Sticky tape is indispensable this time of year for wrapping gifts, but it soon could be essential year-round for a very different purpose: collecting water samples for environmental testing. A simple laser micromachining process can make wispy half-centimeter-long fingers out of the tape that, when exposed to water, become a tiny, reusable robotic claw that captures droplets. Researchers at Purdue University found that the tape — made from a cellulose-acetate sheet and an adhesive — is ideal for the purpose. "It can be micromachined into different shapes and works as an inexpensive smart material that interacts with its environment to perform specific functions," said Babak Ziaie, a Purdue University professor of electrical and computer engineering and biomedical engineering. Laser micromachining turns Scotch tape into a tiny grasping claw that collects droplets of water, an innovation that could be used to gather water samples for environmental testing. The material, seen here, becomes flexible when exposed to humidity and returns to its original shape when dry. Images courtesy of Manuel Ochoa, Purdue University. The idea was born when doctoral student Manuel Ochoa used tape to collect pollen. He noticed that, in humid conditions, the tape curled up: The cellulose-acetate absorbs water, but the adhesive film repels water. "So, when one side absorbs water, it expands, the other side stays the same, causing it to curl," Ziaie said. The researchers used a laser to machine Scotch tape to a tenth of its original thickness, which enhances the curling action. They coated the graspers with magnetic nanoparticles so that they could be collected with a magnet. "Say you were sampling for certain bacteria in water," Ziaie said, "you could drop a bunch of these and then come the next day and collect them.” The grippers close underwater within minutes and can sample one-tenth of a milliliter of liquid. When the tape graspers are coated with magnetic particles, researchers can collect the devices by using a magnet, which could be especially useful to environmental testers in the field. "Although brittle when dry, the material becomes flexible when immersed in water and is restored to its original shape upon drying, a crucial requirement for an actuator material because you can use it over and over," Ziaie said. "Various microstructures can be carved out of the tape by using laser machining. This fabrication method offers the capabilities of rapid prototyping and batch processing without the need for complex cleanroom processes." The materials could someday be "functionalized" to attract specific biochemicals or bacteria in water. Ochoa, Ziaie and doctoral student Girish Chitnis conducted the experiments at Purdue's Birck Nanotechnology Center using 3M Scotch GiftWrap Tape and MagicTape. They will describe their findings in a presentation titled "Laser-Micromachined Magnetically-Functionalized Hygroscopic Bilayer: A Low-Cost Smart Material" during a Materials Research Society meeting to be held in Boston from Nov. 25 to 30. For more information, visit: www.purdue.edu