Using ions to connect life to machines

Every second, electricity flows through the soft, flexible, water-filled cells of living organisms. This electricity enables us to think, move and experience the world and it happens thanks to ions: atoms and molecules carrying positive or negative charge. When our senses are stimulated, ions are triggered into motion across cell membranes, precisely controlled by protein channels, generating an electrical current that fires signals along nerves to the brain.

Conversely, electronic devices – smart phones, computers, displays, you name it – rely on electricity produced by the interaction of negative electrons and positive holes along metal wires embedded in rigid materials. It would seem that ionic and electronic circuits and materials are worlds apart. But to an extent, ions and electrons have co-existed in certain devices for decades, such as batteries, supercapacitors and electrochemical cells. These all rely on ionic and electronic charges interconverting. What’s new, however, is that ionic and electronic signals are increasingly being united with flexible and stretchy conducting polymers, known as ‘ionotronic’ materials.

A growing number of studies are revealing just how the world of ions and electrons can be integrated, offering tantalising glimpses into what merging living matter with machines could look like in years to come. Ionotronic materials can respond to environmental changes in life-like ways, which could be a crucial step in the integration of humans and machines. Such technology could ultimately lead to anything from bionic soft robots, intelligent wearable sensors and cyborg tissues all the way to human–computer interfaces, electronic plants and digital control of biomolecules. So how are researchers going about bringing ions and electrons together?