Angry Birds on stretchy touchpad
A researcher uses a stretchy touchpad on the forearm to play Angry Birds. (Kim et al. / Science)

If you see gamers poking at their forearms to play Angry Birds on the bus in the year 2020, remember when you first heard this would happen. South Korean researchers have developed a clear plastic touchpad that works even when it’s stretched to more than 10 times its normal area.

The touchpad is made of hydrogel – a type of flexible, stretchable substance that’s also used in soft contact lenses, diapers and medical devices. For the experiment described in this week’s issue of the journal Science, the researchers added lithium chloride salts to make the hydrogel electrically conductive.

Electrodes on each end of the touchpad create an electrostatic field across the hydrogel sheet. When you press your finger onto the pad, it closes an electrical circuit and creates a current that can be read by meters on each corner of the sheet.

Microprocessors compare the levels of electrical current to figure out the position of your finger in the pad. The rest is child’s play for programmers. In a series of videos, the researchers demonstrate how the touchpad can be used to play a virtual piano, move chess pieces, write text or play Angry Birds.

Sure, it’s not much different from what you can do today with a smartphone or touchscreen tablet. But the fact that hydrogel is soft and stretchable could open the way to new kinds of bendable, foldable, implantable or wearable interfaces.

The researchers at Seoul National University aren’t the only ones looking into hydrogel-based electronics: Folks at the Massachusetts Institute of Technology, the University of Texas and Stanford University have been working on similar technologies.

Armband touchpads aren’t yet ready for prime time: The South Korean team found that the touchpad’s electrical resistance was found to increase slightly after 100 cycles of stretching – perhaps due to water evaporation in the gel. But once those challenges are overcome, we may all be gellin’.

Authors of the Science paper, titled “Highly Stretchable, Transparent Ionic Touch Panel,” are Chong-Chan Kim, Hyun-Hee Lee, Kyu Hwan Oh and Jeong-Yun Sun. 

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