Fluid Movement Technologies
Fluid Movement Technologies
We at Phase Three Product Development have developed a wide variety of microfluidic disposable and instrument/reader products. A few of us thought it might be nice to collect the various ways that we have moved fluid in products to give others some ideas regarding potential design solutions. Knowing the approaches which have previously been used by others may save some development time and risk. In the spirit of being helpful, here is our list….
We have organized the technologies as “On Board” versus “Off Board” where the fluid movement means is either physically located on the disposable or not. Our hope is that this guide could be appended by others and may eventually become a useful reference.
“On Board” Fluid Movement Means
This technique can be very simple with capillary flow driven by geometry, contact angle, and surface finish. Some possible ways to control flow rate by adding surface chemistry. A common approach for capturing blood droplets for POC disposables into channels for further processing. Flow is only created one time as the channel goes from dry to wet.
The Chip Shop seems to have developed a syringe built into a disposable cartridge for a Gates Foundation project. The idea is for the instrument to connect to the syringe features to create positive or negative induced pressure driven flow. Positive or negative displacement pressure-induced. Flow can be reversible.
3 Chamber Pneumatic Driven Pump
This approach relies on a flexible layer to be present in the disposable over each chamber. The chamber valves are opened and closed, driven by off board pneumatic valves, to open and close each valve and generate positive or negative pressure driven flow. Flow can be reversible (forward and backward in a channel) and volume can be well controlled.
This technique involves applying a voltage potential to a membrane or channel and fluid will move from higher to lower potential. The approach is somewhat misleading as the voltage comes from the host instrument but the electrodes on board the disposable connect to the fluid. Flow speeds are typically a few millimeters per second. Flow can be reversible.
Positive Displacement Features
This category is kind of a “catch-all” category as flow can be induced by squeezing a fluid filled blister, a piston/rod arrangement, or other pressure or volume displacement features which can be added to the disposable. Typically these are one direction flow with less precise control of volume or velocity, but can be very appropriate depending on product requirements. This is a common Point of Care (POC) disposable approach.
Sealed Pressure Vessel on Cartridge
This approach was suggested by Dolomite. It involves creating a chamber on the cartridge that is pressurized positively or negatively and sealed during manufacturing. The stored up pressure is then used to move fluid during the use of the disposable.
“Off Board” Fluid Movement Means
EWOD (Electrowetting on Dielectric)
This approach uses an array of contacts on the wetted surface lower surface on the inside of the disposable and a non-conductive ceiling. This is also sometimes called digital microfluidics. This approach allows ultimate programming of droplets for merging, mixing, moving, and metering. Flows can be any direction between adjacent conductive pads. Maybe should be categorized as “On Board”?
Piezo pumps have gotten smaller and cheaper which has made this an attractive approach for POC readers. Each voltage square wave sent to the pump creates a known volume of pump displacement. Some pumps move approximately 1 ul per pulse. Flow is one direction only. Be aware that the pressure pulse created by each displacement of the pump can generate very short duration high accelerations in the flow which may be unsuitable in some applications.
Syringe pumps have gotten smaller, cheaper and offer an amazingly small volume step size. Flow is reversible. Syringes can be replaceable or not (embedded). There is a wide variety of sizes and shapes from multiple suppliers.
Peristaltic pumps have also gotten smaller, cheaper and offer an amazingly small volume step size. Flow is reversible. This is more of a “closed” solution in that only the tubing comes in contact with the fluid.
Gear pumps have also gotten smaller, cheaper and offer an amazingly small volume step size. Flow is reversible. Be careful to ensure that your sample and systems fluids cannot become contaminated by the pump and vice versa for this option.
Rotary-driven microfluidic systems are driven by an off-board motor that moves the fluid due to centrifugal action on the fluid.
The idea here is to used off-board compressed gas to move fluid to and/or through the disposable. Many of the pumping methods listed can be used to pump gas or fluid to or through the cartridge.