Microfluidic devices fabricated via soft lithography have demonstrated compelling applications such as lab-on-a-chip diagnostics, DNA microarrays, and cell-based assays. These technologies could be further developed by directly integrating microfluidics with electronic sensors and curvilinear substrates as well as improved automation for higher throughput. Current additive manufacturing methods, such as stereolithography and multi-jet printing, tend to contaminate substrates with uncured resins or supporting materials during printing. Here, we present a printing methodology based on precisely extruding viscoelastic inks into self-supporting microchannels and chambers without requiring sacrificial materials. We demonstrate that, in the submillimeter regime, the yield strength of the as-extruded silicone ink is sufficient to prevent creep within a certain angular range. Printing toolpaths are specifically designed to realize leakage-free connections between channels and chambers, T-shaped intersections, and overlapping channels. The self-supporting microfluidic structures enable the automatable fabrication of multifunctional devices, including multimaterial mixers, microfluidic-integrated sensors, automation components, and 3D microfluidics.
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We thank X. Ouyang for assisting in taking images during the bending and stretching tests. We thank Z. Zhu for assisting in the setup of microfluidic pump tests. We thank Z. Fuenning and S. H. Park for suggestions and feedback on the manuscript preparation. Funding: Research reported in this publication was sponsored by the Army Research Office, accomplished under Cooperative Agreement Number W911NF1820175 and basic research funding from the U.S. Army Combat Capabilities Development Command Soldier Center. The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Office or the U.S. government. The U.S. government is authorized to reproduce and distribute reprints for government purposes notwithstanding any copyright notation herein. This work was also supported by the National Institute of Biomedical Imaging and Bioengineering of the NIH under Award Number DP2EB020537. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH. Further support came from the MnDRIVE program at the University of Minnesota. Confocal microscope imaging and analysis were performed at the University Imaging Centers at the University of Minnesota. Portions of this work were conducted in the Minnesota Nano Center, which is supported by the NSF through the National Nano Coordinated Infrastructure Network (award number ECCS-1542202).