The effect of hydroxyapatite crystallinity on hemolysis.

Crystalline hydroxyapatite is a component of bone, teeth, and numerous pathological calcifications. The apatite crystal structure can accommodate a wide variety of atomic substitutions which gives apatite crystals an unusually high degree of variability in biochemical and physical properties. Apatite crystallites interact with numerous cellular systems in vivo, and some of these interactions may lead to altered cellular function. One measure of crystal-membrane interactions is crystal-induced membranolysis of human red blood cells. Hemolytic potentials at constant crystal surface areas were measured at 1, 2, and 4 hours for 29 different preparations of apatite. Each apatite sample was characterized by its morphology, particle size, % CO3, zeta potential, and broadening of the (211), (112), (300), (202), and (002) diffraction maxima. Only the surface area/g and the X-ray powder diffraction line broadening showed a significant inverse correlation with hemolytic potential. These parameters were related to each other, and are indications of the degree of crystallinity.