Abstract
Bone is formed by a series of complex events involving the mineralization
of extracellular matrix proteins rigidly orchestrated by cells with
specific functions of maintaining the integrity of the bone. Bone,
similar to other calcified tissues, is an intimate composite of the
organic (collagen and non-collagenous proteins) and inorganic or
mineral phases. The bone mineral idealized as calcium hydroxyapatite,
Ca-10(PO4)(6)(OH)(2), is a carbonate-hydroxyapatite, approximated
by the formula: (Ca,X)(10)(PO4,HPO4,CO3)(6)(OH,Y)(2), where X are
cations (magnesium, sodium, strontium ions) that can substitute for
the calcium ions, and Y are anions (chloride or fluoride ions) that
can substitute for the hydroxyl group. The current author presents
a brief review of CaP biomaterials that now are used as grafts for
bone repair, augmentation, or substitution. Commercially-available
CaP biomaterials differ in origin (natural or synthetic), composition
(hydroxyapatite, beta-tricalcium phosphate, and biphasic CaP), or
physical forms (particulates, blocks, cements, coatings on metal
implants, composites with polymers), and in physicochemical properties.
CaP biomaterials have outstanding properties: similarity in composition
to bone mineral; bioactivity (ability to form bone apatitelike material
or carbonate hydroxyapatite on their surfaces), ability to promote
cellular function and expression leading to formation of a uniquely
strong bone-CaP biomaterial interface; and osteoconductivity (ability
to provide the appropriate scaffold or template for bone formation).
In addition, CaP biomaterials with appropriate three-dimensional
geometry are able to bind and concentrate endogenous bone morphogenetic
proteins in circulation, and may become osteoinductive (capable of
osteogenesis), and can be effective carriers of bone cell seeds.
Therefore, CaP biomaterials potentially are useful in tissue engineering
for regeneration of hard tissues.
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