| Polymeric micellar drug carriers with good water solubility and biocompatibility as well as suitable dimension,enhance the therapeutic efficiency of anti-tumor drugs with compromised systemic toxicity by efficient passive tumor targeting via enhanced permeability and retention effect（EPR）,attribute to the tailor-made structures and functions.Specifically,polymeric micelles that integrate imaging modalities of fluorescence and magnetic resonance,as well as therapeutic functions of chemical treatment and photodynamic therapy have been widely researched for image-guided cancer therapy,also termed as“theranostics”.Conjugated polymers with the delocalized electronic structure were intensively investigated for the fabrication of optical materials because of the excellent photoelectric properties of easy adjustment,high stability,high sensitivity and resolution.However,the hydrophobicity of conjugated polymers with rigid structures limits their applications in biomaterials.Advances in biological imaging and detection of biological molecules of water-soluble conjugated polymers constructed withπ-conjugated backbones with excellent optical properties and charged or uncharged side chains with good hydrophilicity have been made in the past few decades.Polyfluorene（PF）is one of the most investigated conjugated polymers due to the high fluorescence quantum yield as well as both chemical and thermal stabilities.More importantly,the C9 position of PF could be easily modified with various functional groups,such as-N3 and-OH,thus offering endless possibilities for the construction of versatile bottlebrush conjugated polymers with advanced topological structures for chemistry decorations and biomedical applications via elegant integration of Click and ROP techniques.Conjugated bottlebrush cpolymers based on polyfluorene and its derivatives with good drug loading efficiency and optical property,as well as excellent colloidal satbility and biocompatibility attribute to the steric hinerance effect of functional side chains has been rarely reported likely because of the lack of efficient synthetic approaches.In this thesis,a series of amphiphilic conjugated bottlebrush copolymers with different structures and properties based on polyfluorene and its derivatives were designed and synthesized by elegant integration of various chemical techniques including Suzuki coupling polycondensation,click reaction,ring-opening polymerization（ROP）,atom transfer radical polymerization（ATRP）and so on.The structures and compositions of these synthesized conjugated bottlebrush copolymers were investigated by nuclear magnetic resonance（~1HNMR）and size exclusion chromatography and multi-angle laser light scattering（SEC-MALLS）analyses.The dimensions and morphology of polymer micelles were researched by dynamic light scattering（DLS）as well as the transmission electron microscopy（TEM）.The optical properties of these copolymers were measured by ultraviolet-visible（UV-vis）and fluorescence（FL）spectrophotometer.The biological applications of drug-loaded micelles were evaluated by in vitro cellular cytotoxicity and imaging profiles.The detailed contents are summarized as follows.1.In chapter one,the synthesis methods of bottlebrush polymer,optical properties of conjugated polymer as well as the research status and development of polyfluorene and its derivatives in biomedical materials are introduced systematically.2.In chapter two,a series of the amphiphilic conjugated bottlebrush copolymers with the backbone of polyfluorene and alternating heterografts of hydrophobic brushes of poly（ε-caprolactone）（PCL）as well as hydrophilic chains of poly（oligo（ethylene glycol）methyl ether methacrylate）（POEGMA）were prepared.The degrees of PF and PCL were fixed,and the reaction kinetics of the polymerization process of OEGMA initiated by the macroinitiator of PF-(（g-PCL-OOCCH3）-alt-（g-Br）was evaluated by ~1HNMR and SEC-MALLS.The self-assembly of conjugated bottlebrush copolymers with different ratio of hydrophobic and hydrophilic brushes was measured by DLS and TEM at the same polymer concentration in aqueous.The fluorescence quantum yields（Φ）were examined by FL.The overall results showed that the amphiphilic conjugated bottlebrush copolymers with suitable ratio of hydrophobic and hydrophilic brushes could form unimolecular micelles in aqueous with high fluorescence quantum yield and cellular imaging efficiency.3.The construction of a pyknotic hydrophobic core for drug