Bong-Kee Lee

Fabrication of a Hydrophilic Poly(dimethylsiloxane) Microporous Structure and Its Application to Portable Microfluidic Pump

In this paper, we present a simple and low-cost fabrication technique of a novel hydrophilic poly(dimethylsiloxane) (PDMS) microporous structure (or microsponge) based on a modified sugar leaching technique. A surfactant, Silwet L-77 enabled us to achieve the wettability conversion of PDMS from hydrophobic to hydrophilic. The wettability changes of PDMS surfaces and microsponges were characterized at various weight percentages of Silwet L-77 and it was found that a hydrophilic PDMS microsponge containing 0.6% of Silwet L-77 rapidly absorbed water droplets. The average porosity of the fabricated PDMS microsponges was measured as 0.55. We have successfully demonstrated the hydrophilic PDMS microsponge as a portable pump for a microfluidic device. The hydrophilic PDMS microsponge was firmly bonded at the inlet of a PDMS microchannel via oxygen plasma treatment. A water-phase sample was easily loaded into the hydrophilic PDMS microsponge and it was released and injected into the microchannel by simply pushing the microsponge.

Development of a modularized and sectioned micromold system for microinjection molding of plastic microstructured surfaces with complex features

In this study, a novel modularized and sectioned micromold system (MSMS) is proposed and developed for the replication of various plastic microstructured surfaces with complex features. The developed MSMS consists of sectioned micromold modules (SMMs), each of which has unique cross-sectional microfeatures on one surface. Together, these form the entire micromold surface. After multiple SMMs are precisely prepared, the final MSMS for a micromolding application can be efficiently constructed in various combinations by assembling several SMMs. In order to exemplify the developed MSMS, three prototypes of microstructured surfaces with complex microscale features were realized. These include (i) a complex microstructured surface, (ii) multi-level microstructured surface and (iii) oblique microstructured surface. The SMMs for each case were precisely manufactured using deep x-ray lithography and nickel electroforming. The MSMS for the replication of the microstructured surfaces was then obtained by assembling the fabricated SMMs. Finally, three kinds of prototypes were replicated with a microinjection molding process utilizing the constructed MSMS, verifying the usefulness of the present micromold system in various applications such as the fabrication of functional surfaces for optical, microfluidic and biomedical microsystems.

A novel monolithic fabrication method for a plastic microfluidic chip with liquid interconnecting ports

In the present study, a novel monolithic fabrication method was developed for the manufacturing of a plastic microfluidic chip with liquid interconnecting ports. As the present method can realize both interconnecting ports and through holes, which are essential components for the delivery of working fluids, in the plastic microfluidic chip, no additional processes and external ports are required. Furthermore, the connection of external silicone tubing can be simply achieved by utilizing an elastic deformation of the used tubing. As one representative example, a microinjection molding of a prototype microfluidic chip having two types of interconnecting ports was demonstrated. After obtaining upper and lower plates by the microinjection molding process utilizing mold cores with pin structures, the thermal bonding of the molded plates was carried out, resulting in the prototype plastic microfluidic chip with interconnecting ports. From microfluidic experiments using the fabricated prototype, it was found that the present method could be quite useful in various microfluidic applications.

Replication of Multi-level Microstructures by Microinjection Molding Using Modularized and Sectioned Micromold System

초록: 본 연구에서는 다단 마이크로 구조물의 대량성형을 위하여, 모듈화된 초소형몰드 시스템(MSMS)을 이용한 초소형 사출성형 공정을 수행하였다. 본 연구에서 적용된 초소형몰드 시스템은 여러 모듈들로 구성되어 있으며, 각 모듈들은 다양한 단면 마이크로 구조물을 가지고 있다. 초소형몰드 시스템의 모듈들은 X-선 리소그래피 공정 및 니켈 전주도금 공정으로 제작되었으며, 다양한 모듈들을 조합 및 결합함으로써 복잡한 형상을 가지는 초소형몰드 시스템을 효과적으로 구현할 수 있다. 이와 같은 초소형몰드 시스템을 적용함으로써, 본 연구에서는 다단 구조물의 표면에 마이크로 삼각 프리즘이 주기적으로 배열되어 있는 다단 마이크로 구조물의 초소형 사출성형 공정을 성공적으로 수행하였다. Abstract: In this study, microinjection molding process using the newly developed micromold system, namely modularized and sectioned micromold system (MSMS), has been carried out for a replication of multi-level microstructures. The present MSMS consisted of several micromold modules, each having cross-sectional microstructures on the top surface. The micromold modules were precisely fabricated by deep X-ray lithography and subsequent nickel electroforming. By assembling the micromold modules, an MSMS having multi-level microstructures, which could be used as a mold system in micromolding processes, was obtained. In this manner, polymeric multi-level microstructures, such as the triangular prism microstructures on a stepped surface, were successfully replicated by the microinjection molding process.

Development of Roll Micromold System via Deep X-ray Lithography and Metal Electroforming Processes

In the present study, a novel roll-shaped micromold system, referred to as a roll micromold system (RMS), is proposed and developed by a deep X-ray lithography process and subsequent electroforming. The developed RMS consists of several cylindrical roll micromold modules (RMMs) including various cross-sectional microstructures along their circumferential surface. RMMs with different microstructures are assembled to construct the RMS, which can be utilized in roll-type micromolding processes for the continuous replication of more complicated microstructured sheets and/or films. As a representative example of an RMS, several copper RMMs having triangular, rectangular, and trapezoidal microstructures on their circumferential surface were precisely fabricated. The RMS was successfully obtained by assembling such RMMs. A rolling experiment utilizing the assembled RMS was also carried out to verify its usefulness.