On Dec. 30 2014, researchers at UCSD published a study detailing the first test of stomach acid-powered micromotors in mice. The testing of these tiny zinc-based micromotors has notable implications for the future of medicine, including a more efficient method of drug delivery and biopsies of tumors.

Professors Joseph Wang and Liangfang Zhang of the Nanoengineering Department at the Jacobs School of Engineering are the first to show that these motors can be safely used in a living organism.

 The researchers previously tested similar models of micromotors and fuel systems that can travel in water, blood and other bodily fluids; however, this is the first time that they tested micromotors in a living organism. 

“We thought it was the logical extension of the work we have done to see if these motors might be able to swim in stomach acid,” Wang said in the Jacobs School of Engineering press release. 

To begin the experiment, the mice were orally administered small drops of solution containing hundreds of micromotors. The zinc-based motors quickly reacted with the stomach acid of each mouse to propel the motors toward its stomach lining. They can self-propel within the mouse’s stomach for up to 10 minutes, at a speed of 60 micrometers per second. The motors then lodge themselves into the “viscous layer” of the stomach. They are subsequently dissolved by the stomach acid and disappear within a number of days, leaving no trace of toxic chemicals.

Researchers believe these motors are promising for gastric drug delivery in particular due to their acid-powered propulsion. The self-propulsion of these motors has led to an improvement in retention of their “payloads,” the substance that is administered into the lining of each mouse’s stomach by the micromotors. 

“It’s the motor that can punch into this viscous layer and stay there,” Zhang said in the press release. “Which is an advantage over more passive delivery systems.” 

 To test the payload retention of these micromotors, researchers used vacuum infiltration to load the micromotors with gold nanometers. They found that the motors delivered 168 nanograms of gold nanoparticles per gram of stomach tissue, as opposed to 53.6 nanograms per gram of stomach tissue delivered through the previous methods.

This study, titled “Artificial Micromotors in the Mouse’s Stomach: A Step toward in Vivo Use of Synthetic Motors,” was published online on Dec. 30, 2014 in American Chemical Society Nano.