Nanorobots are machines whose components are on the scale of nanometers (one millionth of a millimeter), and which can be designed in such a way that they can move autonomously in certain environments, be they artificial or natural. Although they are still in the research and development phase, hugely significant progress is being made to turn nanorobots into reality in medical practice. They have a whole host of applications: ranging from the identification and location of tumor cells, the release of drugs in specific parts of the body, to tissue engineering and cellular assistance in inflammatory responses. Among the various, most promising nanorobot systems are those that are self-propelled by catalytic enzymes. However, understanding the collective behavior of these nanorobots is crucial when it comes to progressing towards clinical practice.

In a new study published in the journal Science Robotics, the Radiochemistry and Nuclear Imaging research group at CIC biomaGUNE led by Jordi Llop, together with the Smart Nano Bio Devices group at the Institute for Bioengineering of Catalonia (IBEC) led by ICREA research professor Samuel Sánchez, the Autonomous University of Barcelona (UAB) and the Università degli studi di Roma Tor Vergata, have been able to observe in vivo the collective behavior of a large number of nanorobots designed at the IBEC to move autonomously inside the body through radioactive isotope labelling. "The fact that we have been able to see how the nanorobots move together, as in a swarm, and to follow them inside a living organism, is highly significant, since millions of them are needed to treat specific disorders, such as tumor alterations," said Samuel Sánchez, principal researcher at IBEC. "We have demonstrated, for the first time, that nanorobots can be monitored in vivo using positron emission tomography (PET), a highly sensitive, non-invasive technique currently used in the clinical setting," explained Jordi Llop, principal researcher at CIC biomaGUNE's radiochemistry and nuclear imaging laboratory.

To this end, the researchers first conducted in vitro experiments by monitoring the nanorobots through optical microscopy and positron emission tomography (PET). Both techniques made it possible to observe how the nanorobots blended with the fluids and were able to migrate, collectively, following complex paths. The nanorobots were then administered intravenously to mice and finally inserted via intravesical means into the bladders of these animals. The nanorobots had a built-in enzyme –urease– capable of using urea in the urine as fuel, which is why they were able to move easily in this medium.