A new, stretchable transparent touch pad can be used to write words and play electronic games, and it may even one day be implanted inside the body, its inventors say.

Touch pads and touch screens are on nearly every smart device these days. But they can’t go on anything flexible, such as the human body. Scientists have explored stretchable touch panels based on carbon nanotubes, metal nanowires, and other advanced materials, but the performance of these stretchable touch panels fell off sharply when they were stretched. Just as bad, they also fell apart over time when repeatedly stretched.

To overcome these problems, scientists at Seoul National University created a touch pad made of the same kind of soft and very stretchable hydrogel used to make soft contact lenses. The hydrogel involved contains lithium chloride salts, which are electrically conductive and help the hydrogel hold onto the water it needs to stay soft.

In operation, the same small AC voltage is applied to all four corners of the touch pad. Because the signals are in phase and the hydrogel acts as a capacitor, no current flows until the device is touched. When a grounded object such as a human finger makes contact with the touch pad, it closes the circuit,…[Read more]