Chemical Structural Analysis of Bone by Spectroscopy - Vibrational Spectroscopy for Tissue Analysis - page 189

7
Chemical Structural Analysis
of Bone by S pectroscopy
Introduction
In this chapter, Raman and infrared spectroscopy of natural bones is described.
These two studies on natural bones are presented as case studies. In addition,
we explain how both of the vibrational techniques have been crucial in provid-
ing a baseline for the modification of synthetic apatite powders that are now
routinely used as bone replacement materials. Prior to outlining the proce-
dural details, it is important to understand the chemical structural properties
of natural bone.
Cortical bone consists of two primary components: an inorganic or mineral
phase, which is mainly a carbonated form of a nanoscale crystalline calcium
phosphate, closely resembling hydroxyapatite (HA) [HA: Ca 10 (PO 4 ) 6 (OH) 2 ],
and an organic phase, which is composed largely of type I collagen fibres
[1-4]. Additional calcium phosphate phases have been proposed as minor-
ity constituents of the mineral phase of the bone tissue, such as octacalcium
phosphate and amorphous calcium phosphate [5]. Other constituents of bone
tissue include water and other organic molecules such as glycosaminogly-
cans, glycoproteins, lipids, and peptides. Ions such as sodium, magnesium,
fluoride, and citrate are also present [4], as well as hydrogenophosphate [6].
Hence, the mineral phase in bone may be characterised essentially as nonstoi-
chiometric substituted apatite. Such a distinction is important in the develop-
ment of synthetic calcium phosphates for application as skeletal implants. As
commercial calcium phosphates are generally based on hydroxyapatite, rather
than a biological apatite, it is not surprising that the biological activity of such
implants is less than that of Bioglass™ and AW™ glass ceramic, which develop
oxyhydroxy carbonate (OHC) surfaces [7-8].
An understanding of bone function and its interfacial relationship to
an implant clearly depends on the associated structure and composition.
Traditional techniques used for structural and compositional analysis include
light microscopy, electron microscopy, X-ray diffraction, and chemical analy-
sis [9]. However, in preparation for such analysis, the tissue can be subjected
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