An easy way to remove medical equipment MIT News
Taking advantage of a phenomenon that leads to fractures in metal, MIT researchers have designed medical devices that can be used inside the body as stents, staples or drug depots, then are safely broken on demand. are when they are not needed.
Researchers have shown that biomedical devices made of aluminum can be decomposed by exposure to a liquid metal called eutectic gallium-indium (EGaN). In practice, it may work by painting the liquid onto staples used to hold the skin together, for example, or by administering EGaIn microparticles to patients.
Triggering the dissolution of such devices could eliminate the need for surgical or endoscopic procedures to remove them, the researchers say.
“It’s a really dramatic phenomenon that can be applied to many settings,” says Giovanni Traverso, the Carl Van Tassel Career Development Assistant Professor of Mechanical Engineering at MIT and gastroenterologist at Brigham and Women’s Hospital. “What this enables, potentially, is the ability to have systems that do not require interventions such as endoscopy or a surgical procedure to remove the instruments.”
Traverso’s senior author is the studywhich appears in advanced Materials, Vivian Feig, an MIT postdoc, is the paper’s lead author.
For several years, Traverso’s lab has been working on swallowable devices that can stay in the digestive tract for days or weeks, releasing drugs at a specific time.
Most of those devices are made of polymers, but more recently researchers are exploring the possibility of using metals, which are stronger and more durable. However, one of the challenges of distributing metal tools is finding a way to remove them when they are not needed.
To create devices that can be broken on demand inside the body, the MIT team drew inspiration from a phenomenon known as liquid metal embrittlement. This process has been well studied as a source of failure in metal structures made of zinc and stainless steel.
“It is known that some combinations of liquid metals can actually get into the grain boundaries of solid metals and cause them to weaken and fail dramatically,” Feig says. “We wanted to see if we could use that known failure mechanism in a productive way to manufacture these biomedical devices.”
One type of liquid metal that can induce embrittlement is gallium. For this study, the researchers used eutectic gallium-indium, an alloy of gallium that scientists have discovered to have a variety of applications in biomedicine as well as energy and flexible electronics.
For the devices themselves, the researchers chose to use aluminum, which is known to be susceptible to embrittlement when exposed to gallium.
Gallium weakens solid metals like aluminum in two ways. First, it can diffuse through the grain boundaries of the metal — the boundary lines between crystals that make up the metal — causing fragments of the metal to break. The MIT team showed that they can harness this phenomenon by designing metals with a variety of grain structures, allowing the metals to break into smaller pieces or fracture at some point.
Gallium also prevents aluminum from forming a protective oxide layer on its surface, which increases the metal’s exposure to water and increases its corrosion.
The MIT team showed that when they paint gallium-indium on aluminum devices, the metals disintegrate within minutes. The researchers also created nanoparticles and microparticles of gallium-indium and showed that these particles suspended in liquids can also break aluminum structures.
While researchers began this effort as a way to create devices that could be broken into the gastrointestinal tract, they soon realized it could also be applied to other biomedical devices such as staples and stents.
To demonstrate GI applications, the researchers fabricated a star-shaped device with arms connected to a central elastomer by a hollow aluminum tube. The drug can be carried in the arms, and the shape of the device helps it to remain in the GI tract for extended periods of time. In a study in animals, researchers showed that such a device could be broken down in the GI tract when treated with gallium-indium.
The researchers then created aluminum staples and showed that they could be used to hold tissue together, then dissolved with a coating of gallium-indium.
“Right now, removing staples can actually cause more tissue damage,” Feig says. “We showed that with our gallium formulation we can simply paint it onto staples and decompose them on demand.”
The researchers also showed that an aluminum stent they designed could be implanted into esophageal tissue, then broken up by gallium-indium.
Currently, esophageal stents are either left in the body permanently or removed endoscopically when no longer needed. Such stents are often made from metals such as nitinol, an alloy of nickel and titanium. The researchers are now working to see if they can make dissolvable devices out of nitinol and other metals.
“An exciting thing to explore from a materials science standpoint is this: can we take other metals that are more commonly used in the clinic and modify them so that they also become actively triggerable? Can you?” Feig says.
In this study, researchers conducted a preliminary toxicity study in rodents and found that gallium-indium was non-toxic, even at high doses. However, more studies will be needed to be sure it will be safe for patients, the researchers say.
The research was funded by the Bill & Melinda Gates Foundation, MIT’s Department of Mechanical Engineering, the Brigham and Women’s Hospital Division of Gastroenterology, the Schmidt Science Fellows Program, and the Rhodes Trust.
Other authors of the paper include Eva Remlova, Benjamin Muller, Johannes Kuosmann, Nikhil Lal, Anna Ginzburg, Kewang Nan, Aashka Patel, Ahmed Mujtaba Zebran, Meghan Bantwal, Neora Fabian, Keiko Ishida, Joshua Jenkins, Jan-George Rosenbaum, Sanghyun Park Huh. , Madani Tent, and Alison Hayward.
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