Micro-droplet ejection based on controllable cavity collapse within confined interface

Micro-drop ejection technology has been widely employed in cell analysis, drug delivery, microreactors, and various other fields due to its high accuracy and resolution, which can accurately control and dispense liquid materials. However, the current development of this technology faces challenges due to nozzle diameter limitations. Smaller droplets require finer nozzles for ejection. Nevertheless, fine nozzles cause significant fluid resistance, hindering micro-droplet ejection. Overcoming the constraint posed by nozzle and achieving high-precision micro-droplets ejection has become a challenging task for the industry. Inspired by the phenomenon of cavity collapse in nature, we have developed a micro-droplet ejection technology based on actively controlling the cavity collapse within the confined interface. By analyzing the formation and collapse of the liquid cavity, we have identified three ejection modes: no droplet, single droplet, and satellite droplet, and further delineated the boundary conditions for minimizing droplet size and ejecting satellite-free droplets. Using this technology, we achieved precise control over droplet size within a defined range, with the minimum droplet diameter reaching 34 % of the nozzle diameter. Furthermore, the continuous ejection of single droplets demonstrated excellent stability and repeatability. This innovative technology could provide a novel approach to achieve high accuracy and controllability in micro-droplets ejection, liberating it from nozzle constraints, thus expected to play a significant role in the fields of biomedical research, chemical engineering, and printed electronics.