What Sensome learned developing the world’s smallest electrical impedance sensor for medical devices

Sensome’s big bet on a tiny chip yields useful insights for other device developers.

By Gor Lebedev, Sensome

Gor Lebedev is the chief technology officer and chief operating officer for Sensome. [Photo courtesy of Sensome]

Electrical impedance spectroscopy (EIS) is commonly used to measure body composition, muscle health, and disease detection and progression from outside the body — such as in vitro diagnostic systems — as the technology has required measurement devices and cables too large or thick to be used in vivo.

We recognized the in-vivo potential of EIS to measure differences within and between tissues in order to noninvasively detect disease earlier, monitor its progression and guide physician treatment choice.

But we needed to solve a challenge no one had solved before: how to make a sensor small and thin enough to leverage EIS in the smallest medical devices used in vivo today, such as guidewires.

While the original idea was application-specific to ischemic stroke, once we began designing we realized we wanted to design it from the start as a tissue-sensing platform with endless applications. We quickly recognized our technology needed to be captured in a sensor comprising a microchip and a smaller and more flexible sensor than had ever been developed before to fit on and in the smallest and thinnest medical devices and to measure impedance in a variety of devices. Such a sensor is expensive and time-consuming to build, so having endless applications would make it cost-effective.

Determining the requirements

The Clotild Smart Guidewire System is the first device integrating Sensome’s microsensor technology. [Image courtesy of Sensome]

It was important that we carefully thought through the requirements before going into development. We developed them based on results from in vitro tests on real tissues of different types, and in parallel we did finite element simulations.

We wanted it to be as thin and flexible as possible for tiny devices to navigate narrow vasculature, but to also work for larger devices. What is thin? Our proprietary process gets us to 10-20 microns, significantly thinner than today’s state of the art 50-80 microns. For perspective, most microchips are built on substrates of about 500 microns, which is bigger than most in vivo devices you would want to put it on.

We also wanted our chip to have a wide measurement range in frequency and amplitude to precisely measure many different types of tissues. Our technology can differentiate similar tissues. We liken this to enabling physicians to see in color versus grayscale. This wide range enables a wide variety of applications, well beyond the roughly 1 MHz used by in vitro diagnostics for cancer. 

Finally, we needed to digitalize the signal inside the body, as close as possible to the tissue we are measuring, to deliver the precision we wanted. This meant we had to figure out a way to negate the long, thick cables used with EIS measurement in IVD. By using a microchip, we brought impedance measurement right next to the tissue itself.

Lessons learned

We already had a good understanding of existing technology and processes in semiconductors from our team of specialists. Once we determined our requirements, we decided it would be most efficient to work with a design house to realize the chip. Most thought it was impossible. Our chosen partner had never made a chip this thin before but was fearless and visionary.

It’s a hard path to go straight to a small chip. Most companies would start with larger, existing technology for proof of concept, and then miniaturize it with design iterations to add unanticipated requirements. We bet on the chip from the start and anticipated all the variations needed in a real product. This risky endeavor paid off. Once you have an ASIC/chip, you can easily adapt electrode/sensor design for any particular device.

We and our partner used our imagination and creativity to figure out a way to combine pieces of technology (like Legos) in a way that had never been done before to achieve our miniature sensor. The methods we used are proprietary, but we can share four critical learnings from this project:

1. If you are creating  technology that is beyond state-of-the-art, do it yourself. Subcontractors will not be as invested as you, and owning the technology creates your company’s value.

2. Don’t underestimate the complexity of the industrialization process. It’s one thing to create the technology. It’s another to successfully integrate your technology into existing devices and then scale it up. Doing one but not the other can lead to failure.

3. Think iteratively. Go slow to go fast. Don’t try to make the best possible device in your first pass. Take baby steps in development to get to first-in-human as quickly as possible to generate clinical data, and then enhance from there.

4. Be creative with generating data. Does all your data have to be obtained in vivo? In our case, we recognized we could generate compelling evidence using a significant amount of ex vivo data. Also, keep trials as small as is feasible, focus your objectives, and keep the protocol flexible enough to allow for adjustment based on clinical learnings.

Achieving the world’s smallest EIS sensor was perhaps our biggest achievement, but not the only one. Because the technology is beyond state-of-the-art, everything that goes along with it also had to be invented, from the microfabrication processes, to the automation involved in device manufacturing.

Having solved the extraordinary sensor challenge, we now have a platform technology that can be used for in vivo tissue measurement in real time and, over time, across virtually any medical device. We look forward to partnering with device manufacturers to realize a portfolio measuring the previously unmeasurable.

Gor Lebedev is the chief technology officer and chief operating officer for Sensome. With more than 15 years in advanced microelectronics and material science, seven patents and 30 scientific publications, he specializes in cutting-edge sensor technologies and data analytics at the intersection of hardware and software. 

Read more MDO Contributions and learn how to submit your own

The opinions expressed in this blog post are the author’s only and do not necessarily reflect those of Medical Design & Outsourcing or its employees.