Crystallographic Characteristics of Hydroxylapatite in Hard Tissues of Cololabis saira

Hejing Wang,Lei Yuan,Jiali An

doi:10.3390/cryst7040103

Abstract

X-ray micro diffractometry, transmission electron microscopy, environmental scanning electron microscopy, energy dispersive spectrometry and Fourier transform infrared were employed to investigate the crystallographic characteristics of the inorganic mineral existing in bones of Cololabis saira. The results show that the crystal phase in hard tissues of Cololabis saira is hydroxylapatite (HAP). Chemical composition analysis reveals that the HAP in hard tissues lacks P and is rich in Ca. Refined lattice parameters of HAP show that a = 0.93622–0.93787 nm and c = 0.68549–0.69011 nm. The domain sizes calculated from the Scherrer equation are 18.9–20.7 nm long along the c-axis and about 6.2 nm thick perpendicular to the c-axis, and is well evidenced by TEM data. The crystallinity of HAP is poor compared with natural HAP. In situ X-ray micro diffraction patterns measured from raw hard tissue show a very strong reflection from the (002) and (004) lattice planes on the cross-section of bone and nearly no reflection from the (002) and (004) lattice planes on elongation surface of bone. Compared with the XRD pattern of standard HAP data and from the textural index R values, it indicates that the HAP in the hard tissues of Cololabis saira has a strong preferring orientation along the crystallographic c-axis. This is verified by Fourier transform infrared on the elongation surface of bone and by selected area electron diffraction of HRTEM on the section perpendicular to elongation of bone. A quantitative textural degree index DR is proposed. The crystallographic characteristics of bio-hydroxylapatites (particle size, crystallinity and preferring orientation) are designed by tissue function and controlled by organic matrix to provide a good mechanical performance.

Highlights

Fish is one of the most ancient vertebrates
Compared with the X-ray diffraction technique (XRD) pattern of standard HAP data and from the textural index R values, it indicates that the HAP in the hard tissues of Cololabis saira has a strong preferring orientation along the crystallographic c-axis
We focus on the mineral phase, crystallinity and preferring orientation of minerals in “soft” bones of Cololabis saira by X-ray micro diffractometry (XRMD), and it is anticipated that this work would offer valuable data for discussing the differences in crystallographic performance of minerals among hard tissues and provide an effective basis for research and application of biomineralization

Summary

Introduction

The physical and chemical properties and crystallographic characteristics of biominerals in hard tissues of fish have theoretically important guidance value for biomineralization mechanism, mineralogy, crystallography and environmental sciences studies. The connection between the composition and structural differences with living environment has been a hot spot for discussion, and there have been abundant research results [1,2,3,4]. Some scholars investigated the relationship between scale structure and surface morphology with fish species [5], some studied the biochemical characteristics of scale [6,7] and some explored the applications in biological engineering [8]. A few research papers on microstructure and mechanical properties of fish bones were performed [9]. Different mineral properties are designed by mineral’s chemical compositions and crystal structures. Because organisms control the crystallization of inorganic phases in different levels [10] and regulate the growth morphology of crystals in three-dimensional

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Results

Conclusion