Morphology Control of Apatite Crystallites by Organic Additives
Date Issued
2012
Date
2012
Author(s)
Wu, Yu-Ju
Abstract
Fluorine-substituted hydroxyapatite (FHAp, Ca10(PO4)6Fx(OH)2-x, x ≤ 2) is structurally very similar to the major inorganic species of teeth and bone. Because of its low solubility and excellent biocompatibility, FHAp has been suggested for various biomedical applications. However, the formation mechanism of the complex apatite materials remains poorly known. A better understanding of the issues such as morphology control of FHAp crystallites would be very helpful to develop the FHAp-based biomaterials and realize the biomineralization mechanism.
In Chapter 3, spherical hierarchical structures of FHAp are successfully prepared by using citric acid as the crystal modifier. Under the hydrothermal conditions at 120 degrees C, the formation of calcium fluoride is kinetically favored and for thermodynamic reasons CaF2 would slowly transform to FHAp. Measurements of scanning electron microscope show that the morphology of FHAp crystallites would change from dumbbell-like to spherical as the amount of citrate ions increases. Contrary to the common believe that crystal morphology control of biominerals is generally achieved by macromolecules, we suggest that small molecules may also play an important role in the biomineralization process.
In Chapter 4, we have carried out a series of solid-state NMR experiments, which provide important insights into the structural environment of the citric acid. We show that the hydrogen bonding between the hydroxyl group of citrate ions and the orthophosphate ions of apatite may also help to stabilize nanosized apatite crystallites. Our experimental results may help unravel the interaction mode of other organic molecules on apatite surface.
In Chapter 5, apatite crystallites with asymmetric morphology are successfully prepared by using L- or D-form of glutamic acid and aspartic acid as additives. The findings reveal that the chirality of the additives is a key factor for the asymmetric crystal growth. Moreover, imperfect oriented attachment and the stereospecific interaction between the additives and the crystal surface steps are used to rationalize the observed morphologies of the apatite crystallites. This work may shed light on the adsorption-nucleation process in biomineralization.
Subjects
apatite
biomineralization
calcium phosphate
crystal growth
crystal morphology
solid-state NMR
organic-inorganic composite
Type
thesis
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