Modular pumps as programmable hydraulic batteries for microfluidic devices

Abstract

Simple fl uid pumps have been developed to improve microfl uidic device portability, but they cannot be easily programmed, produce repeatable pumping performance, or generate complex fl ow profi les -key requirements for increasing the functionality of portable microdevices. We present a detachable, paper-based, "hydraulic battery" that can be connected to the outlet of a microfl uidic channel to pump fl uid at varying fl ow rates over time, including step changes, ramping fl ows, and oscillating fl ows.Keywords: Paper Microfl uidics; Capillary Pump; Microfl uidic; Lateral Flow; Microfl uidic Pump; Point of Care. INNOVATIONTh e hydraulic battery demonstrated here is a novel, paper-based pump that uses paper geometry to achieve preprogrammed fl ow rates and durations. Pumps are designed by choosing the dimensions of the resistive neck and absorption region, which control the pumping fl ow rate and volume, respectively. Lamination encapsulates the paper and minimizes the evaporation that plagues other paper microfl uidics, improving pumping reproducibility. Th e pumps are fabricated using a simple, scaleable procedure: here, chromatography paper is laminated and then cut to the desired shape with a laser cutter, although a variety of porous materials can be used. Multiple pumps can be stacked with or without dissolvable delays to create complex fl ow profi les. Using hydraulic batteries, users can generate varying fl ow rate profi les in microfl uidic devices, including both increasing and decreasing step changes, ramping fl ow, and oscillating fl ow. NARRATIVE IntroductionFluid transport in microfl uidic devices is usually controlled by pumps that require external power and cumbersome fl uidic connections, limiting the portability of the system 1 . On-chip pumps exist, but achieving a desired fl ow rate can be an empirical process and the pumps cannot generate complex fl ow behavior [2][3][4][5][6][7] . Capillary pumps have been fabricated via photolithography within microfl uidic devices to pull fl uids through microchannels [8][9][10] , but their integration within the device prevents exchanging or replacing the pumps. To lower the cost and fabrication time of capillary pumps, several groups have used paper connected to the distal end of a microfl uidic channel to pull fl uid [11][12][13][14] . Th ese paper pumps use simple geometric shapes to generate a single fl ow rate but they only work on channels with relatively low fl uidic resistances and are built into the analytical test substrate. Wang et al. demonstrated a clever approach for programming detachable paper-based pumps to pump at progressively slower fl ow rates 15 . However, this strategy cannot be used to create more complex fl ow profi les, such as increasing fl ow rates, oscillating fl ow, or delayed-onset fl ow.Paper devices have been enhanced by improvements such as delays and evaporation barriers, among others. Lamination strategies for paper-based devices include the use of printer toner 16 , tape 17 and lamination with plastic sheets 18,19 . D...

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