biomaterials 2010 fall week11 2-7

7/25/2019 Biomaterials 2010 Fall Week11 2-7

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BiomaterialsBiomaterialsWeek 11Week 11

11/29/201011/29/2010Classes of Materials used inClasses of Materials used in

MedicineMedicine


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2.7 Bioresorbable and2.7 Bioresorbable and

Bioerodible materialsBioerodible materials


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Introduction:Introduction: Bioresorbable and BioerodibleBioresorbable and Bioerodible

De radable im!lant" no need to beDe radable im!lant" no need to beremo#edremo#ed

$em!orar% !resence $em!orar% !resence&otential concern: to'icit%&otential concern: to'icit%


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De(nition relatin to t)e !rocessDe(nition relatin to t)e !rocessor erosion and/or de radationor erosion and/or de radation

*sed to indicate a i#en material*sed to indicate a i#en materiale#entuall% disa!!ear after )a#ine#entuall% disa!!ear after )a#inbeen introduced into li#in or anismbeen introduced into li#in or anism

Biode radationBiode radationBioerosionBioerosionBioabsor!tionBioabsor!tionBioresor!tionBioresor!tion


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De radationDe radation

C)emicalC)emical !rocess!rocessClea#a e of co#alent bondClea#a e of co#alent bond

+%drol%sis+%drol%sis,'idati#e and en-%me mec)anism,'idati#e and en-%me mec)anism


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,#er#ie of current a#ailable,#er#ie of current a#ailablede radable !ol%mersde radable !ol%mers


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,#er#ie of current a#ailable,#er#ie of current a#ailablede radable !ol%mersde radable !ol%mers

Desi n" s%nt)esis of ne " de radableDesi n" s%nt)esis of ne " de radablebiomaterials is currentl% an im!ortantbiomaterials is currentl% an im!ortantresearc) c)allen eresearc) c)allen eIn tissue en ineerin : de#elo!ment ofIn tissue en ineerin : de#elo!ment ofne biomaterials t)at can !ro#idene biomaterials t)at can !ro#ide!redetermined and controlled cellular!redetermined and controlled cellularres!onse needed com!onent of mostres!onse needed com!onent of most!ractical a!!lications of tissue!ractical a!!lications of tissueen ineerinen ineerin


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&ol%dio'anone 5&D 6&ol%dio'anone 5&D 6

&ol% 5et)er ester6&ol% 5et)er ester6in 4o!eninin 4o!enin!ol%meri-ation of !4!ol%meri-ation of !4dio'anone monomerdio'anone monomer

8o to'icit% monomer8o to'icit% monomer8o er modulus t)an8o er modulus t)an&8 or &=&8 or &=*sed in*sed in

Mono(lament sutureMono(lament sutureuture cli!uture cli!Bone !inBone !in


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&ol%5)%dro'%but%rate6 5&+B6&ol%5)%dro'%but%rate6 5&+B6 ""!ol%5)%dro'%#alerate6 5&+;6 and!ol%5)%dro'%#alerate6 5&+;6 and

co!ol%merco!ol%mer&ol%ester from&ol%ester frommicroorganismmicroorganism&+B: cr%stalline and&+B: cr%stalline andbrittlebrittle

Co!ol%mer &+B andCo!ol%mer &+B and&+; acid: less&+; acid: lesscr%stalline more >e'iblecr%stalline more >e'ible*sed: dru release"*sed: dru release"suture" arti(cial skinsuture" arti(cial skinand #ascular raftsand #ascular raftslo de radation timelo de radation time5?00 da%s" @0 A5?00 da%s" @0 Asti ness6sti ness6


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&ol%ca!rolactone 5&C86&ol%ca!rolactone 5&C86

emicr%stallineemicr%stalline!ol%mer!ol%merDe rade at lo er !aceDe rade at lo er !ace

t)an &8t)an &8*sed in dru release:*sed in dru release:acti#e for o#er 1 %earacti#e for o#er 1 %earonto'ic and tissue4onto'ic and tissue4

com!atible materialscom!atible materials*sed in ound*sed in ounddressin s" anddressin s" andde radable sta!lede radable sta!le


