Jeong Byung Chae

A novel drug delivery method by using a microrobot incorporated with an acoustically oscillating bubble

This paper presents an untethered microrobot swimming in human blood vessels through electromagnetic actuation to manipulate bio/micro-objects using an acoustically oscillating bubble attached on the microrobot as a grasping tool. First, for the three-dimensional (3D) propulsion of the microrobot in arbitrary shaped blood vessels, an electromagnetic system consisting of the horizontal and vertical pairs of Helmholtz and Maxwell electric coils is designed and manufactured along with the verification of the magnetic flux density generated from the designed system with theory. Using the developed electromagnetic system, the propulsion of a spherical microrobot (800 μm dia.) made of a cylindrical magnet covered with clay is successfully demonstrated in x-y and x-z plains along with a T-shaped glass channel. Second, an acoustically oscillating bubble induced microstreaming is separately investigated by using a high speed camera integrated with a zoom lens and laser as a light source. When a bubble is acoustically excited by a piezoactuator around its natural frequency, it oscillates and simultaneously generates microstreaming and radiation forces, which can be used to manipulate (pull and push) neighboring objects. Finally, as the concept proof, the manipulation of a fish egg (800 μm dia.) in a microfabricated channel with tandem rectangular hills is experimentally achieved by the microrobot incorporated with an acoustically oscillating bubble.

Investigation on the thickness effect of a hydrophobic layer for operating voltage reduction in EWOD systems

This paper studies the optimum thickness of a hydrophobic layer for operating voltage reduction in electrowetting-on-dielectric (EWOD) systems by investigating the thickness effect on the surface wettability and hysteresis using an atomic force microscopy (AFM). To investigate the surface wettability, the thicknesses of Cytop and Teflon layers coated with different weight percent of Cytop and Teflon solutions are precisely measured by AFM. And the contact angles of D.I. water droplets sitting on the Cytop and Teflon layers with different thicknesses are measured by a microscope from the side. The results show that for Cytop films the contact angles of D.I. water droplets on the Cytop films thicker than 3 nm maintain around 110° on the other hand, the contact angles with the Cytop film thinner than 3 nm suddenly drop and decrease as the film becomes thinner. Teflon films show the similar trend as Cytop films, except the critical thickness (7 nm). The contact angle hysteresis on the different thicknesses of Cytop and Teflon films is separately investigated by the tilting base method. The results show that for the thin hydrophobic films, the contact angle hysteresis is over 10° however, it decreases as the film thickness increases. When the film is thicker than 12 nm, the values of the contact angle hysteresis are approximately halved and saturated. Based on the test results, the optimum hydrophobic film thickness (12 nm) is suggested. Finally, the thickness effect of the hydrophobic film on the operating voltage in EWOD actuation is tested. As expected the operating voltage in thin hydrophobic films is lower than in thick films. For the Cytop film, the saturation voltage in 12 nm is 20 V lower than 500 nm and 40 V lower than 1500 nm, respectively. Similarly, for the Teflon film, the saturation voltage in 12 nm is 20 V lower than 600 nm and 40 V lower than 1600 nm, respectively.

A tunable optical IRIS based on electromagnetic actuation for a high-performance mini/micro camera

This paper presents a tunable iris based on electromagnetic actuation for a tiny high-performance camera in mobile devices such as smart phones and pads. To investigate the effect of a magnetic field on a ferrofluid, the contact angle modification and transportation of a sessile ferrofluid droplet are tested using a neodymium magnet and electric coil. The variation of the contact angle of the ferrofluid droplet is 21.3° for the neodymium magnet and 18.1° for the electric coil based on electromagnetic induction. And the transportation of the ferrofluid droplet is also demonstrated using the neodymium magnet and electric coil. As the concept proof, the pretest of a tunable iris operated by electromagnetic actuation is conducted by using a hollow cylinder cell. In the initial state, the ferrofluid is in the relax state, so the cylinder cell shows the largest aperture (4.06 mm). When an electrical current is applied to an electric coil wound around the outside of the cylinder cell, the ferrofluid initially placed in the hydrophobic sidewall inside the cylinder cell is actuated and pulled to the center. The aperture under the current is modified from 4.06 mm at 0 A to 3.2 mm at 2 A. Finally, the envisioned tunable iris consisted of two connected circular microchannels is realized using a MEMS technology. The iris size is 9×9×2 mm3, and the variation of the aperture diameter is from 1.72 mm at 0 A to 1.09 mm at 2.6 A.

Bubble-induced streaming for micro-object manipulation

A novel micromanipulation method has been developed where alternating current electrowetting-on-dielectric (AC-EWOD)-driven twin bubbles manipulate micro/bio-objects in a microfluidic chip filled with aqueous solution. First, the behavior of a bubble sitting on an EWOD electrode submerged in a water chamber was investigated under different AC-EWOD actuation conditions such as frequencies and voltages. The results show that the bubble oscillation amplitude highly depended on the applied frequency and was proportional to the strength of bubble-induced streaming. To improve the controllability of manipulating objects, twin bubbles-induced streaming patterns in the different distances between the twin bubbles were experimentally studied on patterned EWOD electrodes. To transport bubbles in a microfluidic chip, the arrays of EWOD electrodes were microfabricated and EWOD signals were controlled by a digital I/O board through a custom-made Labview code. The transportation of twin bubbles was successfully demonstrated by sequentially activating the arrays of EWOD electrodes. Finally, as proof of the feasibility of the proposed method, the manipulation of a fish egg by AC-EWOD-driven twin bubbles was experimentally achieved.

Electrowetting-on-dielectric (EWOD) induced flow analysis

This note investigates the principle of alternative current electrowetting-on-dielectric (ac-EWOD) driven micropropulsion. When an air-to-water interface is vertically oscillated by ac-EWOD, two different surface waves and underwater flows are generated depending upon the applied frequency. The effects of the frequency are investigated by flow visualization techniques and confirmed by numerical calculations. The results reveal that at a low frequency (1 Hz), the oscillating flows with quasistatic waves are dominant without generating net momentum, whereas at a high frequency (50 Hz), the quasisteady flows with travelling waves are dominant with the generation of net momentum capable of being used for micropropulsion.