Microfluidics in life science applications

Selecting the correct valves for most fluid applications requires due consideration to the flow, pressure, temperature and fluid viscosity. In life sciences there are valve requirements that often extend the specification of the valves to consider ‘special’ and often expensive fluids and critical processes.

Microfluidics is associated with the control of very small volumes of fluids. Throughout life science industries the precise control of fluids is a major factor in the successful design of devices often used in testing and analysis processes. Accurate and repeatable results and reliable performance can often only be obtained through the use of specialised valve technology.

Critical to the selection of valves are many factors including:

• Material compatibility and fluid isolation ensures that the fluid is not unnecessarily contaminated from any internal surfaces or through the entrainment of foreign substances. The use of materials such as PEEK, EPDM, FKM and Kalrez provide options to suit many biological products and often harsher chemical substances. For most critical applications the operational section of the valve should also be mechanically isolated from the fluid chamber and passages.
• Pumping volume refers to the volume of liquid that is expelled from the fluid chamber by the opening and closing action of the valve. With a traditional diaphragm-style valve, the volume of the fluid chamber varies depending on the ‘on’ or ‘off’ status of the valve; a volumetric difference is discharged into the outlet side of the valve when the valve is switched from ‘on’ to ‘off’. This can often result in waste of expensive chemicals or a loss of valuable biological products and can often adversely influence the results of processes. Using a rocker style of valve there is virtually no change in the volume (often 0.01 µL or less) as the valve is switched from ‘on’ to ‘off’, thus no fluid is discharged into the outlet of the valve as a result of the switching action of the valve.
• Temperature stability is often important to chemical processes and critical analysis applications (ie, blood, urine, immune system analysers). The electric solenoid used to control the function of many process valves can easily transfer unnecessary heat directly to the process fluids. In order to reduce this heat transfer, the selection of a valve should also consider the design and configuration of the solenoid coils and isolation of the heat source.

Valves may be used in standalone configurations where interconnection to the process is through the use of flexible and/or solid tubing.

While this is the traditional method there are a number of other options available. One alternative is to use modern diffusion bonded composite manifold technology.

The correct valve selection can be combined with a customised acrylic manifold solution, incorporating integrated passages engineered to the specific process and thus eliminating the need for unnecessary tubing that often results in leakage and excessive fluid usage. Using diffusion bonded composite manifold technology provides a three-dimensional configuration of fluid passages not achievable by drilling or injection moulding. Composite manifolds can be manufactured from acrylics, polyethermide, polycarbonate, polysulfone and vinyl chloride materials to satisfy a broad range of chemical compatibility, and are suitable for liquids, air and a range of gases at pressures from -100 up to 700 kPa.

In many cases, the electrical circuits often associated with specialised devices can be integrated into the design of the composite manifold.

These features provide a range of benefits to device manufacturers, including: space saving, simplified piping, reduction of the footprint by integrating control equipment such as solenoid valves and sensors onto a manifold, electrical wiring simplified by integrating the printed circuit board onto the manifold, labour costs are significantly reduced, weight reduction is achieved through the use of lightweight manifolds and the unique feature of having a custom-designed solution.