Download - Chemical Properties of Biomaterial
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1.Chemicalstructureandsurface
properties
Interfacialfreeenergy.
Balancebetweenthehydrophilicity and
hydrophobicity onthesurface.
Chemicalstructureandfunctionalgroups.
Typeanddensityofsurfacecharges.
Molecularweightofthematerial.
Surfacetopography
and
roughness.
2.Compatibility
Proteinadsorption.
Celladhesion.
Cytotoxicity.
Bloodcompatibility.
Tissuecompatibility.
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IONIZATION
Happenswhen
enough
energy
sources
is
available
fortheatomsormolecules
maketheatomstoacquirenetelectricalcharge,
changesitselectricalbalance
morecommonlyreferas
losingofelectronsto
formpositiveions
IONIZATIONENERGY
Amountofenergyneededfortheionization
tooccur
Differfordifferentsubstance
Usedinquantifyingchemicalbonds
Periodictable
increaseacross
the
period
decreaseacrossthegroup
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FACTORAFFECTINGIONIZATION
Radiationenergy
Typeofmaterial
Mechanismsofionization
Photoelectriceffect
Comptoneffect
Pairproductioneffect
PhotoelectricEffect
Completeabsorptionofthephotonenergy
Energylevelis10keVto500keV
Photonenergy=energy toliberateelectron+speed
offreeelectron
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ComptonEffect
Photonenergy=liberateelectrons+further
ionization
Energylevelisfrom50keV to3MeV
PairProduction
Annihilationofpositronandemissionof2
newphotons.
Energylevelis1.02MeV andabove
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Corrosion
Corrosionisanunwantedchemicalreaction
ofametalwithitsenvironmentresultinginits
continueddegradationtooxides,hydroxides,
orothercompounds
Theenvironment
for
the
Biomaterial
Water
Dissolvedoxygen
Proteins
Variousionssuchaschlorideandhydroxides
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ElectrochemicalProcess
Theprocessinvolvesinthecorrosion
Everymaterialwillalwaystrytomaintainatthelowestfreeenergystate
Forthemetallicmaterial,thelowestfreeenergystateisinanoxygenatedandhydroxideenvironment,whichisoftheoxide.
Whenthemetalatomionizedandgointothesolution,or
combinewith
oxygen
or
other
species
in
solution
to
form
acompoundthatdissolve,whichknownascorrosion
Pourbaix diagramincorrosion
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DifferentpartsofthebodyhavedifferentpH
valueandoxygenconcentration.
Itcanbeashighas9.0pHintheinfected
wound,andaslowas3.5pHinthewound
also.
Exampleofcorrosionofavailablemetal
Gold
9widelyusedinthedentalrestorationsandon
thatsettinginofferssuperiorperformanceand
longevity.
9 Butnotintheorthopedicapplicationdueits
highdensity,insufficientstrengthandhigh
cost.
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Stainlesssteels containenoughchromiumto
confer
corrosion
resistance
by
passivity.
itisnotasrobustastitanium
Itisvulnerabletopittingandtocrevice
corrosionaroundscrews
DegradationDegradation
Degradationofbiomaterialsmaybe
referredtoasthe deterioration ofthe
materialsusedwhichinteractwith
biologicalsystems
or
under
biological
environments.
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Degradation/deteriorationmechanisms
aredepending
on
the
type
of
materials
Metals:Eithermaterialslossbydissolution
(corrosion)orformationofanonmetallicscale
(oxidation).
Ceramics:Deteriorationathightemperature or
extremeenvironments.
Polymers:Maydissolveorabsorbandswell
whenexposed
to
solvents,
or
deteriorate
in
the
presenceofheat,lightorchemicals(more
commonlyknownaspolymerdegradation).
The
effect
of
solution
environment
on
nonmetallicmaterialinhumanbody
absorbfluidfromthesolutionandswell
releasemoleculesintofluidsolution
caninducechemicalreactioninthematerial
andchanges
its
behavior
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Ficks FirstLawofDiffusion
Ficks SecondLaw
of
Diffusion
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Deterioration
of
Ceramics
Generallyinertmaterialsthatdonotrelease
ionsintosolution.
Althoughabsorptionofceramicsfromthe
surroundingfluidislowbutitcanbe
significant.
.
Its
effect
is
concerned
with
degradation
of
mechanicalpropertiesunderinvivoconditions:
Youngsmodulusandyieldstrengthnot
affectedbyabsorption
Ultimatestrengthcanbereducedduetostatic
fatigue
Fatiguebehaviorisofconsiderableinterest.
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DeteriorationofPolymers
Multipleprocessesactingsimultaneouslycan
acceleratepolymerdegradationsuchas
chemical,thermalandphysicalenvironment.
Effectcanbedirectedat:
Mainbackbonechain
sidegroups
crosslinks
moleculararrangement
Linearpolymers
can
be
attacked
through:
Randomscission breakingofrandom
molecularbonds
Depolymerization shorteningofaverage
moleculelength
Bothacttoreducetheaveragemolecular
weight
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Crosslinkingcaneitherbeinducedordamagedby
chemicalattack
Inducedcrosslinkingoccursinlowdensitypolyethylenewhichmakesitstiffer
Damageofcrosslinksinpolyisoprene rubberresultsinabrittlematerial
Changeinbondstructurecanresultindifferentcompoundwithverydifferentproperties
Eg.
Polyvinyl
acetate
+
water
water
soluble
polyvinylalcohol+aceticacid
Chainscission
(or
Depolymerization)
reduces
Youngsmodulusandyieldstrength
Inducedcrosslinking increasesYoungs
modulusandyieldstrength.
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EffectofDegradationProduct
Tissuereaction
Organdamage
Carcinogenesis
Metabolicchange
Example
Injectedpolymers
Migrationofmaterialwithintissue
Formationof
tissue
masses
Possiblepulmonaryfailures
Leaching
aprocessofextractingcertainmineralsfroma
solidbydissolvingtheminaliquid
causedbythechemicalreactionofmetals
withcertainliquidssuchasacid.
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LeachingRate
Measuredinng/cm s
Speedupbyseveralfactors:
9 concentrationofacid
9 temperatureduringthereaction
9 useofcatalysts
2
LeachingImpacts
Thestructureofthebiomaterialbecomesweak
andunstable,whicheventuallymightfailto
maintainitsfunctionsinsidethepatientbody.
Theproductsofleachingreactionmightbetoxic
tohumanbody(biomaterialsbecomenot
biocompatible).
Theleaching
effect
might
require
replacements
ofbiomaterialswhichcanbewasteful.
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Solutionstopreventleaching
Placethechemicallyinertcoatingsorfilmson
theoutersurfaceofthebiomaterials.
Usethematerialssuchasporcelainwhichis
moreresistantagainsttheacidicliquidsfor
implantationpurposes.
Example
Artificialtooth madeofporcelainbutnotmetal
Bacteriain
the
mouth
produces
acid
which
can
leach
thecalciumawayfromnormalteeth.
Porcelainismorechemicallyresistantagainsttheacid
Prevent/minimizeleachingeffects