Hierarchical structure and crystal chemistry of apatite-based biological hard tissues and their biomimetic analogs.

Biomineralization is the process by which living organisms produce mineral crystals, forming hard tissues with hierarchical structures and distinct chemical and physical properties. This study investigates the principles of apatite-based biomineralization, focusing on the structure and morphogenesis of conodont dental-like hard tissues. By comparing biomimetically grown apatite-gelatin composite aggregates with natural materials, the research seeks to identify similarities and differences in their formation processes. Conodonts, small, primitive, eel-shaped, jawless, but now extinct marine animals, are considered among the earliest vertebrates. Despite their unique fossilized skeletal elements, the architecture and function of these elements remain debated. This study specifically examines the feeding apparatus elements of Polygnathus conodonts from Late Devonian deposits (Middle Frasnian, ~380 million years ago) at the southern coast of Ilmen Lake (Novgorod region, Russia) to analyze the morphology and structure of their dental-like hard tissues. Techniques such as Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), Electron Backscatter Diffraction (EBSD), and Raman Spectroscopy were employed to investigate the morphology, chemical composition, hierarchical structure, and crystallographic orientation of conodont elements. Additionally, a biomimetic synthesis system for strontium/calcium fluorapatite gelatin nanocomposites was developed to simulate controlled mineralization conditions and deepen our understanding of biomineralization principles. By varying parameters such as the strontium/calcium molar ratio and carbonate ion concentration in the solution, the study explores their effects on the structure and morphogenesis of the resulting aggregates. Fourier Transform Infrared Spectroscopy (FT-IR), SEM, EDS, 1 and Powder X-ray Diffraction (pXRD) were utilized to analyze lattice distortion, chemical composition, ionic substitution, and morphology in synthesized powder apatite. This approach aims to bridge the gap between natural biominerals and biomimetic materials, thereby enhancing our understanding of apatite-based biomineralization processes.