The potential applications for miniature robots in medicine are vast, ranging from targeted drug delivery to diagnostic tasks and performing surgical procedures. Researchers have already developed and tested a variety of robots across different scales, from nanometers to centimeters, to tackle these tasks. However, existing miniature robots often face limitations. In microsurgeries, for instance, millimeter-scale robots sometimes lack the strength to transport instruments to their destination inside the body. Additionally, many of these robots move by crawling, but they struggle to navigate the mucus-covered surfaces of various body structures, where they frequently slip. Now, scientists have addressed these challenges by combining several millimeter-sized robots, known as TrainBots, into a single unit equipped with enhanced "feet." For the first time, a robotic convoy was used to perform an electric surgical procedure on an obstructed bile duct in an experimental setting.

Developed by scientists at the German Cancer Research Center (DKFZ, Heidelberg, Germany), the TrainBot unit connects multiple individual millimeter-scale robots, each outfitted with improved anti-slip feet. Working together, these units are able to transport endoscopic instruments. The TrainBot system is wireless, controlled by an external rotating magnetic field that synchronizes the movement of the individual units, allowing precise movement in a plane. The control system is designed to operate over distances appropriate for the human body.

In their study, the researchers simulated a surgical procedure using three TrainBot units. One scenario involved bile duct cancer, where a blocked bile duct can cause bile to back up, posing a serious health risk. In these cases, the blockage must be cleared following an endoscopic diagnosis. Typically, a flexible endoscope is inserted through the mouth, passed into the small intestine, and then guided into the bile duct—a maneuver complicated by the sharp angle between the small intestine and bile duct.

To demonstrate the capabilities of their robot convoy, the researchers used organs extracted from a pig. They successfully navigated the robotic system to maneuver an endoscopic instrument to perform electrical tissue ablation in the bile duct. Once the wire electrode arrived at the site, electrical voltage was applied to remove the tissue blockage through a process known as "electrocauterization." The wire electrode used in the experiment measured 25 cm in length and weighed three and a half times more than an individual TrainBot unit. Following the procedure, another TrainBot convoy could deliver a catheter for fluid drainage or administer medication.

"This is where the flexible robot convoy can show its strengths," said Tian Qiu at the DKFZ who led the research team. "After the promising results with the TrainBots in the organ model, we are optimistic that we will be able to develop teams of miniature robots for further tasks in endoscopic surgery." 

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