I readily admit going into this that the thought of implanting a touchpad inside the body is very disturbing to me. That is exactly what scientists at Seoul National University have come up with. This touchpad can be used to write words and play electronic games according to the inventors. It’s made from the same sort of soft and stretch hydrogel that is used to make soft contact lenses.
The lithium chloride salts in the hydrogel means that it can conduct electricity and the gel stays soft because it holds all the water it needs inside to prevent drying out and becoming brittle. When in use a small AC voltage applied to all four corners of the touchpad generates signals that are in phase. That means that no current flows until the touchpad is actually touched.
Touching it grounds the circuit and the current flows from each corner in proportion to how close the finger is to that particular corner. Integrated sensors measure the difference in current from each corner of the pad and uses that information to determine where the finger has been placed. That in turn can be turned into a precise location on a display nearby.
In testing the scientists were able to use the touchpad to draw a stick figure, write words, play a small digital piano, and play chess. The touchpad continued to function even when stretched to over ten times its normal area. It also functioned normally when bent around a person’s arm. After about 100 cycles of stretching and contraction, the performance decreased slightly due to water evaporating from the hydrogel. That will be addressed in future iterations of the touchpad.
“If you want to interface electronics with biology, you ideally want soft, stretchable electronics with the same kinds of properties seen in biology,” says John Rogers, a materials scientist at the University of Illinois at Urbana-Champaign, who did not take part in this research.”The researchers have demonstrated a nice advance that adds to the growing toolkit of stretchable electronics for interactions with the body. Skin would be a great starting point for such an electronic interface, since implanting there would probably pose minimal health impacts.”