Development of an Automatic Reagent Dispensing System for Micro Passive Pumps

A surface tension pump, a type of passive pumping method, can generate a gentle and low-flow liquid transport in microchannels without external equipment or tubing, even under microgravity conditions. However, its applicability is limited for long-term operation with large liquid volumes due to its reliance on phenomena specific to small liquid volumes. To overcome this limitation, we developed an automatic reagent dispensing system enabling intermittent replenishment of the inlet reservoir in microfluidic devices. The system achieved high positional repeatability, with a maximum error below 781 µm, which was sufficient for operation within the inlet well used in this study. Initial flow-rate characterization demonstrated that the flow behavior could be adjusted through the dispensed droplet volume. The system was further evaluated through an 18 h automated cell-culture experiment, showing cell-retention performance comparable to that obtained by manual medium replenishment. These results demonstrate the feasibility of using automated intermittent replenishment to extend the operating duration of passive pumping systems.