Treating tumors within the GI system is often a difficult challenge, frequently requiring invasive surgery. Scientists at Caltech have now developed self-propelled microrobots that can deliver drugs to precise spots within the intestines, and that can let clinicians monitor and control their activity. Besides drug delivery, the microrobots have the potential to be used in microsurgeries in difficult to reach parts of the body.
The microrobots are tiny spheres of magnesium coated with a drug, gold, and parylene, a polymer that doesn’t break down within the GI tract. They’re also encapsulated within paraffin wax to resist the acidity of the stomach. The coating has a small hole within it that lets digestive juices in to react with magnesium and generate bubbles that stream out of the hole. As the bubbles come out, they push the microrobot in the opposite direction.
In order to be used therapeutically, the microrobots are designed to be ingested and allowed to travel to the treatment site. Once in the vicinity, a photoacoustic computed tomography system, developed at Caltech, uses infrared light pulses to spot the microrobots. Since infrared light is absorbed well by hemoglobin within red blood cells, the hemoglobin molecules begin to vibrate intensely and this vibration can be spotted using ultrasound sensors. Using the technique, tumor sites and the microrobots that target them, can be identified within the intestine.
To activate the microrobots, a continous-wave near-infrared laser is used to melt the paraffin wax surrounding them, exposing them to the digestive juices that flood into the hole within each microrobot and set off the bubbling reaction. The microrobots get pushed in all sorts of directions, since there’s no steering mechanism. Because there’s so many of them and they’re concentrated around the treatment area, many of the microrobts become lodged on the surface of the intestinal wall, releasing the drug within their coating.
“These micromotors can penetrate the mucus of the digestive tract and stay there for a long time. This improves medicine delivery,” said Wei Gao, one of the leaders of the research. “But because they’re made of magnesium, they’re biocompatible and biodegradable.”
Here’s an animation from Caltech demonstrating the microrobot drug delivery system: