Search for: All records

Maneuverable microswimmers/microdrones that navigate in hard-to-reach spaces inside human bodies hold a great potential for various biomedical applications. Acoustically actuated microswimmers have already demonstrated feasibility. However, for eventual translation of this technology, a robust 3-D tracking strategy for the microswimmer is particularly required. This paper presents our lab-designed 3-D ultrasound tracking system for real-time tracking of an acoustically actuated 3-D swimming microdrone. The ultrasound tracking system utilizing two ultrasound probes, a step motor and a host controller, was built to track the 3-D arbitrary motion of the microdrone in real-time. The performance of tracking was evaluated in the benchtop experiments by comparing the reconstructed trajectories with synchronized camera recordings. The ultrasound tracking system showed high reliability, with an average error of less than 0.3 mm across six different trials when compared to camera tracking. The results demonstrated the capability of our lab-designed 3-D ultrasound tracking system in accurately tracking the undetermined motion of the acoustic actuated 3-D swimming microdrone in real-time. The developed tracking system holds promise as a potential approach for biomedical applications and could pave the way for future clinical translation of the microswimmer technology.

 

Mobile microrobots that maneuver in liquid environments and navigate inside the human body have drawn a great interest due to their possibility for medical uses serving as an in vivo cargo. For this system, the effective self-propelling method, which should be powered wirelessly and controllable in 3-D space, is of paramount importance. This article describes a bubble-powered swimming microdrone that can navigate in 3-D space in a controlled manner. To enable 3-D propulsion with steering capability, air bubbles of three lengths are trapped in microtubes that are embedded and three-dimensionally aligned inside the drone body using two-photon polymerization. These bubbles can generate on-demand 3-D propulsion through microstreaming when they are selectively excited at their individual resonance frequencies that depend on the bubble sizes. In order to equip the drone with highly stable maneuverability, a non-uniform mass distribution of the drone body is carefully designed to spontaneously restore the drone to the upright position from disturbances. A mathematical model of the restoration mechanism is developed to predict the restoration behavior showing a good agreement with the experimental data. The present swimming microdrone potentially lends itself to a robust 3-D maneuverable microscale mobile cargo navigating in vitro and in vivo for biomedical applications. 

Remotely activated drug release strategy with controllable dosage is the key factor of various targeting drug delivery methods as minimal invasive treatment. This article describes mass transport in liquid in microscale with a controllability of releasing amount, which is wirelessly excited by an external acoustic excitation. A liquid droplet (releasing agent, or drug in application) is trapped in the middle of a one-end open microtube which has a ratchet-structure on its inner wall. The droplet is trapped in the tube and neighbored by two gaseous air bubbles on both sides. In the presence of acoustic wave, the air bubbles oscillate and resonate. The air bubble near the tube opening segregates the liquid droplet into smaller ones and transport them on the ratchet-surface wall of the microtube. This mass transport occurs in both directions at similar rates: from the surrounding fluid to the trapped droplet and vice versa. As a result, the overall mass of droplet remains similar. Meanwhile, the other bubble positioned back in the tube sealing side enhances mixing between incoming mass from the surrounding and existing mass in the droplet. This mass transport is significant only when the inner wall of the tube has rachets. The exchanging mass between the surrounding and droplet is monotonically proportional to the excitation period, showing high controllability of mass transport. This mass transport phenomenon possibly provides a new mechanism of in vivo, on-demand, dose controllable drug delivery. 

Wirelessly powered and controllable microscale propulsion in 3-D space is of critical importance to micro swimming drones serving as an active and maneuverable in vivo cargo for medical uses. This aritcle describes a 3-D micro swimming drone navigating in 3-D space, propelled by unidirectional microstreaming flow from acoutsically oscillating bubbles. 3-D propulsion is enabled by multiple bubbles with different lengths embedded in different orientations inside the drone body. Each bubble generats propulsion by applying acoustic field at its resonance frequency. Therefore, 3-D propulsion in any direction is achievable by resonating bubbles individually or jointly. The drone with such a complex design was fabricated by a two-photon polymerization 3-D printer. For stable maneuverability, a non-uniform mass distribution of the drone is designed to restore the drone to the designated posture under any disturbances. The restoration mechanism is formulated by a mathematical model, predicting the restoring time and shows an excellent agreemnt with the experimental results. This 3-D micro swimning drone proves its robustness as a manueverable microrobot navigating along programmble path in a 3-D space through selective and joint actuation of microbubbles. 

Objective: The purpose of this paper is to demonstrate the ultrasound tracking strategy for the acoustically actuated bubble-based microswimmer. Methods: The ultrasound tracking performance is evaluated by comparing the tracking results with the camera tracking. A benchtop experiment is conducted to capture the motion of two types of microswimmers by synchronized ultrasound and camera systems. A laboratory developed tracking algorithm is utilized to estimate the trajectory for both tracking methods. Results: The trajectory reconstructed from ultrasound tracking method compares well with the conventional camera tracking, exhibiting a high accuracy and robustness for three different types of moving trajectories. Conclusion: Ultrasound tracking is an accurate and reliable approach to track the motion of the acoustically actuated microswimmers. Significance: Ultrasound imaging is a promising candidate for noninvasively tracking the motion of microswimmers inside body in biomedical applications and may further promote the real-time control strategy for the microswimmers.