Micromotors deliver drugs to treat ulcers

System uses gastric acid for fuel, while rapidly neutralising it, and release their cargo precisely at the desired pH.

Tiny micromotors that speed independently through the stomach have been developed to treat stomach diseases.

The micromotors use gastric acid for fuel, while rapidly neutralising it, and release their cargo precisely at the desired pH. The technique is based on proton-driven micromotors with a pH-dependent polymer coating that can be loaded with drugs.

Adminstering oral pH-sensitive pharmaceuticals, including some antibiotics, to treat stomach diseases can be difficult owing to the gastric acid in the stomach. If a drug needs to be activated in the stomach, for instance to treat ulcers or a bacterial infection, it is usually combined with proton pump inhibitors to block production of acid. When used over long periods, these can cause side effects, including headaches, diarrhoea, fatigue, and in severe cases anxiety or muscle disease.

A team led by Liangfang Zhang and Joseph Wang at the University of California at San Diego has developed drug-delivering micromotors that neutralise gastric acid and produce no side effects.

To make the motors, 20µm magnesium spheres are coated with a nanolayer of gold and then a pH-sensitive polymer into which the drug is embedded. Because the spheres lie on a glass support during the coating process, a small spot on the magnesium core remains uncoated. At this spot, a reaction occurs, consuming protons and forming magnesium ions and releasing tiny bubbles of hydrogen gas. The bubbles propel the motors. This motion results in mixing of the liquid. This causes the reaction to proceed rapidly. Less than 20 minutes after administering the motors, the stomach environment reaches a neutral pH value. The polymer dissolves and releases the payload. The propulsion increases penetration of the microtransporter into the gastric mucosa, which increases the amount of time that the drug is retained in the stomach. 

Wang said: “We hope to pursue clinical testing toward improved therapy of stomach ulcer and infection and explore commercialisation of this exciting nanomachine technology.”