In a single-use cartridge for the point of care, why use pneumatic control of on-board diaphragm valves in the cartridge when a linear actuator against a flexible layer works just as well?
This question was recently posed by a client as they consider their development path from proof of concept. They envision a couple of different product use environments, one involving a benchtop instrument, and another a portable handheld using battery power.
In some cases, the answer might just boil down to personal preference. But from a development perspective, pneumatically controlled on-board valves offer more flexibility in design of the cartridge.
Consider the following:
On-board pneumatically controlled valves have all the air control lines bused to one edge of the card, and interface through a gasket to a manifold. This makes it simple to create a cartridge carrier that clamps the cartridge in place. With pneumatic control, there is no need to worry about the arrangement of electro-mechanical components above or below the device. A more open instrument architecture is possible with fewer components to get in the way of engineering in optics or heating.
During cartridge development, no engineering of a mechanical actuation interface is required, simplifying parallel cartridge/instrument development and de-risking the final integration of the cartridge into the instrument.
For multiplexing applications, a high density of valves is also easily accomplished with on-board pneumatically controlled valves. Our valves have a 2 x 3 mm footprint, and have been made at densities of 6 valves in a 9 mm2 footprint, arrayed in the standard microtiter plate footprint. Actuation of this many valves would be impossible with a mechanical interface.
Pneumatics also provide positive control of both the opening and closing of the valve. With mechanical actuation there is only one control direction, and that’s to close the flexible layer into the body of the cartridge. If fluid passes through after the mechanical actuation is removed from the flexible layer, the return of the flexible layer to the open position will depend on how long it was closed and may contribute to uncontrolled changes in the pressure drop in the fluid circuit, affecting overall performance.
A rechargeable battery can be used to power a pneumatically controlled cartridge with eight solenoid valves in a handheld system. This has been demonstrated in a commercial handheld that is the size of an iphone 6 and about an inch thick. With pneumatic control, a spike current is needed to actuate from one state to another, but requires very low power to remain in that state. When designed correctly, the pneumatic control like the mechanical actuator, requires intermittent power use. The same is true for the pressure and vacuum pumps. Small pumps, about the size of a fingertip, are used to fill an accumulator to the required vacuum or pressure which is typically no more than 10 psi. The pneumatically controlled valves require very little air flow, so the pumps only cycle on intermittently as well.
Because there are fewer moving parts with the use of pneumatic controls, jostling or even dropping a handheld has less risk of compromising the operation of the cartridge, making it more robust in a field application.
In summary the advantages of pneumatic control of on-board diaphragm valves in cartridges includes:
1. Early collection of performance data with a cartridge operated with a simple mechanical interface.
2. No upfront instrument integration required to achieve semi-automated control of the cartridge.
3. De-couples cartridge optimization from the instrument design.
4. Simplifies the instrument design, reduces the number of mechanical components that interface to the cartridge.
Contact us to learn more about our on-board pneumatically actuated valves, and pneumatic controller, the ADEPT.
Our valves have been incorporated into commercial products. We have technical data on the their performance that we can share under confidentiality.