2010CHW

吳俊翰 (Chun-Han Wu)

Using Optical Disc Process to Fabricate Microfluidic Chips for Optimization of Uniform Microcapsules Generation

應用光碟製程製作微流體晶片於均一粒徑微膠囊之生成與最佳化之研究

This study presents a microfluidic platform fabricated by optical disc process for microcapsules generation. In the previous reports, the generation of microemulsion adopted microfluidic methods. The microfluidic chips were fabricated by casting process or by adopting CO2 laser engraving on plastic sheet. However, microfluidic chip of PDMS material is too soft, and can easily induce microchannel clogged. Furthermore, the cycle time for manufacturing the microfluidic substrate is over 3~4 hours. As for CO2 laser engraving, the surface of the microfluidic channels was too rough, uneven, deformed and different from the original designs. Besides, the size of the channels was limited by laser machine, and the cycle time for manufacturing the microfluidic substrate is over 10 minutes. The cycle time for both casting process and CO2 laser engraving process is too long. The long cycle time will be a drawback for mass production. Therefore, we present a new process of optical disc to fabricate microchannels of mold insert and adopt the micromolding technique of optical disc to prevent roughness, unevenness, deformation, and clog of microchannels.

This paper is divided into three sections. (1) a design of microfluidic chip; (2) the fabrication of microfluidic mold insert and microfluidic chip; (3) generation of microemulsion droplet. In the design of microfluidic chip section, the depth of microchannels were 50/200 μm respectively and CFD-RC simulation software was adopted to simulate the motion of fluids and emulsions in microfluidic channels. In the fabrication of microfluidic mold insert, we propose a new process of optical disc to manufacture microfluidic mold insert. This new process can prevent the damage on the mirror plate of the mold caused by the traditional process of optical disc. The mold system is composed of a mold insert (stamper) holder and a vacuum system, which is used to join the mold insert with the mold. In this way, the time to change the stamper is drastically decreased. Therefore, it can improve the utility rate of injection molding. In the microfluidic chips of injection molding, we investigate the influence of controlled factors on the quality properties (depth of replication rate, width deviation, birefringence, tilt and surface roughness) of microfluidic chips. Those controlled factors include mold temperature, cylinder temperature, clamping force and injection speed. In the microemulsion generation, we use cross-junction microchannel to form uniform water-in-oil (w/o) emulsions. We prove that the size of these emulsion drops can be easily controlled by adjusting the ratio of disperser phase flow / continue phase flow. These emulsion drops, consisting of 1.5% (w/v) sodium alginate (Na-alginate), are then dripped into a solution containing 20% (w/v) calcium chloride (CaCl2) to create Ca-alginate microcapsules in an efficient manner. We apply Taguchi method to investigate the influence of controlled factors on the size of microemulsion drops which include the flow rate of dispersed phase flow, flow rate ratio, viscosity and surfactant concentration.

The simulation results demonstrate that the bigger the flow rate ratio (continue phase flow /dispense phase flow) is, the smaller the size of microemulsion drops is, and the faster the speed of the generation microemulsion will become. In the fabrication mold insert, we successfully fabricate two layer of microfluidic mold insert, 300 um in thickness and the back side of mold insert is smooth and even. The proposed method will not damage the mirror of the mold.

In the fabrication of microfluidic chips, we adopt DOE method to investigate the influence of controlled factors on the quality properties. The results indicated 2nd clamping force and injection speed have a greater effect on depth replication rate, width deviation and surface roughness. The injection speed and cylinder temperature have a greater effect on birefringence and the mold temperature has a greater effect on vertical deviation. The cycle time of injection molding is 4 seconds. It can be reduced to more than tenfold compared with the traditional ones. In the generation of microemulsion drops, we apply Taguchi method to investigate the influence of controlled factors on the size of microemulsion drops. The results show that the smallest size is 19.58 μm and coefficient of deviation of emulsion drop is 1.95%, the size of emulsion drop is 23.46% lower and the size deviation of drop is 20.73% lower than original design. We demonstrate that the Au nanoparticles and Immunoglobulins are encapsulated into Ca-alginate microcapsules.

In this paper, we successfully devise the new method of optical disc process to fabricate microfluidic chips. The cycle time of microfluidic chips is 4 seconds. It is faster than traditional methods. The proposed microfluidic platform is capable of generating relatively uniform emulsions and has the advantages of active control of the emulsions diameter, a simple and low cost process, and a high throughput, highly efficient and suitable for mass production.

[1] C.-H. Wu, C.-H. Chen, K.-W. Fan, W. Hsu and Y.-C. Lin (June 2006). Design and Fabrication of Polymer Microfluidic Platform by Optical Disc Process, The 3rd Asia-Pacific Conference of Transducers and Micro-Nano Technology, Singapore.

[2] C.-H. Wu, W. Hsu, K.-W. Fan, Y.-L. Lin, and Y.-C. Lin, “Optimization of an optical disk manufacturing process for polymer microfluidic substrates by using the design of experiment methodology.” Journal of Micro/Nanolithography, MEMS, MOEMS 2010, 9, 031011.

[3] C.-H. Wu, C.-H. Chen, K.-W. Fan, W. Hsu and Y.-C. Lin, "Design and fabrication of polymer microfludic substrates using the optical disc process." Sensors and Actuators A: Physical 2007, 139, 310-317.