Yangkyu Park

Microelectrical Impedance Spectroscopy for the Differentiation between Normal and Cancerous Human Urothelial Cell Lines: Real-Time Electrical Impedance Measurement at an Optimal Frequency.

Purpose. To distinguish between normal (SV-HUC-1) and cancerous (TCCSUP) human urothelial cell lines using microelectrical impedance spectroscopy (μEIS). Materials and Methods. Two types of μEIS devices were designed and used in combination to measure the impedance of SV-HUC-1 and TCCSUP cells flowing through the channels of the devices. The first device (μEIS-OF) was designed to determine the optimal frequency at which the impedance of two cell lines is most distinguishable. The μEIS-OF trapped the flowing cells and measured their impedance at a frequency ranging from 5 kHz to 1 MHz. The second device (μEIS-RT) was designed for real-time impedance measurement of the cells at the optimal frequency. The impedance was measured instantaneously as the cells passed the sensing electrodes of μEIS-RT. Results. The optimal frequency, which maximized the average difference of the amplitude and phase angle between the two cell lines (p < 0.001), was determined to be 119 kHz. The real-time impedance of the cell lines was measured at 119 kHz; the two cell lines differed significantly in terms of amplitude and phase angle (p < 0.001). Conclusion. The μEIS-RT can discriminate SV-HUC-1 and TCCSUP cells by measuring the impedance at the optimal frequency determined by the μEIS-OF.

Anti-Reflux Ureteral Stent with Polymeric Flap Valve Using Three-Dimensional Printing: An In Vitro Study.

PURPOSE This article aims to describe the design of an anti-reflux ureteral stent with a polymeric flap valve and the fabrication methods using three-dimensional (3D) printing. The stent effectively prevents backward flow with a negligible reduction in forward flow. Fabrication of miniaturized valves was easy with high precision and rapid prototyping. MATERIALS AND METHODS The proposed stent comprised a 7F Double-J (DJ) stent and a polymeric flap valve. The valve was made of Tango Plus FLX980 and was fabricated using a 3D printer. Two types of stent were prepared for in vitro tests: DJ stents with (1) an uncoated valve (UCV) stent and (2) a parylene C coated valve (PCV) stent for enhanced biocompatibility. The flow characteristics of each stent were evaluated considering flow direction, parylene coating, and stent side holes, and were compared to the intact DJ stent. RESULTS The forward flow rate for the distal portion of the UCV and PCV stents was 9.8 mL/min and 7.8 mL/min at applied pressure of 15 cm H2O (normal anterograde pressure in patients with stents), respectively. Backward flow rate for the distal portion of the UCV and PCV stents was decreased by 28 times and 8 times at applied pressure of 50 cm H2O (maximum bladder pressure), respectively, compared with the distal portion of the intact DJ stent. Forward flow rates of whole stents were 22.2 mL/min (UCV stent) and 20.0 mL/min (PCV stent) at applied pressure of 15 cm H2O, and backward flow rates of whole UCV and PCV stents were decreased by 8.3 times and 4.0 times at applied pressure of 50 cm H2O, respectively, compared with the intact DJ stent. CONCLUSIONS The anti-reflux ureteral stent was successfully designed and fabricated using a 3D printer. In vitro studies showed that the stent effectively prevented backward flow while minimizing reduction in forward flow.

Ex vivo characterization of age-associated impedance changes of single vascular endothelial cells using micro electrical impedance spectroscopy with a cell trap

We aimed to characterize aging of single vascular endothelial cells, which are indicators of senescence, using micro electrical impedance spectroscopy (μEIS) for the first time. The proposed μEIS was equipped with two barriers under the membrane actuator near the sensing electrodes, increasing its cell-trapping capability and minimizing the interference between the target cell and subsequent cells. The cell-trapping capability in μEIS with barriers was considerably improved (90%) with a capture time of 5 s or less, compared to μEIS without barriers (30%). Cells were extracted from transgenic zebrafish to minimize an initial discrepancy originating from genetic differences. In order to estimate useful parameters, cytoplasm resistance and membrane capacitance were estimated by fitting an electrical equivalent circuit to the data of ex vivo sensor output. The estimated cytoplasm resistance and membrane capacitance in the younger vascular endothelial cells were 20.16 ± 0.79 kΩ and 17.46 ± 0.76 pF, respectively, whereas those in the older cells were 17.81 ± 0.98 kΩ and 20.08 ± 1.38 pF, respectively. Discrimination of each group with different aging showed statistical significance in terms of cytoplasm resistance (p < 0.001) and membrane capacitance (p < 0.001). Considering both of the sensor and cellular level, the optimal frequency was determined as 1 MHz at which the electrical impedance of each group was clearly discriminated (p < 0.001).

