Biomedical Engineering Reference
In-Depth Information
However, Boskey [19] has reported another story: “In 1964, Dr.
Paul Tannenbaum, a graduate student in periodontics at Columbia,
and a research assistant in Dr. Posner's laboratory at hospital for
special surgery, was studying the effect of fluoride on apatite crystal
size. He prepared a synthetic apatite by mixing high concentrations
(~30 mM) of calcium chloride and (~20 mM) sodium acid phosphate
in buffer, and, being anxious to confirm that the precipitate which
formed was apatite, pelleted it by centrifugation, dried it with
acetone and placed it on a holder for analysis by wide-angle X-ray
diffraction. The pattern obtained (Fig. 2.2, bottom) was broad and
diffuse, with a maximum at ~30° 2 theta, had no features, and was
clearly not apatite. Dr. Posner suggested that Dr. Tannenbaum did
not have the settings correct on the X-ray diffractometer, but since
it was late on Friday, decided to correct the settings on Monday. On
Monday, the sample, which had been left on the diffractometer over
the weekend, was again subjected to X-ray diffraction analysis, but
now the pattern had the appearance of a poorly crystalline apatite
(Fig. 2.2, middle). Dr. Tannenbaum was certain that the settings
on the diffractometer were not different from those he had used
previously. Instructed by Dr. Posner to repeat the experiment, he
observed the same phenomenon. Immediately after being mixed,
the precipitate formed was amorphous, while after several hours,
it converted to poorly crystalline apatite. It seemed plausible to
Dr. Posner that were such an “amorphous” material (i.e., one that
did not give a crystalline diffraction pattern) present in bone, along
with the apatite, it might account for the broad diffraction pattern of
bone mineral” [19]. One should stress, that both Chow et al., [99] and
Eanes [100] published corrigenda to this story by Boskey.
In 1960s, both X-ray diffraction and infrared spectroscopic
techniques were used to obtain a quantitative estimate of the
amorphous content of bone mineral and then, based on the methods
used in polymer chemistry, an algorithm to estimate the ACP amount
in bones was developed [101-103]. Early X-ray diffraction estimates
indicated the presence of ~30% or more of a non-crystalline mineral
in bones of several animal species. Later estimates by X-ray radial
distribution analysis placed the upper limit of ~10% ACP in bones
and brought into question whether all X-ray amorphous mineral of
bones was truly non-crystalline [17, 104-107]. However, further
studies by higher-resolution techniques have shown that ~99% of
the mineral in bone is a poorly crystalline ion-substituted CDHA of a
biological origin [19].
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