Swimming microbots mimic bacterial motion for precision tasks

Swimming microbots inspired by bacteria could one day be used to carry out precision tasks such as microscale assembly and targeted drug delivery.

swimming microbots

Swimming micromachines, capable of self-assembling to perform a specific task and then disassembling once that task has been completed, have been the subject of a significant amount of research worldwide.

However, it has so far proven difficult to control individual microbots effectively when they are operating within a large group or swarm, meaning they cannot yet be used for precision tasks such as drug delivery or in microfluidics applications.

To tackle this problem, Dr Tom Montenegro-Johnson, a mathematical biologist at Birmingham University, looked at the way certain bacteria such as E.coli change their shape in order to propel themselves through their environment.

“These bacteria swim by a run-tumble method,” said Montenegro-Johnson. “This means they have a ballistic trajectory for a certain amount of time called a run, where they swim in a straight line, and then they unbundle all of their flagella, and this causes a random re-orientation, and then they swim in a straight line again,” he said.

To recreate this motion strategy, Montenegro-Johnson is developing swimming microbots in the form of flexible filaments made from a shape memory polymer.

Both ends of each filament are coated in platinum. When placed in hydrogen peroxide, the platinum catalyses its reduction into water and oxygen, causing a flow at the surface of the filament.

If the filament is straight, this flow should act as a pump, if it is bent in a U-shape, the filament will translate, or move a certain distance, and if it is bent into an S-shape, it should rotate.

By targeting ultrasound at different points within the fluid, Montenegro-Johnson plans to heat up individual microbots, triggering the shape memory response and causing them to switch between these pre-programmed shapes.

To control the swimmers, Montenegro-Johnson is planning to use a focused ultrasound keyboard developed by Ultrahaptics, a spin out from Bristol University. “They have created something called mid-air touch sensation, which consists of lots of ultrasound emitters that can focus onto an 8mm point in space, which they can then move about 16,000 times a second,” he said.

In this way the microbots should be able to navigate complex environments using a series of straight runs and on-the-spot re-orientations, in the same way as bacteria.