This has potential: an invisible stretchy gel that actually transmits sound. The problem? It eventually evaporates.
This stretchy hydrogel speaker, a prototype invented by a team of Harvard University scientists, was created by combining saltwater and polymers that are then hooked up to electrodes. A thin rubber sheet is sandwiched between two layers of gel, and ions carry a current in the gel that vibrates the rubber to make sound waves. The process is not unlike the way the human body transmits electric signals that tell the heart to beat, which is where the Harvard team got its idea.