With only a single input, tiny motors switch their propulsion mechanism to change direction

Microorganisms can switch between following a positive or negative chemical concentration gradient to help them move toward a proper chemical environment. Engineers are adapting this bioinspired capability, called switchable chemotaxis, for improving micro/nanomotors in applications such as precision drug delivery. Feng et al. developed a micromotor that seamlessly switches between two propulsion mechanisms to change directionality based on a single chemical stimulus.

Under a magnetic field, their device moves depending on the chemical fuel concentration in their current location in relation to a specific equilibrium concentration. To move away from a drop in the concentration, the micromotor would use ionic diffusion to propel itself, by decomposing the surrounding chemicals in its pot-shaped microstructure. On the other hand, when there is a hike in the local concentration, microbubbles would be ejected from the pot-shaped structure of the micromotor, creating a recoil and causing it to swim away.

By switching back and forth between these two processes, the micromotor can turn itself around when it senses a change in its surrounding fuel concentration.

“It is similar to a salmon, which swims into the sea when it is young, and then returns to the lake where it was born to lay eggs when it grows up,” said author Jianguo Guan.

Once the design is further reduced in size, the authors anticipate the micromotor to have potential in a number of biomedical applications. In particular, it can be used to transport drugs in a dynamic environment to help maintain a certain concentration range.

Source: “Self-adaptive enzyme-powered micromotors with switchable propulsion mechanism and motion directionality,” by Youzeng Feng, Yue Yuan, Jieshuo Wan, Chenglin Yang, Xiaomeng Hao, Zhixue Gao, Ming Luo, and Jianguo Guan, Applied Physics Reviews (2021). The article can be accessed at https://doi.org/10.1063/5.0029060 .