Improved Benchtop Connectivity to Complex Microfluidic Devices

Intended impact

Microfluidic devices with many fluidic and pneumatic inlets are difficult to connect to benchtop reservoirs and controllers. Many hours can be spent sorting, untangling, and connecting tubing to a single device. If one then finds that the device is not fully functional, the process must begin again on a new device. Fluid flow into microfluidic devices is typically controlled by either syringe pumps (expensive and big) or pressurized vials (cheap but difficult to handle). The designed devices are intended to simplify and speed up the connection of complex microfluidic devices to benchtop fluid reservoirs and pneumatic valve controllers. Ideally, our technologies will make high-throughput microfluidic systems more accessible to laboratories interested in utilizing microfluidics for high-throughput chemical and biological studies.

Objective(s)

Create an improved method to interface a large number of fluidic inlets and pneumatic control lines with microfluidic devices. Reduce the cost and difficulty of controlling many different fluids on a chip.

Goals

• Simplify connectivity of microfluidic devices by constructing manifolds that make all-at-once connections.
• Platforms should be easy to make and maintain, quick to connect, and reusable, i.e. the device can be removed from the manifold, and the same or a new device can be connected again easily. In this way the manifold could be used to rapidly test quality of devices in a production line.
• Implement a system that is simple, compact, inexpensive, and less sensitive to changes in flow rate due to depletion of fluid in the reservoir (due to gravity). Ideally, it would integrate seamlessly with the manifold.

Technical approach

The concept driving our macro-to-micro interface scheme involves a network of vacuum channels that holds a microfluidic device against a rigid manifold such that fluid can be injected through the manifold and into the device without leakage (Fig 1). We fabricated a PMMA manifold with a vacuum annulus milled around each inlet port. Each port is permanently connected at the back of the manifold to fluid reservoirs and pneumatic controllers. 

Fluidic reservoirs holding 5-mL volumes (much more than is used in a microfluidics experiment) are sealed inside a canister half filled with water, which allows the vials to float. Pressurizing the canister pushes fluid out through needles in the lid. Because the reservoirs float, constant flow rate is maintained even when fluid is drained from reservoirs at different rates.

Fig. 1. The manifold concept illustrated with a simplified microfluidic device having a single microchannel with one inlet and one outlet. (a) Diagram of PDMS device over the PMMA manifold. The PDMS has ports punched out for fluidic/pneumatic access to the microchannels. These ports align with inlet and outlet ports drilled through the manifold and connect to reservoirs and controllers via tubing. Engraved vacuum channels surround the inlet ports and provide an isolated region of contact (a "seal") between the PDMS and PMMA, which, when under vacuum, holds the materials together and prevents leakage of inlet fluids into the vacuum annulus. (b) Photograph of the vacuum channel around the inlet port of the PMMA manifold. (c) Diagram showing assembly of 3-layer PDMS microdevice over a vacuum manifold. Fluid flow within the device denoted by the red curves, valve lines are blue, and the vacuum network etched into PMMA manifold are shown in green. A thin PDMS membrane is bonded between the fluid and pneumatic layer. (d) Image showing the device functioning on a PMMA manifold. Fluids enter/exit the device through 25 inlets (4 are multipurpose I/O) and are controlled by 26 pneumatic valves that switch between negative and positive pressure.