Bioinspired stimuli-responsive spindle-knotted fibers for droplet manipulation

Manipulation of small amounts of liquids is of great importance in bio/chemical analysis, environmental engineering, medical diagnostics, etc. Novel platforms with systematic maneuverability and expanded applications are highly desired. Here, inspired by the directional liquid motion ability of natural fibrous materials, we present light-responsive spindle-knotted microfibers from piezoelectric microfluidics for droplet manipulation. The graphene oxide (GO) and poly(N-isopropylacrylamide) [poly(NIPAM)] components endow the fiber with near-infrared (NIR) stimuli-responsiveness. Besides, its unique structure enables droplet pinning in the knots of the fiber. During NIR irradiation, the fiber can shrink and turn hydrophobic, which resulted in directional droplet migration from one knot to another. Based on this phenomenon, controllable droplet merging could be initiated under light control, and chemical reactions could be carried out on-site. More intriguingly, systematic manipulation of droplet pathways was achieved through a woven fiber network, by which multi-step reactions could occur orderly. These features indicated that the bio-inspired photo-controllable spindle-knotted fibers would find vast opportunities in broad applications, such as micro-reactors and optofluidic systems.