Fabrication And Functional Application Of Stimuli-Responsive Polymersomes

Stimuli-responsive polymers which exhibit reversible or irreversible changes in physical properties or chemical structures to various external stimuli(temperature,light,pH,electromagnetic fields,biological signal,etc.).It is well known that tumors or pathological tissues differ significantly from normal tissues in many physiological parameters.Therefore,application of drug or imaging agent nanocarries based on stimuli-responsive polymers is great importance for early diagnosis and treatment.In this thesis,we focused on the preparation and application of stimuli-responsive vesicular assemblies for controlled drug release,fluorescence imaging and therapy.The dissertation mainly includes the following three parts:1.NAD(P)H:quinone oxidoreductase isozyme 1(NQO1)is a cytosolic enzyme which is overexpressed in many tumor cells and can catalyze the two-electron reduction of quinone.In this chapter,NQO1-responsive fluorogenic precusors for fluorescence imaging and photodynamic therapy(PDT)were firstly synthesized by convalently bridging trimethyl-locked quinone group with 7-amino-4-methylcoumarin(AMC)and Nile blue(EtNBS)moieties,then they were introduced into the side chains of the hydrophobic block of the amphiphilic diblock copolymers via post-polymerization modification affording PEO-b-P(TMQ-co-CMA)(PQ5)and PEO-b-(TMQ-co-EtNBS)(PQ6),respectively.The amphiphilic diblock copolymers can self-assemble into vesicles,in which the CMA or EtNBS moieties were traped in the hydrophobic bilayers and their fluorescence emission was quenched because of the aggregation-induced quchening effect and the photo-induced electron transfer(PET)mechanism.When the vesicles were internalized into tumor cells,NQO1-catalyzed reduction of quinone into hydroquinone groups and the subsequent cyclization degradation,coumarin or Nile blue molecules were released resulting in fluorescence emission turn-on and activation of PDT potency of Nile blue.On the other hand,primary amine groups also can be decaged in the side chains of the hydrophobic blocks through NQO1-triggered reduction,which then underwent inter-chain amidation and protonization causing the traceless crosslinking and the hydrophobic-to-hydrophilic transition in the vesicular bilayers.Therefore,controlled drug release and combined PDT and chemotherapy can be fulfilled.Meanwhile,if convalently loading MR imaging agent moieites into the vesicular bilayers,the enhanced MR imaging signals can be achieved to monitor the drug release process in real time.The cells and animal experiments revealed that nanomedicine system capable of chemotherapy and PDT based on the NQO1-responsive vesicles can effectively induce cancer cells death and inhibit the tumor growth.2.Thermo-responsive and photo-reactive vesicles were fabricated through self-assembly of the amphiphilic block copolymers(BCPs),poly(N-isopropylacrylamide)-b-poly(2-((((2-nitrobenzyl)oxy)carbonyl)amino)ethyl acrylate)(PNIPAM-b-PNBOCA),which were synthesized via consecutive reversible addition-fragmentation chain transfer(RAFT)polymerization.The obtained vesicles irreversibly collapsed upon increasing the temperature above the lower critical solution temperature of PNIPAM blocks(defined as LCST0)(T>LCST0),and further increasing the temperature(T>Tagg,0)led to the formation of larger irregular aggregates of the collapsed vesicles.On the other hand,upon UV irradiation,because of the photo-induced cleavage of the o-nitrobenzyl ester units and the decage of the primary amine groups in the side chains of PNBOC A blocks,the initially hydrophobic PNBOCA bilayers underwent aminolysis-induced cross-linking and hydrophobic-to-hydrophilic transition,resulting in elevated LCST(defined as LCSTuv).Although the thermo-induced collapse of PNIPAM coronas(T>LCSTuv)and the formation of larger aggregates of cross-linked vesicles(T>Tagg,uv)were also observed,the bilayer crosslinked vesicular morphology could be restored when decreasing the temperature to lower than LCSTuv,as opposed to irreversible morphological transition without UV irradiation.The vesicular assemblies were also engineered as nanocarriers for both hydrophilic(doxorubicin hydrochloride,DOX)and hydrophobic(Nile red,NR)payloads.The co-release profiles could be delicately regulated by both temperature variation and UV irradiation.More interestingly,due to the relatively low glass transition temperature of PNBOCA blocks,DOX release could also be regulated by thermo-induced vesicle morphology transition that was caused either by simply increasing the temperature or by near-infrared(NIR)irradiation after co-loading photothermal agents,such as ICG,within the vesicular interiors.Furthermore,nanoreactors were constructed by loading glucose oxidase(GOx)into the aqueous interiors of the vesicles,allowing for activating fluorogenic reactions by UV irradiation and temperature change.3.Ferrocene is a unique type of organometallic complex with a sandwich structure containing iron and two cyclopentadiene ligands.Due to the reversible redox properties,ferrocene and its derivatives have been widely used in asymmetric synthesis,electrochemical catalysis,and functional biological materials.In this chapter,we designed and synthesized three methacrylate derivative monomers,BMEFc,MEFc and BBMEFc,which the ferrocene unit in the hydrophobic side group linked through ester bond with varying hydrophobic block structure.Then a series of amphiphilic diblock copolymers with different hydrophobic block structure and varying block lengths were synthesized via RAFT polymerization.The diblock copolymers self-assembled in aqueous solution into nanoaggretates with different morphologies,such as spherical micelles,vesicles and nanosheets,and the redox-reponsive morphological transformation were investigated.Moreover,the photosensitizer Nile Blue was conjugated into the side groups of the hydrophobic blocks and the prepared diblock copolymer then self-assembled into vesicles in which the ferrocene groups can be oxidized by in-situ generated superoxide radical anion under 660 nm near-infrared light irradiation,thus showing high cytotoxicity toward cancer cells.