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&ol%an)%drides&ol%an)%drides

+%drol%tic instabilit%+%drol%tic instabilit%li!)aticli!)atic .. 5an or anic com!ound )a#in an o!en45an or anic com!ound )a#in an o!en4

c)ain structure6c)ain structure6 !ol%an)%drides de rade: da%s!ol%an)%drides de rade: da%s

romaticromatic 5rin s%stem 5as ben-ene6 containin usuall%5rin s%stem 5as ben-ene6 containin usuall%multi!le con u ated double bonds6multi!le con u ated double bonds6 !ol%an)%drides!ol%an)%dridesde rade: %earsde rade: %earsli!)atic and aromatic co!ol%mer:li!)atic and aromatic co!ol%mer:

intermediate rateintermediate rate+i ) de radation rate: de rade b% surface+i ) de radation rate: de rade b% surfaceit)out catal%st or e'ci!ientsit)out catal%st or e'ci!ients 5inert substance 5as5inert substance 5asum arabic or starc)6 t)at forms a #e)icle 5as for a dru 6 6um arabic or starc)6 t)at forms a #e)icle 5as for a dru 6 6


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eact it) dru containin aminoeact it) dru containin aminorou! or nucleo!)ilic functional rou!rou! or nucleo!)ilic functional rou!eaction it) nucleo!)ile: limit t)eeaction it) nucleo!)ile: limit t)et%!e of dru can be successfull%t%!e of dru can be successfull%incor!oratedincor!oratedmine containin biomolecules couldmine containin biomolecules couldreact it) an)%dride bond on t)ereact it) an)%dride bond on t)esurfacesurfaceucleo!)ile: as an electron4donatinucleo!)ile: as an electron4donatin rea entrea ent


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'cellent biocom!atibilit%'cellent biocom!atibilit%Dru deli#erDru deli#er&re!ared b% com!ression moldin or&re!ared b% com!ression moldin ormicroenca!sulationmicroenca!sulationInsulin" bo#ine ro t) factors"Insulin" bo#ine ro t) factors"an io enesis in)ibitor 5)er!arin"an io enesis in)ibitor 5)er!arin"cortisone6 en-%mecortisone6 en-%meon#iral #ectors of deli#erin D inon#iral #ectors of deli#erin D inene t)era!%ene t)era!%


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&ol%5amino acid6 and !seudo4 &ol%5amino&ol%5amino acid6 and !seudo4 &ol%5aminoacid6acid6

&ronounce tendenc% to s ell in&ronounce tendenc% to s ell ina ueousa ueousDiFcult to !redict dru release rateDiFcult to !redict dru release rateo far" no a!!ro#ed b%


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&ol%5 l%colic acid6 5&= 6 and&ol%5 l%colic acid6 5&= 6 and!ol%5latic acid6 5&8 6 co!ol%mers!ol%5latic acid6 5&8 6 co!ol%mers

In#esti ated in:In#esti ated in:#ascular L urolo ical stents#ascular L urolo ical stentskin substituteskin substitutes

ca old for tissue en ineerinca old for tissue en ineerin $issue reconstruction $issue reconstruction

*nsol#ed issues:*nsol#ed issues:Most cell do not attac) to &= L &8 surface"Most cell do not attac) to &= L &8 surface"

!oor substrate for cell ro t)K for tissue!oor substrate for cell ro t)K for tissueen ineerin used is debatableen ineerin used is debatableDe radation !roduct stron acid accumulate atDe radation !roduct stron acid accumulate atim!lant site" dela%ed in>ammator% res!onseim!lant site" dela%ed in>ammator% res!onse


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!!lications of s%nt)etic"!!lications of s%nt)etic"de radable !ol%mers asde radable !ol%mers as

biomaterialsbiomaterials

Classi(cation of de radableClassi(cation of de radable

medical im!lantsmedical im!lants


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Classi(cation of de radable medicalClassi(cation of de radable medicalim!lantsim!lants

? main t%!e of de radable im!lants:? main t%!e of de radable im!lants: tem!orar% su!!ort de#ice tem!orar% su!!ort de#ice

tem!orar% barrier tem!orar% barriern im!lantable dru deli#er% s%stemn im!lantable dru deli#er% s%stem $)e tissue en ineerin sca old $)e tissue en ineerin sca old

$)e multifunctional im!lant $)e multifunctional im!lant


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$em!orar% barrier $em!orar% barrier

Medical ad)esion !re#entionMedical ad)esion !re#entiond)esion formed bet een t o tissue sections b%d)esion formed bet een t o tissue sections b%clottin blood in e'tra#ascular tissueclottin blood in e'tra#ascular tissue s!aces!acefollo ed b% in>ammation and (brosis.follo ed b% in>ammation and (brosis.

