A spoonful of robots: miniature medical devices go inside the human body

Rich McEachran

City U's robot will crawl to the right location within the body to drop off medicine (Credit: City U)
City U's robot will crawl to the right location within the body to drop off medicine (Credit: City U)

When a doctor wants to perform an endoscopy on a patient to check for signs of stomach cancer, there’s a very small risk they could perforate the lining of the oesophagus. And, while the procedure is usually pain-free, the patient might feel some discomfort.

In the future, patients may no longer need to have a tube fed down their throat into their stomach. Instead they could simply swallow an ingestible device in the form of a pill. 

Engineers at Massachusetts Institute of Technology (MIT) have invented exactly this. It’s made from a jelly-like substance: a combination of water and polymers.

Inspired by the pufferfish, the team of researchers realised that in order for any edible pill to remain in the stomach once it has passed down the oesophagus, and not then pass out through the pylorus, it needed to be inflated.

To achieve this, the team experimented with various solutions, eventually settling on an inner material that contains sodium polyacrylate, which is known for its ability to soak up liquids and inflate. The super-absorbent polymer has numerous commercial uses, including in female hygiene products. 

To make it robust and prevent it from breaking up, the inner material is protected by an outer membrane made up of crystalline chains. 

“We soaked it [the pill] in various solutions that mimic gastric juices and found that it could inflate to 100 times its size,” said Xinyue Liu, a mechanical engineering PhD student at MIT and one of the lead authors of a paper published in the journal Nature Communications. “We also put it through mechanical stress tests, applying greater pressure than it would experience when the stomach contracts thousands of times. This resulted in no damage to the membrane.” 

Embedded with sensors

As for how the swollen device – the size of a ping-pong ball – exits the body, she added that it could be deflated and passed through the pylorus by simply drinking a solution with a calcium level higher than that of milk. 

The current iteration of the device, which was fed to pigs in a trial, is embedded with sensors and can track temperatures. In the future, the technology could also be embedded with tiny cameras that allow the pill to monitor the progress of stomach tumours and ulcers in humans.

“It would be a suitable solution for those who have to take medicine routinely or need to be monitored over a prolonged period,” said Liu.

Tough to swallow

Ingesting miniature devices for health reasons was once the realm of science fiction. In the 1960s Oscar-winning film Fantastic Voyage a team of doctors and their submarine are shrunk to the size of a human cell and injected into a character’s body to remove a blood clot on his brain. Now, technology is driving the reimagination of medicine. 

A team of researchers at City University of Hong Kong (City U) believe micro-robots could be the future of drug delivery.

The caterpillar-like robot they’ve invented, with legs less than a millimetre long, is made from a silicon material, polydimethylsiloxane, and is designed so that it can be controlled remotely through magnetic force. 

“The inside of a human is complex and can be challenging to navigate. There are many different tissues and textures,” said Haojian Lu, one of the co-authors of a 2018 paper, also published in Nature Communications, and a PhD student from City U’s biomedical engineering department. “Our robot can crawl its way to a location and drop off its payload [the medicine].”

Much like the inflatable pill-like device, what goes in must come out. Before the invention can be tested on animals or humans, the team would need to find a way to make it biodegradable, he added.

There’s also a long way to go before the technology can be considered for commercialisation. First, there’s the question of how it would be coated to glide its way down the oesophagus, especially for those that have difficulty swallowing medicine in the first place. 

Second, there’s the issue of a psychological barrier. For most, if not all, people, swallowing caterpillars is the stuff of nightmares and can be difficult to stomach. If the City U team can provide an answer to this challenge, then their invention might just have legs.

Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.

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