Programming magnetic ordering for smart micromachines

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Smart mechanical systems have greatly extended the reach of human beings in sensing, interacting with, and manipulating objects in the microscopic world. In particular, micromachines can expand our capabilities to access small confined and enclosed spaces, and can be employed for monitoring, diagnosis and treatment of diseases. However, developing micromachines for bioanalysis, which requires the smart integration of power sources, multimodal locomotion, dynamic maneuverability and biosensing functions, remain a formidable challenge. In nature, living organisms including magnetotatic bacteria have leveraged ordered structures to develop smart and adaptive behaviors. Moreover, advanced materials have been endowed with highly anisotropic mechanical strength and extraordinary functions by creating ordered micro- and nanostructures in the material composition. Along these lines, the present PhD dissertation focuses on systematic investigation of smart micromachines with magnetic structural order, which are fabricated by two major approaches, including magnetic field-assisted self-assembly and photolithography, and microfluidics-directed compartmentalisation assembly of magnetic building blocks. Based on the above approaches, the first investigation focuses on aquatic micromachines with ordered magnetic nanochains. Multiphase and dynamic maneuverability of micromachines are unlocked, which can bypass the physical constraints of diminishing gravity, dominating surface tension and fluidic drag at the microscale. The 2D planar design of micromachine structures, taking advantage of a Euler’s disk-inspired magnetic steering mechanism, enables the ultralight aquatic micromachines with high motility and large-area maneuverability. The next study investigates a microfluidics-directed assembly of magnetic micro-compartments to build micromachines. The approach is shown to tailor the magnetic coupling between the magnetic building blocks, which endows micromachines with 3D-trackable and differentiable motion. Following this study, a unique set of stray magnetic field fingerprints have been revealed by the inter-compartment magnetic coupling. By hiearachically arranging the magnetic compartments using microfluidic emulsion assembly, a library of encoded magnetic micromachines are generated and shown to be readily decodable by a compact giant magnetoresistance sensor, underlying an streamlined kinetic bioassay platform. In summary, the series of studies presented in this thesis uncover the physics behind a couple of key functionalities, such as multimodal motility, large-area maneuverability, response tunability, and decodability for smart mobile micromachines. The outcomes of this PhD research project, including fundamental robotic control and proof-of-concept demonstration should inspire future development of micromachines for real-world in-vitro and in-vivo bioanalytical applications.
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