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

Iontronics can improve wearable devices, implantable devices, and environmental sensors by replacing traditional 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 instead of metals and electronic 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. While 3D printing has recently gained popularity due to its versatility, we suggest that it has been underutilized for iontronics. By combining multi-material 3D printing and iontronics, we show the ability to rapidly iterate ionic diode design and integrate these diodes within a complex structure with advanced mechanical behavior. With an updated 3D model design, we create a new stretchable diode that is insensitive to strain, a feature that can be crucial for applications requiring soft electronics. To further emphasize the adaptability of printing soft materials, we demonstrate that three components of the based ink (conductive polymers, a thickening agent, and a crosslinker) can be used to optimize print quality and the resulting material properties. In doing so, we thoroughly characterize a mixed ionic-electronic conducing ink using poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) that can provide a foundation for the further development of extrusion printed iontronics. Compared to previously established methods, multi-material printing reduces cost, wasted material, and time required to develop complex devices in a manner that can be personized as well as highly reproducible.