Patterned solvent delivery and etching for the fabrication of plastic microfluidic devices

A very simple method for micropatteming flat plastic substrates that can be used to build microfluidic devices is demonstrated. Patterned poly(dimethylsiloxane) elastomer is used as a template to control the flow path of an etching solvent through a channel design to be reproduced on the plastic substrate. The etching solvent was a acetone/ethanol mixture for poly(methyl methacrylate) substrates or a dimethylformamide/acetone mixture for polystyrene. The method is extremely fast in that duplicate plastic substrates can be patterned in just a few minutes each. We identified conditions that lead to smooth channel surfaces and characterized the rate of etching under these conditions. We determined that, for sufficiently short etching times (shallow channel depths), the etch rate is independent of the linear flow rate. This is very important since it means that the etch depth is approximately constant even in complex channel geometries where there will be a wide range of etchant flow rates at different positions in the pattern to be reproduced. We also demonstrate that the method can be used to produce channels with different depths on the same substrate as well as channels that intersect to form a continuous fluid junction. The method provides a nice alternative to existing methods to rapidly fabricate microfluidic devices in rigid plastics without the need for specialized equipment.