Direct Writing of Elastic Fibers with Optical, Electrical, and Microfluidic Functionality

Direct Ink Writing is an additive fabrication technology that allows the integration of a diverse range of functional materials into soft and bioinspired devices such as robots and human‐machine interfaces. Typically, a viscoelastic ink is extruded from a nozzle as a continuous filament of circular cross section. Here it is shown that a careful selection of printing parameters such as nozzle height and speed can produce filaments with a range of cross‐sectional geometries. Thus, elliptic cylinder‐, ribbon‐, or groove‐shaped filaments can be printed. By using the nozzle as a stylus for postprint filament modification, even filaments with an embedded microfluidic channel can be produced. This strategy is applied to directly write freeform and elastic optical fibers, electrical interconnects, and microfluidics. The integration of these components into simple sensor‐actuator systems is demonstrated. Prototypes of an optical fiber with steerable tip and a thermal actuation system for soft tissues are presented. By harnessing ink deformation during 3D printing, it is shown that simple circular nozzles can produce filaments with ellipse, ribbon, groove, and even microchannel cross sections. Using this approach and a palette of functional inks, elastic electrical wires, optical fibers, and microfluidic channels are directly written. Their integration in soft systems for multimodal sensors and actuators is demonstrated.