Polymer Embossing Tools for Rapid Prototyping of Plastic Microfluidic Devices

In this work, a new MEMS technology for hot embossing using polydimethylsiloxane (PDMS) tools is developed and characterized. The developed technology will permit low cost, simple, and rapid fabrication of disposable microfluidic biochips and plastic microstructures for numerous BioMEMS applications. For traditional planar systems, a negative photoepoxy (SU-8) or thick positive photoresist (AZ4620) on silicon were used to form micromolds, upon which PDMS was cast. Fabrication time of these PDMS tools was considerably less than that of conventional ones made from nickel or silicon, and remained the same regardless of the feature aspect ratios. The developed PDMS tools were used to rapidly prototype microchannels and microfluidic biochips in polymethylmethacrylate (PMMA) of aspect ratios up to two, with depths ranging from 5 to 250 μm, and features as small as 40 μm in width. The use of a soft PDMS tool material increased cycle time and embossing force, and limited the tool lifetime to approximately 20 cycles. The technique was also extended to fabrication of orthogonal 3-D microfluidic systems using multiple lithography steps. In addition to microchannels of the traditional planar systems, these 3-D systems contained features on the microchannel bottom surface, providing obstructions in the flow field. The orthogonal 3-D PDMS tools were fabricated by casting in a micromold formed on silicon substrates using a combination of SU-8 and AZ4620 photoresists. This approach proved to be a much simpler and faster process that the conventional multi-step nickel electrodeposition method. Overall, the developed technique enables simple and low cost fabrication of planar and orthogonal 3-D microfluidic systems, and is particularly well suited for rapid prototyping applications, where fast processing and low cost are important and the number of samples is relatively low. Combined with a high-resolution mask printing on transparencies, a complete microfluidic device could be fabricated in less than 24 hours.