Gilgueng Hwang

Electro-osmotic propulsion of helical nanobelt swimmers

Micro and nanoscale mobile agents capable of self-propulsion in low Reynolds number fluids would have a great technological impact in many fields. Few known mechanisms are able to propel such devices. Here we describe helical nanobelt (HNB) swimmers actuated by an electric field-generated electro-osmotic force. These HNB swimmers are designed with a head and a tail, similar to natural micro-organisms such as bacteria and their flagella. We show that these electro-osmotic propulsion of HNB swimmers achieve speeds (24 body lengths per second), force (1.3 nN), and pressure (375.5 Pa) above those demonstrated by other artificial swimmers based on physical energy conversion. Although nature’s bacteria are still more dynamic, this paper reports that the demonstrated electro-osmotic HNB microswimmers made a big step toward getting closer to their performances. Moreover, an unusual swimming behavior with discontinuous pumping propulsion, similar to jellyfish, was revealed at or above the speculated marginal limit of linear propulsion. These electro-osmosis propelled HNB swimmers might be used as biomedical carriers, wireless manipulators, and as local probes for rheological measurements.

Modeling and Swimming Property Characterizations of Scaled-Up Helical Microswimmers

Micro- and nanorobots capable of controlled propulsion at low Reynolds number are foreseen to change many aspects of medicine by enabling targeted diagnosis and therapy, and minimally invasive surgery. Several kinds of helical swimmers with different heads actuated by a rotating magnetic field have been proposed in prior works. Beyond these proofs of concepts, this paper aims to obtain an optimized design of the helical swimmers adapted to low Reynolds numbers. For this, we designed an experimental setup and scaled-up helical nanobelt swimmers with different head and tail coatings to compare their rotational propulsion characteristics. We found in this paper that the head shape of a helical swimmer does not influence the shape of the rotational propulsion characteristics curve, but it influences the cutoff frequency values. The rotational propulsion characteristics of the helical swimmers with a magnetic head or a magnetic tail are different. The helical swimmers with uniformly coated magnetic tails do not show a cutoff frequency, whereas the ones with a magnetic head exhibit a saturation of frequency.

On-chip Microfluidic Multimodal Swimmer toward 3D Navigation.

Mobile microrobots have a promising future in various applications. These include targeted drug delivery, local measurement, biopsy or microassembly. Studying mobile microrobots inside microfluidics is an essential step towards such applications. But in this environment that was not designed for the robot, integration process and propulsion robustness still pose technological challenges. In this paper, we present a helical microrobot with three different motions, designed to achieve these goals. These motions are rolling, spintop motion and swimming. Through these multiple motions, microrobots are able to selectively integrate a chip through a microfluidic channel. This enables them to perform propulsion characterizations, 3D (Three Dimensional) maneuverability, particle cargo transport manipulation and exit from the chip. The microrobot selective integration inside microfluidics could lead to various in-vitro biologic or in-vivo biomedical applications.

Planar Path Following of 3-D Steering Scaled-Up Helical Microswimmers

Helical microswimmers that are capable of propulsion at low Reynolds numbers have great potential for numerous applications. Several kinds of artificial magnetic-actuated helical microswimmers have been designed by researchers. However, they are primarily open-loop controlled. This paper aims to investigate methods of closed-loop control of a magnetic-actuated helical swimmer at low Reynolds number by using visual feedback. For many in-vitro applications, helical swimmers should pass through a defined path, for example along channels with no prerequisite on the velocity profile along the path. Therefore, the main objective of this paper is to achieve a velocity-independent planar path following task. Since the planar path following is based on 3-D steering control of the helical swimmer, a 3-D pose estimation of a helical swimmer is introduced based on the real-time visual tracking with a stereo vision system. The contribution of this paper is in two parts: The 3-D steering of a helical swimmer is demonstrated by visual servo control; and the path following of a straight line with visual servo control is achieved, then compared with open-loop control. We further expect that with this visual servo control method, the helical swimmers will be able to follow reference paths at the microscale.

Remotely Powered Propulsion of Helical Nanobelts

Reynolds number fluids would have a big technological impact in many fields. Few known mechanisms are able to propel such devices. Here we demonstrate that helical nanobelts can swim in liquid when actuated by an electric field generated by electro-osmotic force. Moreover, we show these devices achieve speeds at or slightly above those demonstrated by natural bacteria. The helical nanobelts were designed and fabricated with a head and tail to mimic natural microorganisms such as bacteria and their flagellae. The electro-osmotic propulsion of helical nanobelts might be used as biomedical carriers, wireless manipulators, and as local probes for rheological measurements.

