Anisotropy in Bone Demineralization Revealed by Polarized Far-IR Spectroscopy

Roman Schuetz,Dmitri Fix,Richard Weinkamer,U Schade ,N.i Timofeeva ,Emad F Aziz ,Admir Mašić

doi:10.3390/molecules20045835

Abstract

Bone material is composed of an organic matrix of collagen fibers and apatite nanoparticles. Previously, vibrational spectroscopy techniques such as infrared (IR) and Raman spectroscopy have proved to be particularly useful for characterizing the two constituent organic and inorganic phases of bone. In this work, we tested the potential use of high intensity synchrotron-based far-IR radiation (50–500 cm−1) to gain new insights into structure and chemical composition of bovine fibrolamellar bone. The results from our study can be summarized in the following four points: (I) compared to far-IR spectra obtained from synthetic hydroxyapatite powder, those from fibrolamellar bone showed similar peak positions, but very different peak widths; (II) during stepwise demineralization of the bone samples, there was no significant change neither to far-IR peak width nor position, demonstrating that mineral dissolution occurred in a uniform manner; (III) application of external loading on fully demineralized bone had no significant effect on the obtained spectra, while dehydration of samples resulted in clear differences. (IV) using linear dichroism, we showed that the anisotropic structure of fibrolamellar bone is also reflected in anisotropic far-IR absorbance properties of both the organic and inorganic phases. Far-IR spectroscopy thus provides a novel way to functionally characterize bone structure and chemistry, and with further technological improvements, has the potential to become a useful clinical diagnostic tool to better assess quality of collagen-based tissues.

Highlights

Bone is a nanocomposite consisting of an organic collagen matrix and inorganic mineral particles of carbonated hydroxyapatite [1,2]
We measured for the first time far-IR spectra of bone where stepwise demineralization with Ethylenediaminetetraacetic acid (EDTA)
Our experiments allowed four interesting observations that are discussed in the following: (1) From the 2nd derivative analysis it results that peaks of the synthetic hydroxyapatite powder (HAP) and the fibrolamellar bone are at similar positions

Summary

Introduction

Bone is a nanocomposite consisting of an organic collagen matrix and inorganic mineral particles of carbonated hydroxyapatite [1,2]. With increase in mineral content the bone gets stiffer, but less tough [4]. The reason of the varying mineral content in bone is a biomineralization process together with the renewal process of bone remodeling [5]. For in vitro demineralization experiments of bone typically Ethylenediaminetetraacetic acid (EDTA) is used to resolve the mineral phase while leaving the structure of the organic phase virtually untouched [14]. The timing of the exposure of bone to an EDTA solution allows producing bone with reduced mineral content and, changed mechanical properties [15,16,17]

Objectives

Results

Conclusion