In the future, when something goes wrong inside the body, perhaps a misfire between the brain and a limb, patients can become their own Local Area Network and fix the problem. This isn't just med-tech, or another aspect of the IoT. It's the Internet of Everything. You've got wearables. Now meet insideables.
Dr. Amin Arbabian and his team at Stanford University have developed a tiny implantable device that uses ultrasound for power and data communication. PCMag recently visited Arbabian Lab to learn more from Jayant Charthad, who is currently pursuing his doctoral research studies there and will be walking in Stanford's 127th Commencement this weekend, after which he'll be Dr. Charthad.
Upstairs from the impressive looking Nanofabrication Facility (hazmat suits alert) at Stanford's Paul G. Allen Building, we discussed the focus of the lab's research, which has received funding from DARPA and NSF. Here are edited and condensed excerpts of our conversation.
Jayant, start off by telling us how you came to this lab.
I came to Stanford for my Masters, after I'd completed my Bachelors in electrical engineering at the Indian Institute of Technology in Bombay. Actually, before Stanford, I worked at Texas Instruments in India too.
In Bengaluru? What were you doing there?
Yes. I was an analog design engineer in the Power Management group at Texas Instruments, designing low-dropout regulators.
But you decided to go back into academia and pursue research.
I came to Stanford, did my Masters, and am now about to defend my PhD thesis in electrical engineering, with a research focus on implantable medical devices and wireless power transfer. I met Professor Arbabian just as he was starting this lab to develop really interesting projects which involve system level research applications in biomedical research, incorporating not just engineering but also biology, physics, and electrical engineering design.
Tell us about these tiny implantable devices.
We've been working on this project since 2012, solving all the different engineering, design, and medical problems along the way. The overarching goal is to develop this technology where tiny implants can be deployed for many different applications, including nerve stimulation, and, as platform, where we can monitor different parameters, and therapies, in response to physiological monitoring.
How big are they?
Our nerve stimulation implant is 6.5mm long by 3mm wide by 2mm tall.
I took a photograph next to my spectacles to show how small they are. Remarkable. Tell us how they work.
Once implanted, these devices can harvest ultrasound energy and convert it to perform a specific medical function. In our system we have an ultrasound transmitter in the form of a wearable device on your skin—like a patch—and this beams ultrasound energy to the implant that is located very deep inside the body, even beyond 10cm.
Give us the tech spec.
It's a piezoelectric receiver that converts ultrasound applied from outside the body to electricity, a capacitor for storing that electricity, two stimulating electrodes, an LED, and a custom chip to control it all. Those components are all inside a biocompatible package.
On this tiny surface area, you've managed to build a fully functioning integrated circuit.
Yes. We designed an IC that integrates all the complex functions required for wireless, reliable and precise nerve stimulation. As is common practice in the IC design space, we first did extensive testing on the IC via computer software. Then built a blueprint, or layout of the integrated circuit chip, before sending it for fabrication.
In the nanofabrication lab downstairs?
Actually no, we sent it to TSMC in Taiwan. When the chip came back, we assembled the integrated circuit into the implant package, under a microscope.
Will the casing be bio-engineered by manipulating the DNA of bacteria like the ones we saw at iGem?
No, it's not an iGem. We use Barium Titanate, which is a ferroelectric ceramic material and has piezoelectric properties.The chip is made of silicon, the electrodes are platinum and we use a polyimide PCB for assembling all these components. The components are encapsulated in PDMS, with additional coatings of parylene-C (a biocompatible polymer).
And all these materials are both safe inside the body, and don't get "rejected" by the body?
Right. We wanted to make sure we chose biocompatible materials and we've begun extensive testing to prove that. Our initial results have been very promising, and we are working on further extending their safety to several years and decades.
They're implanted in the body via minimally invasive surgery [because they're so small]?
Yes, but the idea in the future is that the implant will be even smaller so that it can be injected with a needle rather than through surgery.
What's their shelf life?
We are building towards chronic implants which can always be there and don't need replacing.
Are they "programmable"? Can you send upgrades and repair patches to them?
We can upgrade them from the outside, yes. We program our current stimulation implant by sending digital data bits, in the form of zeros and ones, using the ultrasound waveform, so the data is sent in the form of amplitude modulation.The chip on the implant is intelligent enough to decode the information and apply stimulation of the right intensity and duration to the nerve.
Is the data bi-directional? Is there an "uplink" back from the body?
That's what we've also been working on independently. There could be a very wide variety of information that you can send outside of the body. For example, we have built another implant, within our group, which is a pressure sensor that wirelessly transmits the level of pressure inside the body. So, for instance, it could be used in the case of bladder control for spinal cord injury patients. Based on the bladder pressure information transmitted, you can then control the stimulation of the pudendal or sacral nerves to mitigate bladder incontinence.
Would it be mad to say you're building insideables that create a human Local Area Network?
You could say that. Essentially you could have several of these implants inside the body in a closed loop. Some would provide stimulation and others detect pressure or other physiological parameters, while communicating with each other to ensure everything is working in symbiosis. In another application, for example, when the nerve in someone's arm is broken, then you can measure the signal in the muscle to see if the nerve stimulation has actually worked or not. So that's another way of creating a closed-loop inside the body using these implants.
Are there any (modified) humans walking around yet with these implants?
Not yet. But we're getting close.
What's next for this research?
We see this implant as becoming the foundation of a new research platform, allowing us to test many different types of experiments inside the body.
To learn more, the team's paper appeared in the April issue of IEEE Transactions on Biomedical Circuits and Systems