Mineral phases of calcium phosphate

Abstract

Many studies of calcium phosphate precipitation have been made using relaxation techniques in which the concentrations of the lattice ions are allowed to decrease as equilibrium is approached. Since the nature of the phases that form depend markedly on the solution composition, this decrease can lead to concomitant phase transformations during the crystallization experiments. The results of the present constant composition (CC) studies show that defect apatites may be formed under conditions of sustained supersaturation with a non-stoichiometric coefficient dependent on the pH of the growth medium. An important factor in analyzing these experiments is the initial surface modification and ion-exchange processes involving H+ and Ca2+ ions after inoculation of the supersaturated solutions. Thereafter, active growth sites may be eliminated as the crystals undergo lattice perfection. Transformation of dicalcium phosphate dihydrate to octacalcium phosphate, involving dissolution and subsequent nucleation and growth of the new phase, is also influenced by surface roughening of the initial phase. Typical inhibitors that reduce the rate of growth of seed crystals in supersaturated solutions may actually induce the nucleation of calcium phosphate phases when immobilized on inert surfaces. This may be a factor in the modulation of crystal growth in many biological systems.

<b>Enhancing osteoblast-affinity of titanium scaffolds for bone engineering by use of ultraviolet light tr</b><b>eatment </b>

“…4C). This Ca/P ratio is close to 1.66 : 1 of mature bone (9,18). The structures were almost filling the space between titanium fibers of the scaffold.…”

Bone Formation on Synthetic Precursors of Hydroxyapatite.

“…In supersaturated calcifying solutions, calcium deficient HA (Cain _ HX(PO4)6 (OH)2_X, 0<_ x <_2 ; Ca-deficient HA) (Winand 1965) has been shown to precipitate via the formation of one or more precursors such as amorphous calcium phosphate (Ca3(P04)2.nH2O ; ACP) (Eanes and Meyer 1977;Meyer and Eanes 1978a, b ;Tung and Brown 1983). For that reason, it is believed that precursor phases such as ACP, dicalcium phosphate dihydrate (CaHPO4.2H2O ; DCPD) and octacalcium phosphate (Ca8H2(P04)6.5H2O ; OCP) may participate in biological mineralization (Nancollas et al 1989). In fact, ACP has been detected within matrix vesicles isolated from epiphyseal calcified cartilage (Wuthier and Gore 1977;Aui et al 1978), and also OCP has been detected as one of the components of dental calculus (Schroeder and Bambauer 1966).…”

Quantification of octacalcium phosphate, authigenic apatite and detrital apatite in coastal sediments using differential dissolution and standard addition

“…Given the kinetic constraints of apatite nucleation under supersaturated conditions, more soluble Ca-P species may affect apatite formation according to the Ostwald step rule (Morse and Casey, 1988;Nancollas et al, 1989). Thus other Ca-P minerals, such as OCP and amorphous calcium phosphate (ACP), may represent significant sinks during early diagenesis and may influence soluble P levels.…”