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1、3.051J/20.340J1Lecture4BiomaterialsSurfaces:ChemistryLikemetallicimplants,somepolymersusedinbiomaterialsapplicationsaresusceptibletochemicalreactionsthatleadtodegradationthroughhydrolysis.Inmanycases,apolymerisspecificallychosenforitsabilitytodegradeinvivo.P
2、olymerHydrolysisPolymerhydrolysisinvolvesthescissionofsusceptiblemoleculargroupsbyreactionwithH2O.¾Maybeacid,baseorenzymecatalyzed¾Notsurface-limitedifwaterpenetratesbulka)Molecular&StructuralFactorsInfluencingHydrolysis¾BondStability¾Hydrophobicity:↑hydroph
3、obicity⇒↓hydrolysis¾MW&architecture:higherMW⇒↓hydrolysis¾Morphology•crystallinity↓hydrolysis•porosity↑hydrolysis¾Tg:lessmobility⇒↓hydrolysisBondStabilitySusceptiblelinkagesatbondswhereresonancestabilizedintermediatesarepossible…OO•Esters:R-C-O-R’+H2O→R-C-OH+
4、HO-R’3.051J/20.340J2Example1:poly(lactide-co-glycolide)Properties:rapiddegradation,amorphous,Tg~45-55°CUses:bioresorbablesutures,controlledreleasematrices,tissueengineeringscaffoldsOO(-O-CH(CH3)-C-)x-r-(-O-CH2-C-)ylacticacidglycolicacidExample2:polyethylenet
5、erephthalate(Dacron)Properties:veryslowhydrolysis,semicrystalline,Tg~69°CUses:vasculargrafts,arterialpatches,heartpumpsOO[-OCCO-CH2-CH2-]Nbase-catalyzedpolyesterhydrolysis:—OHOC••••OR’•O•OR—+HOR’+OHCCOHOHRROR’HH•O•••3.051J/20.340J3acid-catalyzedpolyesterhydr
6、olysis:+••HX•O•COR’R+•HXHH•O•O•••COR’RHH•O•••O−HXC••HRO+OO+HOR’+HH3OXR’COHROO•Amides:R-C-NH-R’+H2O→R-C-OH+H2N-R’amideorpeptidelinkage,alsofoundinproteins!OOExample:Nylon6,6(-NH-(CH2)6-NH-C-(CH2)4-C-)Npoly(hexamethyleneadipamide)Properties:~9%H2Ouptake,semicr
7、ystalline,Tg~50°CUses:removablesutures,prostheticjoints3.051J/20.340J4OOOO•Anhydrides:R-C-O-C-R’+H2O→R-C-OH+HO-C-R’OOExample:poly(sebacicacidanyhydride)(-(CH2)8-C-O-C-)NProperties:rapiddegradation(surface-based)Uses:drugdeliverymatrices•Ethers:R-O-R’+H2O→R-C
8、H2-OH+HO-CH2-R’Example:polyethyleneoxide(PEO)(-CH2-O-CH2-)NProperties:watersoluble,semicrystalline,Tg~-60°CUses:hydrogels,protein-resistantcoatingsOO•Urethanes:R-NH-C-O-R’+H2O→R-NH-C-OH+HO-R’Exa
