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.

This Microfluidic Check Valve is a simplified version of a conventional rubber-flap check valve.
These check valves are simplified microscopic versions of conventional rubber-flap check valves that are parts of numerous industrial and consumer products. These check valves are fabricated, not as separate components, but as integral parts of microfluidic devices. A check valve according to this concept consists of suitably shaped portions of a deformable membrane and the two glass wafers between which the membrane is sandwiched (see figure). The valve flap is formed by making an approximately semicircular cut in the membrane. The flap is centered over a hole in the lower glass wafer, through which hole the liquid in question is intended to flow upward into a wider hole, channel, or reservoir in the upper glass wafer. The radius of the cut exceeds the radius of the hole by an amount large enough to prevent settling of the flap into the hole. As in a conventional rubber-flap check valve, back pressure in the liquid pushes the flap against the valve seat (in this case, the valve seat is the adjacent surface of the lower glass wafer), thereby forming a seal that prevents backflow.

A typical sequence for fabricating a microfluidic device for the original intended microCE application includes the following steps:

  1. 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.)
  2. Holes are drilled through the wafers in predetermined locations for flow paths.
  3. The deformable membrane is fabricated.
  4. 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.
  5. 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

Topics:
Aerodynamics Aircraft structures Drag Fabrication Flaps Forming Glass Manufacturing processes Mechanical Components Mechanics Parts Seals and gaskets Seats and seating Valves
This Brief includes a Technical Support Package (TSP).
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Simple Check Valves for Microfluidic Devices

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NASA Tech Briefs Magazine

This article first appeared in the May, 2010 issue of NASA Tech Briefs Magazine (Vol. 34 No. 5).

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Overview

The document is a Technical Support Package from NASA's Jet Propulsion Laboratory (JPL) detailing the development of simple check valves for microfluidic devices, specifically for use in life-detection studies as part of the Urey instrument in the ESA ExoMars mission. The Urey instrument aims to detect amino acids, nucleobases, and polycyclic aromatic hydrocarbons (PAHs) in dilute aqueous solutions on Mars, with a focus on minimizing sample cross-contamination and efficiently storing samples for further analysis.

The microfluidic devices are constructed from a four-layer stack that includes a deformable membrane sandwiched between etched glass wafers. JPL has established high-yield processing techniques for these devices, particularly utilizing fluorocarbon polymers as the membrane material. The document emphasizes the need for a check valve that allows liquid to flow in one direction while preventing backflow, which is crucial for isolating samples during analysis.

The proposed solution involves a simple check valve design that consists of a semicircular cut in the deformable membrane, creating a flap that covers a hole in the middle glass wafer. This design allows liquid to be pumped from a channel in the bottom glass wafer to a reservoir in the upper glass layer, while the flap closes under pressure to prevent reverse flow. This method is noted for its simplicity, as it adds no extra steps to the existing fabrication process, making it compatible with JPL's established techniques.

The assembly process for the microfluidic device includes several steps: patterning channels and valve seats in the glass wafers, drilling holes for fluid entry and exit, fabricating the deformable membrane, and punching holes in the membrane to match those in the glass wafers. The check valve is created using a semicircular punch, with the remaining material acting as a flap to control fluid flow.

Overall, the document highlights the innovative approach taken by JPL to enhance microfluidic devices for space exploration, ensuring that they are efficient, effective, and capable of meeting the stringent requirements of extraterrestrial sample analysis. The advancements in check valve technology are positioned as a significant contribution to the field of microfluidics and planetary exploration.