Ferrofluids are a type of smart materials that respond to external magnetic fields. They are biphasic suspensions of magnetic nanoparticles that are coated with a surfactant to prevent their agglomeration in a carrier liquid while limiting the attractive van der Waals forces acting among them. A ferrofluid flows toward the location with the highest magnetic flux density in a field gradient that can be externally controlled. This unique feature can be exploited to enable novel micro-electro-mechanical systems (MEMS). One device area that significantly benefits from this feature is micro actuators. Our research team previously revealed that miniaturized magnetic rotors/sliders could be levitated by applied ferrofluid as it was attracted onto their poles, providing an extremely simple and near friction-less bearing, a key element for achieving high-performance rotary/linear MEMS actuators. We have developed ferrofluid-assisted electromagnetic micro rotary actuators for their application to medical microsystems. One example is the distal optical scanner for endoscopic probes, with which we demonstrated full 360 side-viewing endoscopy via circumferential scanning of laser beam from the probe tip. The ferrofluid-based scanner offers versatile actuation functionality, from arbitrary fine angular stepping to high-speed continuous revolving, allowing for the use of different imaging modalities. Multimodal endoscopic imaging and analysis have been successfully demonstrated using in-vivo models by coupling this technology with optical coherence tomography and Raman spectroscopy. Our related studies have also led to other new MEMS devices, including optical switches and variable inductors as well as micromanufacturing processes such as those for implantable sensors and microneedles. This talk will highlight recent progress from these studies focused onto the ferrofluid as a promising route to realizing novel microsystems.
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