This paper describes the fabrication method of an all SU-8 microfluidic device with built-in 3D fine micromesh structures. 3D micromesh structures were seamlessly integrated into the SU-8 sealed microchannel. To eliminate gap formation and filling of the microchannel, the built-in micromeshes in the microchannel were formed by photolithography after bonding the SU-8 top-cover layer and the SU-8 bottom substrate. The lift-off method, using lift-off resist as a sacrificial layer, was utilized to release the all SU-8 microfluidic chips. Monolithic SU-8 structures realize uniform physical and chemical surface properties required in microfluidic devices for practical use. As an application, fragmentation of a water droplet in an organic carrier formed by a two-phase flow was demonstrated.

This paper presents the fabrication of all plastic microfluidic devices with built-in 3-D fine microstructures. The built-in micromeshes in the microchannel were formed by the combination of the multi-angle inclined backside exposure and top side exposure of thick Epon SU-8 photoresist on a glass substrate. The lift off method, using LOR (Lift-off Resist) as a sacrificial layer, was utilized to remove the all SU-8 device from the substrate. The monolithic plastic structures realize uniform physical and chemical properties required in microfluidic devices for practical applications. Fragmentation of a water droplet in organic carrier formed by two phase flow was demonstrated.Fabrication process A 3-D micromesh fabrication method and its application for the in-channel microfilters were already reported [1] [2]. These in-channel microfilters consisted of glass, Cr and SU-8. PDMS (polydimethylsiloxane) was used as a cover plate of the microchannel [1]. In this paper, we realized SU-8 in-channel micromeshes fabricated in a SU-8 microchannel. Fig.! shows the fabrication process of a monolithic SU-8 microchannel with built-in micromeshes. The Cr mask layer was patterned on the glass substrate ( Fig.! (a)). LOR was spin-coated as a sacrificial layer to remove the SU-8 devices from the substrate in later step ( Fig.1 (b)). After spin-coating of the first SU-8 ( Fig.1 (c)), UV was exposed through the photomask from front side to form the bottom floor of the SU-8 device (Fig.! (d)). The thickness of the SU-8 second layer defined the depth of the microchannel (Fig.! (e)). During the soft baking of this SU-8 layer, an SU-8 top-cover which was fabricated by single mask photolithography followed by the lift off process was placed on surface of the SU-8 substrate and bonded ( Fig.! (f)). In order to fabricate the in-channel micromesh, UV was irradiated from top to form the channel structure and from bottom to fabricate micromeshes as shown in Fig.! (g) and (h). The irradiation angle conditions were 450 and -450. After development (Fig.! (i)), since LOR was etched by SU-8 developer, the SU-8 monolithic microfluidc chip was removed from the glass substrate ( Fig.1 (j)). Fig.2 shows a photograph of the all SU-8 device fabricated by this method. The chip size is 2cm x 2cm. In order to visualize built-in micromeshes with SEM, the SU-8 top cover structure was partly removed. Fig.3 shows SEM photomicrograph of the fabricated micromeshes. This indicates the fine in-channel micromesh structures were formed successfully. The channel width and height were 800 ,um and 200 ,um, respectively. The thickness of the bottom floor and the top-cover was about 30 jm and 50 gm. Fig.4 shows the magnified view of the micromesh structure. The diameter of the inclined micropillars was I0 ,um.Fragmentation of a droplet formed by two phase flow Using fabricated all SU-8 microfluidic device, fragrnentation of a water droplet in organic carrier formed by two phase flow was performed (Fig.5). The organic phase of butyl acetate was introduced from the two sid...

This paper presents the fabrication method of the functional 3-D micromesh structures coated with TiO2 particles and biocatalyst for high efficient microreactors. The micromesh structures are useful as a micro reaction space because of their large surface area. The TiO2-fixed SU-8 micromesh structures were formed by coating the SU-8/TiO2 mixture on the surface of the SU-8 micromeshes (Fig.l(a)). The biocatalyst-immobilized micromeshes were also formed by coating the biocatalyst/polymer mixture using UV irradiation through the concentric circle patterns ( Fig. 1(b)).Fixation of TiO2 particles Previously, the fabrication method of 3-D micromesh structures and their microfluidic applications were reported'2. In addition, catalytic functions are promoted to the SU-8 micromeshes. At first, we fabricated the micromesh structures by simply using TiO2-contained SU-8. However, the mesh structures were not obtained because UV light could not pass through the TiO2/SU-8 layer due to its large amount of TiO2 particles, as shown in Fig.2. In this case, TiO2 concentration in SU-8 was 0.67%. In order to achieve high efficient microreactors, TiO2 mixed ratio should be larger the better. Coating method of high TiO2 concentrated SU-8 film on the micromesh structures is requested. Fig.3 shows the fabrication process of the TiO2 particle-fixed micromeshes. After the fabrication of micromeshes ( Fig.3(a)), TiO2-contained SU-8 was spin-coated and baked under low temperature (Fig.3(b)). Without UV exposure, this layer was removed with SU-8 developper. Thin TiO2/SU-8 film was remained on the micromesh surface (Fig.3(c)). Cr layer was etched to remove the residual TiO2/SU-8 film on the glass substrate (Fig.3(d)). Additional UV irradiation and hard-baking were performed to achieve strong adhesion between TiO2/SU-8 film and SU-8 micromeshes (Fig.3(e)). Fig.4 shows SEM micrographs of the fabricated TiO2-fixed micromesh structures. TiO2 was coated only on the surface of micromeshes (Fig.4). The TiO2 mixed ratio was dramatically improved from 0.67% to 5.63%. Immobilization of biocatalyst (enzyme)Considering biocatalyst, high temperature process, such as soft/hard baking of photoresist, should be eliminated to avoid denaturing of enzymes. In this work, enzymes were entrapped in cross-linked photopolymer3 of AWP (Azide-unit Pendant Water-soluble Photopolymer) to immobilize the enzyme on the surface of micromeshes. Fig.5 shows the fabrication process of the enzyme-immobilized micromeshes. We utilized Si/Cr double layered concentric circle patterns to cover each inclined micropillars of the mesh with AWP/Enzyme mixture. First, the Si/Cr concentric patterns were formed ( Fig.5 (a)). After the fabrication of the SU-8 micromeshes (Fig.5 (b)), Cr layer was removed to appear the Si openings (Fig.5 (c)). Then, AWP/Enzyme mixture was spin-coated and UV light was exposed through the Si openings from backside (Fig.5 (d)). Finally, AWP/Enzyme layer was developed using D.I. water. As a result, the enzyme-immobilized micromeshes were obtained (Fig.5(e)). Fig....