Bio-inspired flexible fiber brushes that keep liquids in a controlled manner by closing their ends

When brushes are removed from an ink bath, they sometimes show unwanted droplets, which may accidentally drop on surfaces. Our theory predicts that Chinese calligraphic brushes eliminate the unwanted droplets by closing their ends. The ends of the brushes are closed when the length L of their fibers is longer than a critical length Lclo. This principle may be applicable to the design of liquid-transfer devices.