Chemical Properties of Biomaterial

7/27/2019 Chemical Properties of Biomaterial

1/17


2/17

1.Chemicalstructureandsurface

properties

Interfacialfreeenergy.

Balancebetweenthehydrophilicity and

hydrophobicity onthesurface.

Chemicalstructureandfunctionalgroups.

Typeanddensityofsurfacecharges.

Molecularweightofthematerial.

Surfacetopography

and

roughness.

2.Compatibility

Proteinadsorption.

Celladhesion.

Cytotoxicity.

Bloodcompatibility.

Tissuecompatibility.


3/17

IONIZATION

Happenswhen

enough

energy

sources

is

available

fortheatomsormolecules

maketheatomstoacquirenetelectricalcharge,

changesitselectricalbalance

morecommonlyreferas

losingofelectronsto

formpositiveions

IONIZATIONENERGY

Amountofenergyneededfortheionization

tooccur

Differfordifferentsubstance

Usedinquantifyingchemicalbonds

Periodictable

increaseacross

the

period

decreaseacrossthegroup


4/17

FACTORAFFECTINGIONIZATION

Radiationenergy

Typeofmaterial

Mechanismsofionization

Photoelectriceffect

Comptoneffect

Pairproductioneffect

PhotoelectricEffect

Completeabsorptionofthephotonenergy

Energylevelis10keVto500keV

Photonenergy=energy toliberateelectron+speed

offreeelectron


5/17

ComptonEffect

Photonenergy=liberateelectrons+further

ionization

Energylevelisfrom50keV to3MeV

PairProduction

Annihilationofpositronandemissionof2

newphotons.

Energylevelis1.02MeV andabove


6/17

Corrosion

Corrosionisanunwantedchemicalreaction

ofametalwithitsenvironmentresultinginits

continueddegradationtooxides,hydroxides,

orothercompounds

Theenvironment

for

the

Biomaterial

Water

Dissolvedoxygen

Proteins

Variousionssuchaschlorideandhydroxides


7/17

ElectrochemicalProcess

Theprocessinvolvesinthecorrosion

Everymaterialwillalwaystrytomaintainatthelowestfreeenergystate

Forthemetallicmaterial,thelowestfreeenergystateisinanoxygenatedandhydroxideenvironment,whichisoftheoxide.

Whenthemetalatomionizedandgointothesolution,or

combinewith

oxygen

or

other

species

in

solution

to

form

acompoundthatdissolve,whichknownascorrosion

Pourbaix diagramincorrosion


8/17

DifferentpartsofthebodyhavedifferentpH

valueandoxygenconcentration.

Itcanbeashighas9.0pHintheinfected

wound,andaslowas3.5pHinthewound

also.

Exampleofcorrosionofavailablemetal

Gold

9widelyusedinthedentalrestorationsandon

thatsettinginofferssuperiorperformanceand

longevity.

9 Butnotintheorthopedicapplicationdueits

highdensity,insufficientstrengthandhigh

cost.


9/17

Stainlesssteels containenoughchromiumto

confer

corrosion

resistance

by

passivity.

itisnotasrobustastitanium

Itisvulnerabletopittingandtocrevice

corrosionaroundscrews

DegradationDegradation

Degradationofbiomaterialsmaybe

referredtoasthe deterioration ofthe

materialsusedwhichinteractwith

biologicalsystems

or

under

biological

environments.


10/17

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


11/17

Ficks FirstLawofDiffusion

Ficks SecondLaw

of

Diffusion


12/17

Deterioration

of

Ceramics

Generallyinertmaterialsthatdonotrelease

ionsintosolution.

Althoughabsorptionofceramicsfromthe

surroundingfluidislowbutitcanbe

significant.

.

Its

effect

is

concerned

with

degradation

of

mechanicalpropertiesunderinvivoconditions:

Youngsmodulusandyieldstrengthnot

affectedbyabsorption

Ultimatestrengthcanbereducedduetostatic

fatigue

Fatiguebehaviorisofconsiderableinterest.


13/17

DeteriorationofPolymers

Multipleprocessesactingsimultaneouslycan

acceleratepolymerdegradationsuchas

chemical,thermalandphysicalenvironment.

Effectcanbedirectedat:

Mainbackbonechain

sidegroups

crosslinks

moleculararrangement

Linearpolymers

can

be

attacked

through:

Randomscission breakingofrandom

molecularbonds

Depolymerization shorteningofaverage

moleculelength

Bothacttoreducetheaveragemolecular

weight


14/17

Crosslinkingcaneitherbeinducedordamagedby

chemicalattack

Inducedcrosslinkingoccursinlowdensitypolyethylenewhichmakesitstiffer

Damageofcrosslinksinpolyisoprene rubberresultsinabrittlematerial

Changeinbondstructurecanresultindifferentcompoundwithverydifferentproperties

Eg.

Polyvinyl

acetate

+

water

water

soluble

polyvinylalcohol+aceticacid

Chainscission

(or

Depolymerization)

reduces

Youngsmodulusandyieldstrength

Inducedcrosslinking increasesYoungs

modulusandyieldstrength.


15/17

EffectofDegradationProduct

Tissuereaction

Organdamage

Carcinogenesis

Metabolicchange

Example

Injectedpolymers

Migrationofmaterialwithintissue

Formationof

tissue

masses

Possiblepulmonaryfailures

Leaching

aprocessofextractingcertainmineralsfroma

solidbydissolvingtheminaliquid

causedbythechemicalreactionofmetals

withcertainliquidssuchasacid.


16/17

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.


17/17

Solutionstopreventleaching

Placethechemicallyinertcoatingsorfilmson

theoutersurfaceofthebiomaterials.

Usethematerialssuchasporcelainwhichis

moreresistantagainsttheacidicliquidsfor

implantationpurposes.

Example

Artificialtooth madeofporcelainbutnotmetal

Bacteriain

the

mouth

produces

acid

which

can

leach

thecalciumawayfromnormalteeth.

Porcelainismorechemicallyresistantagainsttheacid

Prevent/minimizeleachingeffects

Documents

Chemical Properties of Biomaterial