From-Nanofibers-to-Polymersomes

Self-AssemblyofLinear-DendriticDiblockCopolymers:FromNanofiberstoPolymersomesJesu´sdelBarrio,†LuisOriol,*,†CarlosSa´nchez,*,‡Jose´LuisSerrano,§Aure´lieDiCicco,|PatrickKeller,|andMin-HuiLi*,|,⊥DepartamentodeQuı´micaOrga´nicayQuı´micaFı´sica,FacultaddeCiencias-InstitutodeCienciadeMaterialesdeArago´n,UniVersidaddeZaragoza-CSIC,50009Zaragoza,Spain,DepartamentodeFı´sicadelaMateriaCondensada,FacultaddeCiencias-InstitutodeCienciadeMaterialesdeArago´n,UniVersidaddeZaragoza-CSIC,50009Zaragoza,Spain,InstitutoUniVersitariodeNanocienciadeArago´n,UniVersidaddeZaragoza,50009Zaragoza,Spain,InstitutCurie,CNRS,UniVersite´PierreetMarieCurie,UMR168,LaboratoirePhysico-ChimieCurie,26rued’Ulm,75248ParisCedex05,France,andKeyLaboratoryofMolecularEngineeringofPolymers,FudanUniVersity,Shanghai200433,ChinaReceivedOctober2,2009;E-mail:[e-mail];[e-mail];[e-mail]:Wereporttheformationofcylindricalmicelles,sheet-likemicelles,tubularmicelles,aswellaspolymervesiclesbyanewseriesofamphiphiliclinear-dendriticblock-copolymers(BCs).TheBCs,notedasPEGm-AZOn,arecomposedofpoly(ethyleneglycol)(PEG)chainsofdifferentmolecularweightsashydrophilicblocksandthefirstfourgenerationsofazobenzene-containingdendronsbasedon2,2-bis(hydroxymethyl)propionicacid(bis-MPA)ashydrophobicblocks(mrepresentsthedegreeofpolymer-izationofPEG,andnisthenumberofazobenzeneunitsattheperipheryofdendron).ThepolymericaggregateswereformedbyaddingwatertosolutionsoftheBCsindioxane.Themicellardispersionsinwaterwerefinallyobtainedbyremovingdioxaneviadialysisagainstwater.Themorphologyofthemicellarself-assemblieswasstudiedbytransmissionelectronmicroscopy(TEM),cryo-electronmicroscopy(cryo-TEM),andatomicforcemicroscopy(AFM).Ageneration-dependentaggregationbehaviorwasfoundfortheseriesofBCsPEG45-AZOn.Core-shellstructurednanofiberswithaninnerdiameterof8nmwereobservedforthecopolymerPEG45-AZO2(hydrophilic/hydrophobicweightratioequalto67/33).Lyotropicliquidcrystallinebehaviorwasdetectedfortheaqueoussolutionofthenanofibers.Thecoexistenceofsheet-likeaggregatesandtubularmicelleswasdetectedforthecopolymerPEG45-AZO8inwhichthenumberofcyanoazobenzeneunitsisincreasedto8(hydrophilic/hydrophobicweightratioequalto33/67).Thetubularmicellescouldbeintermediatesinthesheet-likeaggregate-to-vesicletransition.Polymervesicles(polymersomes)withadiameterintherange300-800nmwereobservedforthecopolymerPEG45-AZO16(hydrophilic/hydrophobicweightratioequalto20/80).Themembraneofthesheet-likeaggregates,tubularmicelles,andpolymersomeswasshowntohaveabilayerstructure,asrevealedbycryo-TEM.UVilluminationoftheaqueouspolymersomedispersioninducedtheformationofwrinklesinthevesiclemembrane,thusshowingthatthistypeofpolymericaggregateisphotoresponsive.IntroductionThesustainedinterestinmicellaraggregatesobtainedfromamphiphilicblockcopolymers(BCs)arisesfromtheirpotentialnumerousapplicationssuchasdrugdeliverysystems,1-4nanoreactors,5-8andnanotemplates.9Whencomparedtomi-cellesfromtraditionalsurfactants,polymericself-assemblieshaverecentlybeenrecognizedforadvantagessuchassuperiorstability,toughness,micellizationdependingonselectivesol-vents,andtheabilitytotrapmetastablestructuresduetoslowkinetics.10-13Moreover,polymericself-assembliesoffernumer-ouspossibilitiestotailorphysical,chemical,andbiologicalpropertiesbyvariationoftheblockcopolymerchemicalstructureorbyconjugationofbiomolecules.14Inmanyinstances,themorphologyofthepolymericself-assemblyanditsapplica-tionarecloselyrelated.Thus,controllingthemorphologyof†DepartamentodeQuı´micaOrga´nicayQuı´micaFı´sica,ICMA;Uni-versidaddeZaragoza-CSIC.‡DepartamentodeFı´sicadelaMateriaCondensada,ICMA;UniversidaddeZaragoza-CSIC.§InstitutoUniversitariodeNanocienciadeArago´n,UniversidaddeZaragoza.|InstitutCurieandCNRS.⊥FudanUniversity.(1)Savic,R.;Luo,L.;Eisenberg,A.;Maysinger,D.Science2003,300,615.(2)Discher,D.E.;Ortiz,V.;Srinivas,G.;Klein,M.L.;Kim,Y.;Christian,D.;Cai,S.;Photos,P.;Ahmed,F.Prog.Polym.Sci.2007,32,838.(3)Gilles,E.R.;Frechet,J.M.J.J.Am.Chem.Soc.2002,124,14137.(4)Gilles,E.R.;Dy,E.;Frechet,J.M.J.;Szoka,F.C.Mol.Pharmacol.2005,2,129.(5)Chan,Y.N.C.;Schrock,R.R.;Cohen,R.E.Chem.Mater.1992,4,24.(6)Vriezema,D.M.;Hoogboom,J.;Velonia,K.;Takazawa,K.;Christianen,P.C.M.;Maan,J.C.;Rowan,A.E.;Nolte,R.J.M.Angew.Chem.2003,115,796.PublishedonWeb03/01/201010.1021/ja90839462010AmericanChemicalSociety37629J.AM.CHEM.SOC.2010,132,3762–3769theassembledstructuresfromBCsisofgreatpracticalvalue.Polymermicellemorphologyandsizecanbedesignedthroughtheadequateselectionofthenatureandlengthofthedifferentblocks,theuseofcontrolledelectrostaticinteractionsbetweenpolymericchains,orthemodificationofthemacromoleculararchitecture.15-28Agreatdealoftheexperimentalresearchhasbeendirectedtowardthestudyoftheself-assemblyoflinearcoil-coilandrod-coilBCs.However,theintroductionofadendriticstructureasabuildingblockinthedesignofnovelBCsprovidessomeinterestingopportunities.29-36Dendriticmoietieshaveawell-definedbranchedarchitectureandahighlyorganizedinnerpart.37-39Moreover,thesesystemscanbemadeamphiphilicthroughappropriat