Cause !ain" functional im!airment" and !roblemsCause !ain" functional im!airment" and !roblemsdurin subse uent sur er%durin subse uent sur er%ur ical ad)esions: caused of morbidit%" andur ical ad)esions: caused of morbidit%" andre!resent one of t)e most si ni(cant com!licationsre!resent one of t)e most si ni(cant com!licationsof a ide ran e of sur ical !rocedures suc) asof a ide ran e of sur ical !rocedures suc) ascardiac" s!inal" and tendoncardiac" s!inal" and tendon sur er%sur er%In#esti ated for sealin of breac)es of t)e lunIn#esti ated for sealin of breac)es of t)e luntissue t)at cause leaka etissue t)at cause leaka e


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n im!lantable dru deli#er%n im!lantable dru deli#er%de#icede#ice

B% necessit% a tem!orar% de#iceB% necessit% a tem!orar% de#ice $)e de#ice ill e#entuall% run out of $)e de#ice ill e#entuall% run out ofdru or t)e need for t)e deli#er% of adru or t)e need for t)e deli#er% of as!eci(c dru is eliminated once t)es!eci(c dru is eliminated once t)ediseased is treateddiseased is treatedMost idel% in#esti ated a!!licationMost idel% in#esti ated a!!licationof de radable !ol%mersof de radable !ol%mers


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$issue en ineerin sca old $issue en ineerin sca old

De radable im!lantDe radable im!lant t)at is desi ned to act as ant)at is desi ned to act as anarti(cial e'tracellular matri'arti(cial e'tracellular matri' b% !ro#idinb% !ro#idin s!ace fors!ace forcells to rocells to ro into and reco ni-e into functionalinto and reco ni-e into functionaltissuetissue

Man madeMan made im!lantable !rost)eses doim!lantable !rost)eses do not functionnot functionas ell as t)e nati#e tissueas ell as t)e nati#e tissue,r maintain t)e functionalit% of nati#e tissue o#er,r maintain t)e functionalit% of nati#e tissue o#erlon !eriods of timelon !eriods of timeInterdisci!linar% (eld t)at utili-es de radableInterdisci!linar% (eld t)at utili-es de radable!ol%mers" amon ot)er substrates and biolo ics" to!ol%mers" amon ot)er substrates and biolo ics" tode#elo! treatments t)at ill allo t)e bod% to )ealde#elo! treatments t)at ill allo t)e bod% to )ealitself it)out t)e need for !ermanentl% im!lanted"itself it)out t)e need for !ermanentl% im!lanted"arti(cial !rost)etic de#icesarti(cial !rost)etic de#ices


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Ideal case" a tissue en ineerin sca old is im!lantedIdeal case" a tissue en ineerin sca old is im!lantedtoto restore lost tissue function" maintain tissuerestore lost tissue function" maintain tissuefunction" or en)ance e'istin tissue functionfunction" or en)ance e'istin tissue functionCan take t)e form of feltlike material obtained fromCan take t)e form of feltlike material obtained from

knitted or o#en (bers or from (ber mes)esknitted or o#en (bers or from (ber mes)es;arious !rocedures be used to obtain foams or;arious !rocedures be used to obtain foams ors!on ess!on es&ore interconnecti#it%&ore interconnecti#it% is a ke% !ro!erties: as cellsis a ke% !ro!erties: as cellsneed to be able to mi rate and ro t)rou )out t)eneed to be able to mi rate and ro t)rou )out t)e

entire sca oldentire sca old,!en !ore structure,!en !ore structureMa% be !reseeded it) cells in #itro !rior" follo ed b%Ma% be !reseeded it) cells in #itro !rior" follo ed b%t)e safe resor!tion of sca old materialt)e safe resor!tion of sca old material


