Inspired by the old classic movie "Fantastic Voyage" and the relatively recent movie "Inner Space", many scientist and engineers have investigated and developed medical microswimmers that possibly navigate inside human body for the purpose of drug delivery, bio-sensing, imaging, micro surgery, etc. in the hard-to-reach spots. So far, several methods for microswimmers have been developed including magnetic actuation, harness of bacteria, use of biological chemical/biological fuels, etc. However, these methods have many drawbacks including high bulkiness, high cost and incompatibility with human body. In addition, all the above methods were never or rarely integrated with feedback control or tracing systems to maneuver the microswimmer in a three-dimensional space. This National Robotics Initiative (NRI) award supports fundamental research on manufacturing three-dimensionally maneuverable, biodegradable, untethered, micro swimming drones, studying/developing feedback control algorithms to control their three-dimensional trajectory, and evaluating them in biological environments. The proposed micro drone is propelled by acoustically excited micro bubbles such that its driving system can be integrated with the current clinical ultrasound system with minimal amendment. The proposed drone has tremendous impact with societal benefits on various potential medical applications: local treatments of tumors, removal of fatty deposits on blood vessel walls, break or removal of blood clots, kidney stones, liver stones, gouts, burn cleaning and wound debriding, attack and removal of parasites, removal and break of tar in lungs, drug delivery and controlled release, etc. This research project will also have significant impact on education by (i) re-engineering coursework for both undergraduates and graduates in inter/multi-disciplinary areas; (ii) having graduates and undergraduates involved in research especially from the underrepresented groups; and (iii) demonstrating results from this project in K-12 schools and in public websites and hosting a robotics workshop for underrepresented high school students. Finally, the completion of experimental setups in this research will improve infrastructure for training in science and engineering at University of Pittsburgh.
The 3-D micro swimming drone will be microfabricated from biodegradable materials. The drone has gaseous bubbles being oscillated by externally applied ultrasound waves. The waves with focused or unfocused excitation allows individual drones to maneuver in a 3-D space. A dynamic inversion-based feedback controller and a state observer will control the frequency and amplitude of the exciting US waves to force the drone to follow/track a user-defined 3-D path. The developed drone integrated with actuation and control units will be tested under hydrodynamic conditions similar to living organs to explore possible practical applications. In parallel, the underlying physics of 3-D manufacturing, bubble/fluid dynamics, ultrasound beamforming method, and a Lyapunov stability based feedback controller-estimator configuration will be investigated. In addition, stability and convergence guarantees in control will be provided. The fabrication and assembly technique of 3-D structures can be readily applied to many fields whose applications otherwise remain on 2-D structures. Novel beamforming technologies developed for US actuating/imaging of micro object can be adapted for high quality ultrasound imaging for broader, general applications. Advances in understanding and new findings of nonlinear (bubble) cavity oscillation and associated fluid dynamics will help develop the best imaging strategy for microbubbles inside microvasculature structures. In addition, the Lyapunov stability-based nonlinear control design method with a state estimator can be applied to control other robots (and other nonlinear systems with zero dynamics) where only partial information is available. The research results will be disseminated through academic/industrial meetings and publications and integrated with multi-/inter-disciplinary education and public outreach programs.
