Investigation on Microliter Free Jetting Using a Piezoelectric Micro Pump

By avoiding any interaction with surfaces, especially free jetting of liquid pharmaceuticals has numerous advantages such as no cross-contamination of substances, less waste in pipetting, or the possibility of needlefree subcutaneous injections. Dispensing a defined amount of a liquid into air without surface contact requires the formation of a free jet. Therefore, jet generation by a micro pump presents a solution which is versatile in jet volumes while providing minimal dimensions. Jetting is achieved by the quick actuation of the piezoelectric actuator on the pump, leading to the ejection of a volume package that is fast enough to overcome the surface tension at the outlet's interface, for example a dosing needle. Size and formation of the jet are controlled by matching the micro pump's driving parameters such as peak-to-peak voltage and signal waveform. The feasibility of this setup is tested as well as parameters optimized for free jetting aqueous solution. Furthermore, the influence of different actuation parameters on the dosing precision is evaluated. A rectangular signal with 250 Hz sine flanks is determined as suitable waveform for the jet generation with the evaluated 20 mm stainless steel micro pump. Simultaneously, varying and matching the amount of pump strokes and voltage amplitude results in adjustable dosing volumes.