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=uided tissue re eneration 5=$ 6:=uided tissue re eneration 5=$ 6:traditionall% used in dentistr%traditionall% used in dentistr%ca old encoura e t)e ro t) ofca old encoura e t)e ro t) ofs!eci(c t%!e of tissues!eci(c t%!e of tissue

$reatment of !eriodontal disease" $reatment of !eriodontal disease"fa#or ne bone ro t) in t)efa#or ne bone ro t) in t)e!eriodontal !ocket o#er soft tissue!eriodontal !ocket o#er soft tissuein ro t)sin ro t)s


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C)allen es in t)e desi n of tissue en ineerinC)allen es in t)e desi n of tissue en ineerinsca old is t)e need tosca old is t)e need to ad ust t)e rate ofad ust t)e rate ofsca old de radation to rate of tissue )ealinsca old de radation to rate of tissue )ealin&ol%mer ma% need to function on t)e order of&ol%mer ma% need to function on t)e order of

da%s to mont)sda%s to mont)s


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Multifunctional de#icesMultifunctional de#ices

Combinin se#eral functions as oneCombinin se#eral functions as onesin le de#icesin le de#ice

$)ese a!!lications en#ision t)e $)ese a!!lications en#ision t)ecombination ofcombination of se#eral functionsse#eral functionsit)in t)e same de#iceit)in t)e same de#ice and re uireand re uiret)e desi n of custom4made materialst)e desi n of custom4made materialsit) narro ran e of !redeterminedit) narro ran e of !redeterminedmaterials !ro!ertiesmaterials !ro!erties


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*ltra)i )4stren t) !ol%5lactic acid6*ltra)i )4stren t) !ol%5lactic acid6biode radable bone scre sbiode radable bone scre s and bone nailsand bone nailso!ens t)e !ossibilit% of combinin t)eo!ens t)e !ossibilit% of combinin t)emec)anical su!!ort3 function of t)e de#icemec)anical su!!ort3 function of t)e de#iceit) ait) a site4s!eci(c dru deli#er%3site4s!eci(c dru deli#er%3 functionKfunctionK biode radable biode radable bone nailbone nail t)at )olds t)et)at )olds t)efractured bone in !lace can simultaneousl%fractured bone in !lace can simultaneousl%stimulate t)e ro t) of ne bone tissue at t)estimulate t)e ro t) of ne bone tissue at t)efracture site b% slo l%fracture site b% slo l% release bone ro t)release bone ro t)factors t)rou )outfactors t)rou )out its de radation !rocessits de radation !rocess


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Biode radable stents for im!lantation intoBiode radable stents for im!lantation intocoronar% artiescoronar% artiestents are desi ned totents are desi ned to mec)anicall%mec)anicall%

!re#ent to colla!se and restenosis!re#ent to colla!se and restenosis 5 ecurrence5 ecurrence

of stenosisof stenosis OO constriction or narro in of a duct or !assa eP constriction or narro in of a duct or !assa eP afterafter

correcti#e sur er% on a )eart #al#e6correcti#e sur er% on a )eart #al#e6 of arteries t)atof arteries t)at)a#e been o!ened b% balloon an io!last%)a#e been o!ened b% balloon an io!last%*ltimatel%" t)e stents could*ltimatel%" t)e stents could deli#er andeli#er anantiin>ammator% or antit)rombo enicantiin>ammator% or antit)rombo enica enta ent directl% to t)e site of #ascular in ur%directl% to t)e site of #ascular in ur%


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Most im!ortant multifunctional de#ice for futureMost im!ortant multifunctional de#ice for futurea!!lications isa!!lications is a tissue en ineerin sca old t)ata tissue en ineerin sca old t)atalso ser#e as a dru deli#er% s%stemalso ser#e as a dru deli#er% s%stem for c%tokines"for c%tokines"ro t) )ormones" or ot)er a ents t)at directl%ro t) )ormones" or ot)er a ents t)at directl%a ect cells and tissue it)in t)e #icinit% of t)ea ect cells and tissue it)in t)e #icinit% of t)e

im!lanted sca oldim!lanted sca old. . bone re eneration sca old t)at is !laced. . bone re eneration sca old t)at is !lacedit)in a bone defect to allo t)e re eneration ofit)in a bone defect to allo t)e re eneration ofbone )ile releasin bone mor!)o enic !roteinbone )ile releasin bone mor!)o enic !rotein5BM&6 at im!lant site.5BM&6 at im!lant site.

