Researchers propose a new way to transport materials through tiny devices

Scientists in China have trapped bacteria in 3D-printed structures and used them to pump materials along customised paths. Transporting materials in the microscopic world is complex. Conventionally, macroscopic pumps drive motion, but pumps are bulky and not ideal for miniaturisation. Now, Hepeng Zhang and colleagues at Shanghai Jiao Tong University have tackled this problem using native inhabitants of the microscopic world – motile bacteria. Not only are they already present in the media, but their energy conversion efficiency is estimated to be greater than existing man-made micro-motors. Five confined bacteria create a measurable fluid flow, as shown by the colour-coded trajectories on the right

Each structure has many micro-sized cavities. When a bacterium swims into a cavity, its inability to swim backwards leaves it trapped. Microorganism locomotion expert Saverio Spagnolie from the University of Wisconsin in the US describes these cavities as ‘tiny covered garages.’ Scientists have investigated monolayers of beating flagella before, he says, but this new work ‘achieved much greater control of the flow field. An important inverse problem is then: given a desired flow field, how should you design the microbial parking lot?’

Zhang anticipates that microorganisms with higher swimming speeds will allow them to ‘make the generated flow faster and cover a larger area’.