Skin Patch Powers Electronics Using Muscle Movements

photo credit: National University of Singapore

There’s no denying we’re all addicted to our gadgets, but while technology has come on leaps and bounds in the past couple of decades, modern battery technology always seems to lag behind and is generally disappointing. Realizing the need for a viable solution, people round the world are starting to come up with smart ways to keep us connected with our electronics, such as energy-generating shoe insoles.

Now, it seems we have another innovative new device in the pipeline, as scientists from the University of Singapore have generated a skin-based generator that harvests energy from your muscle movements. This tiny, friction-powered generator produces static electricity using your skin, which then helps to convert energy from motion (mechanical energy) into electrical energy.

Although you won’t be able to charge your iPad with the device, according to IEEE Spectrum, it supposedly creates enough energy to be capable of powering small electronics, such as wearables. This means that in the future, rather than relying on batteries, devices such as health or fitness sensors could be powered by our day-to-day activities, such as walking or even just picking things up.

The capabilities of the postage stamp-sized device were showcased last week at the IEEE MEMS 2015 conference, where its developers demonstrated how a light finger tap can produce 90 volts of open-circuit voltage and 0.8 mW of power, or enough energy to light up 12 LEDs. Although some scaling-up will be required before it can be used to power electronics, it can already act as a wearable sensor that tracks a user’s daily activity.

To produce energy, the device takes advantage of a static charge phenomenon called the triboelectric effect, which is responsible for the small shock you sometimes receive when you touch a car door. This effect occurs when certain materials become electrically charged after coming into close contact with a different material, for example through pressing them together or friction. Some materials have a tendency to donate electrons from the atoms they consist of, whereas others have a stronger pull on electrons and tend to “steal” them from other atoms. Therefore, if two different materials are used, the electrons jump from one to the other when they are pulled apart, creating a current which can then be harvested.

In this situation, one of the triboelectric surfaces is our skin, which has a tendency to donate electrons. This means that, in order to create an efficient device, the other surface should have a tendency to steal electrons. For this second layer, the researchers used a flexible silicone layer atop a 50 nm-thick gold film which acts as an electrode to collect the current. The rubber layer is also covered in tiny structures designed to increase the surface area that is in contact with the skin, which in turn creates more friction.

When the device is stuck to a user’s neck, it can produce 7.5V from talking, and when it’s adhered to someone’s forearm, it can generate 7.3V from a simple fist-clench. Although this is nowhere near enough to charge a large device like a smartphone, it could be useful in small wearable devices such as sensors or smartwatches, and could possibly eliminate the need for batteries in such technologies.

Nitrogen-Fed Bacteria Could Power Our Future

photo credit: Breah LaSarre, Indiana University. These Zymomonas mobilis don't look like much, but they could represent a major step forward in clean transport fuels

A bacterium that doesn't need its nitrogen preprocessed could breathe new life into environmentally friendly ethanol production, turning mowing the lawn from a chore into an income source.

Most ethanol is currently produced from corn or sugar, competing with food for the raw materials while also combating rising prices, among other problems. If the transportation systems of the future are to be powered by low carbon biofuels, we need something better.

Cellulosic ethanol is widely promoted as the great hope. Vast quantities of cellulose and lignin produced by grasses rot around the world every day. Ethanol made from cellulose and lignin would, in theory, emit no more carbon dioxide than is released naturally, and no more than the plants draw from the atmosphere to grow in the first place. In the real world, inefficiencies creep in, but even so, cellulosic ethanol is likely to have about one-sixth of the Greenhouse impact of fossil fuels for the same amount of energy. 

So far, however, cellulosic production has proven to be frustratingly slow and expensive. The recent collapse in oil prices has left biofuels even further from being cost-competitive, so something big is needed.

The bacteria or yeasts used to turn sugars from cellulose, hemicelluse and lingin into ethanol need nitrogen to grow, but the switchgrass or lawn clippings to feed them are lacking in this regard. Current producers add nitrogen-rich chemicals to drive the process, adding millions of dollars a year to the cost of the currently small amount of ethanol produced in this way, and forming a major obstacle to growth.

However, Indiana University's Dr. James McKinlay has announced in the Proceedings of the National Academy of Sciences that this isn't always necessary. Zymomonas mobilis is an ethanol-producing bacterium that can use nitrogen gas (N2) instead. As the most common component in the atmosphere, nitrogen is hardly in short supply.

Most living things can't get their nitrogen directly from the atmosphere, instead depending on symbiotic prokaryotes to “fix” it for them. While McKinlay hadn't expected his first finding, the next observation surprised him even more.

“When we discovered that Z. mobilis could use N2 we expected that it would make less ethanol. N2 utilization and ethanol production demand similar resources within the bacterial cell so we expected resources to be pulled away from ethanol production to allow the bacteria to grow with N2,” McKinlay said. “To our surprise the ethanol yield was unchanged when the bacteria used N2. In fact, under certain conditions, the bacteria converted sugars to ethanol much faster when they were fed N2.”

The university has patented the process for using nitrogen-fed Z. mobilis to convert sugars from cellulose into ethanol. But this is not the big breakthrough cellulosic ethanol needs. The corn steep liquor and diammonium phosphate currently used are less expensive than the raw plant material and the enzymes that turn it into sugar, “But we recognize nitrogen fertilizers as a smaller, yet considerable, cost contributor that could potentially be more readily addressed,” said McKinlay.