$)e release of BM& )as been re!orted to stimulate $)e release of BM& )as been re!orted to stimulatebone ro t) and t)erefore )as !otential tobone ro t) and t)erefore )as !otential toaccelerate t)e )ealin rateaccelerate t)e )ealin rate


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$)e !rocess of bioerosion $)e !rocess of bioerosion

$ransformation from solid into ater4 $ransformation from solid into ater4soluble materialssoluble materialsssociated it)ssociated it)

Macrosco!ic c)an e in a!!earanceMacrosco!ic c)an e in a!!earance&)%siomec)anical&)%siomec)anical&)%sical !rocess&)%sical !rocess

ellinellinDeformationDeformation

tructural disinte rationtructural disinte rationWei )t lossWei )t lossDe!letion of druDe!letion of dru8oss of function8oss of function


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uence t)e rate ofuence t)e rate ofbioerosionbioerosion

lt)ou ) t)e solubili-ation of intact !ol%merlt)ou ) t)e solubili-ation of intact !ol%meras ell as se#eral distinct mec)anisms ofas ell as se#eral distinct mec)anisms ofc)emical de radation )a#e been reco ni-edc)emical de radation )a#e been reco ni-edas !ossible causes for t)e obser#ed bioerosionas !ossible causes for t)e obser#ed bioerosion

of a solid" !ol%meric im!lant" #irtuall% allof a solid" !ol%meric im!lant" #irtuall% allcurrentl% a#ailable im!lant materials erodecurrentl% a#ailable im!lant materials erodebecause of t)ebecause of t)e )%drol%tic clea#a e)%drol%tic clea#a e of t)eof t)e!ol%mer backbone 5mec)anism III in


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In t)is case" t)e main factors t)at determine t)e o#erallIn t)is case" t)e main factors t)at determine t)e o#erallrate of t)e erosion !rocess arerate of t)e erosion !rocess are

t)e c)emical stabilit% of t)e )%drol%ticall%t)e c)emical stabilit% of t)e )%drol%ticall%susce!tible rou!s in t)e !ol%mer backbone t)esusce!tible rou!s in t)e !ol%mer backbone t)e)%dro!)ilic/)%dro!)obic c)aracter of t)e re!eat)%dro!)ilic/)%dro!)obic c)aracter of t)e re!eat

units"units"t)e mor!)olo % of t)e !ol%mer"t)e mor!)olo % of t)e !ol%mer"t)e initial molecular ei )t an molecular ei )tt)e initial molecular ei )t an molecular ei )tdistribution of t)e !ol%mer"distribution of t)e !ol%mer"t)e de#ice fabrication !rocess used to !re!are t)et)e de#ice fabrication !rocess used to !re!are t)ede#ice"de#ice"t)e !resence catal%sts" additi#es" or !lastici-ers" andt)e !resence catal%sts" additi#es" or !lastici-ers" andt)e eometr% 5s!eci(call% t)e surface area tot)e eometr% 5s!eci(call% t)e surface area to#olume ratio6 of t)e im!lanted de#ice.#olume ratio6 of t)e im!lanted de#ice.

f


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$)e susce!tibilit% of t)e !ol%mer backbone $)e susce!tibilit% of t)e !ol%mer backboneto ardto ard )%drol%tic clea#a e)%drol%tic clea#a e is !robabl% t)e mostis !robabl% t)e mostfundamental !arameter.fundamental !arameter.=enerall% s!eakin "=enerall% s!eakin " an)%dridesan)%drides tendtend toto)%drol%-ed faster t)an)%drol%-ed faster t)an ester bondsester bonds t)at in turnt)at in turn)%drol%-e faster t)an amide bonds.)%drol%-e faster t)an amide bonds.

