3D-printed Microfluidic Control Systems

Abstract

Microfluidic devices are tools for manipulating fluids in microchannels to achieve a variety of functions, for instance, sample mixing, analytes testing and detection, dispensing, etc. These functions provided by microfluidic devices can be applied to different fields such as biology and medicine. Although microfluidic devices have revolutionized the research and development in drug delivery, oncology studies, cell culture and so on, fluids in the current devices are still not well automatically controlled. The devices are required to be either manipulated with complicated and time-consuming pipetting processes or connected with external control elements which make the whole system even larger (compared to the conventional devices or instruments lacking microfluidic technologies). Therefore, the integration of control systems into microfluidic devices is essential for improving their functionality, efficacy, and effectiveness. 3D printing is a new method for fabricating microfluidic devices and some of the advantages provided by 3D printing may not exist in the conventional approach to microfluidic device manufacturing. Well-trained personnel is not required to conduct the fabrication and the manufacturing time is shortened dramatically, from ~24 hours (soft lithography) to ~ 2 hours (3D printing). Here we demonstrate one of the most important components in a microfluidic control system, which is a 3D-printable microvalve that is transparent, built with a biocompatible resin, and has a simple architecture that can be easily scaled up into large arrays.1 The open-at-rest valve design is derived from Quake's PDMS valve design. We used a stereolithographic (SL) 3D printer to print a thin (25 or 10 μm-thick) membrane (1200 or 500 μm-diam.) that is pneumatically pressed (∼3–6 psi) over a bowl-shaped seat to close the valve. We used poly(ethylene glycol diacrylate) (MW = 258) (PEG-DA-258) as the resin because it yields transparent cytocompatible prints. Although the flexibility of PEG-DA-258 is inferior to that of other microvalve fabrication materials such as PDMS, the valve benefits from the bowl design and the membrane's high restoring force since it does not need a negative pressure to re-open. We also 3D-printed a micropump by combining three Quake-style valves in series. The micropump only requires positive pressure for its operation and profits from the fast return to the valves' open states. Moreover, we printed a 64-valve array constructed with 500 μm-diam. valves to demonstrate the reliability and scalability of the valves. Overall, we demonstrate the 3D-printing of compact microvalves and micropumps using a process that precludes the need for specialized, time-consuming labor. In this thesis, the control system device development process and the related experimental characterizations and setups are introduced, including the membrane (in the 3D printed Quake-style valve) thickness testing with resin study, membrane deflection simulation, 3D printer setup and optimization, design flow and device performance examination. Future work is placed in the last part of the thesis to suggest some potential work that can be done for improving the printing quality and functionality of the device.