New wearable touchpad can help you write, play games

Researchers have developed a highly stretchable touch panel that can be used to write words and play electronic games, an advance that could lead to flexible and wearable devices with a variety of applications.

While various types of conductors such as carbon nanotubes and metal nanowires have been explored for stretchy touchpads, they are all based on hard materials. To help solve this problem, Chong-Chan Kim from Seoul National University in South Korea and colleagues developed a touchpad made of hydrogel, a network of hydrophilic polymers that are soft and very stretchable. They used a polyacrylamide hydrogel containing lithium chloride salts, which act as a conductor and help retain water in the hydrogel.

"Electrodes on the ends of the hydrogel panel apply similar voltages, which creates a uniform electrostatic field across the system," researchers wrote in the journal Science. When a finger touches the panel, it closes the circuit within the hydrogel, allowing current to flow from both ends of the strip to the touch point. At each corner of the strip, metres that capture current detect the electrical signals; the researchers developed a controller board to facilitate communication between the ionic touch panel and a computer.

Using the touchpad, they were able to draw a stick figure, with the data conveyed onto a computer screen. With the thin touchpad placed on their arms, they were able to write words and to play the piano and games. The touchpad was still able to operate when it was stretched to more than 1,000 per cent of its normal area, researchers said.

After 100 cycles the resistance was found to increase slightly, which the researchers suggest may be due to water evaporation in the gel.