$)us" !ol%an)%drides ill tend to de rade faster $)us" !ol%an)%drides ill tend to de rade fastert)an !ol%esters t)at in turn ill )a#e a )i )ert)an !ol%esters t)at in turn ill )a#e a )i )ertendenc% to bioerode t)an !ol%amides.tendenc% to bioerode t)an !ol%amides.Based on t)e kno n susce!tibilit% of t)e !ol%merBased on t)e kno n susce!tibilit% of t)e !ol%merbackbone structure to ard )%drol%sis" it isbackbone structure to ard )%drol%sis" it is!ossible to make !redictions about t)e bioerosion!ossible to make !redictions about t)e bioerosionof a i#en !ol%mer.of a i#en !ol%mer.

) ) f


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+o e#er" t)e+o e#er" t)e actual erosion rateactual erosion rate of a solidof a solid!ol%mer cannot be !redicted on t)e basis of!ol%mer cannot be !redicted on t)e basis oft)et)e !ol%mer backbone structure!ol%mer backbone structure alone.alone.

$)e obser#ed erosion rate is stron l% $)e obser#ed erosion rate is stron l%de!endent on t)e abilit% of ater moleculesde!endent on t)e abilit% of ater moleculesto !enetrate into t)e !ol%meric matri'.to !enetrate into t)e !ol%meric matri'.

$)e )%dro!)ilic #ersus )%dro!)obic c)aracter $)e )%dro!)ilic #ersus )%dro!)obic c)aracterof t)e !ol%mer" )ic) is a function of t)eof t)e !ol%mer" )ic) is a function of t)e

structure of t)estructure of t)e monomeric startin materialsmonomeric startin materials ""can t)erefore )a#e an o#er )elmincan t)erefore )a#e an o#er )elminin>uence on t)e obser#ed bioerosion rate.in>uence on t)e obser#ed bioerosion rate.

) i ) f


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$)e obser#ed bioerosion rate is furt)er in>uenced b% $)e obser#ed bioerosion rate is furt)er in>uenced b%t)e mor!)olo % of t)e !ol%mer.t)e mor!)olo % of t)e !ol%mer.&ol%mers can be classi(ed as eit)er semicr%stalline&ol%mers can be classi(ed as eit)er semicr%stallineor amor!)ous.or amor!)ous.

t bod% tem!erature 5E7QC6 amor!)ous !ol%merst bod% tem!erature 5E7QC6 amor!)ous !ol%mersit) $ abo#e E7QC ill be in a lass% state" andit) $ abo#e E7QC ill be in a lass% state" and!ol%mers it) a!ol%mers it) a $ belo E7QC ill in a rubber% $ belo E7QC ill in a rubber%statestate ..In t)is discussion it is t)erefore necessar% toIn t)is discussion it is t)erefore necessar% to

consider t)ree distinct mor!)olo ical states:consider t)ree distinct mor!)olo ical states:semicr%stalline"semicr%stalline"amor!)ousR lass%" andamor!)ousR lass%" andamor!)ousRrubber%.amor!)ousRrubber%.

) ) f) i ) f


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In t)e cr%stalline state" t)e !ol%mer c)ains areIn t)e cr%stalline state" t)e !ol%mer c)ains aredensel% !acked and or ani-ed into cr%stallinedensel% !acked and or ani-ed into cr%stallinedomains t)atdomains t)at resist t)e !enetration of aterresist t)e !enetration of ater ..Conse uentl%"Conse uentl%" backbone )%drol%sis tendsbackbone )%drol%sis tends totooccur in t)eoccur in t)e amor!)ous re ionsamor!)ous re ions of aof asemicr%stalline !ol%mer and at t)e surface ofsemicr%stalline !ol%mer and at t)e surface oft)e cr%stalline re ions.t)e cr%stalline re ions.

$)is !)enomenon is of !articular im!ortance $)is !)enomenon is of !articular im!ortance

to t)e erosion of de#ices made ofto t)e erosion of de#ices made of !ol%584lactic!ol%584lacticacid6 and !ol%5 l%colic acid6acid6 and !ol%5 l%colic acid6 )ic) tend to)ic) tend to)a#e )i ) de rees of cr%stallinit% around ?0A.)a#e )i ) de rees of cr%stallinit% around ?0A.

