Simple synthesis of self-assembled nacre-like materials with 3D periodic layers from nanochitin via hydrogelation and mineralization

Abstract

The superb mechanical properties of some natural materials usually result from highly ordered, multiscale and hierarchical architectures such as bone, nacre, exoskeleton, etc. Nonetheless, the involved gene regulated process cannot be realized artificially. Here we report bioinspired 3D structures with similar performance following a rapid, green, one-pot synthesis route based on the concept of “brick-and-mortar” biomineralization by introducing Ca²⁺ and PO₄³⁻ into a nanochitin dispersion followed by ammonia vapor diffusion. The process leads to self-stratified, periodic assemblies formed under ion diffusion gradients and hydrogelation of nanochitin with simultaneous mineral coprecipitation. Specifically, an organic hydrogel network is formed from partially deacetylated chitin nanofibers together with hydroxyapatite. The components are structured in periodic bands by alternating (organic/inorganic) precipitation as layer-by-layer stacks. The layer space is adjustable by changing the ion concentration and temperature of regulators. Endowed with directional diffusion, customizable 3D forms are self-assembled and demonstrated to function as optical waveguides with selective light transmission. Upon hot pressing, the synthesized material shows structural similarity to natural nacre and displays exceptional strength. This artificial method can reduce the synthesis time from years in nature to a few days in a lab, with no need for complex treatments or facilities; moreover, the designable structure can be customized for uses ranging from structural support in biomedical implants to optical waveguides.