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Biomimetic Mineralization of Apatite on Bacterial Cellulose
mineralization. of. inorganic. particles. in. the. form. of. small. apatite. crystals.
(Nge.and.Sugiyama.2007),.which.will.be.discussed.in.this.chapter.
The. growth. and. form. of. biologically. relevant. minerals,. such. as. calcium.
phosphate.(in.bone.tissue).and.calcium.carbonate.(in.mollusk.shell).involve.
the. deposition. of. these. solids. in. the. presence. of. organic. molecules.. Bone.
. tissue.is.a.type.I.collagen.fiber–apatite.composite.in.which.hierarchical.structure. collagen. fibrils. are. calcified. by. deposition. of. calcium. and. phosphate.
in.the.form.of.small.apatite.crystals..The.bone.cells.integrating.within.the.
mineralized.collagen.matrix.are.biochemically.active.and.communicate.with.
each.other.as.well.as.with.cells.outside.the.tissues..In.this.way,.the.mineral.
becomes.an.integrated.system.capable.of.functional.adaptation,.accommodating.the.mechanical.force.encountered.in.bone.tissues.(Gilmcher.1998).
Therefore.bioceramic.composites.based.on.calcium.phosphates.are.important. materials. for. bone. substitution,. repair,. and. tissue. engineering. applications.. It. was. reported. that. bioactive. materials. such. as. Bioglass ® ,. sintered.
hydroxyapatite,.and.glass-ceramic.apatite-wollastonite.(A-W).have.the.. ability.
to. form. a. carbonate-containing. hydroxyapatite. (bonelike. apatite). layer. on.
their.surface.in.the.living.body.and.bond.to.host.living.bony.tissue.through.
this.apatite.layer.(Kokubo.1991)..Formation.of.bonelike.apatite.on.the.surface.
of.the.artificial.implant.is.thus.essential.for.bonding.the.implant.to.the.living.
bone.without.intervention.of.the.fibrous.tissues.(Kokubo.1993)..A.biomimetic.
route.for.the.formation.of.bonelike.apatite.on.various.materials.such.as.metals.
(Uchida.et.al..2003).and.polymers.(Bigi.et.al..2002;.Maeda.et.al..2002;.Takeuchi.
et.al..2003).was.developed.to.improve.bonding.abilities.
Fabrication.of.matrix-assisted.bioceramic.composites.by.in.situ.precipitation.
or.mineralization.on.biocompatible.and/or.biodegradable.polymers.using.a.
biomimetic.approach.has.become.an.attractive.method.because.the.polymer.
matrices.serve.as.not.only.templates,.but.also.binders.to.prevent.migration.of.
the.mineral.particles,.as.well.as.improve.mechanical.integrity.of.the.developed.
materials.owing.to.their.toughness.and.flexibility..The.biomimetic.approach.
involves.soaking.the.template.materials.either.in.a.simulated.body.fluid.(SBF).
having.equal.ion.concentrations.to.that.of.human.blood.plasma.at.physiological.pH.and.temperature.(Kokubo.et.al..1990),.or.alternatively.in.calcium.and.
phosphate.solutions.prepared.with.a.calcium.(Ca):phosphorus.(P).ratio.of.1.67,.
similar. to. the. Ca:P. ratio. of. synthetic. hydroxyapatite. (HA; Ca 10 (PO 4 ) 6 (OH) 2 )..
The.concept.of.mineralization.includes.the.heterogeneous.nucleation.of.apatite.crystals.in.the.presence.of.surface.functional.groups.of.polymer.matrices.
and.the.increased.supersaturation.of.the.surrounding.fluid.to.accelerate.the.
nucleation.process.and.growth.
Since.surface.chemical.structures.exert.a.significant.influence.on.the.formation. of. the. apatite. layer. on. materials. surfaces,. activation. of. the. BC. surface.appears.to.be.a.prerequisite.for.biomimetic.mineralization..Granja.et.al..
(2001a).reported.that.the.derivatization.of.the.cellulose.with.anionic.phosphate. groups. or. pretreatment. of. cellulose. with. calcium. dichloride. (Granja.
et.al..2001b).activated.the.deposition.of.apatite.on.cellulose.from.SBF.under.