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Micro Motor Drug Delivery

8/31/17     Researchers at the University of California San Diego have created micromotors to treat bacterial infections in the stomach. These micro sized vehicles (half the width of a human hair) swim rapidly through the stomach to release antibiotics at a desired pH. This micromotor-enabled delivery approach is a promising new method for treating stomach and gastrointestinal tract diseases with acid-sensitive drugs.

When people take orally administered drugs such as antibiotics and protein-based pharmaceuticals, gastric acid in the stomach can wreck havoc with them. Because of this, drugs used to treat bacterial infections, ulcers and other diseases in the stomach are normally taken with additional substances, called proton pump inhibitors, to suppress gastric acid production. The problem arises when taken over longer periods or in high doses, proton pump inhibitors can cause adverse side effects including headaches, diarrhea and fatigue. In more serious cases, they can cause anxiety or depression. To conquer this, the micromotors have a built-in mechanism to neutralize gastric acid and effectively deliver their drug payloads in the stomach, without the use of proton pump inhibitors.

Each micromotor consists of a spherical magnesium core coated with a protective layer of titanium dioxide, followed by a layer of the antibiotic clarithromycin, and an outer layer of a positively-charged polymer called chitosan that enables the motors to stick to the stomach wall. This binding is enhanced by the propulsion of the micromotors, which is fueled by the stomach’s own acid. The magnesium cores react with gastric acid, generating a stream of hydrogen microbubbles that propel the motors around inside the stomach. This reaction temporarily reduces the amount of acid in the stomach, increasing the pH level enough to allow the micromotors to release the drug and perform treatment. The normal stomach pH is restored within 24 hours.

Clinical trials on mice with Helicobacter pylori infections were done. The micromotors, loaded with clarithromycin, were administered orally once a day for five consecutive days. Afterwards, researchers evaluated the bacterial count in each mouse stomach and found that treatment with the micromotors was slightly more effective than when the same dose of antibiotic was given in combination with proton pump inhibitors.

So what happens to these micromotors after they deliver their drug? Since they are made of mostly biodegradable materials, the magnesium cores and polymer layers are dissolved by gastric acid without producing harmful residues.