Researchers have developed a highly stretchable touchpad that can be used to write words and play electronic games. The development could lead to flexible, 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, researchers 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.
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, meters 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 1000% of its normal area. After 100 cycles the resistance was found to increase slightly.