MIT researchers have developed an ingestible pill that swells up to the size of a ping-pong ball upon reaching the stomach, allowing it to remain in the body and take measurements from within – for weeks at a time. The pill's creators hope that it could be used for a multitude of purposes, from tracking stomach pH levels to observing the growth of tumors and ulcers.
One of the key issues with ingestible electronics is the size of the devices. If a pill containing a sensor is small enough to pass through the throat, or esophagus of a patient unaided, it is also small enough to exit the stomach and pass into the small intestine.
The team of scientists behind the development of the new technology sought to prevent this from happening, by designing a pill capable of swelling up multiple times its original size once it reaches the stomach.
As is so often the case with medical advancements, the researchers looked to nature for inspiration, and found it in the form of one of Earth's stranger aquatic denizens – the pufferfish. Upon detecting a threat, it is able to suck in water at an impressive speed, forcing its body to expand to more than twice its normal size.
The pill that the researchers were hoping to design would need to expand with pufferfish-like efficiency, in the limited time frame before the stomach pushed it on to the next step in the digestive system.
To this end it was decided that the interior of the pill would be made up of superabsorbent particles of sodium polyacrylate. However, if placed in the gut unprotected, the juices present in the stomach would break the concentration of particles apart and push them into the small intestine as individual beads.
Foreseeing this complication, the team covered the absorbent core in a hydrogel layer comprised of nanoscopic crystalline chains arranged in a gridlock pattern.
The team tested the newly-devised pill in a laboratory setting by dunking it in solutions designed to mimic the acidic liquids found in the average person's stomach. In just 15 minutes, the pill was observed to swell to roughly 100 times its normal size (see photo above). According to the team, the expanded pill had a tofu-like softness, making it more biologically friendly than the harder plastics and metals used in the production of currently available ingestible sensors.
Despite being soft, the hydrogel exterior was found to be extremely tough in the face of stress testing. The pill was squeezed with pressures thousands of times higher than the contractions that take place in a healthy human gut.
"The stomach applies thousands to millions of cycles of load to grind food down," explains study co-author Shaoting Lin, a PhD student at MIT's Department of Mechanical Engineering. "And we found that even when we make a small cut in the membrane, and then stretch and squeeze it thousands of times, the cut does not grow larger. Our design is very robust."
Once a pill has outlived its usefulness, the researchers discovered that a patient would need only to drink a solution of calcium ions in order to shrink it back down to its normal size, allowing it to make a natural exit through the intestines, and beyond.
Alongside laboratory testing, the pill also underwent animal trials. Researchers embedded thermometers inside a number of devices and fed them to pigs. It was discovered that the sensors were able to accurately track the animals' activity patterns for up to 30 days.
The pill has the potential to be extremely versatile. It could house any number of sensors, ranging from the type of thermometer employed in the recent tests, to equipment used either to measure pH levels, or to seek out the biomarkers of bacteria and viruses present in the stomach.
The researchers believe that small cameras could also be attached to the pill that would be capable of monitoring the growth of ulcers and tumors. The delivery system also has the potential to offer a less invasive approach to the gastric balloon weight loss treatment, which currently requires a relatively firm balloon to be threaded down a patient's throat using an endoscope.
A paper detailing the development has been published in the journal Nature Communications.
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