Fused Filament Additive Manufacturing of Ionic Polymer-Metal Composite Soft Active 3D Structures

This paper describes a new three-dimensional (3D) additive manufacturing (AM) technique in which electroactive polymer filament material is used to build soft active 3D structures, layer by layer. The proposed manufacturing process is well-suited for creating electroactive soft complex structures and devices, whereby the entire system can be manufactured from an electroactive polymer material. For the first time, the unique actuation and sensing properties of ionic polymer-metal composite (IPMC) is exploited and directly incorporated into the structural design to create sub-millimeter scale cilia-like actuators and sensors to macro-scale soft robotic systems. Because ionic polymers such as Nafion are not melt-processable, in the first step a precursor material (non-acid Nafion precursor resin) is extruded into a thermoplastic filament for 3D printing. The filament is then used by a custom-designed 3D printer to manufacture the desired soft polymer structures, layer by layer. Since, at this stage the 3D-printed samples are not yet electroactive, a chemical functionalization process follows, consisting in hydrolyzing the precursor resin in an aqueous solution of sodium hydroxide (NaOH) and dimethyl sulfoxide (DMSO, C2H6OS). Upon functionalization, metal electrodes are applied on the samples through an electroless plating process, which enables selected areas of the 3D-printed electroactive structures to be controlled by voltage signals for actuation, while other parts can function as sensors. This innovative AM process is described in detail and experimental results are presented to demonstrate the potential and feasibility of creating 3D-printed IPMC actuator samples.