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

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.

Studies on fish scale collagen of Pacific saury (Cololabis saira)

“…There is another strategy in application of fish scale collagen. Fish scale is a natural composite material consisting of hydroxyapatite crystals and collagen fibrils, like a plywood-like hierarchical supramolecular structure as described previously in Introduction [12][13][14][15][16][17]. Therefore it can be used as transparent biomaterials of both elasticity and high tensile strength after removal of calcium phosphate (hydroxyapatite).…”

“…Thin layers of the oriented collagen fibrils are piled up to form the fibrillary plate under the osseous layer [12]. The direction of the fibrils in each thin layer differs from each other.…”

“…The direction of the fibrils in each thin layer differs from each other. This plywood-like hierarchical supramolecular structure provides the high mechanical strength of scales, and it is of great interest to researchers in the field of biomaterials [12][13][14][15][16][17]. Fish collagen is present not only in scales but also in skin, bones, fins, and cartilage [9,10].…”

“…Although collagens from various fish species have been extracted from scales and skin and characterized [12][13][14][15][16][17][18][19][20][21][22][23], this study is the first to describe Type I collagen from the Pacific saury. We purified and characterized Type I collagen from the scales of C. saira and compared it with red sea bream and porcine collagen.…”

A Fish Scale–Derived Collagen Matrix as Artificial Cornea in Rats: Properties and Potential

“…Tilapia (Oreochromis mossambicus) are farmed for consumption under controlled circumstances 23 and the specific size of the fish can be selected on harvesting. Their scales consist of parallel-arranged collagen fibers packed in layers oriented approximately 90 degrees, 24 mimicking the human corneal stroma. This scaffold supports the growth of corneal cells and is highly permeable for oxygen.…”