For the first time, tiny artificial motors have voyaged through the body of a living animal, successfully delivering a cargo of nanoparticles directly into the stomach wall. Although it will still be many years before we see microscopic machines scurrying around our own bodies and carrying out various medical tasks, the brains behind the current study see this as a significant step towards this ultimate goal.
There has been a lot of interest in the development of micromachines for medicine in recent years as their wide range of potential uses has become apparent. Scientists envisage that one day, tiny synthetic robots could be used to deliver drugs to specific areas of the body to treat various medical conditions, repair damaged tissues such as blood vessels, or even manipulate individual cells.
Progress has already been made in developing such devices, but they had only ever been tested out on cells in a dish, meaning no one knew how they would fare when actually released inside the body. Now, a group of scientists from the University of California, Berkeley, have made progress in the field by testing out tiny man-made motors inside mice, and they have reported their findings in the journal ACS Nano.
For the study, the researchers designed a type of microscopic motor that effectively becomes a torpedo in acidic solutions, propelling itself and whatever cargo it’s loaded with through the environment without the need for additional fuel. To do this, they coated polymer tubes, just 20 micrometers long and 5 micrometers wide, with zinc. When placed in harsh acidic environments, the zinc reacts to generate bubbles of hydrogen which are then forced out of one end of the tube, propelling the tiny motor through the acid.
According to the researchers, these motors are ideal for use inside living organisms because they don’t rely on chemical fuels such as hydrogen peroxide, which some previous self-propelled motors have, and they self-destruct without leaving behind any residual toxic compounds. Furthermore, several of their features suggest that they could potentially be an ideal candidate for a novel gastric drug delivery system, such as their unique acid-powered propulsion and autonomous release of cargo.
To find out whether this could indeed be the case, the researchers tested out their micromotors on whole organisms for the first time. They loaded the motors with a test cargo of gold nanoparticles and fed them to mice, alongside a group of control mice fed only the gold nanoparticles. Sure enough, the motors could propel themselves fast enough through the stomach acid to lodge in the mucus lining and deliver the payload. Although the control mice also retained gold nanoparticles in their stomach linings, the mice fed the motors possessed three times as many, suggesting they are superior to simple passive diffusion.
Although the team readily admits that much more work is needed to evaluate the performance of these motors, the study represents an important step in the progression of the micromotors field.