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Crystals 2018, 8(8), 308;

Habit Change of Monoclinic Hydroxyapatite Crystals Growing from Aqueous Solution in the Presence of Citrate Ions: The Role of 2D Epitaxy

Dipartimento di Scienze della Terra, Università degli Studi di Torino, Via Valperga Caluso 35, 10125 Torino, Italy
Author to whom correspondence should be addressed.
Received: 9 July 2018 / Revised: 25 July 2018 / Accepted: 25 July 2018 / Published: 27 July 2018
(This article belongs to the Special Issue Biomimetic Growth of Calcium Phosphate Crystals)
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Calcium hydroxyapatite (HAp) has been crystallized from aqueous solutions in the presence of citrate ions, in two temperature intervals. At lower temperature, where citrate could form the stable 3D-ordered phase Ca-citrate-tetrahydrate (Ca-Cit-TH), only the monoclinic (P21/c) HAp polymorph occurs and assumes the shape of fence-like aggregates, built by sharply [010] elongated lamellae dominated by the pinacoid {001}. This pronounced anisotropic growth habit is compared with the usually considered rod-like pseudo-hexagonal occurring in pure aqueous solution growth. The habit change is interpreted by assuming that 2D islands of Ca-citrate-tetrahydrate can be adsorbed as epi- monolayers of thickness d001 onto the different growth forms: {001}, {100}, {102¯}, {010}, and {101¯} of HAp. A comparison is made among the corresponding coincidence lattices, in order to explain on reticular basis the selective adsorption of citrate on the {001} HAp form. The role exerted by the 2D-epitaxially adsorbed Ca-Cit-TH as a “mortar” in the monoclinic HAp “brick” assembly is outlined as well. View Full-Text
Keywords: hydroxyapatite; Ca-citrate; adsorption; 2D epitaxy; biomineralization hydroxyapatite; Ca-citrate; adsorption; 2D epitaxy; biomineralization

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Pastero, L.; Bruno, M.; Aquilano, D. Habit Change of Monoclinic Hydroxyapatite Crystals Growing from Aqueous Solution in the Presence of Citrate Ions: The Role of 2D Epitaxy. Crystals 2018, 8, 308.

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