How to Shrink Implantables Using Piezoelectricity and Ultrasound

The quest for new technologies that can enable the development of miniaturized medical devices has occupied designers, engineers, and manufacturers for years.

Now, researchers at Stanford University have announced that they can miniaturize medical devices using a combination of the piezoelectric effect and ultrasound. Eventually, the researchers foresee that their technology could be used in a host of applications, including neural recording, cardiac mapping, temperature and pressure sensing, blood monitoring, deep-brain stimulation, peripheral nerve stimulation, and chronic pain relief.

Based on semiconductor technology, the new chip is powered using the piezoelectric effect, according to Marcus Weber. Weber, together with co-researchers Jayant Charthad and Ting Chia Chang, belongs to a research team at Stanford headed by Amin Arbabian, an assistant professor of electrical engineering. When pressure is applied to a piezoelectric material, the material is deformed, causing an electrical charge to be deposited on the electrodes of the device. This effect creates a voltage. When the pressure abates, the device returns to its original form, causing the voltage to disappear. The voltage in the electrodes is then harvested and stored internally.

But how do the researchers activate the piezoelectric effect? Ultrasound. Using ultrasound, they can apply pressure to the piezoelectric receiver 1 million times per second.

Known for being safe, ultrasound has been used for decades in such applications as fetal imaging, Weber notes. To ensure that this technology is practical in the real world, the researchers are conforming to thresholds for imaging applications set by FDA.

“Ultrasound has very low losses in the body, and we are able to focus the energy to specific points within the tissue so that we do not require large amounts of ultrasound to obtain significant power at the implant," Weber comments. "Thus, we obtain high link efficiency.” For example, the team has demonstrated that at less than 10% of the FDA limit, its current design provides sufficient power for deep-brain stimulation. Moreover, the researchers believe that they can reduce this power level even further.

So what does all of this have to do with miniaturization? Current-generation medical device implants, Weber remarks, are generally powered by large batteries. In addition, such implants require wires to target the region of interest, necessitating invasive and costly surgery. In contrast, by shrinking the size of the power source, the researchers hope that their technology will enable the design of new miniaturized implants that can be injected into the body. As for the ultrasound element, an external wearable power source could beam it to the implanted device.

The Stanford team’s piezoelectric-ultrasound technology isn’t ready for prime time just yet. Nevertheless, in 2015, it plans to conduct animal tests with added stimulation and sensing functionality. “We think clinical trials are possible within a couple of years,” Weber says.