Ok Chan Jeong

All PDMS pneumatic microfinger with bidirectional motion and its application

This paper describes the experimental results on static and dynamic bending motions of all polydimethylsiloxane (PDMS) pneumatic microfinger. The proposed pneumatic microfinger consists of two PDMS diaphragms with different thicknesses or material properties. The microfinger is fabricated through PDMS molding process and the PDMS-to-PDMS bonding process. The out-of-plane motion of the microfinger is achieved by using the pulling force of the inflated actuator diaphragms while the square wave pneumatic force is supplied to the balloon actuators. In the case of the microfinger with different thickness of two diaphragms, the pressure-dependent dual-bending motion of the microfinger is available. The proposed working principle is confirmed from the steady-state bending angle measurement of the two types of the microfingers with different thicknesses of the bottom PDMS layers. While the pneumatic force is less than 20 kPa, the top diaphragm of Type A microfinger is fully inflated and the microfinger moves downward. Around 20 kPa, the bending direction of the microfinger starts to be changed from downward to upward. The microfinger with two types of PDMS films with different mixing ratio of base polymer and curing agent is also proposed for the improvement of the PDMS-to-PDMS bonding strength, the material property change, and the rapid manufacturing process. The microfinger moves only upward because the top PDMS diaphragm with excess of silicon hydride group is relatively stiffer than the bottom PDMS diaphragm with excess of vinyl group. The dynamic bending motion of the single microfinger and the object-lifting motion of the microfinger array are observed to evaluate their performance. The dynamic bending angle of the microfinger with golden air bone length is about 179deg at 1 Hz, while the square wave input pressure of 250 kPa is supplied to finger structure

Pneumatic micro hand and miniaturized parallel link robot for micro manipulation robot system

This paper reports the pneumatic PDMS micro hand as an end-effector of robot and miniaturized parallel link robot (guide robot) for manipulating a tiny and delicate object. Micro finger structure for the micro hand consists of bonded two films having different stiffness. Balloon structures are designed between the two films. Swelling of the balloon structure by applied pressure generates bending motion of the micro finger. This combination of the micro hand is based on the human beings finger and/or hand. The guide robot has several design specifications such as multi degrees of freedom joint as a human, small size, highly accurate directional control and water/ sterilization proof. Micro manipulation robot system is developed by assembling the micro finger with two or three degree of freedom, the guide robot and VR (virtual reality) interface device. The hybrid motion and the manipulation of a single egg (phi1 mm) of fish and a hair (phi100 mum) in macro world is successfully realized

Fabrication of a peristaltic micro pump with novel cascaded actuators

This paper presents the fabrication of an all-PDMS (polydimethylsiloxane) micro pump with novel cascaded actuators as dynamic valves. The micro pump consists of three pneumatic actuators in series and a micro fluidic channel connecting two fluidic inlet and outlet ports. The three-layer bonded pump structure is fabricated through a typical moulding process of PDMS and a simple heating process for the PDMS-to-PDMS bonding. The total size of the micro pump is 5 mm × 5 mm. The dynamic valve pattern of the single actuator is observed under various operational conditions of the square-wave input signal for the estimation of its volume stroke. The maximum volume stroke of the pneumatic actuator for liquid is about 85% of the volume of the liquid chamber. Three types of liquid-pumping tests are performed for characterization of the micro pump such as backpressure, frequency and viscous liquids. The flow rate of the de-ionized (DI) water is about 73.9 nl min−1 at zero backpressure. As the hydraulic difference between inlet and outlet ports increases, the flow rate gradually decreases. In the case of the frequency responses, the micro pump has the maximum flow rate of the DI water at 2 Hz. The viscosity-dependent flow rate of the working fluids is also observed.

The self-generated peristaltic motion of cascaded pneumatic actuators for micro pumps

This paper presents a new actuation mechanism for the self-generated peristaltic motion of cascaded actuators and its application to micro pumps. The operational method is based on the fluidic circuit of an elastic tube. The elastic tube is modeled as a ladder network consisting of fluidic resistances in series and fluidic capacitances in parallel like multi-stage low-pass filters in an electrical circuit. All segments of the lumped model of the elastic tube have different dynamic characteristics because their time constants are different. In other words, all segments should be deformed sequentially like peristaltic motion. This phenomenon has good potential to cause peristaltic motion of the cascaded actuators in response to the application of single-phase pneumatic signals. Analogues between the electrical and fluidic circuits were applied to a pneumatic micro pump with a micro fluidic channel and three pneumatic actuators connecting a unique micro channel for supplying the compressed air. The polymeric micro pumps were fabricated with soft lithography using only polyimethylsiloxsane. The proposed working principle was verified through simulation of the static deformation of the cascaded actuator diaphragms and the actuator, as well as tested experimentally. The dual operational modes of the proposed device (i.e., rubber-seal valve and peristaltic pumping mode) were also verified and successfully demonstrated in a liquid pumping test of the single and double pumps.

Improved porous silicon microarray based prostate specific antigen immunoassay by optimized surface density of the capture antibody.

