Microfluidics have been around for some time as convenient and portable diagnostic tools for testing very small volumes of fluid for specific blood chemistry, screening for drugs, and other biochemistry tests. The devices designed for these applications are fast becoming commoditized as more complex “lab-on-a-chip” and smartphone connectivity expand the capabilities of these advanced bioanalytical devices. One of the big questions today centers around how to manufacture these increasingly-complex tools using many of the materials and robust processes currently in use for many single-use diagnostics. Engineers will need to know, or be able to determine, how sensitive their microfluidic device will be to variations in edge quality, channel depth, contact angle, and other specifications to align with an appropriate manufacturing method.
The manufacturing techniques for microfluidic devices vary from mechanical die-cutting and polymer laminates to advanced additive processing, like 3D printing. For the most common devices, especially those that are designed for point-of-care, clinical setting, or field usage, the die-cutting and lamination process is easier, faster, and more cost-efficient to produce. The process starts with a polymeric film or metalized film with a layer of hydrophilic material coated or laminated on top of it. The layered materials are then processed through a precision press where the channels are die-cut to the exact geometry and dimension to enable capillary action of the fluids on the hydrophilic surface. The depth of the channel is essentially set by the thickness of the cut material. The channel widths can get as low as 0.050” (1270 µm) and geometries can be cut to create many of the common unit operations. Alternatively, some microfluidic applications can be created through laser processing which may provide for some additional design options depending on the channel requirements.
Microfluidic product engineers should also work with their converter partners to select the correct materials for the application. Hydrophilic adhesives and coatings, such as Adhesive Research’s ARflow®, can be tailored to a specific high surface tension, which enables the biological fluid to flow at a prescribed rate for that particular application. The manipulation of flow rates ensures the stable transport of the fluid through the microfluidic device to the reagent assay where the diagnostic results will be analyzed.
Quite often, it is important to build prototypes that can be tested and verified by the converter as well as the customer’s validation lab, before the microfluidic components are ready for mass production. Typically speaking, this is where the experience of the converter comes into play as knowing the specific performance characteristics, such as flow rates, for the device, as well as having a certified clean-room environment to manufacture and package components for the next step in the process.