title: In situ hydrothermal crystallization of hexagonal hydroxyapatite tubes from yttrium ion-doped hydroxyapatite by the Kirkendall effect.
abstract: An in situ hydrothermal crystallization method with presence of glutamic acid, urea and yttrium ions was employed to fabricate hexagonal hydroxyapatite (HAp, Ca5(PO4)3(OH)) tubes with length of 200 nm-1 μm. Firstly, yttrium ion-doped HAp (Y-HAp, Ca(5-x)Y(x)(PO4)3(OH)) was synthesized after hydrolysis of urea and HPO4(2-) ions at 100°C with a dwell time of 24h. The shift of X-ray diffraction peaks of HAp to high angle was caused the substitution of Ca(2+) ions by small-sized Y(3+) ions. At 160°C, further hydrolysis reactions of urea and HPO4(2-) ions resulted in the generation of ample OH(-) and PO4(3-) ions, which provided a high chemical potential for the dissolution of Y-HAp and recrystallization of HAp and YPO4. Finally, HAp tubes were formed in situ on Y-HAp according to the Kirkendall effect as a result of the difference of diffusion rate of cations (Ca(2+) ions, outward and slow) and anions (OH(-) and PO4(3-) ions, inward and fast). The formation process of HAp tube was simulated by the encapsulation of fluorescein molecules in precipitates. Photoluminescence properties were enhanced for HAp tubes with thick and dense walls. This novel tubular material could find wide applications as carriers of drugs, dyes and catalysts.
authors.affiliation: School of Materials Science and Engineering, Shandong University of Technology, 255049 Shandong, PR China. Electronic address: cfli@sdut.edu.cn.
authors.forename: Chengfeng
authors.initials: C
authors.lastname: Li
authors.affiliation: School of Science, Shandong University of Technology, 255049 Shandong, PR China.
authors.forename: Xiaolu
authors.initials: X
authors.lastname: Ge
authors.affiliation: School of Materials Science and Engineering, Shandong University of Technology, 255049 Shandong, PR China.
authors.forename: Guochang
authors.initials: G
authors.lastname: Li
authors.affiliation: School of Materials Science and Engineering, Shandong University of Technology, 255049 Shandong, PR China.
authors.forename: Hao
authors.initials: H
authors.lastname: Lu
authors.affiliation: School of Materials Science and Engineering, Shandong University of Technology, 255049 Shandong, PR China.
authors.forename: Rui
authors.initials: R
authors.lastname: Ding
mesh_terms: D003460:Crystallization; D017886:Durapatite / Q000737:chemistry*; D018698:Glutamic Acid / Q000737:chemistry; D007477:Ions / Q000737:chemistry; D008855:Microscopy, Electron, Scanning; D010710:Phosphates / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D014508:Urea / Q000737:chemistry; D014961:X-Ray Diffraction; D015019:Yttrium / Q000737:chemistry*
chemical_list: D007477:Ions; D010710:Phosphates; D018698:Glutamic Acid; D015019:Yttrium; D014508:Urea; D017886:Durapatite
keywords: Biomaterials; Hollow structure; Hydroxyapatite; Kirkendall effect; Tube