# Enabling the Fabrication of Complex Soft Iontronics Using Multi‐Material 3D Extrusion Printing

## TL;DR

This paper introduces a 3D printing method to create complex soft iontronic devices that can mimic biological tissues and respond to mechanical strain.

## Contribution

The novel contribution is using multi-material 3D printing to fabricate ionic diodes and integrate them into soft, strain-sensitive structures.

## Key findings

- Multi-material 3D printing enables rapid fabrication and iteration of ionic diodes with tunable strain sensitivity.
- Integrated iontronic circuits demonstrate bio-inspired strain-stiffening behavior and function underwater.
- The method allows for high reproducibility and adaptability in creating soft devices with advanced mechanical properties.

## Abstract

Iontronics can improve soft robotics, including wearable devices and environmental sensors, by replacing rigid electronics with viscoelastic materials that mimic biological tissue. Circuit components have been fabricated with soft materials that utilize ionic current, but the process can be tedious and widely applicable manufacturing methods are lacking, hindering the development of complex iontronic circuits for real‐world applications. With 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. Print quality and material properties can be tuned by adjusting the concentration of the ink's components. To emphasize the rapid iteration enabled by 3D printing, a library of the ionic diodes with varying sensitivity to strain is 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. These devices are functional directly from the 3D printer, are extremely flexible, and can be submerged in water without losing functionality. The adaptability afforded by multi‐material extrusion printing make it an ideal candidate for enabling the next generation of iontronics capable of advanced computational and mechanical functionality.

Using multi‐material 3D printing, ionic diodes and logic circuits are created using only one fabrication technique and are integrated into metamaterial scaffolds with advanced mechanical behavior, paving the way for soft devices with tunable sensitivity to mechanical strain. This easily adaptable approach with high reproducibility creates a foundation for the accelerated progress in fields like soft robotics and wearable devices.