Easy-Access Manifold for Fluid Delivery to Microfluidic Devices

MicroPlumbers Microsciences LLC, Bothell, WA 98021

Research in nano biotechnologies often involves the delivery of very small volumes of multiple fluids (liquids and gases) into a microfluidic device at precise flow rates. The most common way to deliver fluid into a device is manually with a syringe or pipette. While this method gets the fluid into the device, it can deleteriously affect the quality of the analysis by delivering imprecise volumes of fluid or introducing contaminants or air bubbles into the fluid channels. Another way to introduce fluids to a device is to use miniature inlet ports that mate with tubing. While increasing the control of introduced fluids, these take time to design, take up valuable space on the device surface, and must be attached to each card individually. All this takes time away from the researcher’s primary interest: conducting research.

MicroPlumbers Microsciences LLC has developed a manifold to aid the precise delivery of fluid into a microfluidic device constructed from a wide variety of materials over a wide range of flow rates. The manifold increases the ease and reliability of fluid introduction by creating a single leak-proof connection between a microfluidic device and up to 6 different fluid sources. Its transparency allows direct viewing of the entire fluidic process while facilitating an automated sequence of fluid introductions into the device. The manifold is easy to use, disassemble and reassemble. It can be cleaned with alcohol, bleach, or lab detergents and sterilized by autoclaving. It can accept devices of various size and thickness. All that is required are simple fluid ports of 1mm diameter (or less) spaced 5 mm apart. To help ensure that the input/output ports line up every time, two indexing holes (or grooves) are recommended in the microfluidic device. These indexing holes provide alignment and location of the clamping force.

With the simple leak-proof connection between the microfluidic device and the manifold, fluids can be delivered at a wide range of flow rates (flow rates ranging from 0.1 to 1,000 μL/min are most common). The only limitation to the flow rates used will be due to the design of the microfluidic device. Leak-proof sealing is achieved by o-rings in the ports of the manifold that are compressed by tightening of thumb screws connecting upper and lower parts of the manifold (Fig. 1). An alternative sealing method is an elastomeric surface layer on the card. As a custom configuration, this can enable surface-mount valves and diaphragms, activated pneumatically by the manifold, to be located anywhere on the card.

Since the o-ring connections and thumb screws allow adjustment of the clamping force, a leak-proof seal can be provided for various combinations of fluid pressures and card materials of different stiffness. Thus, microfluidic devices made from a large variety of materials, such as PDMS, glass, silicon, or plastic, may be used with the manifold. This allows use of the manifold with a variety of microfluidic devices fabricated by different methods, including injection molded plastic, hot embossing, cast elastomers, and plastic film laminates.

Figure 1. Upper and lower parts of a manifold.

The use of the manifold can make the design and use of microfluidic devices much less complicated. The need to add sophisticated input/output ports to the card that can be difficult to build is eliminated. Instead, only simple channel openings on the surface are used for input/output of desired fluids (Fig. 2).

Figure 2. Connecting a microfluidic device to a manifold. Fluid ports of the device are simple round openings at the ends of the channels.

Figures 3 and 4 show an example use of the manifold for supplying fluids in a microfluidic device. It uses all 6 fluid ports for two separate channel networks in a demonstration of mutual diffusion in two fluids that flow at identical flow rates in merging channels. In Fig. 4A, the channels merge in such a way that the two fluids are mixed rapidly. In contrast, in Fig. 4B, the two fluids flow side-by-side in an identical width channel without significant mixing. The portion of the channel filled with each fluid is controlled by adjusting their relative flow rates. The use of a manifold in this experiment demonstrates its capability to easily deliver fluids at controlled flow rates to a microfluidic device.

Figure 3. An example microfluidic device connected to the manifold. The fluids passing through the manifold are clearly visible on the left.

Figure 4. Mixing of fluids in channels that merge in 2 different fashions: A. Channels merge vertically and mix rapidly; B. Channels merge horizontally and fluids flow side by side with little mixing; control of the relative flow rates determines the portion of the channel taken up by each fluid.