Two new approaches in flow controlled micropumps open up innovation potential for medical applications. Their small size, low power consumption and price level provides attractive characteristics for medical devices. With either the new, patented, low cost, intrinsic sensing solution or hybrid system, including silicon flow sensors, different accuracies and flow ranges can be achieved.

The micropump mp6 is a micro membrane pump actuated by a double configuration of piezo elements, in combination with passive valves. The two actuator stages have been combined in a single pump for the first time. Besides providing a pressure of up to 500 mbar, the double actuator principle assures self-filling of the pump at startup and reliable function. Having only a single polymeric material (certified in accordance to ISO 10993 and USP class VI) in contact with the medium, and due to the fact that the pump is produced by automated assembly, allowing tracking of components and process parameters paves the way towards medical use.

However, looking at the behaviour of membrane pumps, the performance is dependent on the pressure levels at the inlet and outlet. On the other hand, viscosity changes — for example, due to temperature influences — will result in varying flow rates. In membrane pumps this effect is observed as stronger than in syringe pumps, as membrane pumps do not exhibit high pressure stability and are more strongly affected by changes of the liquid itself. The demand in medical applications for constant flow rates with low deviation at different environmental conditions, like temperatures and pressures, leads to the necessity of closed loop control of these pumps.

The flow control in micropumps can be realised by two different approaches:

1/The mp6 micropump with the double actuator provides an intrinsic sensor function. The reversible piezo effect can be used for actuation (pumping) and sensing mode. By continuous operation between pumping and feedback mode, no significant drop of pump performance is observed. Lower accuracy, in the order of 10%, — as requested for passive solutions, like drop infusion systems — can be achieved based on the intrinsic sensor function for the feedback signal. Especially at higher flow ranges, under varying system conditions (e.g. pressure conditions at the inlet and outlet), the piezo sensor principle provides constant performance.

2/For applications in the lower flow range with higher accuracy demands, as for example dosing systems for drug delivery, the closed-loop can be achieved by micropumps equipped with thermal flow sensors as the sensing element. Accuracies in the range of 2–5% can be achieved by such hybrid systems.

In both cases, smart system electronics will give the user access to the system status and also allow the manual administration of additional bolus rates. Both approaches offer interesting new potential for various medical applications, especially where small, portable and battery powered systems are required. Depending on the detailed requirements, a custom fit system can be evaluated and realised.