Battery-free bioelectronic implants

When Swedish doctors performed the first fully implantable cardiac pacemaker surgery in 1958, the device they had invented was powered by a rechargeable nickel–cadmium battery, connected to a wire coil that enabled magnetic induction wireless recharging across the skin. The battery, coil and controlling electronics were housed in a shoe-polish-sized can implanted in the abdomen, with leads running to the heart to deliver the pulsed electrical stimulus.

Millions of people with a slow or irregular heartbeat have since benefited from a pacemaker implant – which soon evolved to use longer-lasting batteries that were replaced surgically every few years, rather than requiring a weekly recharge. More than six decades later, however, the basic pacemaker design – a remotely located can containing the bulky battery pack and electronics, connected to the heart by long leads – remains unchanged.

As bioelectronics has advanced, experimental implants have been demonstrated that enable people with severe spinal cord injuries to walk again, or people who have lost a limb to control and experience a sense of touch from a robotic prosthetic. To turn these experimental prototypes into practical devices that could be implanted at target sites around the body, developing miniaturised all-in-one implants could be key. The limitation on miniaturisation is not the electronics, but the power available after shrinking the battery.