Harvesting Power From the Gut
For several years, researchers at MIT and Brigham and Women’s Hospital have been designing and experimenting with sensors that can measure heart rate and body temperature from inside the comfy confines of the gastrointestinal tract. The ingestible devices—which offer greater biomonitoring accuracy than external measuring tools—transmit the data via wifi to a nearby external device, and they do it over the course of several hours as they wend their way through the digestive tract. But in order for these prototype sensors to one day be clinically useful, they need a power source that would allow them to continue collecting data for days, not hours.
To make a battery that would be safe to ingest, gastroenterologist and biomedical engineer Giovanni Traverso and his team took a cue from the classic “lemon battery” experiment, whereby acid from a lemon dissolves two metal electrodes, creating an electrochemical reaction. As described in a recent paper published in Nature Biomedical Engineering, the new ingestible battery is powered by stomach acid. Traverso joins Ira to discuss the research.
Giovanni Traverso is a gastroenterologist and biomedical engineer at Brigham and Women’s Hospital and Harvard Medical School, and a research affiliate at MIT in Cambridge, Massachusetts.
IRA FLATOW: They say these days there’s a pill for everything. It is a bit of an exaggeration, and now researchers have taken things a step further– ingestible sensors, tiny devices that you swallow that collect health data from inside your digestive tract. They are just prototypes so far, being tested in pigs, but to make them viable you have to find a way to power the devices. Well, why not use the gastric juices found in the stomach? A battery that runs on stomach acid. Hello! And that’s just what my next guest did.
Giovanni Traverso, a gastroenterologist and biomedical engineer, Brigham and Women’s Hospital. Also a research affiliate at MIT. Dr. Traverso, welcome to Science Friday.
GIOVANNI TRAVERSO: Hi there, Ira. Thanks so much for having me on the show.
IRA FLATOW: What would be a good use for these ingestible sensors?
GIOVANNI TRAVERSO: Great question. I think it’s worth just taking a step back. And the thing that we’re really interested in is exploring the concept of having systems inside of the GI tract for a variety of applications, including sensing, but then also drug delivery.
But really when you start thinking about keeping a system inside of the body for a long time, as you highlighted, powering that system becomes a challenge, and that’s exactly what we tried to aim to address here with this study.
IRA FLATOW: Did a little light bulb go off and somebody said, hey you know the stomach’s full of acid. We make a battery. We have an electrolyte sitting right there?
GIOVANNI TRAVERSO: We’re very fortunate that we are collaborating with a group of electrical engineers at MIT, and we started to explore. And a couple of ideas, I think thinking back to the high school days, one of the concepts was sort of applying the lessons from the lemon battery, and recognizing that there isn’t a static environment in the stomach really motivated further development down that path.
IRA FLATOW: Has this idea already been tried in animals to see how well it works?
GIOVANNI TRAVERSO: Absolutely. So we showed in pigs that we could actually power these systems for almost a week, and before this worked, the longest that had been achieved through systems was more on the order of minutes to about an hour. And so we’re really encouraged by the possibility of long-term powering of such systems.
IRA FLATOW: And is that the time that you would need, just minutes to an hour or so? Well, the kinds of things that we’re interested are really monitoring and providing the sensors from within on the order of weeks and potentially even months following a single ingestion.
IRA FLATOW: This is Science Friday, from PRI, Public Radio International. In case you just joined us, I’m talking with Giovanni Traverso of MIT and Brigham and Women’s Hospital. So what about differences in diet? Would you be facing challenges when people swallow it and then eat stuff? Would it interfere with the acid?
GIOVANNI TRAVERSO: No. Great question. Part of the reason that we wanted to test these in a large mammal was to start to address that. And what we observed, at least over the course of a week, know these animals were going about their daily business as they would otherwise, eating and drinking their food. And we were encouraged by overall the amount of power that we were able to harvest period.
But I think absolutely as part of the next set of studies that certainly would be one of the aspects that we would look at, specifically how much energy is available to be harvested during those times of feeding versus ones during fasting times.
IRA FLATOW: Now I would imagine with all the battery in there and the electronics and the sensing materials, you’ve got a pretty big pill, or as my dad used to say a horse pill.
GIOVANNI TRAVERSO: In this case I guess it was more of a pig pill, but it was a little bit– but this was a prototype, and it was on the larger side, but it was the first prototype that was made, and the initial concept was built with off-the-shelf components. And so certainly we see the possibility of significant reduction in size for the next step, this next stage of development.
IRA FLATOW: Now the pill, is it made to just stay in the stomach acid in the stomach? Or can it actually travel past it into the small intestine?
GIOVANNI TRAVERSO: So these actually could make it out of the body, and they did. And actually we monitored the animals until these passed out of the GI tract. And one of the interesting things that we did was actually to characterize how much energy could be harvested from the stomach and whether we could harvest from the small intestine. And even though it’s not acidic, we actually show that there is some energy that can be harbored from the intestine, which I think is also an encouraging observation here for future systems in the body.
IRA FLATOW: I imagine you would also have to make it the right shape so that it does pass through the system, right?
GIOVANNI TRAVERSO: Exactly. And I think depending on what the goal was, and so some of our work actually has to do with having systems stay in the stomach for prolonged periods of time and then either having that shape change, for example, to enable the transit through the body. So it really depends on the kind of time that you’re interested in monitoring for example, an individual.
IRA FLATOW: And then the things that you could monitor. Heart rate or how much acid is in the stomach? Or what other kinds of things?
GIOVANNI TRAVERSO: Absolutely. The first thing we showed here in this study was temperature. And we communicated that to an external receiver over the course of the week. But we’ve done some other work in the past looking at measuring heart rate, respiratory rate, and we’re doing some other work looking at movements of the actual GI tract. And then sensing different proteins and toxins to help service systems for early detection.
IRA FLATOW: I guess, as you say, you could engineer it to stay or move around where you’d like it to be and maybe even self dissolve depending on how you design it?
GIOVANNI TRAVERSO: Exactly. A lot of the work that we do is on material development and thinking about materials that you can, for example, trigger to dissolve in a certain timescale or to dissolve immediately to exactly as you said to enable the passage down the GI tract.
IRA FLATOW: And to give off any medicines it might have in it.
GIOVANNI TRAVERSO: Exactly. Exactly.
IRA FLATOW: I see nano words here coming to mind, nanotechnology stuff. Thank you very much, Dr. Traverso.
GIOVANNI TRAVERSO: Thank you.
IRA FLATOW: Giovanni Traverso is a gastroenterologist and biomedical engineer at Brigham and Women’s Hospital. That’s a research affiliate at MIT.