Acoustic Fabric

Having trouble hearing? Just turn up your shirt. That’s the idea behind a new “acoustic fabric” developed by engineers at MIT and collaborators at Rhode Island School of DesignThe team has designed a fabric that works like a microphone, converting sound first into mechanical vibrations, then into electrical signals, similarly to how our ears hearAll fabrics vibrate in response to audible sounds, though these vibrations are on the scale of nanometers — far too small to ordinarily be sensed. To capture these imperceptible signals, the researchers created a flexible fiber that, when woven into a fabric, bends with the fabric like seaweed on the ocean’s surface.

The fiber is designed from a “piezoelectric” material that produces an electrical signal when bent or mechanically deformed, providing a means for the fabric to convert sound vibrations into electrical signalsThe fabric can capture sounds ranging in decibel from a quiet library to heavy road traffic, and determine the precise direction of sudden sounds like handclaps. When woven into a shirt’s lining, the fabric can detect a wearer’s subtle heartbeat features. The fibers can also be made to generate sound, such as a recording of spoken words, that another fabric can detectA study detailing the team’s design appears in Nature. Lead author Wei Yan, who helped develop the fiber as an MIT postdoc, sees many uses for fabrics that hear.

Wearing an acoustic garment, you might talk through it to answer phone calls and communicate with others,” says Yan, who is now an assistant professor at the Nanyang Technological University in Singapore. “In addition, this fabric can imperceptibly interface with the human skin, enabling wearers to monitor their heart and respiratory condition in a comfortable, continuous, real-time, and long-term manner.”

Yan’s co-authors include Grace Noel, Gabriel Loke, Tural Khudiyev, Juliette Marion, Juliana Cherston, Atharva Sahasrabudhe, Joao Wilbert, Irmandy Wicaksono, and professors John Joannopoulos and Yoel Fink at MIT, along with collaborators from the Rhode Island School of Design (RISD), Lei Zhu from Case Western Reserve University, Chu Ma from the University of Wisconsin at Madison, and Reed Hoyt of the U.S. Army Research Institute of Environmental Medicine.


How to Fix Arthritis in Damaged Knee

By stimulating cells to reproduce, electricity has already been shown to help heal soft tissue injuries. Now, an electricity-producing implantable material likewise appears to boost the regrowth of cartilage in compromised joints. In a study conducted at the University of Connecticut, a team led by Asst. Prof. Thanh Nguyen and postdoctoral fellow Yang Liu explored the use of a “tissue scaffold” made out of nanofibers of a biodegradable polymer known as poly-L lactic acid (PLLA). It had previously been used to accelerate the healing of broken bones.

So-called tissue scaffolds take their name from the fact that they have a scaffolding-like three-dimensional internal structure, which acts as a sort of roosting place for adjacent cells to migrate into and reproduce. Eventually, the scaffolding dissolves and is replaced entirely by the cells, resulting in a solid piece of biological tissue.

Unfortunately, according to the scientists, joint cartilage that has been regrown using conventional scaffolds has tended to be weaker than the original cartilage, causing it to quickly break down under regular use. That’s where the PLLA comes in. Along with being biocompatible, it’s also a piezoelectric material, meaning that it produces a small electrical current when mechanically stressed. Therefore, it was believed that if a tissue scaffold made of the material were to be implanted in an arthritic knee joint, it would continuously produce cartilage-boosting electricity as it was squeezed during activities such as walking. In order to test that theory, pieces of the material were placed in the injured knee joints of rabbits, which regularly hopped on a slowly-moving treadmill. It was found that after one to two months, strong, robust cartilage proceeded to grow back within the joints. By contrast, a control group that received non-piezoelectric tissue scaffolding experienced little healing of the damaged cartilage.

Importantly, the material didn’t contain any chemical growth factors, which may cause unwanted side effects. The researchers now want to test the technology on larger, older animals, and to monitor the regrown cartilage for at least a year or two.


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.


Battery-free Pacemakers Powered By A Patient’s Heartbeat

A new device powered by the heart could finally solve the pacemaker problem. Some 1.5 million Americans have pacemakers implanted to keep their hearts beating steadily. The devices are life-saving, but they don’t last forever. Currently, most pacemaker batteries have to be replaced every five to 12 years, and doing so means invasive surgery each time. Researchers at the National Key Laboratory for Science and Technology in Shanghai, China have developed a tiny device that piggybacks off the heart itself to generate energy – meaning a pacemaker battery would never have to be replaced.

A healthy heart can keep time for itself, by way of an internal pacemaker called the sinus node in the upper right chamber. It fires off an electrical charge some 60 to 100 times a minute, and that electrical energy sets off a series of contractions of heart muscle which in turn pumps blood throughout the body. But as the heart ages or once it becomes diseased, the sinus node takes a hit, too, and may fail to keep the heart beating in time or at all. Fortunately, since the late 1950s, we’ve been able to substitute a small, implantable, battery-powered device to send these electrical signals once the heart can’t any more. Even 60 years later, however, we haven’t figured out what to do about the device’s power supply, however.

Surgery to place the pacemaker and wires that feed its electrical pulses to the heart is complex, requiring doctors to open the chest cavity. The pacemaker itself is tucked away in a ‘pocket’ much closer to the skin surface. Once the battery runs out, usually only a local anesthetic is required to remove the old device and put a new, fully charged one.  Still, the procedure is an unpleasant hassle that comes with a risk of infection, and it’s expensive to have done. Depending on the pacemaker, the device itself may cost anywhere from $19,000 to $96,000, according to Costhelper – and that doesn’t include the expenses for the operation.

But the new Chinese-developed device shows promise to end the procedure.  The new pacemaker accessory can actually harness the heart’s beats to power a pacemaker. The key to innovation is its flexible plastic frame, which allows the device to capture more energy from the heart than previous hard cases have done. At the device’s center are layers of piezoelectric material, which generates power whenever it is bent. Many materials acquire an electrical charge when force is applied to them, including natural ones in our bodies. Crystals, DNA and even bone are capable of capturing electrical energy. The trick is to apply enough force to a piezoelectric material, then supercharge it, because, on their own, these materials don’t work up all that much energy.

Scientists have long been looking to piezoelectricity as an elegant solution to recapturing otherwise wasted energy, and some have even applied it to the pacemaker before. But, previously, other researchers have not been able to create a device that bends enough to generate sufficient power. Now, the Chinese scientists have shown their device can fuel a pacemaker and keep a pig’s heart beating. The devices frame allows it to flex significantly with as little movement as is created by a heartbeat. While the pacemaker itself is implanted in its usual place, near the collar bone and just under the skin, the new power device is tucked underneath the heart, where the organ’s contractions bend it rhythmically.  In tests in pigs, the new pacemaker generated just as much power as a pacemaker, using a completely renewable energy source.