Flexible device could treat hearing loss without batteries

Some people are born with hearing loss, while others acquire it with age, infections or long-term noise exposures. In many instances, the tiny hairs in the inner ear’s cochlea that allow the brain to recognize electrical pulses as sound are damaged. As a step toward an advanced artificial cochlea, researchers in ACS Nano report a conductive membrane, which translated sound waves into matching electrical signals when implanted inside a model ear, without requiring external power.

An electrically conductive membrane implanted inside a model ear simulates cochlear hairs by converting sound waves into electrical pulses; wiring connects the prototype to a device that collects the output current signal.

When the hair cells inside the inner ear stop working, there’s no way to reverse the damage. Currently, treatment is limited to hearing aids or cochlear implants. But these devices require external power sources and can have difficulty amplifying speech correctly so that it’s understood by the user. One possible solution is to simulate healthy cochlear hairs, converting noise into the electrical signals processed by the brain as recognizable sounds. To accomplish this, previous researchers have tried self-powered piezoelectric materials, which become charged when they’re compressed by the pressure that accompanies sound waves, and triboelectric materials, which produce friction and static electricity when moved by these waves. However, the devices aren’t easy to make and don’t produce enough signal across the frequencies involved in human speech. So, Yunming Wang and colleagues from the University of Wuhan wanted a simple way to fabricate a material that used both compression and friction for an acoustic sensing device with high efficiency and sensitivity across a broad range of audio frequencies.

To create a piezo-triboelectric material, the researchers mixed barium titanate nanoparticles coated with silicon dioxide into a conductive polymer, which they dried into a thin, flexible film. Next, they removed the silicon dioxide shells with an alkaline solution. This step left behind a sponge-like membrane with spaces around the nanoparticles, allowing them to jostle around when hit by sound waves. In tests, the researchers showed that contact between the nanoparticles and polymer increased the membrane’s electrical output by 55% compared to the pristine polymer. When they sandwiched the membrane between two thin metal grids, the acoustic sensing device produced a maximum electrical signal at 170 hertz, a frequency within the range of most adult’s voices. Finally, the researchers implanted the device inside a model ear and played a music file. They recorded the electrical output and converted it into a new audio file, which displayed a strong similarity to the original version. The researchers say their self-powered device is sensitive to the wide acoustic range needed to hear most sounds and voices.

Source: https://www.acs.org/

Flexible Generators Turn Movement Into Energy

Wearable devices that harvest energy from movement are not a new idea, but a material created at Rice University may make them more practical. The Rice lab of chemist James Tour has adapted laser-induced graphene (LIG) into small, metal-free devices that generate electricity. Like rubbing a balloon on hair, putting LIG composites in contact with other surfaces produces static electricity that can be used to power devices. For that, thank the triboelectric effect, by which materials gather a charge through contact. When they are put together and then pulled apart, surface charges build up that can be m.

In experiments, the researchers connected a folded strip of LIG to a string of light-emitting diodes and found that tapping the strip produced enough energy to make them flash. A larger piece of LIG embedded within a flip-flop let a wearer generate energy with every step, as the graphene composite’s repeated contact with skin produced a current to charge a small capacitor.

An electron microscope image shows a cross-section of a laser-induced graphene and polyimide composite created at Rice University for use as a triboelectric nanogenerator. The devices are able to turn movement into energy that can then be stored for later use

This could be a way to recharge small devices just by using the excess energy of heel strikes during walking, or swinging arm movements against the torso,” Tour said.

LIG is a graphene foam produced when chemicals are heated on the surface of a polymer or other material with a laser, leaving only interconnected flakes of two-dimensional carbon. The lab first made LIG on common polyimide, but extended the technique to plants, food, treated paper and wood.

The project is detailed in the American Chemical Society journal ACS Nano.

Source: http://news.rice.edu/