia metasurfaces for electronically programmable microfluidic manipulation, was published in Nature on May 25. Wei Wang, who is working on his Ph.D., is the main author.

"There are lots of ways to make artificial cilia that respond to light, magnetic or electrostatic forces," Wang said. "But we are the first to use our new nano actuator to demonstrate artificial cilia that are individually controlled."

The project is based on a platinum-based, electrically powered actuator engineered to make microscopic robots walk. The way those bending bot legs work is close, but the cilia system does different things and can be used in different ways.

Manipulating each cilia independently

"What we're showing here," said Itai Cohen, lead author and professor pf physics, "is that once you can individually address these cilia, you can manipulate the flows in any way you want. You can create multiple separate trajectories, you can create circular flow, you can create transport, or flows that split up into two paths and then recombine. You can get flow lines in three dimensions. Anything is possible."

"It's been very hard to use existing platforms to create cilia that are small, work in water, are electrically addressable and can be integrated with interesting electronics," Cohen said. "This system solves these problems. And with this kind of platform, we're hoping to develop the next wave of microfluid manipulation devices."

A normal device is a chip with 16 square units, each with 8 cilia arrays and 8 cilia. Each cilium is about 50 micrometers long, so there are about a thousand artificial cilia on the "carpet." As the voltage on each cilium goes up and down, its surface oxidizes and reduces. This causes the cilium to bend back and forth, which lets it move fluid at a rate of tens of microns per second. Different arrays can be turned on separately, which makes it possible to create an infinite number of flow patterns that mimic the flexibility of their biological equivalents.