Editor's note: One of the major drawbacks of most wearable and implantable devices is still their batteries. Their limited capacity limits their long-term use. The Atlantic Monthly publishes an article explaining that scientists are trying to solve this problem. Disadvantages of various methods. Including piezo, triboelectricity, bioelectricity, etc., but the idea is the same, so that the device to obtain energy from the host body.
Piezoelectric speaker.
In "ISingtheBodyElectric", poet Walt Whitman expressed the 'action and power' of 'beautiful, curious, breathing, laughing body'. After more than 150 years, MIT's materials scientist, engineer Canna · Candan Dagdeviren and her colleagues gave new meaning to Whitman's poems. They invented a device that can distort power generation by reacting to the heartbeat.
Electronic technology is very powerful now. The computing power of a smartphone exceeds the computing power NASA had when it put the first group of people on the moon in 1969. Over time, technology has made extraordinary progress. People want to wear Devices that are even implanted in the body can also become more powerful.
One of the major drawbacks of most wearable and implantable devices is still their batteries. Their limited capacity limits their long-term use. When the pacemaker is depleted, the last thing you want to do is replace the battery. And to perform an operation on a patient. The solution to this problem may be inside the human body because it is rich in energy, chemistry, heat and mechanics. This prompted scientists to study a variety of ways to get equipment from the host Energy, Daddwellen and her colleagues detailed this in the 2017 Annual Review of Biomedical Engineering.
For example, the bellows-like movement made by a person while breathing can produce 0.83 watts of energy; the heat from the body, up to 4.8 watts; the energy of a person's arm movement, up to 60 watts. If you consider the pacemaker only It takes five millionths of a watt to keep it for seven years. Hearing aids need one thousandth of a watt to last five days. A smart phone needs one watt to maintain five hours. This is not meaningless.
Nowadays, Daddwillen and others are designing machines that use the body as an energy source. More and more researchers are testing this wearable or implantable device in animal models and humans.
An energy harvesting strategy involves converting energy from vibrations, pressures, and other mechanical stresses into electrical energy. This method produces so-called piezoelectric effects, typically used for speakers and microphones.
A commonly used piezoelectric material is lead zirconate titanate. Its lead content raises concerns that it may be too toxic to the human body. 'But if you want lead to disassemble from the structure, you must heat them above 700 degrees Celsius. The temperature,' said Daddwillon. 'You will never reach this temperature in your body.'
To take advantage of the piezoelectric effect, Daddwillen and her colleagues have developed a flat device that can be applied to organs, muscles such as the heart, lungs and diaphragms. These devices are 'mechanically invisible' because of their The mechanical properties are similar to the materials they are laminated on, so they do not hinder these tissues when they are in motion.
So far, this device has been tested on cattle, sheep and pigs. All animals have approximately the same heart as the human heart. 'When these devices are mechanically twisted, they generate positive and negative charges, voltages and currents. - You can collect this energy to charge the battery,' explains Dadvenen. 'You can use them to run a biomedical device like a pacemaker instead of changing every sixty-seven years when the battery is exhausted. Once. '
Scientists are also developing wearable piezoelectric energy harvesters that can be used on joints such as knees or elbows, as well as on shoes, pants or underwear. This way, a person can walk or bend his arm Power generation for electronic devices.
When designing a piezoelectric device, people may counter intuitively do not want to use the materials that are best at generating electricity. For example, you may only want a material that is only 2% or less efficient, instead of choosing a material that can be 5% A material that converts mechanical energy into electrical energy, if it converts more, 'it may add more load to the body, you don't want it to make you tired,' said Daddwillen.
A different energy harvesting method is to use thermoelectric materials to convert body heat into electrical energy. 'Your heart beats more than 40 million times a year,' said Daddvilleen. All of this energy is emitted in the body in the form of heat - this Is a rich source of potential energy that can be used for other purposes.
Thermoelectric generators do face some key challenges. They rely on temperature differences, but people's bodies usually maintain a fairly constant temperature, so the resulting temperature difference is usually not enough to generate large amounts of electricity. However, if the body is kept at a constant temperature The device is also exposed to relatively cold air, which is not a problem.
