Professor Amin Arbabian and team are looking for ways to power tiny devices that may be used to pinpoint and repair problems deep inside the body without the trauma of major surgery or the side effects of systemic treatments like chemotherapy.
Ideally, the 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.
There are many challenges that stand between concept and execution, one of which is providing power to the devices. EE professor Amin 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.
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 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.
"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.
Excerpted from Stanford Engineering, "How implants powered by ultrasound can help monitor health," December 4, 2017.