Buoyant magnetic milliswimmers reveal design rules for optimizing microswimmer performance

Area of Science:

• Robotics
• Materials Science
• Biotechnology

Background:

• Magnetically-actuated microrobots are promising for micro-scale manipulation.
• Existing microswimmers suffer from polydispersity, hindering performance prediction and optimization.
• Current design parameters like link shape and aspect ratio are difficult to correlate with velocity.

Purpose of the Study:

• To develop a novel experimental platform for building customizable, two-link, buoyant milliswimmers.
• To isolate the effects of design parameters from physical dimension variations.
• To establish ground truth data for understanding milliswimmer performance and developing design guidelines.

Main Methods:

• Utilized two-photon polymerization to fabricate fully customizable two-link, buoyant milliswimmers.
• Engineered integrated flexible linkers enabling underactuated, asymmetric cyclic motion and net translation.
• Systematically varied actuation frequency, aspect ratio, and linker stiffness to study their impact on swimming speed.

Main Results:

• Demonstrated control over swimming direction and repeatability of performance.
• Found that neither first-order nor second-order models accurately capture milliswimmer performance.
• Identified three key approaches to increase swimming speed: tuning actuation frequency, adjusting aspect ratio, and using weaker linker stiffness.
• Observed that spherical two-link swimmers with dissimilar link diameters match cylindrical link performance, unlike those with equal diameters.

Conclusions:

• The developed platform provides unprecedented control for studying microswimmer design.
• Current theoretical models are insufficient for predicting milliswimmer behavior.
• Established practical design guidelines for enhancing microswimmer speed and performance.