In “I Sing the Body Electric,” poet Walt Whitman waxed lyrically about the “action and power” of “beautiful, curious, breathing, laughing flesh.” More than 150 years later, MIT materials scientist and engineer Canan Dagdeviren and colleagues are giving new meaning to Whitman’s poem with a device that can generate electricity from the way it distorts in response to the beating of the heart.
Despite tremendous technological advances, a key drawback of most wearable and implantable devices is their batteries, whose limited capacities restrict their long-term use. The last thing you want to do when a pacemaker runs out of power is to open up a patient just for battery replacement.
The solution may rest inside the human body—rich in energy in its chemical, thermal, and mechanical forms.
The bellows-like motions that a person makes while breathing, for example, can generate 0.83 watts of power; the heat from a body, up to 4.8 watts; and the motions of the arms, up to 60 watts. That’s not nothing when you consider that a pacemaker needs just 50 millionths of a watt to last for seven years, a hearing aid needs a thousandth of a watt for five days, a smartphone requires one watt for five hours.
Increasingly, Dagdeviren and others are investigating a plethora of ways that devices could make use of these inner energy resources and are testing such wearable or implantable devices in animal models and people.
One energy-harvesting strategy involves converting energy from vibrations, pressure, and other mechanical stresses into electrical energy. This approach, producing what is known as piezoelectricity, is often used in loudspeakers and microphones.
To take advantage of piezoelectricity, Dagdeviren and colleagues have developed flat devices that can be stuck onto organs and muscles such as the heart, lungs and diaphragm. Their mechanical properties are similar to whatever they are laminated onto, so they don’t hinder those tissues when they move.
Scientists are also developing wearable piezoelectric energy harvesters that can be worn on joints such as the knee or elbow, or in shoes, trousers, or underwear. People could generate electricity for electronics whenever they walk or bend their arms.
A different energy-harvesting approach uses thermoelectric materials to convert body heat to electricity. “Your heart beats more than 40 million times a year,” Dagdeviren notes. All that energy is dissipated as heat in the body—it’s a rich potential source to capture for other uses.
Thermoelectric generators face key challenges. They rely on temperature differences, but people usually keep a fairly constant temperature throughout their bodies, so any temperature differences found within are generally not dramatic enough to generate large amounts of electricity. But this is not a problem if the devices are exposed to relatively cool air in addition to the body’s continuous warmth.
Scientists are exploring thermoelectric devices for wearable purposes, such as powering wristwatches. In principle, the heat from a human body can generate enough electricity to power wireless health monitors, cochlear implants and deep-brain stimulators to treat disorders such as Parkinson’s disease.
Scientists have also sought to use the same effect behind everyday static electricity to power devices. When two different materials repeatedly collide with, or rub against, one another, the surface of one material can steal electrons from the other, accumulating a charge, a phenomenon known as triboelectricity. Nearly all materials, both natural and synthetic, are capable of creating triboelectricity, giving researchers a wide range of choices for designing gadgets.
