ABSTRACT
Pure. crystalline. hydroxyapatite. (HA). has. the. composition. of. Ca10(PO4)6(OH)2. with. the. calcium. to.phosphor.mole.ratio.Ca/P.=.1.67..The.main.composition.of.the.biological.bone.is.nanograined. hydroxyapatite.(HA).with.the.grain.size.of.about.5.to.50.nm.(see.Figure.22.1)..In.a.physiological. environment,.bone.is.a.nonstoichemical.HA.of.Ca/P.mole.ratio.=.1.5.to.1.67,.dependent.on.the.age. and.bone.site..Some.ions.such.as.HPO 4
3− .and.OH-1..Some. other.earth.elements.such.as.Mg2+.and.Sr2+.can.replace.Ca2+,.too..The.common.formula.should.be. Ca10-x+y(PO4)6-x(OH)2-x-2y,.where.0.<.x <.2.and.0.<.y <.x/2..For.example,.the.bone.composition.can. be.represented.by.the.formula.of
Bone.is.a.living.tissue.and.undergoes.constant.change.in.composition.by.either.dissolving.or.deposition.of.bone.minerals.through.osteoclast.and.osteoblast.cells,.respectively..The.nano-HA.has.a. nanocrystalline.feature.similar.to.the.bone,.thus.being.used.as.the.bone.substitute.material.[1-3].
