Biomedical Engineering Reference
In-Depth Information
Chapter 2
2.1
Introduction
In nature, amorphous phases exist extensively with readily
moldable isotropic properties and of structure materials. For
example, amorphous structures represent ~20% of approximately
60 different inorganic compounds and minerals formed by
living organisms. These biologically formed minerals are often
called biominerals, while the process of their formation is called
biomineralization [1]. A recent review on the subject indicates that
many biominerals are formed from amorphous precursors and,
furthermore, the amorphous phases may possess fluidic properties
that impart new processing capabilities to the system [2]. Among
the existing biogenic amorphous minerals, those composing from
calcium orthophosphates are most abundant in teeth and exoskeletal
structures of marine invertebrates [2-6]. On the other hand, the
existence of similar amorphous calcium phosphate (ACP) minerals in
vertebrate organisms has not been well established experimentally
except in highly specialized locations such as the inner ear structures
of embryonic sharks [1], mammalian milk [7, 8], dental enamel [9], as
well as in mitochondria [1] and sarcoplasmic reticulum [10] of some
cells. Despite the intensive efforts, accumulated evidences for ACP as
an integral mineral component in major hard tissues, such as bones
and teeth, are equivocal and for many years have been the subject of
considerable debates [11-24]. However, recent studies on bone and
teeth formation have suggested a presence of transient amorphous
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