Biomedical Engineering Reference
In-Depth Information
Chapter 7
Apatites in Acids
7.1
Introduction
Calcium apatites (HA and FA — see Table 1.1) appear to be of a
special interest to the human being, because natural apatites are the
main source of inorganic phosphorus in nature [1], while calcified
tissues (bones and teeth) of mammals consist of ion-substituted
calcium apatites of biological origin [2-4]. That is why such different
processes like fertilizer production, dental caries, osteoporosis, as
well as both
biodegradation of artificial bone
grafts might be simulated by apatite dissolution in acids. The latter
resulted in a great number of research papers published on apatites
and calcium orthophosphates (extensively reviewed in both Refs.
[5-7] and the previous chapters of this topic) and their dissolution
(see further in this chapter).
In chemistry, a reaction mechanism is the step-by-step sequence
of elementary reactions by which the overall chemical change occurs
[8]. Regarding the dissolution process of calcium apatites in acids,
eight models have been already proposed to explain the processes
involved. These models already provided the important information
about the factors associated with solution (pH, composition,
saturation, and hydrodynamics), bulk solid (chemical composition,
solubility, particle sizes), and surface (defects, adsorbed ions,
“history”, phase transformation) of the apatite crystals. These
in vitro
and
in vivo
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