# Integrated 3D Printing of Liquid Metal and Elastomer for Soft Robots and Electronics

## TL;DR

This paper introduces a new 3D printing method that combines liquid metal and elastomer to create soft robots and electronics in a single step, enabling complex and functional designs.

## Contribution

A novel multimaterial 3D printing strategy for fabricating soft robots and electronics with embedded conductive coils in a single process.

## Key findings

- A 4-layer-coil soft electromagnetic actuator was fabricated in one step without manual bonding.
- Three functional devices demonstrated the strategy's potential for multifunctional and miniaturized designs.
- A bio-inspired soft robot achieved a swimming speed of 29 mm/s using the integrated printing method.

## Abstract

Soft robots and stretchable electronics, typically composed of stretchable elastomers and embedded conductive coils, have been widely investigated for applications in actuation, sensing, and communication. However, their fabrication still relies heavily on multistep and labor-intensive conventional methods. Here, we present a multimaterial 3-dimensional (3D) printing strategy based on direct ink writing technology, which enables the one-step fabrication of stretchable elastomers embedded with high-conductivity multilayer coils. This is achieved by alternately printing elastomer and nickel-particle-modified liquid metal (NLM) coil layers in a program-controlled sequence, with vertically printed NLM cones connecting adjacent NLM layers. With this strategy, we achieved one-step fabrication of a 4-layer-coil soft electromagnetic actuator (SEMA) and a self-sensing SEMA integrating sensing and driving modules, without the need for manual bonding or post-processing. We further built 3 functional devices to show the potential applications of this integrated 3D printing strategy: a sensor-integrated soft gripper capable of perceiving its own grasping state, a bio-inspired manta-like soft electromagnetic robot that achieves a swimming speed of 29 mm/s, and a SEMA integrated with a Hall sensor and a red light-emitting diode, which exhibits strong mechanical robustness. Overall, the integrated 3D printing strategy not only simplifies the fabrication but also enables the multifunctional and miniaturized design of soft robots and electronics.