PURDUE (US) — After the holiday gift wrapping is done, Scotch tape may have a new job as a shape-changing “smart material” that can collect water samples for environmental testing.

Researchers used a laser to form slender half-centimeter-long fingers out of the tape. When exposed to water, the four wispy fingers morph into a tiny robotic claw that captures water droplets.

The Scotch tape—made from a cellulose-acetate sheet and an adhesive—is uniquely suited for the purpose, says Babak Ziaie, professor of electrical and computer engineering and biomedical engineering at Purdue University.

The graspers were coated with magnetic particles, which could allow researchers to retrieve the devices in the field by using a magnet. (Credit: Manuel Ochoa/Purdue University)

“It can be micromachined into different shapes and works as an inexpensive smart material that interacts with its environment to perform specific functions.”

While using tape to collect pollen, doctoral student Manuel Ochoa noticed that it curled when exposed to humidity. 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 says.

A laser was used to machine the tape to a tenth of its original thickness, enhancing the curling action. The researchers 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 says. “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.

“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 says.

“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 clean-room processes.”

Further, the materials might be “functionalized” so that they attract specific biochemicals or bacteria in water, Ziaie says.

Findings will be detailed in a presentation during a meeting of the Materials Research Society ^[1] this week in Boston.

The material, seen here, becomes flexible when exposed to humidity and returns to its original shape when dry. (Credit: Manuel Ochoa/Purdue University)

Source: Purdue University ^[2]