Enriching the surface density of immobilized capture antibodies enhances the detection signal of antibody sandwich microarrays. In this study, we improved the detection sensitivity of our previously developed P-Si (porous silicon) antibody microarray by optimizing concentrations of the capturing antibody. We investigated immunoassays using a P-Si microarray at three different capture antibody (PSA - prostate specific antigen) concentrations, analyzing the influence of the antibody density on the assay detection sensitivity. The LOD (limit of detection) for PSA was 2.5 ng mL(-1), 80 pg mL(-1), and 800 fg mL(-1) when arraying the PSA antibody, H117 at the concentration 15 μg mL(-1), 35 μg mL(-1), and 154 μg mL(-1), respectively. We further investigated PSA spiked into human female serum in the range of 800 fg mL(-1) to 500 ng mL(-1). The microarray showed a LOD of 800 fg mL(-1) and a dynamic range of 800 fg mL(-1) to 80 ng mL(-1) in serum spiked samples.

All PDMS pneumatic balloon actuators for bidirectional motion of micro finger

This paper decribes design, fabrication, and characteristics of all PDMS (polydimethylsiloxane) pneumatic balloon actuators for the bidirectional motion of the microfinger. The actuation mechanism of the balloon actuator is based on pressure-dependent swelling and saturation phenomena of two flexible diaphragms with different thicknesses. Two types of microfingers with balloon actuators are fabricated by the simple silicon molding process and pneumatically tested. From the pneumatic test result, it is confirmed that the out-of-plane motion of the microfinger depends on the thickness of the bottom diaphragm of pneumatic balloon actuators. When the applied pressure is 50 kPa, the generated force and the bending angle of type A finger are 0.17 mN and 59/spl deg/, respectively.

A cross-contamination-free SELEX platform for a multi-target selection strategy

Multi-target aptamer selection, known as multiplex systematic evolution of ligands by exponential enrichment (SELEX), is rapidly drawing interest because of its potential to enable high-speed, high-throughput aptamer selection. The parallelization of chemical processes by integrating microfluidic unit operations is a key strategy for developing a multiplex SELEX process. One of the potential problems with on-chip multiplexing chemical processes is cross-contamination. In order to avoid this, we propose a microfluidic network platform that uses pneumatic valves to allow the serial loading and incubation of aptamers with sol-gel entrapped target proteins. After target binding inside the sol-gels, the cross-contamination-free parallel elution of specifically bound aptamers is performed. The platform allows selective binding with five different targets immobilized in sol-gel spots. When eluting bound species, cross-contamination is avoided by sealing the adjacent elution chambers from each other using the pneumatic microvalves. Consequently, we demonstrate specific aptamer binding to the respective protein target and subsequent aptamer elution without any cross-contamination. This proof of concept opens the way to increased automation and microscale parallel processing of the SELEX methodology.

Peristaltic PDMS Pump with Perfect Dynamic Valves for Both Gas and Liquid

This paper presents for the first time experimental results on the peristaltic PDMS pump with perfect dynamic valves for both gas and liquid. Micropump consists of the three peristaltic-type actuators and the micro channel connecting with chambers and the inlet/outlet port. Micropump is fabricated by SU8 mold process and the two-step curing process for the irreversible bonding of PDMS layers. The diameter and the thickness of the actuator diaphragm are 1 mm and 98 μm, respectively. The total size of micro pump is about 5 mm x 5.5 mm. The dynamic gas and liquid valve actions of the single actuator are observed to verify effect of the fluidic mass and viscosity of the working fluid. Perfect peristaltic motions and robust pumping actions of the micro pump are confirmed by the flowrate test of micropump with the air and the ink.

Pneumatic micro finger as endeffecter of robot

This paper reports the pneumatic PDMS micro finger as an endeffector of robot. The micro finger structures consist of two PDMS films with different mixing ratio of the base polymer and curing agent. An applied air pressure mainly contributes to the generation of the pulling force of the top PDMS layer with excess Si-H group and the large deformation of the flexible bottom layer with excess vinyl group. This combination of the micro finger or hand with a rigid PDMS layer and a flexible one is based on the human beings finger or hand. For the proper structural design rule, in this paper, the micro finer structures with different balloon shape are fabricated and tested by a pneumatic force. While the thickness ratio of the bottom layer and the top one is about 3, the bending angle of micro finger is most sensitive to the applied air pressure. During the repeat test for about 5 hours, there are no any noticeable degradation on the bending motion and the structural failure. The hybrid motion of the micro finger with two or three degree of freedom in micro world and the guide robot in macro world is successfully realized by using VR (virtual realty) system

Hydrophilicity of Surfactant-Added Poly(dimethylsiloxane) and Its Applications

This paper discusses the hydrophilicity of surfactant-added poly(dimethylsiloxane) (PDMS) and its applications. The contact angle of water droplets was measured in order to study the short- and long-term stability of the hydrophilicity of PDMS combined with various concentrations of the surfactant Silwet L-77 as a wetting agent. In the short-term, the contact angle was measured every 20 s for 10 min and decreased dramatically with time as the concentration of surfactant was increased from 0 to 1%. In water droplets observed for 800 h, the hydrophobic recovery of the surfactant-added PDMS was very weak and minor. As applications, a micropump and pneumatic actuators were fabricated using only surfactant-added PDMS. The basic properties of surfactant-added PDMS, such as the contact angle of the water head in the microchannel and Youngs modulus, were measured and discussed.