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

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.