# Synthetic fascia for stiff and tough 4D printed multifunctional structures that detect and tolerate damage

## TL;DR

Researchers developed a 4D printed material inspired by muscle tissue that is both stiff and tough, allowing it to morph shapes, detect damage, and maintain function after breaking.

## Contribution

A novel multi-material 4D printing method inspired by muscle fascia that achieves high stiffness and toughness while enabling damage tolerance and controlled actuation.

## Key findings

- The composite design improves toughness without reducing stiffness in printed structures.
- The material maintains functionality after multiple fractures and can detect extreme loads.
- Applications include a high-performance lifting robot and damage-tolerant actuators.

## Abstract

Creating shape-morphing structures with time-responsive materials is a key goal of 4D printing, but combining high stiffness (E) and toughness (K) in a single material remains difficult. Soft materials stretch but lack strength, while stiff materials resist deformation but are brittle. Nature overcomes this trade-off in skeletal muscle by surrounding strong fibers with soft, tough tissue for protection and support. Inspired by this strategy, we develop a multi-material printing method that combines stiff synthetic muscle with a soft, stretchable adhesive to form a composite structure. Here, we show that this design greatly improves toughness without sacrificing stiffness, enables controlled actuation, and maintains function after multiple fractures. We demonstrate these properties in a damage-tolerant actuator, a lifting robot with record performance, and a lattice that detects and withstands extreme loads while remaining operational.

Creating shape morphing structures with stiff and tough time-responsive materials is a challenge for 4D printing. Here, the authors address this challenge showing a multi-material printing method that combines a stiff synthetic muscle with a stretchable adhesive to form actuators that can generate large specific force and detect and tolerate damage.