Microscopy and Microanalysis

Biological Applications

Minerals and Aligned Collagen Fibrils in Tilapia Fish Scales: Structural Analysis Using Dark-Field and Energy-Filtered Transmission Electron Microscopy and Electron Tomography

Mitsuhiro Okudaa1a2, Nobuhiro Ogawaa1, Masaki Takeguchia2 c1, Ayako Hashimotoa3, Motohiro Tagayaa1, Song Chena1, Nobutaka Hanagataa1 and Toshiyuki Ikomaa4

a1 Biomaterials Center, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan

a2 Advanced Nano-Characterization Center, National Institute for Materials Science, 3-13 Sakura, Tsukuba, Ibaraki 305-0003, Japan

a3 International Center for Young Scientists, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan

a4 Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1-S7-6 Ookayama, Meguro-ku, Tokyo 152-8550, Japan

Abstract

The mineralized structure of aligned collagen fibrils in a tilapia fish scale was investigated using transmission electron microscopy (TEM) techniques after a thin sample was prepared using aqueous techniques. Electron diffraction and electron energy loss spectroscopy data indicated that a mineralized internal layer consisting of aligned collagen fibrils contains hydroxyapatite crystals. Bright-field imaging, dark-field imaging, and energy-filtered TEM showed that the hydroxyapatite was mainly distributed in the hole zones of the aligned collagen fibrils structure, while needle-like materials composed of calcium compounds including hydroxyapatite existed in the mineralized internal layer. Dark-field imaging and three-dimensional observation using electron tomography revealed that hydroxyapatite and needle-like materials were mainly found in the matrix between the collagen fibrils. It was observed that hydroxyapatite and needle-like materials were preferentially distributed on the surface of the hole zones in the aligned collagen fibrils structure and in the matrix between the collagen fibrils in the mineralized internal layer of the scale.

(Received January 04 2011)

(Accepted July 11 2011)

(Online publication September 08 2011)

Correspondence:

c1 Corresponding author. E-mail: TAKEGUCHI.Masaki@nims.go.jp