# 3D printable strong and tough composite organo-hydrogels inspired by natural hierarchical composite design principles

## TL;DR

This paper presents a 3D-printable composite hydrogel inspired by natural design principles, combining ceramic platelets and a polymer matrix to achieve high strength and toughness for flexible electronics.

## Contribution

A hierarchical fabrication strategy for ceramic-reinforced organo-hydrogels inspired by natural composite design principles is introduced.

## Key findings

- The composite hydrogel achieves fracture energy up to 31.1 kJ/m² through multi-scale energy dissipation.
- The material exhibits high stiffness, strength, and toughness suitable for flexible electronics.
- Silane-treated interfaces and aligned ceramic platelets enhance mechanical and functional properties.

## Abstract

Fabrication of composite hydrogels can effectively enhance the mechanical and functional properties of conventional hydrogels. While ceramic reinforcement is common in many hard biological tissues, ceramic-reinforced hydrogels lack a similar natural prototype for bioinspiration. This raises a key question: How can we still attain bioinspired mechanical mechanisms in composite hydrogels without mimicking a specific composition and structure? Abstracting the hierarchical composite design principles of natural materials, this study proposes a hierarchical fabrication strategy for ceramic-reinforced organo-hydrogels, featuring (1) aligned ceramic platelets through direct-ink-write printing, (2) poly(vinyl alcohol) organo-hydrogel matrix reinforced by solution substitution, and (3) silane-treated platelet-matrix interfaces. Unit filaments are further printed into a selection of bioinspired macro-architectures, leading to high stiffness, strength, and toughness (fracture energy up to 31.1 kJ/m2), achieved through synergistic multi-scale energy dissipation. The materials also exhibit wide operation tolerance and electrical conductivity for flexible electronics in mechanically demanding conditions. Hence, this study demonstrates a model strategy that extends the fundamental design principles of natural materials to fabricate composite hydrogels with synergistic mechanical and functional enhancement.

The preparation of composite hydrogels can allow for mechanical properties to be enhanced, and hierarchical structures can be effective. Here, the authors report improved mechanical properties by the addition of ceramic platelets to an organohydrogel in direct ink writing.