Study: Tiny 'submarines' deliver acid-sensitive drugs to stomach in mice

Stomach acid can sabotage certain drugs that need to work in the stomach, including some antibiotics. Researchers from the University of California, San Diego, have developed tiny motors that interact with stomach acid to move through the stomach and release a preloaded drug at a specific pH level.

The team, led by UCSD’s Liangfang Zhang and Joseph Wang, tested the tiny “submarines” in mouse models. The devices are 20 µm magnesium spheres coated with a very thin layer of gold and a pH-sensitive polymer in which the drug is embedded, according to a statement. The micromotors have a small uncoated spot on their surface, where the magnesium reacts with stomach acid, releasing hydrogen bubbles that propel the devices.

This active movement and neutralization of stomach acid distinguishes the devices from other, passive nanocarriers, said Jinxing Li, first author and a PhD candidate at UCSD.

The propulsion essentially stirs the stomach contents, mixing the micromotors with the acid and speeding up the reaction. It also helps the “submarines” penetrate the stomach’s mucous membrane, which keeps the drug in the stomach for longer. Once the liquid in the stomach reaches a neutral pH, the polymer coating dissolves, releasing the drug.

The “submarines” could be an alternative delivery method for pH-sensitive drugs. Drugs intended to work in the intestines may be coated in an acid-resistant layer to survive the journey through the stomach, but drugs that must act in the stomach are routinely combined with proton pump inhibitors to block acid production. The latter method has some side effects, including headache, fatigue, and in severe cases, anxiety, depression or rhabdomyolysis.

The micromotors safely and quickly neutralized stomach acid while simultaneously delivering drugs, mouse models showed. The microdevices avoided the side effects caused by proton pump inhibitors and the stomach returned to its normal pH within 24 hours.

The team is considering testing the devices in larger animals, Li said. Conditions that could be treated with this method include stomach ulcers and Helicobacter pylori infection, the scientists said. Their findings are published in Angewandte Chemie.