Synthesis Of Hyperbranched Polymers Via RAFT Polymerization And Their Biological Applications

Hyperbranched polymers(HBPs)are an important class of dendritic macromolecules with highly branched,three-dimensional globular nanopolymeric architectures.The distinctive features of HBPs,such as highly branched topological structures,adequate spatial cavities,and numerous terminal functional groups have enabled them as promising candidates for many applications in polymer science,material science,nanotechnology and biological research.However,the rational design and control over the architectures and functions of HBPs are still challenge in this field,preventing them from being used for real biomedical applications.To address these problems,in this dissertation,the reversible addition-fragmentation chain transfer polymerization(RAFT)was introduced to the HBP synthesis.Integrating the advantages of RAFT polymerization and HBPs,we synthesized a series of functional HBPs with good biocompatibility by molecular design,which were further employed to construct nonfouling materials,drug delivery systems,and intracellular probes for drug release.This dissertation is divided into six sections,and the details and key conclusions are listed as follows: 1.Hyperbranched polymers synthesized by RAFT polymerization and their protein resistant propertiesThe interactions between the biomaterials and proteins are very important for many biomedical applications.Herein,a new strategy to optimize the protein resistant properties of polymers on a gold surface has been proposed by only adjusting the architecture of hydrophilic polymers.Owing to the prominent nonfouling properties of polyethylene glycol(PEG),poly(ethylene glycol)methacrylate(PEGMA)with PEG moieties was polymerized with S-(4-vinyl)benzyl S'-propyltrithiocarbonate(VBPT)by RAFT copolymerization to result in the synthesis of hyperbranched poly(VBPT-co-PEGMA)(HPVBEG).In our study,a series of HPVBEGs with different branched architectures were synthesized and the degree of branching(DB)could be finely tuned by varying the molar ratios of PEGMA to VBPT.The exact DBs of these HPVBEGs were calculated according to the quantitative analysis of 13C-NMR spectra.Upon aminolysis,by trithiolcarbonate terminals of HPVBEG convert into thiol groups,HPVBEGs were further grafted onto the gold surfaces via thiol-gold bond formation.Thereafter,morphologies and hydrophilicities of the modified gold surfaces were characterized by AFM imaging and water contact angle measurement.Finally,nonfouling properties of the surfaces were evaluated by fluorescence and quartz crystal microbalance(QCM)analysis.It could be noticed that the protein resistance of the HPVBEG modified surface significantly enhanced by reducing the DB of the coated HPVBEG.2.Construction of hyperbranched polymer-gold nanocomposite for drug release trackingPolymeric drug delivery systems offer efficient and localized drug transportation as well as reduce associated side effects.In order to better understand the polymeric drug delivery system,precise observation of drug delivery and release process is required.In our study,hyperbranched polymer-gold nanocomposites were successfully synthesized and used for drug delivery and release tracking.First,the HPVBEG was synthesized by RAFT polymerization,and then,the anticancer drug doxorubicin(DOX)was conjugated to HPVBEG via p H-sensitive schiff base linkage,resulting in p H responsive hyperbranched polymer-drug conjugates(HPVBEG-g-DOX).Second,the conjugates further reacted with gold nanoparticles to form hyperbranched polymer-gold nanocomposites(HPVBEG-g-DOX-GNP).Under neutral condition,the nanocomposites were stable and DOX was bound to the surface of gold nanoparticles.At this stage,the surface-enhanced Raman spectrum of DOX could be observed,but the red fluorescence of DOX was quenched by gold nanoparticles.When the composites were uptaken by tumor cells,due to the lysosome acid microenvironment,DOX was released by cleavage of the schiff base linkage.As such,Raman enhancement of DOX was greatly reduced as shown in the Raman spectra and its fluorescence signal could be recorded by confocal fluorescence microscopy.Based on the results from Raman spectra and fluorescence imaging,intracellular trafficking DOX release process,and the anticancer effect of the nanocomposites were throughly investigated and discussed.3.The synthesis of hyperbranched multithiol polymer and redox-responsive polymeric prodrugCompared to well-studied small molecule drugs and their conventional drug delivery systems,stimuli-responsive polymeric prodrugs exhibit many advantages.Herein,a novel kind of redox-responsive polymeric prodrug has been successfully designed and prepared through the coupling of hyperbranched multithiol polymers and thiol-containing drugs.Regarding to this,HPVBEG was synthesized by one-pot reaction via RAFT copolymerization.Subsequently,the hydrophobic thiol-containing anticancer drug 6-mercaptopurine(MP)was conjugated to HPVBEG by thiol-disulfide exchange reaction,resulting in the formation of HPVBEG-S-S-MP conjugate.Due to its amphiphilicity,HPVBEG-S-S-MP conjugate self-assembled into amphiphilic micelles in aqueous solution.Under a reductive environment,the disassembly of polymeric micelles resulted in the MP release.Flow cytometry and confocal laser scanning microscopy(CLSM)demonstrated that the HPVBEG-S-S-MP micelles could be taken up by Raji cells(a Burkitt lymphoma cell line).The viability of the Raji cells incubated with the glutathione(GSH)mediated HPVBEG-S-S-MP micelles were investigated by Cell Counting Kit-8(CCK-8)assay,which showed that the HPVBEG-S-S-MP could inhibit the growth of Raji cells.4.The synthesis of backbone redox-responsive hyperbranched polymers and construction of targeting drug delivery systemThe aim of active targeting of internalization-prone cell-surface receptors,overexpressed by cancer cells,is to improve the cellular uptake of the nanocarriers.Thus,the active targeting is particularly attractive for the intracellular drug delivery.The enhanced cellular internalization is responsible of the anticancer efficiency of actively targeted nanocarriers.Herein,a backbone redox-responsive drug delivery system with active targeting moieties was constructed.Disulfide bonds were introduced into the structure of RAFT inimer 2-((2-(acryloyloxy)ethyl)disulfanyl)ethyl 4-cyano-4-(((propylthio)carbonothioyl)thio)pentanoate(ACPP),and ACPP copolymerized with PEGMA via RAFT polymerization.The backbone redox-responsive hyperbranched poly(ACPP-co-PEGMA)(HPAEG)was succesfully synthesized.Then,the active targeting aptamers(AS1411)were conjugated to HPAEG by Michael addition,resulting in an active targeting redox-responsive drug delivery system.Due to the existence of hydrophobic disulfide-containing backbones and hydrophilic PEG segments,the self-assembly of HPAEG in aqueous solution was realized.The resulting micelles possess the core/shell structure with narrow size distribution.The hydrophobic anticancer drugs(DOX)were loaded by the micelles and rapidly transported into the nuclei of the tumor cells.Under reductive microenvironment in the tumor cells,the DOX was quickly released from the AS1411 containing micelles due to the cleavage of disulfide bonds in the backbone of HPAEG.Moreover,the anticancer effect of aptamer modified drug carriers was better than that of micelles without targeting ligands.