Rappers could one day be part of a health-monitoring regimen—or at least their music could be. A prototype device that can track blood pressure in damaged blood vessels or monitor the bladders of incontinent patients draws its power from the low-frequency vibrations in rap music rather than from batteries.
In a paper presented 30 January at the 25th IEEE International Conference on Micro Electro Mechanical Systems in Paris, researchers described the guts of their 2-centimeter-long device. A small lever, which converts vibrations into electricity, powers a sensor that takes readings and transmits data. The lever, made of a thin layer of lead zirconate titanate (PZT) coating a glass core, responds to vibrations at 435 hertz.
This lever is connected to a capacitor, which stores the electricity until the vibrations stop. Once they stop, the released energy triggers a pressure sensor to take a reading and then transmit its data via a radio signal to a receiver. Patients with this implant could conceivably monitor their blood pressure by playing a couple of minutes of J. Cole's latest to charge the sensor, and then have it send the data to a receiver. And having a self-contained device to control conditions such as incontinence would be more convenient than having to insert a catheter or rush to the restroom all the time.
"Nothing happens when you stop playing music," says electrical engineer Babak Ziaie of Purdue University in West Lafayette, Indiana. The implant works only when exposed to specific frequencies. And because of design constraints that dictate the length of the vibrating lever, those frequencies are most often found in rap music.
Not a fan of hip hop? No problem, Ziaie says. It wouldn't be hard to change the lever's length or thickness to respond to different musical preferences. "I like listening to classical music," he says, but his graduate student Albert Kim, who worked on the device, prefers rap. Changing the lever's dimensions changes the frequency it responds to, so Tchaikovsky buffs aren't stuck listening to Jay-Z.
The researchers tested their device in a water balloon to approximate human soft tissue. When they pressed the balloon to a metal plate attached to speakers (to ensure even sound distribution) playing rap music, their receiver picked up signals from the sensor 10 to 15 centimeters inside. That means that you can power a sensor deep in the body, Ziaie says.
Current medical devices run on batteries that need to be changed periodically or rely on precise alignment of the sensor and the receiver to work properly, Ziaie says. The new device addresses those issues because music can power the sensor via the vibrating lever, and a receiver does not have to be perfectly positioned relative to the new sensor to achieve an accurate reading. As long as it can pick up a radio frequency, the receiver can get the data.
The music part sounds cool, writes Robert Langer, a biomedical engineer at the Massachusetts Institute of Technology in Cambridge, who was not involved with this research. But he cautions that some of the materials used in this device, such as PZT, merit careful packaging to ensure they don't leach out of their container.
"If you have lead in a biological system, it's a big concern," says Zhong Lin Wang, a nanotechnology and materials science engineer at the Georgia Institute of Technology in Atlanta, who also was not involved with this research. Wang thinks another material, such as zinc oxide, would be much better to use as a lever. Zinc oxide is biocompatible and much cheaper to fabricate than PZT, he says.
Ziaie writes that they used PZT in their prototype because it was commercially available and it works well. And he agrees that the lead can be an issue for long-term implants. "One [would need] to hermetically seal the device in these cases," he says, "which is easily doable by sealing the glass capsule with a laser."
After some modifications to make the device smaller and safe for use in the body, Ziaie says his team plans on testing it by monitoring bladders in pigs.