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ChitinAntimicrobialActivity Chitinisthesecondmostabundantbiopolymerinnature..foundinthe

shellsofcrustaceans,thecuticlesofinsects,andthecellwalloffungi.

Chitosan,adeacetylated productofchitin,hasmanyinterestingproperties,suchasantimicrobialactivityandnontoxicity.Itisobtainedfromshrimpandcrabshellchitinbyalkalinedeacetylation

Biomacromolecules,2007,8 (5),pp 13591384

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SiliconeBiomaterials

SourceInformationforthefollowingslides:1)B.Ratner,A.Hoffman,F.Schoen,andJ.Lemons:BiomaterialsScience, 2ndedition(SanDiego:ElsevierAcademicPress.2004).

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SiliconeBiomaterialsChemicalStructureandNomenclature

Otherwiseknownaspolysiloxanes

Inorganicpolymerbackbonewithorganicpendantgroups

Polydimethylsiloxane (PDMS)isthemostcommonmaterialinthisclass

Inorganic/organiccombinationgivesrisetouniqueproperties Fluids,emulsions,compounds,resins,elastomers

Usedinabroadrangeofapplicationsincludingelectronics,aerospace,coatings,adhesives,andbiomaterials

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TMSterminatedPDMSmostcommonamongpolysiloxanes Linearpolymersremainliquidsevenforhighvaluesofn

Generalpropertiesofsilicones LowTg,lowtemperatureflexibility

Propertiesretainedoverawidetemperaturerange(100to250C)

Stabletohightemperatures,oxidation,chemicalandbiologicalenvironments

PropertiesaconsequenceofthelongSiObond(1.64comparedto1.54 forCC)andwideSiOSibondangle(143 comparedto109.5 forCCC)

SiObondisstrongerthanCCbond(450vs.350kJ/mol)

O Si

CH3

CH3O SiSi

CH3

CH3H3C

CH3

CH3CH3

n

(n =0, 1, 2,...)

Trimethylsilyloxy terminated PDMS

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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 81.

ShorthandNotation

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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 81.

ShorthandNotation

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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 80.

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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 82.

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SiliconeElastomers

Siliconepolymersareeasilytransformedintocrosslinked elastomersusingoneofseveralmethods

Radicalcrosslinking

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SiliconeElastomers

Siliconepolymersareeasilytransformedintocrosslinked elastomersusingoneofseveralmethods

Condensationcrosslinking

PreparedfromhydroxyterminatedPDMSandlargeexcessofmethyltriacetoxysilane

Uponexposuretomoisture,acetoxygroupsarehydrolyzedallowingcondensationofresultingsilanols

B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 83.

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Condensationcrosslinking(cont)

B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 84.

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Twopartcondensationcuringusingatetrafunctional alkoxysilane and

organotin catalyst.

Alcoholreleasedresultinginslightshrinkage

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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 85.

ElastomerFiller

Mostsiliconeelastomersincorporatefiller

Fillerreinforcesthecrosslinked matrix

Preferredfillerformostmedicalapplicationsisfumedsilica(CabOSil,

Aerosil) Reinforcementobtainedthroughhydrogenbondinginteractionofsilanol

groupsonhighsurfaceareasilicawiththesiliconepolymer

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B. Ratner, A. Hoffman, F. Schoen, and J . Lemons: Biomaterials Science, 2nd edition (San Diego: Elsevier Academic Press. 2004). 85.

PhysicochemicalPropertiesofSilicones SiXandCXcompoundsbehaveverydifferently

Lowerelectronegativityofsilicon(Si 1.80vs. C 2.55) resultsinmorepolarbondscomparedtocarbon

Bondpolaritycontributestostrongsiliconbonding,i.e.SiObondishighlyionicandhasalargebondenergy.

Consequently,siliconesareresistanttohomolytic cleavage

PolarSiObondswouldleadtostrong

intermolecularinteractionswithoutprotectionofthemethylgroups. Methylgroupsinteractweaklywithoneanotherandshieldthemainchain

LowbarriertorotationaroundtheSiObondallowssiloxane chaintoadoptconfigurationthatexposesmaximumnumberofmethylgroupstoexterior

Leadstolowsurfaceenergymaterials

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SurfaceActivityofSilicones

LowbarriertorotationaroundtheSiObondallowssiloxanechaintoadoptconfigurationthatexposesmaximumnumberofmethylgroupsatmanyinterfaces Leadstolowsurfacetension

Lowsurfaceenergy

Lowintermolecularinteractions,

Resultinginalowoveralllevelofinteractionsattheirsurfaces..biocompatibility!!

PDMS lowsurfacetensionyieldscapabilityofwettingmostsurfaces

Siliconesingeneralcanwetthemselves,promotesgoodfilmformationandgoodsurfacecoverage

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Otherconsequencesoflowintermolecularinteractioninsilicones Tg verylow

Highfreevolumecomparedtohydrocarbonsresultsinhighsolubilityandhighdiffusioncoefficientofgasesintosilicones

Highpermeabilitytooxygen,nitrogen,watervapor(eventhoughliquid

watercannotwetthesiliconesurface

Compressibilityisalsohigh

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Siliconeelastomers. PeterJerschow. Shawbury,U.K.:Rapra TechnologyLtd.,2001.

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Siliconeelastomers. PeterJerschow. Shawbury,U.K.:Rapra TechnologyLtd.,2001.

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