Scientific use for sticky tape

Sticky tape, that versatile household staple and a mainstay of gift wrapping, may have a new scientific application as a shape-changing ‘smart material’.

Researchers used a laser to form slender half-centimetre-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 researchers used sticky tape to create a tiny grasping claw that collects droplets of water, an innovation that could be used to collect water samples for environmental testing. The material, seen here, becomes flexible when exposed to humidity and returns to its original shape when dry. Credit: Manuel Ochoa, Purdue University.

The innovation could be used to collect water samples for environmental testing, said Babak Ziaie, a Purdue University professor of electrical and computer engineering and biomedical engineering.

The sticky tape - made from a cellulose-acetate sheet and an adhesive - is uniquely suited to 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,” he said.

Doctoral student Manuel Ochoa came up with the idea. While using tape to collect pollen, he 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 said.

A laser was used to machine the tape to a tenth of its original thickness, enhancing this 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 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 millilitre of liquid.

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.

“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 even be ‘functionalised’ so that they attract specific biochemicals or bacteria in water.

These findings were detailed in a presentation briefly titled ‘Laser-Micromachined Magnetically-Functionalized Hygroscopic Bilayer: A Low-Cost Smart Material’ at the Materials Research Society meeting in Boston (25-30 November). Experiments at Purdue’s Birck Nanotechnology Center were conducted by Ochoa, doctoral student Girish Chitnis and Ziaie.