Study On The Stimulation Responsiveness Of β - Cyclodextrin Star Polymers And The Study Of β - Cyclodextrin Polymers As Multifunctional Gene Carriers

Cyclodextrins (CDs) are a series of natural cyclic oligosaccharides composed of a-1,4-coupled D-glucose units. There are mainly three kinds of cyclodextrins, namely α-CD, β-CD and y-CD, which consists of 6,7,8 D-glucose units, respectively. CDs display a bucket-like structure with a hydrophobic inner cavity and hydrophilic outer shell. And the cavity can form complexes with various guest molecules through host-guest interaction. What’s more, CDs possess various hydroxyls with different reaction activity, which can be modified to synthesis cyclodextrin polymers. Since CDs exhibit lower cytotoxicity and better biocompatibility, the cyclodextrin materials have obtained wide applications in drug delivery, gene transfection, food additives and so on.In this thesis, two kinds of cyclodextrin polymers were successfully prepared by atom transfer radical polymerization (ATRP). The synthetic conditions, biocompatibility, and applications in drug and gene delivery systems of the cyclodextrin polymers were investigated in detail. The main contents are as follows:1. Synthesis, thermo-responsiveness and biocompatibility of the star-shaped cyclodextrin polymerIn this study, hydrophilic star-shaped polymers were prepared, these star polymers were synthesized by atom transfer radical polymerization from β-cyclodextrin with multi-initiator site (CD-Br). The arm of the star polymer is composed of a cationic block poly[2-(dimethylamino) ethyl methacrylate] (PDMAEMA) and a zwitterionic block poly(sulfobetaine methacrylate) (PSBMA).The influences of arm length, arm density, pH value and salt concentration on thermo-responsive behaviors of the star polymers were investigated in detail by means of dynamic light scattering (DLS) and transmission electron microscopy (TEM). The star polymers showed only upper critical solution temperature (UCST) behavior, since zwitterionic PSBMA outer blocks shielded the lower critical solution temperature (LCST) behavior of PDMAEMA midblocks. However, PDMAEMA blocks had significant influence on the thermo-induced associations of the star polymers, and resulted in a tunable critical aggregation temperature with varying arm density or pH value of solution. Finally, biocompatibility evaluations showed that the star polymers could effectively reduce the adsorption of BSA in PBS solution and had insignificant cytotoxicity to MCF-7 cells. These results demonstrate they are good candidates for potential applications in biomedically relevant fields.2. Synthesis and characterization of coil-comb cationic polymerA novel coil-comb cationic cyclodextrin polymer was successfully synthesized. First of all, macromolecule initiator PEG-Br was prepared by the esterification reaction between CH3-PEG-OH and 2-bromoisobutyryl bromide (BriBB), the degree of polymerization of which was 120. And a new mono-methacrylate substituted CD monomer was easily prepared in a mild reaction condition. Then the diblock copolymer PEG-b-PGAC can be conducted via atom transfer radical polymerization (ATRP) of the CD monomer from poly (ethylene glycol) macroinitiator PEG-Br. The hydroxyl groups of the CD on diblock copolymer were reacted with BriBB to prepare macroinitiator PEG-b-P(GAC-Br). Finally, the coil-comb polycationic brushes PEG-b-P(GAC-g-PDMA) was synthesized via ATRP of DMAEMA from the macroinitiator PEG-b-P(GAC-Br). Well-defined brushes with narrow molecular weight distribution can be obtained by adjusting the reaction condition.3. The application of the coil-comb polymer as dual carrier of drug and geneBenefiting from host-guest interaction, a drug-loaded nanoparticles was formed between the hydrophobic cavity of the coil-comb cationic cyclodextrin polymer and the hydrophobic small molecular drug (doxorubicin). The in vitro release of DOX is pH-responsive. The cell uptake of DOX-NPs in MCF-7 was dependent on the drug concentration and incubation time. Then, a dual carrier containing drug and gene was obtained by using the drug-loaded nanoparticles to condense pDNA. The size and zeta potential of the dual carrier were characterized by dynamic light scattering (DLS). Gel retardation assay confirmed that pDNA could be effectively condensed by the positive charged drug-loaded nanoparticles. Drugs and genes could be co-delivered into the cell for drug release and gene expression. Furthermore, cytotoxicity of the carriers, which loaded both DOX and p53 plasmid, was detected in MCF-7 cell. Results displayed that greater cytotoxicity were obtained, which is attributed to the synergistic effect of co-delivered DOX and p53 encoding gene.4. The application of the coil-comb polymer as folic acid receptor (FR) targeting gene carrierLinear PEG chain with folic acid end-group on one side and adamantyl end-group on other side was entrapped in the cyclodextrin cavity of the cationic coil-comb polymer to form stable FR targeting complexes. Then the cationic complexes were used to condense pDNA to form FR targeting gene carriers (100-200 nm). Cytotoxicity of the FR targeting gene carrier performed a concentration dependent manner, and was much lower than the standard control of PEI 25 kDa. In vitro transfection experiments results show that, the transfection efficiency of the targeting carrier was associated with content of folic acid group. Under a certain N/P ratio, the transfection efficiency was improved with the increase of folic acid content. Comparing to the one without folic acid group, FR targeting gene carrier showed equivalent or higher transfection efficiency, which is attributed to the positive targeting effects.In summary, a hydrophilic star-shaped cyclodextrin polymer and a coil-comb cationic cyclodextrin polymer were successfully prepared in this study. Star polymer exhibits an adjustable response to environmental stimuli-responsive and excellent biocompatibility, which was favored for the potential applications in biological related fields. Coil-comb cationic polymer can be used as multifunctional carrier (dual carrier of drug and gene or folic acid targeting gene carrier), which exhibits excellent functions and effects in the delivery system. In addition, the methods we used in this thesis are universal, a variety of CD polymers with different functions can be prepared by altering the synthesis conditions or the type of guest molecules, which results good prospects in biomedical field.