Nanoscale assembly processes revealed in the nacroprismatic transition zone of Pinna nobilis mollusc shells

TL;DR

This study uncovers nanoscale assembly mechanisms at the nacre-prism interface in Pinna nobilis shells, revealing how nanoparticle aggregation leads to nacre formation, providing insights into biomineralization processes.

Contribution

It provides detailed nanoscale insights into nacre formation, highlighting nanoparticle aggregation and transition to mature nacre in mollusc shells, a novel observation in biomineralization research.

Findings

Nanoparticle aggregation initiates nacre formation.

Transition from nanofibrillar to mature nacre observed.

Nacre assembly driven by nanoparticle packing and merging.

Abstract

Intricate biomineralization processes in molluscs engineer hierarchical structures with meso-, nano-, and atomic architectures that give the final composite material exceptional mechanical strength and optical iridescence on the macroscale. This multiscale biological assembly inspires new synthetic routes to complex materials. Our investigation of the prism-nacre interface reveals nanoscale details governing the onset of nacre formation using high-resolution scanning transmission electron microscopy. A wedge polishing technique provides unprecedented, large-area specimens required to span the entire interface. Within this region, we find a transition from nanofibrillar aggregation to irregular early-nacre layers, to well-ordered mature nacre suggesting the assembly process is driven by aggregation of nanoparticles (~50-80 nm) within an organic matrix that arrange in fiber-like polycrystalline configurations. The particle number increases successively and, when critical packing is reached, they merge into early-nacre platelets. These results give new insights into nacre formation and particle-accretion mechanisms that may be common to many calcareous biominerals.