Micro Machining of Injection Mold Inserts for Fluidic Channel of Polymeric Biochips

Micro Machining of Injection Mold Inserts for Fluidic Channel of Polymeric Biochips

Abstract

Recently, the polymeric micro-fluidic biochip, often called LOC (lab-on-a-chip), has been focused as a cheap, rapid and simplified method to replace the existing biochemical laboratory works. It becomes possible to form miniaturized lab functionalities on a chip with the development of MEMS technologies. The micro-fluidic chips contain many micro-channels for the flow of sample and reagents, mixing, and detection tasks. Typical substrate materials for the chip are glass and polymers. Typical techniques for micro-fluidic chip fabrication are utilizing various micro pattern forming methods, such as wet-etching, micro-contact printing, and hot-embossing, micro injection molding, LIGA, and micro powder blasting processes, etc. In this study, to establish the basis of the micro pattern fabrication and mass production of polymeric micro-fluidic chips using injection molding process, micro machining method was applied to form micro-channels on the LOC molds. In the research, a series of machining experiments using micro end-mills were performed to determine optimum machining conditions to improve surface roughness and shape accuracy of designed simplified micro-channels. Obtained conditions were used to machine required mold inserts for micro-channels using micro end-mills. Test injection processes using machined molds and COC polymer were performed, and then the results were investigated.

Introduction

Recently, with the development of MEMS (micro electro-mechanical system) technologies, conventional biotechnological analytical processes can be rapidly performed using miniaturized biochips. Typical biochips can be categorized into two groups; micro-array and micro-fluidic chips. The micro-array has an array of miniaturized test sites on a chip. The number of micro-arrays varies from a hundred to a few thousand; and the typical size of the test sites ranges from 10 to 500µm. Because the micro-fluidic chip can perform multiple tasks in a typical biochemical analysis laboratory, such as mixing, reaction, separation, and detection, etc., it is often called as LOC (lab-on-a-chip) or µTAS (micro total analysis system).[1,2] Advantages of the LOC are; (1) required time for analysis is much shorter, (2) very small amount of specimen and reagent are required, (3) low cost, high analysis accuracy, low contamination, and easy to use, etc. Thus, the micro-fluidic chips have been focused as a leading technology in related fields.[3-6] Unlike the micro-array, the micro-fluidic chip contains many micro-channels to connect the unit tasks for consecutive processing steps.[1] The continuous flow of input test samples and reagents through the micro-channels can make the analytical process to be performed on a chip by minimizing sample contamination and processing time. Typical substrate materials for micro-fluidic chip fabrication are glasses (such as fused silica glass, etc.) or polymers (such as PDMS (polydimethyl siloxane), PMMA (polymethyl metacrylate), COC (cyclic olefin copolymer) etc.). The substrates for micro-fluidic chips should be biocompatible since most of they are used for biological analysis. Besides, various material properties such as mechanical strength, porosity, and hydrophobicity, etc., are required for real application. Fabrication procedures of such substrate depend on the used material and complexity of the chip. Typical technique for micro-fluidic chip fabrication is based on the soft lithography, such as wet-etching, micro-contact printing, and hot-embossing, micro injection molding, etc.[2-5] Also, LIGA and micro powder blasting processes are applied to form required micro-channels on the biochips.[7] Several studies were performed to replicate microchips using metal mold masters which were prepared by CNC micro-milling processes. [8-11] In the studies, brass [7] and aluminum masters [9-11] with micro-channels were machined to replicate PMMA and thermosetting resin by hot embossing.

In this study, to establish the basis of the micro pattern fabrication and mass production of polymeric micro-fluidic chips using injection molding process, micro machining method was applied to form micro-channels on the LOC molds. As a first step, simplified micro-channels were designed based on existing research results. Then, a series of machining experiments using micro end-mills were performed to determine optimum machining conditions to improve better surface roughness and shape accuracy. Obtained conditions were used to machine required mold inserts for micro-channels using micro end-mills of 400µm diameter. Finally, test injection processes using machined molds and COC polymer were performed, and the results were investigated. As the results, it can be observed that the required micro-fluidic chips can be obtained using injection molding process.

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