Using an algorithm developed by Drexel University researchers, new bacteria-powered microrobots spot obstacles and adjust course when needed. Like boats carried by a current, the microbots can be pushed in any direction by electric fields.

Serratia marcescens bacteria have a natural negative charge, and can therefore be manipulated with an electric field. The bacteria's flagella reduce friction while helping the robot move in a fluid environment.

The bacteria is applied to a substrate, a photosensitive material called SU-8. The bacteria’s whip-like flageella keep the robot suspended in the fluid environment while also providing a small bit of forward propulsion.

Two perpendicular electric fields turn the fluid into an electrified grid. Since the bacteria are negatively charged, the Drexel team can manipulate the robots simply by adjusting the strength of the current.

“We have shown that we can manually direct the robots or give it a set of coordinates to get it from point A to point B, but our goal in this research is to enable the microrobots to navigate a course with random impediments blocking its way,” said MinJun Kim, PhD, a professor in the College of Engineering and director of Drexel’s Biological Actuation, Sensing & Transport (BAST) Lab.

A control algorithm enables the tiny robots to effectively use the shape of the electric field the bots are riding as a way to detect and avoid obstacles. The team discovered how the electric field changed when encountering insulator objects: The electric field was distorted near the corners of the obstacle.

The researchers used the field deformation as input data for their steering algorithm. When the robot senses a change in the pattern of the field, the algorithm automatically adjusts its path of to dodge the obstacle.

In addition to the electric field information, the algorithm also uses image-tracking from a microscope-mounted camera to locate the initial starting point of the robot and its ultimate destination.

The next step for Kim’s lab is to develop a system consisting of multiple bacteria-powered microrobots that is able to perform manipulation of multiple live cells in vitro.