encapsulation might be compromised by the alternating POEGMA/PCL brushes without the over-stretching of PCL from POEGMA,leading to a relatively low drug loading content（DLC）and entrapment efficiency（EE）.In chapter three,a series of enzyme-responsive amphiphilic conjugated bottlebrush copolymers with the backbone of PF derivative containing phenyl and enzyme-degradable side chains of amphiphilic polytyrosine-block-poly（oligo（ethylene glycol）methyl ether methacrylate）（PTyr-b-POEGMA or PTyr-b-（POEGMA）2）copolymers were prepared for enhancing drug loading efficiency and promoting micelle destabilization in tumor tissue.The effects of the length of hydrophobic PTyr and the structure of hydrophilic POEGMA on the drug loading efficiency of copolymers were investigated by UV-vis spectrophotometer.The therapeutic efficiency of drug-loaded micelles was studied by in vitro cellular cytotoxicity and in vivo antitumor profiles.The overall results presented that the drug-loaded micelles base on the enzyme-responsive amphiphilic conjugated bottlebrush copolymers with high drug loading efficiency and good biocompatibility showed simultaneously enhanced antitumor efficiency and prominent systematic tolerance.Interestingly,the fluorescence resonance energy transfer（FRET）from the PF backbone to DOX was observed likely ascribed to somewhat overlap between the emission peak of PF and the absorption peak of DOX.4.In chapter four,a series of enzyme-responsive zwitterionic conjugated bottlebrush copolymers with the backbone of PFONPN containing N-phenyl-1,8-naphthalimide and enzyme-degradable side chains of zwitterionic polytyrosine-block-poly（oligo（ethyleneglycol）methylether methacrylate-co-2-（methacryloyloxy）ethyl]dimethyl-（3-sulfopropyl）ammonium hydroxide）（PTyr-b-P（OEGMA-co-SBMA）2）copolymers were prepared for the higher drug loading efficiency and antifouling property,as well as enhancing FRET between polymer and DOX.The effects of constitution and proportion of hydrophilic brushes on the stability and drug loading efficiency of polymer micelles were measured by DLS and UV-vis spectrophotometer.The optical properties of drug-loaded and blank micelles were studied by FL.The overall results presented that the enzyme-responsive zwitterionic conjugated bottlebrush copolymers with a lower proportion of hydrophilic brushes could form unimolecular micelles in aqueous with greatly improved drug loading efficiency due to the super-hydrophilic zwitterionic brushes.The abundant overlap between the emission peak of PFONPN and the absorption peak of DOX resulted in the obvious FRET from the PFONPN backbone to DOX.However,the presence of abundant pendant phenol groups on the side chains of PTyr blocks not only increased the drug loading efficiency byπ–πstacking with DOX,but also decreased the fluorescence quantum yield because of possible occurrence of nonradiative pathways in the relaxation of excited states of PFONPN.5.There is inevitable leakage and premature release of polymeric drug-loaded micelles by physical encapsulation via hydrophobic interaction because of the diffusion of drug molecules as well as different concentrations of drug molecules around polymer micelles in the physiological conditions.In chapter five,the p H/enzyme dual-responsive zwitterionic conjugated bottlebrush copolymer-based prodrugs with the backbone of PFONPN,enzyme-degradable side chains of polyornithine（POrn）conjugated with DOX by p H-responsive imine linkage and zwitterionic brushes of P（OEGMA-co-SBMA）was prepared for enhancing the stability of loaded cargoes,promoting micelle destabilization in tumor tissue and decreasing the effect of side chains on the optical property of the conjugated backbone.The Zeta potential and FRET of the prodrugs with different DLC were investigated.The overall results presented that the Zeta potential changed from obviously positive potential to slightly negative potential along with the increase of DLC,identifying the successful linkage of DOX.The fluorescence intensity of DOX increased evidently accompanied with the decrease of fluorescence intensity of the backbone of PFONPN along with the increase of proportion of DOX from 0%to 11%,in addition,the ratio of fluorescence intensity between the backbone and DOX showed the linear correlation with the proportion of DOX,confirming the potential applications of the conjugated bottlebrush polymer for monitoring the release of DOX. |
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