NIST and IEEE Challenge for MagPieR: The Fastest Mobile Microrobots in the World

Recent advances in micro/nanotechnologies and microelectromechanical systems have enabled micromachined mobile agents. Highly dynamic mobile microrobots are believed to open the gate for various future applications. However, at the submillimeter scale, the adhesion effects dominate physics, especially in the air environment. Although many studies have been performed to avoid or reduce this effect, the sticking phenomena are still one of the biggest challenges in achieving highly dynamic micromobile robots. Subsequently, intrinsic challenges at the given scale (hundreds of micrometers) are the powering technique themselves. Although often designed from active materials, actuation may only be performed by means of various external fields that often require a lot of space around the scene. In this context, the National Institute of Standards and Technology (NIST) and the IEEE initiated an annual state-of-the art microrobotics challenge, boosting the development of novel mobile agents with precise and highly dynamic propulsion mechanisms and controllability. During our first participation in this competition in 2010, the French team Centre National de la Recherche Scientifique (CNRS) proposed a magnetic and piezoelectric mobile microrobot called MagPieR, which dramatically enhanced the propulsion speed to 28 ms for the so-called 2-mm dash task. It literally cut the former record to a quarter. In the meantime, during the 2011 challenge, MagPieR won the mobility challenge thanks to some optimized coil setup and control law. The continuous technical advances in terms of dynamic performance are now shifting, and the focus of the next challenge is more agile-demanding and controllable tasks. Combining different physical effects is a promising key for the future of highly dynamic mobile microsystems and associated applications in micromanipulation, microassembly, or minimally invasive surgery.

Scaled-up helical nanobelt modeling and simulation at low reynolds numbers

Micro and nanorobots can change many aspects of medicine by enabling targeted diagnosis and therapy, and minimal invasive surgery. A helical nanobelt with a magnetic head was proposed as a microrobot driven by rotating magnetic field in prior works. Magnetically coated tails were already shown in some works. However the control of such surface magnetic tails is not clearly realized yet. This paper aims to obtain control parameters for the modeling and simulation of the influence of surface magnets onto the swimming performances. For this, we created scaled-up helical nanobelts and the experimental testbed to get the control parameters and to prepare future closed-loop control.

Note: Resistance spot welding using a microgripper.

Interest in thin-film nanostructures as building blocks for nanoelectronics and nanoelectromechanical systems (NEMS) is increasing. Resistance spot welding (RSW) on a nano or micro scale can play a significant role; similar to that of its macro counterpart for forming connections in device assembly processes. This Note presents a novel micron scale RSW technique using a microgripper as mobile spot welding electrodes to assemble ultra-thin film nanostructures. As an example, assembly of three-dimensional helical nanobelt (HNB) based device was successfully demonstrated using the proposed system. The spot-welding process was fully monitored by the built-in capacitive micro force sensor of the microgripper. Experiments show that RSW, using the microgripper, provides a stable electrical contact with sufficient mechanical strength for the construction of devices such as HNB based devices demonstrated here.

Multi-flagella helical microswimmers for multiscale cargo transport and reversible targeted binding

In-vivo and in-vitro micro-interventions by mobile robotic agents require their precise control. Numerous types of microrobotic swimmers have been developed, assuming different peculiar applications, but often suffering from a lack of mobility and robustness, due to their unique propulsion mode. Hence we present in this paper the multi-flagella helical microswimmers that combine complementary propulsion modes for covering different motions and applications. The numerous possibilities of motions make the robots capable of moving rapidly, on long distances and in hard conditions, as expected in biological organisms. Besides, our microswimmers prove to be able of precise targeted binding, reversible binding, and multi-scale cargo transport moving particles from 5 to 30 μm large. Thus the demonstrated skillful multi-flagella helical microswimmers are very promising for future interventions in microfluidic chips and biological organisms, such as cell manipulation, precise drug delivery, minimally invasive surgery.

Note: Helical nanobelt force sensors

We present the fabrication and characterization of helical nanobelt force sensors. These self-sensing force sensors are based on the giant piezoresistivity of helical nanobelts. The three-dimensional helical nanobelts are self-formed from 27 nm-thick n-type InGaAs/GaAs bilayers using rolled-up techniques, and assembled onto electrodes on a micropipette using nanorobotic manipulations. The helical nanobelt force sensors can be calibrated using a calibrated atomic force microscope cantilever system under scanning electron microscope. Thanks to their giant piezoresistance coefficient (515 × 10(-10) Pa(-1)), low stiffness (0.03125 N/m), large-displacement capability (~10 μm), and good fatigue resistance, they are well suited to function as stand-alone, compact (~20 μm without the plug-in support), light (~5 g including the plug-in support), versatile and large range (~μN) and high resolution (~nN) force sensors.