posted on 2022-07-06, 21:07authored byGisele
M. L. Dalmônico, Dris Ihiawakrim, Nathaly Ortiz, Amaro Gomes Barreto Junior, Caio Felippe Curitiba Marcellos, Marcos Farina, Ovidiu Ersen, Andre L. Rossi
Calcium phosphate materials are widely
investigated for the study
of biomineralization processes and for the development of new biomaterials.
It has been proposed that the crystallization of hydroxyapatite in
aqueous media occurs in steps and not directly by ion-by-ion accretion.
Prenucleation nanoclusters aggregate to form amorphous spheres and
further crystallize into hydroxyapatite. However, conventional analytical
techniques cannot visualize phase transformations over time continuously,
and the nonclassical crystallization of hydroxyapatite is still under
debate. In situ liquid-phase transmission electron microscopy (TEM)
is a novel technique that allows us to follow reactions occurring
during TEM in real time and thus to visualize the formation of calcium
phosphate crystals from the formation of the first mineral nucleus
to the final crystallized phase. In this work, in situ TEM was performed,
and videos showed the exact moment of hydroxyapatite nucleation and
crystallization. During the experiment, different amorphous calcium
phosphate nanoparticles were identified prior to the formation of
the plate/needle-like hydroxyapatite particles. Crystallization was
achieved only after particle elongation. A combined kinetic model
that considered the thermodynamic nonideality of the electrolyte solution
was applied. Sensitivity analyses were performed to interpret the
thermodynamic environment of the liquid cell and the possible species
formed over time.