Self-Centering Effect of a Thickness-Gradient Dielectric of an Electrowetting Liquid Lens

The experimental verification of the electrical centering effect of a thickness-gradient dielectric in an electrowetting micro liquid lens is presented. This device features an efficient centering scheme and easy fabrication. Two types of liquid lenses with a thickness-gradient and uniform-thickness dielectric layer are fabricated and experimentally compared. Repeatability tests for the off-centering error of the fabricated lenses are carried out for the same tuning range of focal length. The acquired maximum off-centering error for a thickness-gradient dielectric layer is 20 μm (equivalent to a tilt angle of 0.05°), whereas the lens with a uniform-thickness dielectric layer is 162 μm. Off-centering is considerably improved, even compared to the mechanical centering method using a conical geometry (50 μm). Moreover, the thickness-gradient dielectric layer could be easily fabricated using a photoresist reflow process, which reduces the required processing steps, making it suitable for mass production.

Adjustable Tilt Angle of Liquid Microlens With Four Coplanar Electrodes

We present a novel method to adjust the beam tilt angle and tune the axial focus of an electrowetting on dielectric liquid microlens encapsulated by parylene film. The lens system consists of four control electrodes with two immiscible spherical liquid lenses of different refractive indexes encapsulated by a flexible polymer. To tilt the incident beam, the lateral position and curvature of the inner lens were modulated by ac voltage applied to the electrodes. The measured lateral position and curvature of the inner lens allowed us to estimate the position of the focal point. The tunability of the tilt angle was increased by ±2.13° at an applied voltage of

Micro electrical impedance spectroscopy on a needle for ex vivo discrimination between human normal and cancer renal tissues

45.3~V_{\mathrm {rms}}

Lateral positioning of tunable liquid microlens with four coplanar electrodes

when using thin dielectric layers. The resolvable image was 80% and 68% of the aperture diameter for 20 and 50 L&S/mm, respectively, assuming that the critical modulation transfer function value was 50% for quality imaging.

Gimbal-Less Two-Axis Electromagnetic Microscanner with Twist Mechanism

The ex-vivo discrimination between human normal and cancer renal tissues was confirmed using μEoN (micro electrical impedance spectroscopy-on-a-needle) by measuring and comparing the electrical impedances in the frequency domain. To quantify the extent of discrimination between dissimilar tissues and to determine the optimal frequency at which the discrimination capability is at a maximum, discrimination index (DI) was employed for both magnitude and phase. The highest values of DI for the magnitude and phase were 5.15 at 1 MHz and 3.57 at 1 kHz, respectively. The mean magnitude and phase measured at the optimal frequency for normal tissues were 5013.40 ± 94.39 Ω and -68.54 ± 0.72°, respectively; those for cancer tissues were 4165.19 ± 70.32 Ω and -64.10 ± 0.52°, respectively. A statistically significant difference (p< 0.05) between the two tissues was observed at all the investigated frequencies. To extract the electrical properties (resistance and capacitance) of these bio-tissues through curve fitting with experimental results, an equivalent circuit was proposed based on the μEoN structure on the condition that the μEoN was immersed in the bio-tissues. The average and standard deviation of the extracted resistance and capacitance for the normal tissues were 6.22 ± 0.24 kΩ and 280.21 ± 32.25 pF, respectively, and those for the cancer tissues were 5.45 ± 0.22 kΩ and 376.32 ± 34.14 pF, respectively. The electrical impedance was higher in the normal tissues compared with the cancer tissues. The μEoN could clearly discriminate between normal and cancer tissues by comparing the results at the optimal frequency (magnitude and phase) and those of the curve fitting (extracted resistance and capacitance).

Feasibility study of the OCT probe using MEMS optical scanner array for high speed inspection

This paper presents an electro-wetting on dielectric (EWOD) based liquid lens which focal point is tunable axially and laterally as well. The conductive inner liquid for a variable focus is covered by another non-conductive liquid, which is spherically encapsulated by a thin layer of parylene. The lateral position of focal point is controllable using four fan-shaped coplanar electrodes. The tunable liquid microlens shows the maximum lateral movement of 340 μm with a negligible coupling to the other lateral direction.

Two-axis quasistatic gimbal-less microscanner with concentrically tilted stationary comb electrodes

We present an electromagnetically driven microscanner based on a gimbal-less twist mechanism. In contrast to conventional microscanners using a gimbal-less leverage mechanism, our device utilizes a gimbal-less twist mechanism to increase the scan angle in optical applications requiring a large scanning mirror. The proposed gimbal-less scanner with twist mechanism increases the scan angle by 1.55 and 1.97 times for the slow and fast axes, respectively, under the same force; 3.64 and 1.97 times for the slow and fast axes, respectively, under the same maximum stress, compared to the gimbal-less leverage mechanism. The scanner with a 3-mm-diameter mirror and a current path composed of a single-turn coil was fabricated, and it showed the maximum scan angle of 5° (quasi-static) and 22° (resonant) for the slow and fast axes, respectively. The experimentally estimated crosstalk was as small as 0.47% and 0.97% for the fast and slow axes affected by the other axes, respectively, which was determined using a newly employed methodology based on fast Fourier transform.