Ultrastructural analyses of nanoscale apatite biomimetically grown on organic template
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K.H. Lee Department of Nano-materials Engineering, Chungnam National University, Taejon, 305-764, Korea
M.E. Outslay Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2099
D.H. Kohn Department of Biologic and Materials Sciences, University of Michigan, Ann Arbor, Michigan 48109-1078; and Department of Biomedical Engineering, University of Michigan, Ann Arbor, Michigan 48109-2099 (Received 16 July 2007; accepted 2 November 2007)
The ultrastructure of nanoscale apatite biomimetically formed on an organic template from a supersaturated mineralizing solution was studied to examine the morphological and crystalline arrangement of mineral apatites. Needle-shaped apatite crystal plates with a size distribution of ∼100 to ∼1000 nm and the long axis parallel to the c axis ([002]) were randomly distributed in the mineral films. Between these randomly distributed needle-shaped apatite crystals, amorphous phases and apatite crystals (∼20–40 nm) with the normal of the grains quasi-perpendicular to the c axis were observed. These observations suggest that the apatite film is an interwoven structure of amorphous phases and apatite crystals with various orientations. The mechanisms underlying the shape of the crystalline apatite plate and aggregated apatite nodules are discussed from an energy-barrier point of view. The plate or needle-shaped apatite is favored in single-crystalline form, whereas the granular nodules are favored in the polycrystalline apatite aggregate. The similarity in shape in both single-crystalline needle-shaped apatite and polycrystalline granular apatite over a wide range of sizes is explained by the principle of similitude, in which the growth and shape are determined by the forces acting upon the surface area and the volume.
I. INTRODUCTION
Using a biomimetic approach to induce calcium– phosphate deposition from supersaturated solutions of simulated body fluid (SBF), bone-like apatite can be deposited on metals, ceramics, glasses, and polymers.1–7 Currently, this method is used to coat permanent implants1–4 with the aim of improving biological compatibility and osteoconductivity, as well as degradable scaffolds that support skeletal tissue repair and regeneration.5–8 Because direct bonding between an implant and bone can occur if a layer of bone-like mineral forms on the surface of the implant,9 it has been hypothesized that
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Address all correspondence to this author. e-mail: [email protected], [email protected] DOI: 10.1557/JMR.2008.0051 478
http://journals.cambridge.org
J. Mater. Res., Vol. 23, No. 2, Feb 2008 Downloaded: 16 Mar 2015
the formation of such a mineral layer within the pores of a scaffold may enhance the conduction of host cells into the scaffold and also enhance the osteogenic differentiation of transplanted cells.6 Because changes in mineral composition, structure, and morphology lead to biological changes in vitro and in vivo, the material characterization of the mineral layer interfacing with the biological milieu is of importance. The mac
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