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Sometimes doctors insert a shunt in a patient’s body to drain unwanted fluid from a specific organ. For example, to treat hydrocephalus, more commonly known as “water on the brain”, where an abnormal amount of cerebrospinal fluid has accumulated, a thin walled and tiny diameter vinyl plastic tube is inserted from the patient’s brain to another region in the body, usually the stomach, to allow drainage.

Although this procedure has been employed over the last 50 years, there are serious failure modes that can occur over time. Besides being foreign objects in one’s body, shunts are prone to malfunctioning, often caused by blockages due to a build-up of sediment. This calcification not only narrows and hinders liquid flowing through the shunt, but it also affects the shunt’s flexibility. This leads to patients sometimes needing repeated invasive surgeries throughout their lives to replace the shunt.

The surgery not only is risky, especially for the elderly and children, but is prone to side effects such as infection. When the shunt stops draining because it is fully blocked a flexible rotating tool can be employed, something like a micro “roto-rooter” but as you can imagine this procedure is very dangerous and includes the possibility of damaging the inner shunt wall with the rotating tool, or worse, poking a hole in it. Although the obstruction can usually be removed the internal tubing wall is invariably scratched leaving an area likely to suffer another buildup.

Short pulses of infrared light generated by a surgical laser conducted along a light fiber have also been investigated as a method to remove such occlusions but again, this is also an invasive procedure since the fiber has to be threaded along the pipeline.

Just last week, researchers at the University of Essex in Colchester, England, announced a new method to remove these block-ups by grinding them away with tiny magnets controlled by an external magnetic field applied to the patient’s body. Their paper, “A Novel Non-invasive Intervention for Removing Occlusions From Shunts Using an Abrading Magnetic Microswarm”, published in the August 2022 edition of IEEE Transactions on Biomedical Engineering, details this interesting technique.

The team, led by microrobotics expert Dr Ali Hoshiar from Essex’s School of Computer Science and Electronic Engineering, has shown that by manipulating the applied magnetic field in a controlled manner along with the use of specially designed scratchy ferro-magnetic particles, one can create a non-invasive alternative to ridding blockages in plastic shunts. The authors experimentally examined how swarms of these scraping particles can wear away a hard deposit sediment inside the tubing and applied their results to standard models of erosion.

Their prototype device was fabricated to provide a proof of concept with the grinding nanoparticle approximately 45 nm in diameter created from iron chloride. After injecting the magnetic nanoparticles into the shunt using a fine syringe, the magnetic field, generated by a powerful permanent magnet located on the body surface, was set into motion moving the magnetic nanoparticles along the shunt tubing.

The magnetic field captures the abrasive magnetic nanoparticles much like a bar magnet pulls iron filings along its poles. By moving the field back and forth, the particles “hacksaw” the calcification by slightly abrading its surface as they travel and after many oscillations, the shunt is cleared. Since most shunts eventually discharge into the stomach or another region in the body pathway, the nanoparticles at the end of the process can be moved along when the job is completed by using a guiding magnetic field.

The magnetic nanoparticles used have very high biocompatibility and, therefore, should not cause toxicity. To minimize the risk of unintentional damage to the shunt tubing, the experimental observations were compared with simulation models to gauge the indentation depth. Five different abrading models were examined for fit with the results indicating that the Hoeprich theory model was the best option, being limited to approximately 12.1% error.

Throughout the paper the researchers used a moving magnetic field that ranged between 0.1 and 0.3 Tesla and a velocity between 1 to 12 cm/second to form their results. The number of “strokes” with the magnetic swarm of particles was over ten thousand in some cases, but since the movements were small and the abrasion rate high, the entire procedure took 60 minutes to wear away 50 milligrams of calcium carbonate 1.5 mm thick.

Although this system looks promising at this point, one of the challenges listed in the paper deals with the intensity of the magnetic field applied to the patient. In the experiments conducted, the distance between the shunt and the magnetic field was only 2 millimeters. To be fair, in realistic scenarios, where the shunt is placed inside the patient’s body, the distance that must be spanned may be greater than 2 centimeters, an increase by a factor of ten. Somehow to mitigate this drawback, the suggestion was made by the author’s that stronger permanent magnets must be employed.

Gary Hanington is Professor Emeritus of physical science at Great Basin College. He can be reached at gary.hanington@gbcnv.edu.

Here is an old one attributed to Fibonacci: A man bought a pair of rabbits. How many pairs of rabbits can be produced from the original pair in a year if it is assumed every month each pair begets a new pair that can reproduce after two months?

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