Biomedical Engineering Reference
In-Depth Information
Infrared Spectroscopy of Bone
Fourier transform infrared (FTIR) spectroscopy is a widely used analytical
technique that is routinely applied to the characterization of biomaterials.
However, preparing samples of biomaterials for infrared spectroscopy is
often a tedious process. The main sampling problem in FTIR characteri-
sation of biomaterials is that nearly all solid materials are too opaque in
their normal forms for direct transmission analysis in the mid-infrared
region. This problem can be solved by reducing the optical density of sam-
ples to a suitable level by employing various sampling techniques [25,26].
These procedures, however, can alter the nature of the sample and are
time-consuming.
Various alternative techniques, such as diffuse reflectance (DRIFT)
and attenuated total reflectance (ATR) can be employed, but are limited
in applications due to stringent surface requirements. Another approach
is to avoid totally the opacity of the mid-infrared spectral region and
work within the near-infrared region by using overtone and combination
absorbance bands for analysis, where absorption coefficients are relatively
lower and samples are less opaque [27]. Unfortunately, a limited amount of
information is available within the near-infrared spectral region, whereas,
the mid-infrared region provides most spectral bands for the required
characterization.
Photo-acoustic sampling (PAS) provides a solution to these problems.
A photo-acoustic signal is generated when infrared radiation absorbed by
a sample is converted into heat within the sample. This heat diffuses to the
sample surface and into the adjacent atmosphere. Thermal expansion of this
gas produces the PAS signal. The signal generation process isolates a layer
extending beneath the sample's surface, which has a suitable optical density
for analysis, without altering the sample. The technique directly measures
the absorbance spectrum of this layer.
The PAS technique in conjunction with FTIR can be employed to char-
acterise natural bones and apatites, which helps to identify differences
between the carbonated and standard hydroxyl-apatites and allows com-
parison of commercial hydroxyapatite powders from different sources. The
contribution of the PAS-FTIR technique in the spectrochemical analysis of
biomaterials proves to be an ideal technique, where neat samples (without
the need of sample preparation) are analysed.
In addition to the human and sheep bone samples, commercial hydroxy-
apatite (HA) powders (P88, P120, P141, P149) from Plasma Biotal, HA
powder from Merck, and carbonated apatite synthesized within our
laboratories were also analysed to develop a relationship between the
natural and synthetic apatites. The natural apatite was from human and
sheep bone.
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