Hsi-Wen Tung

Noncontact manipulation using a transversely magnetized rolling robot

A type of magnetic, wireless microrobot has been designed for non-contact manipulation of micro-objects in liquids. The agent, named the RodBot, has typical dimensions of 300 μm × 60 μm × 50 μm. The RodBot is transversely magnetized and rolls around its long axis on a surface in a rotating external magnetic field. In liquid environments, the RodBot generates a rising flow in front of it and a vortex above its body. The flow and vortex are efficient for picking-up and trapping micro-objects of sizes ranging from microns to one millimeter. In viscous solutions, a RodBot can transport objects many times its own size and weight.

Polymer-Based Wireless Resonant Magnetic Microrobots

This paper presents a new generation of wireless resonant magnetic microactuator (WRMMA) type microrobot, named PolyMite. A polymer is used as a spring material in the design of the PolyMite. Compared with the previous generation of such devices, the use of a polymer, i.e., SU-8, as a spring material enables the design of a stable spring system without a significant increase in stiffness. A speed of over 20 mm/s (40 body lengths per second) was measured when the PolyMite was driven in air. Micromanipulation abilities of the PolyMites in wet environments have also been demonstrated. The agents were capable of transporting microobjects such as light polystyrene beads and heavier glass beads in water. The large output force, remote actuation, and biocompatible outer surface (SU-8 and gold) make the PolyMite an exciting candidate for biomedical applications.

Generating mobile fluidic traps for selective three-dimensional transport of microobjects

We demonstrate noncontact transport of microscale objects in liquid environments using untethered, magnetic microrobots. The flow and vortices generated by the rotating microrobot are efficient for selective and gentle trapping, stable transport, and targeted delivery of microscale cargo. The motion of the microrobots can be precisely controlled even at very low frequencies using an advanced magnetic control signal. The design and control methodology presented here can be followed to develop microrobots utilizing the generated fluid flows and performing a variety of biomedical manipulation tasks.

Cooperative manipulation and transport of microobjects using multiple helical microcarriers

Manipulation and transport of microscale objects in 3D with high spatiotemporal resolution require precise control over the applied forces. We report a strategy that uses specially engineered microbars having engagement points and multiple helical microcarriers that can apply reversible loads onto these holders. The helical microcarriers are actuated by externally generated, low strength magnetic fields. By optimizing the design of helical structures for precise manipulation, we fabricated microcarriers that swim with little wobbling even at low rotating frequencies. The cooperation of microcarriers generates higher propulsive forces while application of forces at multiple locations results in motion control with multiple degrees of freedom (DOF). The microbar loaded with multiple microcarriers can be employed as a single mobile device for the realization of higher order manipulation tasks.

Polymer-based Wireless Resonant Magnetic microrobots

We present a class of Wireless Resonant Magnetic Microactuator (WRMMA) that integrates a polymer spring/body structure with electroplated ferromagnetic masses. The new devices, which we call PolyMites as they are derived from our previous MagMites, are simpler, faster and cheaper to fabricate than the MagMite. Like their predecessor, they are capable of moving on planar surfaces in dry and wet environments. Their improved biocompatibility also extends their potential for biological applications. PolyMites are 500 μm in diameter and 55 μm in height. In air they have attained a speed of 13 mm/s, approximately 26 body lengths per second. PolyMites are capable of micromanipulation on a surface, which is demonstrated by pushing and releasing micro-objects such as polystyrene beads in water.

RodBot: A rolling microrobot for micromanipulation

We introduce the modelling and control of a rolling microrobot. The microrobot is capable of manipulating micro-objects through the use of a magnetic visual control system. This system consists of a rod-shaped microrobot, a magnetic actuation system and a visual control system. Motion of the rolling microrobot on a supporting surface is induced by a rotating magnetic field. As the robot is submerged in a liquid this motion creates a rising flow in front, a sinking flow behind, and a vortex above the robot, thus enabling non-contact transportation of micro-objects. Besides this fluid-vortex approach, the microrobot is also able to manipulate micro-objects via a pushing strategy. We present the design and modelling of the 50×60×300 μm micro-agent, the visual control system, and an experimental analysis of the micromanipulation and control methods.

Non-Contact Manipulation for Automated Protein Crystal Harvesting Using a Rolling Microrobot

Abstract In this work, a visual control system for magnetically-driven, automated protein crystal harvesting is proposed. The system consists of a rod-shaped microrobot, a magnetic actuation system and a visual control system. The rolling motion of the microrobot on a surface is induced by a rotating magnetic field. As the robot is submerged in a low Reynolds number liquid this motion creates a vortex above the robot which enables the non-contact transportation of protein crystals towards an extraction point. We present the micro-agent, the actuation system and the visual control system to achieve this automated procedure.

Microrobots for Active Object Manipulation

Active manipulation of objects that are smaller than 1 mm in size finds its application in tasks such as assembly and pick-and-placement. Here, we present the design of a family of microrobots capable of object manipulation in a fluidic environment. The microrobots are fabricated from polymer (SU-8) with internal soft-magnetic posts (CoNi) that align to an external magnetic field and have a maximum dimension of \(50 \times 200 \times 600\,\upmu \mathrm{m}\). Actuation of the device can be enforced with either a rotating or stepping magnetic field and corresponds to the method of object manipulation. In particular, a rotating magnetic field enables a fluidic-based noncontact manipulation technique, while a stepping magnetic field enables a contact manipulation technique. The capabilities of these designs are analysed and demonstrated with respect to the generated motion and the manipulation of objects.

Non-contact manipulation for automated protein crystal harvesting using a rolling microrobot

In this work, a magnetic visual control system for automated protein crystal harvesting is proposed. The system consists of a rod-shaped microrobot, a magnetic actuation system and a visual control system. A rotating magnetic field induces the microrobot to roll on the supporting surface, thereby creating a vortex in a liquid environment. This vortex enables the robot to trap and transport even delicate objects in a non-contact manner to a pre-defined position. We present the micro-agent, the actuation system and the visual control system to achieve this automated procedure.

The RodBot approach to automated crystal harvesting

Automated crystal harvesting is the main gap in the otherwise highly automated process of structure determination by X-ray crystallography. Many approaches have been presented, but few have proceeded beyond the initial, developmental stage. We recently introduced a rod-shaped microrobot1 (the “RodBot”) to assist in the harvesting process. Driven by rotating magnetic fields to roll on a substrate, RodBots induce fluid flows that can lift crystals off the surface and trap them in a cylindrical vortex that travels with the RodBot. The gentle, fluidic force acting on the crystals is in the range of a few nanoNewtons to tens of nanoNewtons, and is spread over the whole surface of the crystal. Forces of this magnitude enable the RodBot to safely manipulate crystals ranging from a few microns to sub-millimeter size. With this technique individual crystals can be selected and brought to a loop positioned in the growth droplet to accept it. Harvesting and flash-cooling is then possible using a simple mechanical linkage. In this way the whole operation of crystal selection, harvesting and flash-cooling is remotely and gently carried out without the operator jitter or application of excessive strain that lead to high late-stage failure rates in crystal harvesting. Guidance is provided by the driving magnetic field, and can involve either manual input with a joystick or fully automated algorithms with feedback control. Because of this option of remote operation, RodBots can also be used for harvesting in hostile, sensitive or inconvenient environments such as anaerobic chambers, controlled humidity environments or cold rooms. The system is compatible with existing crystallization hardware and can be integrated readily into typical laboratory setups or high-throughput platforms.