On the way to more targeted treatment: Researchers have developed sophisticated fibers that could one day transport therapeutic microparticles against the bloodstream to blockages in vessels or to tumors. Like a chain of microscopic buckets, special particles migrate to their destination along magnetic stepping stones on a polymer fiber. Nature provided the inspiration for the concept: The microtubules of the cells were the inspiration for this promising technology, say the scientists.
Precision and power are required! Various research groups around the world are currently developing particle and micro-robot systems that are intended to deliver powerful drugs as precisely as possible to the places in the body where they are needed. However, one problem is often that the free-swimming tiny creatures have to contend with the complex flow of liquids in the human body.
“Therefore, the particles often scatter. But what you really want to achieve is that the greatest concentration of the therapeutic agent is in one place and it doesn’t spread anywhere else, because that could lead to health threats,” says Arnold Mathijssen of the University of Pennsylvania in Philadelphia. So far, catheters and microneedles have been used to enable application that is as accurate as possible. But these structures cannot be slimmed down at will. Because if they fall below a certain size, they no longer transport microscopically small objects effectively. This is why even the most filigree catheters and microneedles have not been able to reach finer blood vessels in the body.
Bio-inspired transport system
In order to find solutions to the previous problems of the precise application of active ingredients, Mathijssen and his colleagues drew inspiration from biology. “There is a wonderful solution in the cells: microtubules, which are part of the cytoskeleton, use molecular propulsion systems to transport loads to different locations in the cell,” says Mathjissen. This transport system also copes with flow fluctuations similar to those we find in blood vessels and elsewhere in the body. So we set out to develop a system that can act as a similar transport mechanism using nanotechnology,” says Mathjissen.
As the scientists report, they succeeded in developing an artificial version of the microtubules. These are thin fibers whose basic material consists of elastic polymers. With a width of just 80 micrometers, these artificial microtubules are narrow enough to slide through narrow blood vessels, the researchers explain. The functional units are magnetic nickel plates that are integrated into the fibers at certain intervals like stepping stones. By applying a rotating magnetic field around the artificial microtubules, these nickel stepping stones become magnets. This allows them to set metallic micro-robots in forward motion. “We place the microtubules in a rotating magnetic field, like an MRI machine. If you rotate the field slowly, the particles move,” explains Mathijssen.
Micro highways for therapeutic particles
To explore the potential of the concept, the researchers performed experiments testing the performance of the transport mechanism in blood vessel-like networks. It was shown that the microparticles could migrate along the artificial microtubule fiber even with liquid flows that correspond to the dynamics of blood flow. By fine-tuning the magnetic field, the scientists were able to ensure that the particles reached exactly the intended location, even in complex vascular networks.
So far, the results are a “proof of concept”: The researchers say that further development work is now necessary to bring their concept into a form that can be used in practice. For example, the toxic nickel in the magnetic stepping stones must be replaced with unproblematic materials – iron oxide is an option. The team is convinced that the system could then develop into an interesting tool for medicine: the targeted delivery of medication and the removal of blood vessel deposits are obvious possible applications. “We believe that these ‘micro-highways for microrobots’ can offer an alternative solution to free-swimming microrobots and other current technologies, bringing robust biomedical microtransport much closer to reality,” concludes Mathijssen.
Source: University of Pennsylvania, professional article: Nature Machine Intelligence, doi: 10.1038/s42256-022-00510-7