# Nacre-Inspired Composite Coatings with Hierarchical Architecture for Durable Surface Protection

## TL;DR

This paper presents a bioinspired coating that mimics nacre to protect cultural heritage, offering durability and aesthetic compatibility.

## Contribution

A novel multilayer coating system inspired by nacre is developed for cultural heritage protection.

## Key findings

- The coating exhibits mechanical properties comparable to natural nacre.
- Color changes remain below perceptual thresholds under acidic conditions.
- The layered architecture effectively dissipates stress and inhibits damage propagation.

## Abstract

A bioinspired multilayer coating is developed for the
protection
of built cultural heritage, emulating the hierarchical architecture
of natural nacre. The system is fabricated through the alternating
deposition of mineralized calcium carbonate (CaCO3) and
organic layers composed of chitosan and cellulose nanofibrils (CNFs),
with poly­(acrylic acid) (PAA) acting as a mineralization-directing
agent. A CO2-controlled environment promotes the formation
of continuous crystalline CaCO3 layers with strong interfacial
adhesion to marble substrates. The resulting composite multilayers
exhibit stratified organization and mechanical properties comparable
to those of the biogenic minerals. Nanoindentation and stiffness mapping
reveal hardness and modulus values in the range of natural nacre,
along with enhanced reinforcement with increasing numbers of multilayers.
Mechanical durability under acidic conditions confirms the preservation
of both structural integrity and aesthetic compatibility, with color
changes remaining below perceptual thresholds (ΔEab < 5).
The observed crack resistance, cohesive strength, and mechanical compatibility
with the substrate highlight the effectiveness of the layered architecture
for dissipating stress and inhibiting damage propagation. These results
contribute to the development of an emerging class of bioinspired
protective coatings that integrate mechanical resilience, chemical
stability, and visual compatibility by establishing a groundwork for
advanced materials tailored to the complex demands of cultural heritage
conservation.