Microswimmers adapt swimming behavior by deforming in response to environmental stimuli

Some microorganisms use spiral-shaped, shape-changing flagella to help them move more smoothly through their surrounding environments, but the direction and velocity of the swimmers is controlled by elements, like magnetic fields, because the organisms' bodies cannot deform. 

This discovery was announced in a July 6 Advanced Science News report.

Researchers Koki Yoshida and Hiroaki Onoe used finite stimulation to identify an important element in acceleration and deceleration of motility: pattern angle used by the spiral swimmers to move. The soft, spiral-shaped flagella has potential medical applications in micro-object transport, micro-fluid manipulation and target drug delivery.

For example, E. coli controls its swimming velocity and direction by deforming its spiral-shaped flagella in response to temperature, chemical and mechanical changes in its environment.

“Functions of autonomous swimming control based on morphology changes are functionally attractive for autonomous microrobots because these swimming control systems are effective and valuable in the sub micrometer scale to the submillimeter scale," the report states.

The microswimmers in this study were composed of hydrogel and magnetic nanoparticles that are excited by magnetic fields and use rotational motion to propel themselves through their environments. The hydrogel component of the microswimmer responds to stimuli and changes size and shape by swelling or shrinking.

This research builds on previous work, which proposed micromachines control their propulsion by changing body geometry. Acceleration and deceleration of microswimmers changes when adjusting the pitch angle and pattern angle, and as the thickness of the stimuli layer increases.

Yoshida and Onoe conclude their study with the following summary:

“We demonstrated the soft spiral-shaped microswimmer for autonomous swimming control by detecting surrounding environments. The dimensionless velocity of the fabricated bilayered spiral swimmer was successfully changed by applying the thermal stimuli. Our bilayered spiral swimmers could be characterized using the ability to encapsulate various functional materials, including other stimuli-responsive hydrogels. Moreover, complex compartmentalization of the spiral swimmer characterized by a laminar flow inside the capillary can also contribute to the optimization of their internal structure and functionality enhancement. The proposed soft spiral-shaped microswimmer can open new avenues for various microscale biochemical applications, such as autonomous soft-robots and soft micro-probes for intricate, miniscule environment.”