Self Propelling Motors

This article was about a new way of delivering drugs and/or imaging agents to a specific area of the intestines. Two scientists, Liangfang Zhang and Joseph Wang, led a team at the University of California, San Diego, which created self-propelling motors that can travel through the human digestive track. The motors are 15 um long and 5 um wide hollow cylinders made of gold and poly(3,4ethylenedioxythiophene). The cylinders are filled with magnesium particles and a fluorescent dye; they are then coated in a pH-sensitive methacrylate-based polymer. This coating allows the cylinders to withstand acids in the stomach but begins to dissolve in the neutral pH intestinal fluid. By adjusting the thickness of the coating, researchers can control how far through the digestive system the cylinder travels. The thicker the coating is, the further the cylinder will travel. Once the cylinder reaches its target destination and the coating has dissolved, both ends of the cylinder open up and release the magnesium particles into the intestinal fluid. The magnesium then reacts with water to produce hydrogen bubbles that propel the tubes forward, creating a motor. The propulsion results in a collision with the mucus layer that lines the intestines and traps the tubes into place.

To test this experiment, researchers fed mice suspensions of micro motors. The mice were divided into four groups which were either fed uncoated devices or devices with varying thickness of coating. The various coatings were 0.3, 0.8, and 1.2 um. By measuring the gold content of the animal’s intestines using a mass spectrometer, researchers were able to find that 79% of the uncoated devices stayed in the stomach.  Most of the coated devices reached their target destinations, just as researchers had expected. The researchers hope to further their experiment by filling the devices with drugs and testing how well they will deliver the drug in mice.