Microbots appear promising for tumor treatment

Targeting medical treatment on a part of the sick body is a practice as old as medicine. A bandage is placed on a skinned knee. The drops go into the itchy eyes. A broken arm enters a casting.

But often what hurts us is inside the body and is not so easy to reach. In such cases, treatment such as surgery or chemotherapy may be necessary. Two researchers at Caltech's Division of Engineering and Applied Sciences are working on a whole new form of treatment: microbots that can deliver drugs to specific areas of the body while monitoring and controlling them. from the outside.

"The microrobot concept is really great because you can get micromachines exactly where you need them," says Lihong Wang, professor of medical engineering and electrical engineering at Bren Caltech. "It could be a drug, or a predefined microsurgery."

Microbots are a joint research project of Wang and Wei Gao, badistant professor in medical engineering, and are intended for the treatment of tumors of the digestive tract.

Microbots consist of microscopic spheres of metallic magnesium coated with thin layers of gold and parylene, a polymer resistant to digestion. The layers leave a circular part of the sphere discovered, a bit like a porthole. The uncovered portion of magnesium reacts with the fluids of the digestive tract, generating small bubbles. The flow of bubbles acts like a jet and propels the sphere forward until it collides with neighboring tissues.

Spherical magnesium zoom microrobots alone may be useful, but they are not particularly useful. Wang and Gao made some changes to them from novelty to drug delivery.

VIDEO: https: //www.Youtube.com /watch? v =YWK3gg6J8ng

First, a drug layer is sandwiched between an individual microsphere and its parylene layer. Then, to protect the microbots from the harsh environment of the stomach, these are wrapped in paraffin wax microcapsules.

At this stage, the spheres are able to carry drugs, but still do not have the crucial ability to deliver them to the desired location. For this, Wang and Gao use photoacoustic tomography (PACT), a technique developed by Wang that uses pulses of infrared laser light.

Infrared laser light diffuses through tissues and is absorbed by the hemoglobin molecules carrying oxygen into the red blood cells, causing them to vibrate ultrasonically. These ultrasonic vibrations are picked up by sensors pressed against the skin. The data from these sensors is used to create images of the body's internal structures.

Previously, Wang had shown that variations in PACT could be used to identify bad tumors or even individual cancer cells. With regard to microbots, the technique has two uses. The first is the imagery. Using PACT, researchers can look for tumors in the digestive tract and also locate microbots, which appear clearly in PACT images. Once the microbots arrive near the tumor, a near-infrared high-power laser beam is used to activate them. Because microrobots so strongly absorb infrared light, they briefly heat up, melting the wax capsule that surrounds them and expose them to digestive fluids. At this point, the bubble jets of the microrobots activate and the microbots start to swarm. The jets are not steerable. The technique is rather a shotgun approach: not all microbots will affect the target area, but many will be. When they do, they stick to the surface and begin to release their load of drugs.

"These micromotors can penetrate the mucus of the digestive tract and stay there for a long time, which improves drug delivery," says Gao. "But because they're made of magnesium, they're biocompatible and biodegradable."

Animal model tests show that microbots are working as expected, but Gao and Wang have announced plans to continue to advance research.

"We have demonstrated the concept that you can reach the diseased area and activate the microbots," Gao said. "The next step is to evaluate their therapeutic effect."

Gao also said that he would like to develop variants of microbots that can run in other parts of the body and with different types of propulsion systems.

Wang says that his goal is to improve the interaction of his PACT system with microbots. The infrared laser light it uses has difficulty reaching the deepest parts of the body, but it should be possible to develop a system that can penetrate further.

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The article describing research on microbots, entitled "A microrobotic system guided by photoacoustic tomography for targeted navigation in the intestines in vivo, "appears in the July 24 issue of Robotic science. Zhiguang Wu, Li Lei, Yiran Yang (MS-18), Yang Li and So-Yoon Yang of Caltech; and Peng Hu from Washington University in St. Louis. Funding for the research was provided by the Bioengineering Center Donna and Benjamin M. Rosen from the National Institutes of Health and Caltech.