Abstract
The mesocrystal system fluoroapatite—gelatine grown by double-diffusion is characterized by hierarchical composite structure on a mesoscale. In the present work we apply solid state NMR to characterize its structure on the molecular level and provide a link between the structural organisation on the mesoscale and atomistic computer simulations. Thus, we find that the individual nanocrystals are composed of crystalline fluorapatite domains covered by a thin boundary apatite-like layer. The latter is in contact with an amorphous layer, which fills the interparticle space. The amorphous layer is comprised of the organic matrix impregnated by isolated phosphate groups, Ca3F motifs and water molecules. Our NMR data provide clear evidence for the existence of precursor complexes in the gelatine phase, which were not involved in the formation of apatite crystals, proving hence theoretical predictions on the structural pre-treatment of gelatine by ion impregnation. The interfacial interactions, which may be described as the glue holding the composite materials together, comprise hydrogen bond interactions with the apatite PO43− groups. The reported results are in a good agreement with molecular dynamics simulations, which address the mechanisms of a growth control by collagen fibers, and with experimental observations of an amorphous cover layer in biominerals.
Highlights
Mesocrystallization[11,12]
As it is obvious that the fundamental principles of mineral growth, passivation and stabilization are already included in the early stages of composite growth, in the present work we focus on the study of the hexagonal prismatic seeds and dumbbells, the initial states of growth of fluorapatite/gelatin composites
scanning electron microscopy (SEM) images of the fluorapatite-gelatine composite demonstrate that the sample under study represents a combination of prismatic seeds (Fig. 1a) and dumbbell-like aggregates (Fig. 1b,c)
Summary
Mesocrystallization[11,12]. Since biominerals combine complex morphology and unique functional properties as the result of evolution-optimized processes, comprehensive insights into the biomineralization mechanisms open up promising approaches for bioinspired and biomimetic materials design[11,13]. In our previous studies of synthetic hydroxy- and fluorapatite mesocrystals a disordered (amorphous) layer, which covers the apatite crystalline domains and is coordinated to water and the organic matrix, has been identified by solid-state NMR20,21. Using solid state NMR we studied the interfacial mineral-organic structure in large spherical aggregates up to 100 μ m in size, which represent the final growth state of the fractal-grown fluorapatite-gelatin composites[20,21]. As it is obvious that the fundamental principles of mineral growth, passivation and stabilization are already included in the early stages of composite growth, in the present work we focus on the study of the hexagonal prismatic seeds and dumbbells, the initial states of growth of fluorapatite/gelatin composites. The measurements were performed before and after heating to 250 °C to study the effect of release of hydroxyl groups and water from the crystal structure
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
