Evidence for a liquid precursor to biomineral formation

TL;DR

This study provides microscopy evidence supporting the existence of a dense liquid-like precursor phase in natural biomineral formation, specifically in sea urchin spines, bridging the gap between synthetic models and biological systems.

Contribution

It presents direct imaging evidence of a liquid precursor in natural biomineralization, a phenomenon previously observed only in synthetic systems.

Findings

Evidence of a dense liquid-like precursor in sea urchin spines

Precursor originates in tissue and transforms into calcite crystal

Supports liquid-liquid phase separation in natural biomineralization

Abstract

The crystals in animal biominerals such as sea urchin spines, mollusk shells, and coral skeletons, form by attachment of amorphous particles that subsequently crystallize. Do these solid amorphous precursor particles have liquid precursors? Polymer-induced liquid precursors (PILP), or prenucleation clusters coalescing into a liquid precursor to calcium carbonate crystallization have been observed extensively in synthetic systems. Molecular dynamics simulations also predict liquid-liquid phase separation. However, evidence for liquid precursors in natural biominerals remains elusive. Here we present Scanning or PhotoEmission Electron Microscopy (SEM, PEEM) evidence consistent with a dense liquid-like precursor in regenerating sea urchin spines. The observed precursor originates in tissue and ultimately transforms into a single crystal of calcite (CaCO3) with complex stereom morphology.