A simple design concept for check valves has been adopted for microfluidic devices that consist mostly of (1) deformable fluorocarbon polymer membranes sandwiched between (2) borosilicate float glass wafers into which channels, valve seats, and holes have been etched. The first microfluidic devices in which these check valves are intended to be used are micro-capillary electrophoresis (microCE) devices undergoing development for use on Mars in detecting compounds indicative of life. In this application, it will be necessary to store some liquid samples in reservoirs in the devices for subsequent laboratory analysis, and check valves are needed to prevent cross-contamination of the samples. The simple check-valve design concept is also applicable to other microfluidic devices and to fluidic devices in general.
A typical sequence for fabricating a microfluidic device for the original intended microCE application includes the following steps:
- Channels and valve seats are patterned in the two glass wafers between which the deformable membrane is to be sandwiched. (Altogether, there are three glass wafers, but the third wafer is irrelevant to the innovation described here.)
- Holes are drilled through the wafers in predetermined locations for flow paths.
- The deformable membrane is fabricated.
- Holes are punched in the membrane at locations matching those of holes, valve seats, and flow-channel orifices in the upper and lower glass plates. However, holes are not punched at locations where check valves are required.
- At each check-valve location on the membrane, the check-valve flap is formed by use of an approximately semicircular punch. No membrane material is removed.
The ideal cut for forming a check-valve flap is an arc somewhat greater than a semicircle but less than a full circle. The resistance to flow through the check valve can be reduced by increasing the arc length of the punch. It is worth emphasizing that implementation of this concept entails nothing more than the use of additional punches for forming the flaps in the fabrication process.
This work was done by Peter A. Willis, Harold F. Greer, and J. Anthony Smith of Caltech for NASA’s Jet Propulsion Laboratory. For more information, download the Technical Support Package (free white paper) at www.techbriefs.com/tsp under the Mechanics/Machinery category. NPO-45933
This Brief includes a Technical Support Package (TSP).

Simple Check Valves for Microfluidic Devices
(reference NPO-45933) is currently available for download from the TSP library.
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