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Tiny, Wireless, Implantable Chips Use Ultrasound to Physiological Monitoring

Wireless, miniaturized implantable medical devices for in vivo and in situ physiological monitoring.

Researchers at Columbia University have developed the smallest implantable chip system that is a complete functioning electronic circuit for physiological monitoring. This tiny implantable chip visible only in a microscope and has a total volume of less than 0.1 mm3. To put that in perspective, the chip is as small as a dust mite.

Microscopic chips can be injected into the body with a hypodermic needle to monitor medical conditions which then beam their readings wirelessly to external displays such as patient monitors and smartphones.

Implantable Chips and Medical Devices

Implantable chips and medical devices are widely used to provide the monitoring and mapping of biological signals, the support and enhancement of physiological functions, and the mitigation and treatment of diseases. They are having a transformative impact on health care and improving the quality of life for millions of people.

Particularly, implantable devices for monitoring physiological parameters, such as temperature, blood pressure, glucose, and respiration, to inform an individual’s health state are of great importance and interest for both the diagnostic and therapeutic procedures.

These devices perform in vivo sensing and recording of relevant signals directly at the target locations for early diagnosis of health issues, allowing necessary interventions to be deployed at the onset of adverse events.

Conventional implanted electronics are highly volume inefficient, generally requiring multiple chips, packaging, wires, and external transducers; batteries are often required for energy storage. A constant trend in electronics has been the tighter integration of electronic components, often moving more and more functions onto the integrated circuit (IC) itself.

This has usually been driven by lower cost and improved electronic functions through the reduction in interconnect parasitics. In the context of implanted chips and electronics, this integration brings additional values through marked increases in this volume efficiency, defined as the number of functions per unit displaced implant volume.

Researchers at Columbia Engineering report that they have built what they say is the world’s smallest implantable chip system, consuming a total volume of less than 0.1 mm3. The system is as small as a dust mite and visible only under a microscope. To achieve this, the team used ultrasound to both power and communicate with the device wirelessly.

Tiny, Wireless, Implantable Chips Use Ultrasound to Physiological Monitoring
1) An SEM image of the mote, where the PZT transducer is monolithically integrated on the surface of the sensor. The mote is 300 μm wide, 380 μm long, and 570 μm thick (0.065 mm3); it weighs 0.3 mg. 2) Seven motes loaded in a 1-ml syringe filled with PBS solution.

“We wanted to see how far we could push the limits on how small a functioning chip we could make,” said the study’s leader Ken Shepard, Lau Family professor of electrical engineering and professor of biomedical engineering.

“This is a new idea of ‘chip as a system’ – this is an implantable chip that alone, with nothing else, is a complete functioning electronic system. This should be revolutionary for developing wireless, miniaturized implantable medical devices that can sense different things, be used in clinical applications, and eventually approved for human use.”

The implantable chip design was done by doctoral student Chen Shi, who is the first author of the study. Shi’s design is unique in its volumetric efficiency, the amount of function that is contained in a given amount of volume.

Traditional RF communications links are not possible for a device this small because the wavelength of the electromagnetic wave is too large relative to the size of the device.

Because the wavelengths for ultrasound are much smaller at a given frequency because the speed of sound is so much less than the speed of light, the team used ultrasound to both power and communicate with the device wirelessly.

They fabricated the “antenna” for communicating and powering with ultrasound directly on top of the chip.

The implantable chip, which is the entire injectable mote with no additional packaging, was fabricated at the Taiwan Semiconductor Manufacturing Company with additional process modifications performed in the Columbia Nano Initiative cleanroom and the City University of New York Advanced Science Research Center (ASRC) Nanofabrication Facility.

Shepard commented, “This is a nice example of ‘more than Moore’ technology – we introduced new materials onto standard complementary metal-oxide-semiconductor to provide new functionality. In this case, we added piezoelectric materials directly onto the integrated circuit to transducer acoustic energy to electrical energy.”

Konofagou added, “Ultrasound is continuing to grow in clinical importance as new tools and techniques become available. This work continues this trend.”

The team’s goal is to develop chips that can be injected into the body with a hypodermic needle and then communicate back out of the body using ultrasound, providing information about something they measure locally.

The current devices measure body temperature, but there are many more possibilities the team is working on.

Primary Reference

  1. Application of a sub–0.1-mm3 implantable mote for in vivo real-time wireless temperature sensing. Chen Shi et. al. Science Advances  07 May 2021. Vol. 7, no. 19, eabf6312
  2. Columbia University / Department of Biomedical Engineering
  3. Columbia University / Department of Electrical Engineering

 

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