Branched Polymeric Prenucleation Assemblies Initiate Calcium Phosphate Precipitation

Area of Science:

• Biomineralization
• Materials Science
• Crystallization

Background:

• Calcium phosphate (CaP) formation deviates from traditional nucleation-growth models.
• Soluble prenucleation species play a role, but their properties are poorly understood.

Purpose of the Study:

• To comprehensively characterize CaP crystallization from the prenucleation stage.
• To elucidate the structural features, stability, and transformation of solution-state precursors.

Main Methods:

• Integrated time-resolved NMR, turbidimetry, SAXS, cryo-TEM, and calcium-potentiometry.
• Investigated the role of prenucleation clusters (PNCs) and polymeric assemblies.

Main Results:

• CaP nucleation initiated by transformation of branched polymeric assemblies into amorphous calcium phosphate (ACP) spheres.
• Branched species, often undetectable, are evidenced by SAXS and precede ACP formation.
• Mineralization pathway controlled by Ca2+/Pi ratio, extending transient species lifetime.

Conclusions:

• CaP crystallization involves complex intermediates, including branched polymeric assemblies.
• ACP spheres form via dissolution and densification of specific domains.
• Kinetic control of mineralization pathway is achievable via ion ratio manipulation.