It presents asmart anisotropic-unidirectional spreading of droplet that is controlled effectively by a hydrophilic
component (chitosan, CHI) gradient on aligned PET (poly ester)/CHI fi brous surface. A CHI-composition gradient
is formed along the aligned fi bers by using a lifting-dissolution method. Thus various WGs can be introduced onto the aligned fi ber surface to control the liquid-spreading behaviors. In addition, a V-shaped WG surface is used to control two droplets in opposite direction to move together in a liquid reaction. The study introduces a mechanism of the integrative cooperative forces between anisotropic contact line force and WG force that result from anisotropic aligned fi bers and CHI-composition gradient. This fi nding offers an insight into the design of the systems and devices that can control the microfl uid movement effectively.
