Biomimetic Individual and Group Behaviors of Bubble-Thrusted Tubular Micro Sonobots: Unveiling the Mechanism Behind Phenomena

To overcome the propulsion difficulties in low Reynolds number environment, natural species have developed their exclusive swimming strategies after 1000 years of evolution. Inspired by those fascinating creatures, diverse artificial microrobots are proposed to achieve distinctive biomimetic motions. However, the lack of cognition for the propulsion mechanism hinders the exploration of the multimode biomimicking for the microrobots, especially at high-speed locomotion. Herein, biomimetic behaviors of the micro sonobot featured with multiple-layer tubular constructions and trapped microbubbles serving as powerful microengines are reported. The observed speed achieves tens of millimeters per second. Different from previously reported bubble-loaded microrobots, it is observed that primary Bjerknes forces originating from the nonhomogeneous acoustic field make a great contribution to orientation. Along with the streaming propulsion and secondary Bjerknes forces, distinctive biomimetic behaviors including individual locomotion and group aggregation are emerged and theoretically analyzed. The multimode biomimetic motion of micro sonobots offers marvelous potentials in building multifunctional micro/nanosystems for nanosurgery, lab-on-a-chip biosystems, chemical and biological engineering, environmental detoxification, etc.