Structural, Morphological, and Sorption Characteristics of Imperfect Nanocrystalline Calcium Hydroxyapatite for the Creation of Dental Biomimetic Composites

Using a set of structural-spectroscopic analysis methods, the relationships between the structure, morphology, and sorption characteristics of samples of nanocrystalline carbonate-substituted calcium hydroxyapatite synthesized with the use of a biogenic source of calcium (avian eggshell) by chemical precipitation from a solution are studied. Using X-ray diffractometry and X-ray microanalysis, impurities are found to enter the structure of the synthesized material from the avian eggshell, which leads to a change in the unit-cell parameters of the hydroxyapatite crystal without the formation of additional phosphate phases. Using optical spectroscopy and electron paramagnetic resonance, it is established that, as a result of the inheritance of a set of carbonate-ion impurities, a structure of B-type hydroxyapatite is formed. An increase in the content of the PO₄ phosphate groups during the process of synthesis of materials in the atmosphere results in a decrease in the content of structurally related CO₃ groups. A decrease in the pH of the solution at the synthesis stage, due to an increase in the content of \({\text{PO}}_{4}^{{3-}}\) anions, affects the morphology of the samples by increasing the size of defects, i.e., nanopores on the surface of the nanocrystals. Such a change in the morphology of the materials results in changes in the sorption characteristics of the samples, determined by the method of the thermal desorption of nitrogen. The specific surface area of the powders is ~55.5 ± 0.9 m²/g, which many times exceeds known analogs. Despite the developed surface, the samples of carbonate-substituted calcium hydroxyapatite remain stable in an atmosphere of saturated water vapors, and the main losses during polarization are associated with Maxwell–Wagner losses. Analysis of the characteristics of carbonate-substituted hydroxyapatite samples obtained from a biogenic source of calcium shows their potential significance for creating biomimetic materials that imitate the structure, morphology, and anisotropy of the native solid tissue of a human tooth.