Tiny, Sound-Powered Chip To Serve As Medical Device

Stanford engineers can already power this prototype
 medical implant chip without wires by using ultrasound.
Now they want to make it much smaller.
Image: Arbabian Lab / Stanford School of Engineering
Medical researchers would like to plant tiny electronic devices deep inside our bodies to monitor biological processes and deliver pinpoint therapies to treat illness or relieve pain.
But so far engineers have been unable to make such devices small and useful enough. Providing electric power to medical implants has been one stumbling block. Using wires or batteries to deliver power tends to make implants too big, too clumsy, or both.
Now, Stanford engineers are developing a way to send power, safely and wirelessly, to "smart chips" programmed to perform medical tasks and report back the results. Their approach involves beaming ultrasound at a tiny device inside the body designed to do three things: convert the incoming sound waves into electricity; process and execute medical commands; and report the completed activity via a tiny built-in radio antenna. The team recently presented a working prototype of this wireless medical implant system at the IEEE Custom Integrated Circuits Conference in San Jose.
The researchers chose ultrasound to deliver wireless power to their medical implants because it has been safely used in many applications, such as fetal imaging, and can provide sufficient power to implants a millimeter or less in size. Now they are trying to develop sound-powered implants for a variety of medical applications, from studying the nervous system to treating the symptoms of Parkinson's disease.
The Stanford medical implant chip is powered by "piezoelectricity," a word that means electricity caused by pressure. In a piezoelectric material, pressure compresses its molecular structure much like a child jumping on a bed compresses the mattress. When the pressure abates, the piezoelectric material's molecular structure, like the mattress, springs back into shape. Every time a piezoelectric structure is compressed and decompressed a small electrical charge is created. The researchers created pressure by aiming ultrasound waves at a tiny piece of piezoelectric material mounted on the device. The implant is like an electrical spring that compresses and decompresses a million times a second, providing electrical charge to the chip.
The piezoelectric effect is the power delivery mechanism. In the future, the team plans to extend the capabilities of the implant chip to perform medical tasks, such as running sensors or delivering therapeutic jolts of electricity right where a patient feels pain.The "smart chip" also contains a radio antenna to beam back sensor readings or signal the completion of its therapeutic task.
The current prototype is the size of the head of a ballpoint pen. In order to design a next-generation implant one-tenth that size, team members have been collaborating with two additional Stanford colleagues who are experts in ultrasonics. The goal is to produce smaller devices that could be used to create a network of electrodes to study the brains of experimental animals in ways not currently possible.