Pop culture is littered with imaginary futures where man and machine have fused together as one – from the plugged-in urbanites of the Matrix to the infamous villains of Star Trek, the Borg. A future where human biology is wired into machine is not as far-fetched as it may sound.
Surgical implants from titanium hip replacements to carbon heart valves are already commonplace. These stalwarts of prosthetic medicine are sturdy but static. Human ingenuity has also engineered machines that actively interact with our bodies, such as the artificial pacemaker that delivers electrical impulses to the heart to keep it beating in rhythm. This life-saving device is powered by the humble battery and so is destined, at some point, to run flat. The next step in the evolution of medical machines is therefore to forego the need for batteries, and tap into an energy source closer to home – namely the human body.
Forget Robocop and think more Robo-guinea pig. Though this furry critter may seem far removed from a human being, when it comes to our ability to hear, we have lots in common. Scientists have therefore developed a prototype device, no bigger than a peanut, which draws energy from electrical impulses generated by the inner ear of a guinea pig. This remarkable piece of kit also measures these electrical impulses, called endocochlear potentials, and transmits this information across the airwaves. The device, called an endoelectronics board, is more affectionately referred to as an energy harvester.
So how does it work? Sound is the key. More specifically, the apparatus mammals have evolved to detect sound. The inner ear is the business end of the mammalian hearing system, responsible for the physical detection of sound as well as balance. Within the inner ear lies the cochlea - Greek for snail owing to its spiral shape. The cochlea picks up sound waves that enter the ear and converts them to changes in electrical impulses. When it comes to electrical activity, whether from a bolt of lightning, a pylon or even from an ear, it can be captured, collected and used to power any number of devices.
The energy produced by the inner ear of the guinea pig was harvested by hooking up a small electronics board to the cochlea, using electrodes. The board contained a capacitor to store the energy and a radio transmitter to wirelessly send out information on the electrical potentials being generated. Initial experiments managed to keep this set-up running for five hours, sending wireless data feeds every minute or so, while leaving the hearing of these furry fellows intact.
There is still much to troubleshoot, develop and importantly miniaturise, before testing in humans is possible. However should these devices prove successful the world of medical implants will be set to change. Be it pacemakers or hearing aids, without the need for cumbersome batteries the ‘nano’ tag synonymous with Apple may find itself hitched onto the end of many a medical device.