| Summary: | 碩士 === 國立臺灣大學 === 化學研究所 === 103 === Fluorine-substituted hydroxyapatite (FHAp) has been one of the most studied biomaterials due to its high stability and excellent biocompatibility. Crystallites of FHAp formed in ambient solution usually have rod-like shape, while various other morphologies would be observed in the presence of organic additives. To date, the growth mechanism of FHAp crystallites is still unclear. Therefore, we aim to build a two-dimensional crystal-growth model that can mimic the crystal morphology of FHAp in order to provide some insights into the crystallization mechanism.
In our model the basic structural unit is added one at a time to imitate the crystal growth process. For each addition, the orientation and position of the crystal unit is sampled by the Monte Carlo method. The interaction energy among the crystal units includes various terms accounting for the effects of Debye length, excluded volume, and crystal dislocation. As a validation of the simulation codes, we successfully obtained rod-like morphology for the resultant crystal. To mimic the effect of organic additive on the crystallization process of FHAp, we have also repeat the simulation in the presence of a set of blocks with smaller size, which would disturb the orientation of the neighboring crystal units. Starting from some judiciously prepared initial configurations, we are able to reproduce certain morphology observed experimentally. We believe that the results are due to the configuration competition of different crystal-unit stackings. Additional morphology analyses are currently underway to narrow down the physical principles governing the morphology selection in the crystallization process.
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