Instability-induced patterning of a jelling jet

TL;DR

This paper investigates how a jelling alginate jet forms helical coils due to fluid drag, analyzing the instability onset and evolution through experiments, theory, and simulations, enabling 3D filamentous structure printing.

Contribution

It introduces a method to control filament properties and instabilities during extrusion, allowing for the creation of complex 3D structures in fluid environments.

Findings

Instability onset can be predicted and tuned via experimental parameters.

Co-extrusion allows control over filament buoyancy and shape.

Complex 3D filament structures can be printed using instability harnessing.

Abstract

When a thin stream of aqueous sodium alginate is extruded into a reacting calcium chloride bath, it polymerizes into a soft elastic tube that spontaneously forms helical coils due to the ambient fluid drag. We quantify the onset of this drag-induced instability and its nonlinear evolution using experiments, and explain the results using a combination of scaling, theory and simulations. By co-extruding a second (internal) liquid within the aqueous sodium alginate jet and varying the rates of co-extrusion of the two liquids, as well as the diameter of the jet, we show that we can tune the local composition of the composite filament and the nature of the ensuing instabilities to create soft filaments of variable relative buoyancy, shape and mechanical properties. All together, by harnessing the fundamental varicose (jetting) and sinuous (buckling) instabilities associated with the extrusion of a jelling filament, we show that it is possible to print complex three-dimensional filamentous structures in the ambient fluid.