A Novel Fabrication Technique for Liquid-Tight Microchannels by Combination of a Paraffin Polymer and a Photo-Curable Silicone Elastomer

A novel abrasive water jet machining technique for rapid fabrication of three-dimensional microfluidic components

Microfluidic lab-on-a-chip devices are usually fabricated using replica molding, with poly(dimethylsiloxane) (PDMS) casting on a mold. Most common techniques used to fabricate microfluidic molds, such as photolithography and soft lithography, require costly facilities such as a cleanroom, and complicated steps, especially for the fabrication of three-dimensional (3D) features. For example, an often-desired 3D microchannel feature consists of intersecting channels with depth variations. This type of 3D flow focusing geometry has applications in flow cytometry and droplet generation. Various manufacturing techniques have recently been developed for the rapid fabrication of such 3D microfluidic features. In this paper, we describe a new method of mold fabrication that utilizes water jet cutting technology to fabricate free-standing structures on mild steel sheets to make a mold for PDMS casting. As a proof-of-concept, we use this fabrication technique to make a PDMS chip that has a 3D flow focusing junction, an inlet for the sample fluid, two inlets for the sheath fluid, and an outlet. The flow focusing junction is patterned into the PDMS slab with an abrupt, nearly stepwise change to the depth of the microchannel junction. We use confocal microscopy to visualize the 3D flow focusing of a sample flow using this geometry, and we also use the same geometry to generate water-in-oil droplets. This alternative approach to create microfluidic molds is versatile and may find utility in reducing the cost and complexity involved in fabricating 3D features in microfluidic devices.

Electrowetting on Dielectric (EWOD) Device with Dimple Structures for Highly Accurate Droplet Manipulation

Digital microfluidics based on electrowetting on dielectric (EWOD) devices has potential as a fundamental technology for the accurate preparation of dangerous reagents, the high-speed dispensing of rapidly deteriorating reagents, and the fine adjustment of expensive reagents, such as the preparation of for positron emission tomography (PET). To allow single substrate type EWODs to be practically used in an automatic operation system, we developed a dimple structure as a key technique for a highly accurate droplet manipulation method. The three-dimensional shape of the dimple structure is embossed onto a disposable thin sheet. In this study, we confirmed that the dimple structure can suppress unintended droplet motion caused by unidentified factors. In addition, the stability of the droplets on the dimple structures was evaluated using a sliding experiment. On a flat substrate, the success rate of a droplet motion was lower than 70.8%, but on the dimple structure, the droplets were able to be moved along the dimple structures correctly without unintended motion caused by several environmental conditions. These results indicated that the dimple structure increased the controllability of the droplets. Hence, the dimple structure will contribute to the practical application of digital microfluidics based on single substrate type EWODs.