2024-02-14 19:03:51
Dr. Gilles Soulez and his postdoctoral fellow Ning Li
Credit: CHUM
The idea of injecting microscopic robots into the bloodstream to heal the human body is not new. It’s not science fiction either.
Guided using an external magnetic field, miniature and biocompatible robots, made of magnetizable iron oxide nanoparticles, can theoretically deliver a drug in a very targeted manner.
Until now, a technical obstacle persisted: the force of gravity of these microrobots exceeds that of the magnetic force, which limits their guidance when the tumor is located higher than the injection site.
Although the magnetic field of an MRI machine is high, the magnetic gradients, used for microrobots navigation and to produce images, are weaker.
“To solve this problem, we designed an algorithm that determines in which position the patient’s body should be in the MRI machine to take advantage of gravity and combine it with the magnetic navigation force,” explains the Dr Gilles Soulezdirector of the Department of Radiology, Radiation Oncology and Nuclear Medicine at the University of Montreal and researcher at the CHUM Research Center.
“This combined effect facilitates the movement of microrobots towards the arterial branches which will nourish the tumor,” he says. By varying the direction of the magnetic field, we can guide them precisely to the sites to be treated and thus preserve healthy cells.”
Towards more precision
Published in the journal Science Robotics, this proof of concept could modify interventional radiology approaches used to treat liver cancers.
The most common of these, hepatocellular carcinoma, is responsible for 700,000 deaths per year worldwide and is often treated today by transarterial chemoembolization.
Requiring highly qualified personnel, this invasive treatment consists of administering chemotherapy directly into the artery feeding the liver tumor and blocking the blood supply using microcatheters guided by X-rays.
“Our magnetic resonance navigation approach could be done using an implantable catheter like those used in chemotherapy,” says Dr. Soulez. The other advantage is that MRI allows tumors to be visualized better than X-rays.”
For this study, Dr. Soulez’s team collaborated with those of Sylvain Martel (Polytechnique Montréal) and Urs O. Häfeli (University of British Columbia). The study’s first author, Ning Li, is a postdoctoral fellow in Dr. Soulez’s lab.
Thanks to the development of an injector for microrobots compatible with MRI, scientists were able to assemble “particle trains”, aggregates of magnetizable microrobots, on demand. Equipped with greater magnetic force, they are more easily controllable and identifiable on the images provided by the MRI machine.
The team can thus ensure not only that the train is going in the right direction, but also that the dose of medication is appropriate. Because, ultimately, each microrobot will carry a portion of the treatment to be administered. Knowing their number is therefore essential for radiologists.
A good sense of direction
“We carried out tests on 12 pigs in order to get as close as possible to the anatomical conditions of humans. This turned out to be conclusive: the microrobots preferably navigated in the branches of the hepatic artery that were targeted by the algorithm and reached their destination,” mentions Dr. Soulez.
His team ensured that the location of the tumor in different parts of the liver did not influence the effectiveness of such an approach.
“Thanks to an anatomical atlas of human livers, we were able to simulate the control of microrobots on 19 patients treated by transarterial chemoembolization,” he emphasizes. They had a total of around thirty tumors placed in different locations on their liver. In more than 95% of cases, the location of the tumor was compatible with the navigation algorithm to reach the tumor target.”
Despite this scientific advance, the clinical application of this technology is not for tomorrow.
“We must first optimize, using artificial intelligence, the real-time navigation of the microrobots by detecting their location in the liver and also possible blockages in the branches of the hepatic artery nourishing the tumor,” specifies Dr. Soulez.
Scientists will also have to model blood flow, the patient’s position and the direction of the magnetic field using software simulating the flow of fluids in the vessels. This will make it possible to evaluate the impact of these parameters on the transport of microrobots to the target tumor and thus improve the precision of the approach.
According to the Canadian Cancer Society, 4,700 Canadians will be diagnosed with liver or intrahepatic bile duct cancer in 2023.
About the study
L’article «Human-scale navigation of magnetic microrobots in hepatic arteries”, by Ning Li and colleagues, was published online on February 14, 2024 in the journal Science Robotics.
Funding for the study was provided by the Natural Sciences and Engineering Research Council of Canada, the Canadian Institutes of Health Research, the Fonds de recherche du Québec – Santé, the Fondation de l’Association des radiologists du Quebec, the National Natural Science Foundation of China, the Shanghai High-end Foreign Expert Project and the Shanghai Rising-Star Program.
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