Morphological evolution of calcium apatites from nanorods to hollow spheres mediated by acetic acid
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patite (HAp) and brushite (DCPD) are two important compounds of the calcium apatite family with excellent bioactivity and osteoconductive properties in vivo. This work aimed to investigate the stability of HAp nanorods synthesized by the hydrothermal method in acetic acid aqueous solution. The results illuminated that HAp nanorods were converted into hollow nanospheres, and it was found that the concentration and amount of the acetic acid and the reaction time significantly affected the degree of the morphological evolution. Transmission electron microscope, high-resolution transmission electron microscope, and x-ray diffraction were performed for characterizing the samples. I. INTRODUCTION
Calcium apatite family has a variety of derivatives including hydroxyapatite (HAp), brushite (known also as dicalcium phosphate dihydrate, DCPD), monocalcium phosphate monohydrate (MCPM), tricalcium phosphate (OCP), and so on.1,2 Calcium apatites occur as the principal inorganic constituents of normal (bones, teeth, fish enamel, deer antlers, and some species of shells) and pathological (dental and urinary calculus and stones, atherosclerotic lesions) calcifications. This determines that it is a class of chemical compounds of special significance in many fields such as geology, chemistry, biology, food science, medicine, tissue engineering, and so on.3–10 In recent years, calcium apatite family increasingly shows its prominent importance and attracts widespread attention. As one of the members in the family, HAp is well known for its biocompatible, osteoconductive, nontoxic, noninflammatory, nonimmunogenic agent and bioactive properties, especially the ability to form a direct chemical bond with living tissues.11–13 Various methods have been used to study the controlled synthesis and physical/ chemical properties of HAp.14–19 DCPD, another calcium phosphate family member, has been proposed as an intermediate in both bone mineralization and enamel dissolution.20 Because of similar biological activity to HAp, DCPD has recently been studied mainly for its role in drug delivery and tissue engineering.21–23 In this article, the morphological evolution of calcium apatite from HAp nanorods to DCPD hollow nanospheres a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2009.0305 J. Mater. Res., Vol. 24, No. 8, Aug 2009
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mediated by acetic acid was investigated. It was found that the dissolution of surfactants from the surface of the HAp nanorods and the in situ formation of micelles-like structures were the key for the transformation process. We believe that this interesting study could provide excellent help to further deepen the understanding and use of calcium phosphate salt. II. EXPERIMENTAL A. Preparation
All chemicals were of analytical grade and used asreceived without further purification, and purchased from Beijing Chemical Factory (Beijing, China). In a typical experimental process, uniform nanorods of HAp were synthesized by the hyd
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