Unlocking the flexibility of multi-material 3D extrusion printing for soft iontronics

Iontronics can improve soft robotics, like wearable devices and environmental sensors, by replacing rigid electronics with viscoelastic materials that mimic biological tissue. Circuit components, including diodes, transistors, and power sources, have been fabricated with soft materials that utilize ionic current. However, the fabrication of these iontronic components can be tedious, and widely applicable manufacturing methods are lacking, thus hindering the development of complex iontronic circuits for real-world applications. By utilizing multi-material 3D printing, this work demonstrates the ability to rapidly iterate ionic diode design and integrate these diodes within complex structures with biomimetic mechanical behavior. The print quality and resulting material properties can be tuned by adjusting three components (the conductive polymers, the thickening agent, and the crosslinker). To emphasize the rapid iteration enabled by 3D printing, a library of the ionic diodes with varying sensitivity to strain are evaluated. The utility of these ionic diodes is demonstrated by integrating them within logic circuits that respond to mechanical cues and demonstrate bio-inspired strain-stiffening behavior. The adaptability of both the ink and geometry afforded by extrusion printing make it an ideal candidate for enabling the next generation of iontronics with advanced computational and mechanical functionality.