29 August 2017

Microbots in the stomach

Micro-motors with antibiotics were used for the first time to treat mice

Grigory Kopiev, N+1

Researchers from the University of California, San Diego have successfully tested micro-motors to protect and release drugs in the stomach. Unlike the previous work, this time the scientists conducted for the first time tests of the delivery of a real drug, and not a fluorescent dye. The effectiveness of the antibiotic proved to be as high as when taking the drug without micro-motors, but at the same time, proton pump inhibitors should not be used in combination with the drug, which have side effects with prolonged use. The study is published in the journal Nature Communications.

Despite the fact that the acidic environment of the stomach is necessary for the normal functioning of digestion, it makes it difficult to take many medications. For medicines that are absorbed in the intestine, special shells are used, but if it is necessary to treat various diseases and ulcers directly in the stomach, such shells are not suitable. To neutralize the acidic environment, proton pump inhibitors are used, which temporarily suspend or reduce the production of gastric juice, however, prolonged use of such inhibitors can cause a number of side effects.

American researchers decided to find a safer method that does not cause serious side effects. To do this, they developed micro–motors - spheres about 20 micrometers in size, the core of which is made of magnesium reacting with acid. Then several other layers are applied to this core: titanium dioxide to protect magnesium, then a layer of medicine mixed with a polymer sensitive to the level of acidity, and a layer of chitosan is applied to it, which allows micromotors to stick to the walls of the stomach. The application process is arranged in such a way that all these layers are applied to the particles lying on the substrate from above, and uncoated magnesium remains from below. When such a micromotor enters the stomach, this magnesium begins to react with acid and release hydrogen. This gas flow creates a reactive force, thanks to which the micromotors move for several minutes. Due to the reaction of acid with magnesium, the pH in the stomach rises to a level at which the drug is no longer neutralized by gastric juice, after which the acid-sensitive polymer releases the antibiotic.

In previous work, researchers have already tested their development on mice, but then they used a fluorescent dye instead of a drug. This time, the scientists conducted a full-fledged testing of the technology, and applied the antibiotic clarithromycin to the micromotors. These micromotors were injected into mice infected with Helicobacter pylori bacteria for five days. The same antibiotic was administered to a control group of mice together with a proton pump inhibitor.

a. Scheme of applying layers to a magnesium particle;
b. The principle of movement of micro-motors in the stomach;
c. Activity of micro-motors for several minutes.

It turned out that the difference between the effectiveness of these methods is not statistically significant. But at the same time, micromotors can be used without causing serious side effects of proton pump inhibitors. During the day, the pH in the stomach returned to normal. Scientists also note that these micromotors are made almost entirely of biodegradable materials that dissolve in the stomach and are excreted without leaving dangerous substances.

Many scientists are developing various miniature devices for medical applications. Chinese scientists have developed micro robots for moving through blood vessels, and another group of scientists has developed micro robots for manipulating single cells.

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