Though it may sound like science fiction or the stuff movies is made off, is now possible for minute “submarines” to speed through the stomach independently. The subs use gastric acid for fuel (while rapidly neutralizing it), and release their cargo at precisely the desired PH. In an article in the journal Angewandte Chemie, scientists introduced this new method to treat stomach diseases with acid-sensitive drugs. The system is based on proton driven micro motors that are coated with a pH-dependent polymer and can be loaded with drugs.

Gastric acid, although useful for protection from pathogens and for digestion, can be destructive to pH-sensitive pharmaceuticals that are administered orally, including some antibiotics and protein-based drugs. Substances intended to work in the intestines can however easily be protected by applying a coating that is resistant to gastric juices. When drugs needs to be activated in the stomach, for example to treat a Helicobacter pylori bacterial infection, or stomach ulcers, the drug is frequently combined with proton pump inhibitors that block acid production. When these are used over extended periods, it can cause various side effects in patients, including depression, fatigue, headaches, diarrhea and, in severe cases, rhabdomyolysis (a muscle disease), or anxiety.

A team led by Joseph Wang and Liangfang Zhang at the University of California, San Diego (La Jolla, USA) has introduced a novel approach with their micro motors. Their approach neutralizes gastric acid, but avoids the normal side effects. At the same time, it also acts as a drug transport mechanism that will only release its cargo when the required pH is reached.

The motors are manufactured by using 20-micrometer magnesium spheres coated with a nano layer of gold. The drug is then embedded into the next pH sensitive polymer layer. A small spot on the magnesium core remains uncoated as the spheres lie on a glass support while being coated. An electrochemical reaction occurs at this spot. The reaction consumes protons, forms magnesium ions and releases tiny bubbles of hydrogen gas. The bubbles are used to push the motors.

This movement results in effectively mixing of the liquid and this in turn causes the reaction to proceed rapidly. The stomach environment reaches a neutral pH value in less than 20 minutes after the motors have been administered. Once the PH is neutral, it triggers the polymer to dissolve and release the payload. The propulsion also increases penetration of the micro transporter into the gastric mucosa. This lengthens the amount of time that the drug is kept in the stomach. The micro motors are safe to use in the stomach and biocompatible. As the normal pH value is re-established within 24 hours, the stomach’s functions are not affected.

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