Calcium phosphate colloids with hierarchical structure controlled by polyaspartates

Precipitation of calcium phosphate in a double-jet experiment in the presence of sodium polyaspartic acid results in a structural evolution of stable colloidal objects with a variety of unconventional morphologies. This structural evolution is characterized by a combination of techniques, namely static and dynamic light scattering, small-angle and wide-angle X-ray scattering, and transmission electron microscopy. It is shown that after immediate formation of amorphous precursor nanoparticles with a "parachute architecture", the system transfers into a hollow sphere morphology in the 500-nm region and is composed of plateletlike nanocrystals, and again is transferred into a final, "snowball-like" morphology of high structural definition and monodispersity. The kinetics depends on the amount and the molecular weight of the polymer, but similar structural elements are found in all the cases examined. When repeated in a triple jet experiment, which also ensures a constant polymer concentration, it was possible to intercept a postulated intermediate structure in practically complete yield, namely crystalline hydroxyapatite nanofibres with extremely high axial ratios which form an interwoven gel.