Preparation Of Smart Sugar-based Polyelectrolyte Nanogels And Their Application In Drug Delivery

Nowadays, the design of versatile smart nanocarriers targeting for solid tumor microenviroment or active receptor molecules on tumor cells has become a vital key to solve difficult in tumor chemotherapy. Stimuli-responsive nanogels are one of the mainstream smart nanocarriers and very potential for biomedical applications. Polysaccharides, as outstanding biomaterials, are very suitable for preparing nanogels due to their excellent biocompatibility, biodegradability and non-toxicity. Amongst them, several natural polysaccharides containing amino or carboxyl groups are natural polyelectrolytes (e.g., chitosan). On the other hand, synthetic glycopolymers with pendent sugar moieties are not only able to interact with lectins as multivalent ligands in a similar manner to natural glycoproteins, but also exhibit a strong affinity towards glucose transporters (GLUTs) which are over-expressed on the cytomembrane of tumor cells. In view of this, the design of smart and novel sugar-based polyelectrolyte nanogels has deeply attracted us. In this thesis, we have proposed three different smart sugar-based nanogels using natural chitosan or synthetic glycopolymers via electrostatic interactions, which possess pH-sensitive, cancer-specific and redox-sensitive/cancer-specific, respectively.pH-sensitive nanogels, which enable to respond the weak acid circumstance (pH 5.0-6.5) of tumors, are potential nanocarriers for loading and releasing drug. They are beneficial to increase the accumulation of released drug into tumor tissue and then enhance the therapeutic outcomes. Chitosan has an intrinsic pKa of 6.5, and it only can be dissolved in acidic aqueous solution, so the most response mechanism of chitosan-based polyelectrolyte nanogels is take advantage of the swell behavior caused by protonation of amino groups in chitosan or carboxyl group in opposite polyanion, which is a big restrict for preparing chitosan-mediated acid-labile polyelectrolyte nanogels. In this work, citraconic amide-functionalized chitosan (CA-CS) and quaternary ammonium chitosan (QA-CS) were synthesized and used as oppositely charged polyelectrolyte pairs to form citraconic amide-mediated pH-sensitive chitosan polyelectrolyte nanogels (CA-based nanogels). Firstly, the hydrolysis of CA-CS was monitored using fluorescamine assay and it was found that CA-CS could selectively dissociated in acidic media due to the isomerization during the addition of citraconic anhydride to chitosan. Secondly, the self-assembly behaviors of different CA-CS/QA-CS polyelectrolyte pairs were investigated via colloidal titration assays. Results showed that stable CA-based nanogels only formed when citraconic amide-functionalized chitosan oligosaccharide (CA-COS) added into quaternary ammonium middle viscosity chitosan (QA-MVCS), where the polymer chain length of QA-MVCS was very larger than that of CA-COS. Furthermore, the physicochemical properties and acid-labile behavior of such QA-MVCS/CA-COS nanogels were comprehensively characterized by DLS and TEM. At pH 7.4 and 37℃, the nanogels kept stable, but at pH 5.0 and 37 ℃, they quickly disintegrable in 0.5 h.It is well known that poly(ethylene glycol) (PEG) is the most common stealth material for protecting nanocarriers from immune clearance during circulation. However, PEG can interfere with interactions between nanocarriers and targeting cells, finally negatively influence the therapeutic effect. Glycopolymers, by contrast, are good alternatives for PEG, which exhibit excellent biocompatibility and unique bioactivity for active targeting. In this work, we report novel glycosylated polyelectrolyte nanogels (glyco/CS-nanogels) formed by block ionomer complexes (BIC) method between synthetic glycopolymers and QA-CS. Firstly, well-defined hydrophilic-block-anionic glycopolymers (PMAG-b-PMAA) were synthesized via RAFT polymerization. Then, the electrostatic self-assembly behaviors of PMAG-b-PMAA/QA-CS polyelectrolyte pairs with varying QA-CS and titration orders were investigated. Under optimal conditions, glyco/CS-nanogels with compact PMAA/QA-MVCS ionic cross-linking cores and glucose coronas were obtained and represented good colloidal stability in 10 mM HEPES buffer solution (pH 7.4,0.15 mM NaCl). Furthermore, their specific binding ability to lectin (Con A) and high affinity towards K562 cancer cells were well investigated.In addition to the above glyco/CS-nanogels, we also reported a novel glycosylated nanogels with biodegradable cross-linked cores for delivery of chemotherapeutic agents (glyco-nanogels/Cys). Firstly, block ionomer complexes of PMAG-b-PMAA and Ca2+ were utilized as templates. Then, disulfide bonds were introduced into the ionic cores by using cystamine as biodegradable cross-linker. The resulting nanogels showed a time-dependent degradation in the conditions mimicking the intracellular reducing environment and allowed to achieve a very high encapsulation efficiency for DOX (95.6%). The fluorescence images confirmed glyco-nanogels/Cys exhibited a enhanced affinity towards Hela cells than L929 cells. Moreover, DOX-loaded glyco-nanogels/Cys showed more potent cytotoxicity against Hela cells as compared to free DOX when CDOX≥10μg/mL.