Scientists are exploring thermoelectric devices for wearable devices, such as powering watches. In principle, heat from the body can generate enough power to power wireless health monitors, cochlear implanters, and deep brain stimulators. Treatment of diseases such as Parkinson's disease.
Scientists also try to use the effects of everyday static electricity to power the device. When two different materials repeatedly collide or rub against one another, the surface of one material steals electrons from the surface of the other, accumulating the charge. This phenomenon is called For the triboelectricity. A key advantage of triboelectricity is that almost all materials, whether natural or synthetic, can create it, giving researchers the possibility of designing equipment.
'The more I study about triboelectricity, the more exciting it is and the more applications it has,' said co-author of the report, Wang Zhonglin, a nanotechnologist at Georgia Institute of Technology. 'I can see myself picking For the next 20 years, I have been working on this.
The surface of the triboelectric devices is different, and the amount of electricity that they can produce also varies, so scientists are experimenting with various forms and structures. Researchers have created cubic grids similar to microscopic urban blocks, similar to the nanowires of bamboo forests. Fields and arrays similar to the Giza Pyramid. Wang Zhonglin said that these materials are not only 'looks beautiful', but also very effective. They cover a surface with pyramids and can increase power generation by 5 times compared to flat panels.
Pacemakers, heart monitors and other implantable devices powered by respiratory and heartbeat friction have been tested on rats, rabbits and pigs. 'We are also observing whether triboelectricity can be used in vivo to stimulate cell growth and Promote wound healing,' Wang Zhonglin said. 'In addition, we have begun experiments with triboelectric stimulation of nerves to see if we can contribute to neuroscience.'
Wang Zhonglin and his colleagues also designed triboelectrically-driven wearable devices. For example, they created a triboelectric cloth that can be used to charge flexible belts containing lithium-ion batteries. This can power a wearable heart rate meter. The instrument uses Bluetooth technology to wirelessly transmit its data to a smartphone. 'The mechanical energy of human daily movement can be converted into electricity through our cloth,' Wang Zhonglin said.
Another strategy relies on what is called a biofuel cell, which generates electricity by a chemical reaction between the enzyme and the fuel molecules in the body, such as glucose in the blood, or through fuel molecules released from the body (such as sweat (Lactate secreted in the medium) to generate electricity. For example, the enzymatic cellobiose dehydrogenase from the fungus Phanerochaetesordida can break down sugar and generate electricity when it adheres to a carbon nanotube that is only nanometer (billionths of a meter) wide.
The choice of enzymes can be tricky. For example, several groups of scientists have discovered that glucose oxidase can produce electricity in biofuel cells implanted in laboratory rats, but this enzyme also produces hydrogen peroxide, a common Bleach. This may degrade performance, and in the long run it is also harmful to the body.
Scanning electron micrographs of carbon nanotubes for use in experimental biofuel cells that generate electrical energy from the human body. Tubes are covered with enzymes that treat natural fuels, such as lactate in sweat or glucose in the blood. They are electrically active. , and provide a broad surface area for enzyme deposition, allowing more electricity to be generated from a given volume.
French scientists have developed a biofuel cell made from enzyme-coated carbon nanotubes. The volume is only about half a teaspoon. After implanted in rats, it can generate enough energy from blood sugar. Or digital thermometer power supply. Experiments have also shown that biofuel cells woven in clothing such as headbands and wristbands can easily generate enough electricity by chemical reaction with lactic acid sweat to power the watch.
According to Daddwillen, these devices are not yet on the market. However, she expects them to be available on the market for less than 10 years. In the future, energy harvesting equipment may become more fit for the body. Dadvelen and her colleagues They are even studying the dissolvable version of their device.
'Imagine,' she said, 'put a device in your body, after it works for a while, it will break down to the molecular level in your body fluid. You can take it out without cutting your chest: we can use Biodegradable materials, such as silk and zinc oxide, which can degrade over time.