Rapid fabrication of rounded microchannels via extrusion printing of molds using a thixotropic ink

This paper reports a direct-write strategy that rapidly produces rounded cross-sectional molds for casting of microfluidic channels in polydimethylsiloxane (PDMS). Robotically controlled microextrusion of a thixotropic ink through a micronozzle onto a substrate surface generates user-defined positive relief structures that serve as molds. Printed lateral resolutions of less than 10 μm can be achieved by using a micronozzle with dimensions of a few micrometers and microscopic visual feedback. The cross-sectional geometries of the microchannels can be easily adjusted by regulating parameters such as the printing speed, applied pressure, micronozzle-substrate distance, and number of stacks. As a result of the “liquid rope coiling” effect, this technique provides a straightforward way of producing a serpentine microchannel. To demonstrate the feasibility of extrusion printing, several complex microfluidic structures were cast in PDMS from their printed molds. This strategy provides a simple but flexible approach to on-demand prototyping of microfluidic molds with controllable, rounded cross-sections for microfluidic structures.