Getting medical devices into our stomachs is harder than you might think — the human body just isn’t geared up for such an invasion. In fact, the first endoscopies — procedures where the doctor inserts a device into the gastrointestinal tract of a patient — were tested on sword swallowers. But now, in the modern era, scientists at the Massachusetts Institute of Technology (MIT) have developed medical devices that can not only be easily inserted into the body — they can also later be dissolved, simply by pointing an infrared light at their location.
The technology is a long way from the last major innovation in this field — flexible glass fibers called the “fibrescope,” invented by British scientist Harold Hopkins developed a device in the 1950s. By contrast, the new method allows for medical devices to be swallowed and then dissolved — all without having to resort to surgery. That matters for people who need to have these devices fitted to treat, track, and diagnose GI conditions.
“We are developing a set of systems that can reside in the gastrointestinal tract, and as part of that, we’re looking to develop different ways in which we can trigger the disassembly of devices in the GI tract without the requirement for a major procedure,” says Giovanni Traverso, an assistant professor at MIT, and the senior author of the study, in a press statement.
The new research was published Friday in the journal Science Advances.
How to craft a smart, stretchy polymer
The device uses a light-responsive hydrogel. Hydrogels are essentially a network of polymers that can hold large capacities of water. Some hydrogels respond to light — typically visible light. On exposure, hydrogels can be manipulated, meaning their composition and how they behave can be controlled. But in the dark crevasses of the human body, there isn’t much visible light to be had.
That’s the key for this new device: It doesn’t rely on visible light. Instead, it relies on ultraviolet, or UV, light. To test the device, the team used pig stomachs to model our own. Inside the stomachs, they were able to disintegrate their hydrogels using a small UV LED light.
Breaking down these devices is a crucial part of their usage. The researchers behind this paper have tried various mechanisms to trigger self-destruction. Varying the pH levels within the body, for example, or adjusting temperature, may also dissolve medicinal capsules.
“Given our interests in developing systems that can reside for prolonged periods in the gastrointestinal tract, we continue to investigate a range of approaches to facilitate the removal of these systems in the setting of adverse reaction or when they are no longer needed,” Traverso said. “We’re really looking at different triggers and how they perform, and whether we can apply them to different settings.”
In the case of this polymer, it is constructed with chemical bonds that break apart after remote exposure to a wavelength of light between 405 and 365 nanometers, which ranges from blue to UV. By using UV light, the rarity of exposure to other forms of light within the human body becomes a benefit — most people rarely encounters UV light in their day-to-day lives, reducing the chance of accidental destruction.
The choice of trigger also allowed the researchers to make certain choices in their design for the polymer. To work, the method relies on strong polymers that hold together without difficulty. They chose polymers like polyacrylamide, which has the ability to push solids to the edges of liquids when they’re mixed together. This process, known as flocculation, is used in water treatment plants and allows for the capsules to keep their strength and still dissolve when the time is needed. The material uses what the researchers describe as a “double network.”
“You’re forming one polymer network and then forming another polymer network around it, so it’s really entangled. That makes it very tough and stretchy,” Ritu Raman, a post-doctoral student at MIT and author on the paper, said in a statement.
Making light of surgery
The team tested their stretchy polymers with two types of devices: a seal for a bariatric balloon, used for weight loss, and an esophageal stent, which is used to allow patients to swallow food when suffering from esophageal cancer. In the case of the bariatric balloons, these typically have to be removed via surgery after six months of use.
But instead of surgery, the hydrogels worked their magic in just 30 minutes. That is all it took for a blue light operating outside the test pig’s body to dissolve the swallowed capsule.
With the hydrogel testing complete, that leaves the MIT team to the next step: determining what practical uses it can provide.
“This study is a proof of concept that we can create this kind of material, and now we’re thinking about what are the best applications for it,” Traverso said.