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How implants powered by ultrasound can help monitor health

Using safe sound waves to deliver both energy and instructions, a team of researchers unveil a family of ‘electroceuticals’ — tiny devices designed to diagnose and treat disease.

Researchers are developing wireless implants that can monitor organs such as the heart, kidney and ear drum. | Illustration by Stefani Billings

The first rule of medicine is “Do no harm.” Taking this to heart, researchers are looking for ways to pinpoint and repair problems deep inside the body without the trauma of major surgery or the side effects of systemic treatments like chemotherapy

Among the alternatives being considered is the idea of planting tiny electronic devices, sometimes called electroceuticals, deep inside the body. Ideally, such implants could be placed alongside vital organs to take sensor readings, deliver tiny amounts of drugs, provide remedial jolts of electricity or combinations of the above.

But many challenges stand between concept and execution, starting with the need to deliver power to electronic implants without using wires that could introduce infections or loading up these tiny devices with bulky batteries.

Stanford electrical engineer Amin Arbabian and his team believe they’ve already solved the power problem by showing how to use ultrasound, the same technology used to take fetal images, to safely beam energy to a single miniaturized implant.

But what gets them really excited is the possibility of creating entire networks of implants by using ultrasound waves to do double-duty, by also serving as a communications technology. Imagine several devices, at strategic positions throughout the body, communicating with each other and coordinating their activities in what medical researchers call a closed-loop system to diagnose and treat disease. The team has already applied this wireless scheme to design several implantable sensors and stimulators.

“Nothing like this currently exists,” Arbabian says.

Clinical applications remain years away, but the team has already started working with Stanford medical researchers to begin preliminary animal tests. These are a necessary prelude to even contemplating the creation of closed-loop systems designed to reduce blood pressure, treat diabetes or manage epilepsy.

How it works

Arbabian and his team, including graduate students Marcus Weber, Jayant Charthad and Ting Chia Chang, have been working on this approach for years, putting together electronic components in a modular design to create something new: an implantable device platform the size of a grain of rice that is designed to let engineers swap essential modules depending on the functions desired.

“Think of our implant platform as the chassis of a car that we can customize for different applications,” Weber said.

Each implant contains a power-receiving module that can convert the energy from ultrasound waves into usable electricity. This is based on the well-known principle of piezoelectricity – the subtle pressure exerted by sound waves can compress certain crystals in a way that creates a flow of electrons. According to tests thus far, their implants can be powered beyond 12 centimeters below the skin, or a bit under 5 inches – which is sufficient for targeting most any vital organ in the body. The researchers believe they can implant devices even deeper in the future.

To store power between ultrasound charges, the engineers equipped the implant with capacitors instead of bulky batteries. The nanocapacitors store enough of a charge to run the onboard processor that controls each implant and power the implant’s ultrasound transmitter.

Clever engineering

The system uses infinitesimal amounts of energy. The nanocapacitor, for instance, stores one billionth of the energy of a AAA battery, and would be periodically recharged by an external skin patch.

The low power requirements derive from clever engineering. The team is designing a skin patch that will serve as the control hub and a central power source for their closed-loop system. The skin patch draws on advice from Butrus “Pierre” Khuri-Yakub, research professor of electrical engineering, to think of it like the cell tower in a mobile phone network, relaying signals and orchestrating the activity of two or more implants in different parts of the body.

An example scenario: One implant senses an organ’s health state and instructs another implant, via the skin patch, to deliver therapy; e.g., electrical stimulation of nerves. The researchers have already designed implants with communication, stimulation, drug delivery and sensing capabilities. They recently demonstrated their ultrasonic communication scheme and an implantable pressure sensor at the IEEE ISSCC and VLSI 2017 conferences.

“We anticipate that as we further refine and test the system, we will find multiple applications beyond epilepsy, hypertension and diabetes, including bladder incontinence, chronic pain and cardiac arrhythmia,” Arbabian says.

Read about the IEEE demonstrations at ISSCC and VLSI, or learn more about the lab’s implant work.

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