) i ) f) i ) f


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not)er ood illustration of t)e in>uence of t)enot)er ood illustration of t)e in>uence of t)e!ol%mer mor!)olo % on t)e rate of bioerosion is!ol%mer mor!)olo % on t)e rate of bioerosion is!ro#ided b% a com!arison of !ol%584lactic acid6 and!ro#ided b% a com!arison of !ol%584lactic acid6 and!ol%5D" 84lactic acid6:!ol%5D" 84lactic acid6:lt)ou ) t)ese t o !ol%mers )a#e c)emicall%lt)ou ) t)ese t o !ol%mers )a#e c)emicall%identical backbone structures and an identical de reeidentical backbone structures and an identical de reeof )%dro!)obicit%" de#ices made ofof )%dro!)obicit%" de#ices made of !ol%584lactic acid6!ol%584lactic acid6tend to de radetend to de rade muc) moremuc) more slo l%slo l% t)ant)an identicalidenticalde#ices made of !ol%5D" 84lactic acid6.de#ices made of !ol%5D" 84lactic acid6.

$)e slo er rate of bioerosion of !ol% !ol%584lactic $)e slo er rate of bioerosion of !ol% !ol%584lacticacid6 is due to t)e fact t)at t)isacid6 is due to t)e fact t)at t)is stereore ularstereore ular!ol%mer!ol%mer is semicr%stalline" )ile t)e racemicis semicr%stalline" )ile t)e racemic "#$"#$ 55 %% 66

!ol%5D" 84lactic acid6 is an amor!)ous !ol%mer.!ol%5D" 84lactic acid6 is an amor!)ous !ol%mer.

) i ) f) i ) f


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8ike ise" a !ol%mer in its8ike ise" a !ol%mer in its lass% statelass% state isisless !ermeable to aterless !ermeable to ater t)an t)e samet)an t)e same!ol%mer )en it is in its rubber% state.!ol%mer )en it is in its rubber% state.

$)is obser#ation could be of im!ortance in $)is obser#ation could be of im!ortance incases )ere an amor!)ous !ol%mer )as acases )ere an amor!)ous !ol%mer )as alass transition tem!erature t)at is not forlass transition tem!erature t)at is not forabo#e bod% tem!erature 5E7QC6.abo#e bod% tem!erature 5E7QC6.In t)is situation" ater sor!tion into t)eIn t)is situation" ater sor!tion into t)e!ol%mer could lo er its $ belo E7QC"!ol%mer could lo er its $ belo E7QC"resultin inresultin in abru!t c)an es in t)eabru!t c)an es in t)ebioerosionbioerosion rate.rate.

) i ) f< t t) t i > t) t f


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$)e $)e manufacturin !rocessmanufacturin !rocess ma% also )a#ema% also )a#ea si ni(cant e ect on t)e erosion !ro(le.a si ni(cant e ect on t)e erosion !ro(le.


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$)e !recedin e'am!les illustrate an im!ortant $)e !recedin e'am!les illustrate an im!ortanttec)nolo ical !rinci!le in t)e desi n of bioerodintec)nolo ical !rinci!le in t)e desi n of bioerodinde#ices:de#ices:

$)e bioerosion rate of a i#en !ol%mer is not an $)e bioerosion rate of a i#en !ol%mer is not an

unc)an eable !ro!ert%" but de!ends to a #er%unc)an eable !ro!ert%" but de!ends to a #er%lar e de ree on readil% controllable factors suc)lar e de ree on readil% controllable factors suc)asas

t)e !resence of !lastici-ers or additi#es"t)e !resence of !lastici-ers or additi#es"t)e manufacturin !rocess"t)e manufacturin !rocess"t)e initial molecular ei )t of t)e !ol%mer" andt)e initial molecular ei )t of t)e !ol%mer" andt)e eometr% of t)e de#ice.t)e eometr% of t)e de#ice.


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$o be continued $o be continued

biomaterials 2010 fall week11 2-7

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