# Nacre and Nacre-Inspired Materials: Historical Background, Definition, Fabrication Techniques and Gaps

## TL;DR

This paper reviews the historical and modern use of nacre and nacre-inspired materials, focusing on their composition, fabrication techniques, and mechanical properties.

## Contribution

The paper provides a comprehensive review of nacre's biomineralisation process and modern fabrication techniques for nacre-inspired materials.

## Key findings

- Nacre's mechanical properties arise from its hierarchical structure and organic-inorganic interactions.
- Modern fabrication techniques like 3D printing and freeze casting enable the creation of nacre-inspired materials.
- The organic matrix plays a critical role in controlling crystal nucleation and growth in nacre.

## Abstract

From Palaeolithic ornaments to modern biomimetics, the use of nacre and shells has evolved. Initially utilised for jewellery and tools, they now inspire the development of advanced materials. This paper reviews the current knowledge on nacre’s composition, focusing on the highly regulated biomineralisation process wherein amorphous calcium carbonate (ACC) transforms into crystalline aragonite. It examines the important role of the organic matrix (specifically soluble, insoluble, and acidic proteins) in controlling crystal nucleation, growth, and polymorph selection. Scientists study natural nacre formation to create nacre-inspired composites for various applications. Charles Hatchett’s in 1799 shell categorisation, Sorby and Sowerby’s 19th-century microscopy, Taylor, Beedham, Bøggild, and Currey’s mid-20th-century research on bivalve structures, and mechanical property investigations in the 1970s are some of the major developments. The hierarchical structure, cooperative plastic deformation, surface asperities, organic–inorganic interactions, and interphase in such complex composite materials give rise to impressive mechanical properties. In the early 2000s, with the emergence of biomimetics, inspired by nacre, several macroscopic structural materials with uniform micro- and nanoscale architectures have been synthesised in recent decades, and their mechanical properties and potential applications have been explored. Modern nacre-inspired fabrication utilises 3D printing for precision, freeze casting for sustainability, and mineralisation for scalability. Techniques like layer-by-layer assembly and nanomaterial integration enhance mechanical performance through advanced interfacial engineering.