| Polymeric materials as drug delivery vectors have various advantages, such as optimizing drug pharmacokinetics, increasing drug content in target organs, reducing toxic effects, increasing the drug permeability through cell membrane and overcoming the biological barrier in vivo. Using nucleic acids in gene therapy faces various inevitable hurdles for instance: large size, negative surface charge, tissue clearance and inefficiency for systemic delivery. A key challenge in addressing the problem in gene therapy lies in the development of specially designed gene delivery systems that are capable to carry therapeutic genes into mammalian cells for gene expression.Natural polysaccharides are very suitable candidates for the design of novel biomaterials, because they are renewable, nontoxic, biodegradable and excellent biocompatible materials, large amount of literatures have have reported polysaccharides as drug delivery vectors in biomedical area. However, natural polysaccharides are unable to meet the requirements of practical applications, such as unable to load drug and complex with target genes effectively, unable to respond to pH changes and the presence of serum in vivo, unable to deliver the cargo to the desired site, etc. Therefore, more and more attentions have been paid to the modification of natural polysaccharides. The requirements are rigorous, especially for drug delivery and gene transfection system. The current available carriers may be several characteristics, such as biodegradability, low immunogenicity and minimal cytotoxicity. Polysaccharides as carriers have attracted attention in this field. However,it’s hard to be dissolved for most of the polysaccharides in common organic solvents,and it is difficult to be modified in a homogeneous reaction system. Moreover, the methods of modification are complex and the organic solvents are toxic, etc. How to get the modified materials based on polysaccharides by the simple andenvironmentally methods, and design the drug carriers based on modified polysaccharides requiring further research. Based on the above facts, we successfully designed and synthesized a series of polymer materials based on natural polysaccharides possession with pH-responsive property. And the properties of polysaccharide-based materials were deeply discussed, especially in the aspects of cell viability, drug delivery and gene transfection system. In particular, the preparation of the modified polysaccharides was prepared by using the low toxic dimethyl sulfoxide(DMSO) as the reaction solvent and synthesized by direct esterification.This dissertation can be further categorized into four main parts as described below:(1) New pH-responsive hydrogels based on curdlan derivatives were obtained by conjugating curdlan with Boc-histidine(CUR-HIS). The morphologies of the hydrogels were analyzed by scanning electron microscopy(SEM) and the chemical composition was studied by 1H NMR, FTIR spectroscopy and Elemental analyses(EA). These xerogels possessed highly porous structures. The main characteristics of these new hydrogels such as the swelling degree in various pH solutions and the exchange capacity were also discussed. Interestingly, the addition of NaCl provoked a sharp shrinking of swelling ratio of CUR-HIS hydrogels. The hydrogels were loaded with BSA, which was taken as a model protein drug. The drug release experiments performed at different pH values indicated that the drug release rate increased with the pH. The CUR-HIS hydrogels revealed low cytotoxicity against the HepG2 cell line. Above all, these results allow us to propose these materials as useful candidates for biomedical applications such as protein delivery systems.(2) New pH-responsive pectin-based colloidal particles(His-Pectin) were designed and synthesized by esterificating pectin with Boc-histidine. The physicochemical properties of the colloidal particles were confirmed by UV-vis spectra, dynamic light scattering(DLS) and transmission electron microscopy(TEM). We found that the His-Pectin colloidal particles displayed considerably enhanced buffering capacity. In addition, curcumin as hydrophobic drug model, we explored the encapsulation of His-Pectin particles withcurcumin, the His-Pectin@curcumin colloidal particles morphology, drug loading and release properties at different pH conditions. Moreover,curcumin can be efficiently encapsulated in His-Pectin colloidal particles. The mean diameter of the curcumin colloidal particles was about 200 nm with narrow size distribution. Under various pH conditions, drug carriers showed different drug release kinetics. The result of cytotoxic assays of His-Pectin colloid particles showed good cell compatibility. The cytotoxic assays of His-Pectin@curcumin colloidal particles demonstrated high inhibitory effect on HepG2 cell growth compared to the free curcumin. It is concluded that His-Pectin colloidal particles can efficiently encapsulate curcumin in vitro and promote the inhibition of HepG2 cell growth in vitro.(3) A series of dextran-based biodegradable comb-like glycopolymers containing random copolymer Poly[2-lactobionamidoethyl methacrylate-co-N,N-(dimethylamino)ethyl methacrylate](P(LAMA-co-DMA)) as polymer chains have been successfully synthesized via the subsequently ATRP. The reaction kinetics of ATRP was obtained by 1H NMR and the optimum reaction conditions were confirmed.The chemical composition was studied by 1H NMR and FTIR spectroscopy. The result of acid-base titration showed that, compared to NaCl, we found that the dextran-based glycopolymers displayed considerably enhanced buffering capacity,especially at pH=5.0-8.0. With the increasing of DMA content, buffering capacity rose obviously. DNA gel electrophoresis showed that stable complexes were formed when the weight ratio of dextran-based glycopolymers to plasmid DNA was 2:1,while the weight ratio was 0.25:1 when adding PEI(25K). The cell viability of dextran-based glycopolymers was found to be about 80% at the concentration of 100μg/mL. All the dextran-based glycopolymers exhibited rather low cytotoxicity in comparison with PEI. In vitro gene transfection showed that only glycopolymers can complex with DNA, the transfection efficacy was lower than PEI-dextran-based glycopolymers-DNA ternary complexes. What’s more, PEI-dextran-based glycopolymers-DNA ternary complex exhibited much higher transfection efficacy than PEI-DNA complexes. Especially, the presence of 20% percent serum medium did not decrease the transfection efficiency. The dextran-based glycopolymers have great potential to be a new type of safe and efficient gene vectors.(4) The hydrophobic macromolecular initiator was obtained by two step esterification reactions. The Dex-P(GAMA-co-DMA)-His amphiphilic glycopolymers were obtained by random polymerization of 2-gluconamidoethyl methacrylate(GAMA) glycomonomer and N, N-(dimethylamino)ethyl methacrylate monomer. The reaction kinetics of ATRP was obtained by 1H NMR and the optimum reaction conditions were confirmed. The chemical composition was studied by 1H NMR and FTIR spectroscopy.The particle size of the amphiphilic glycopolymers was investigated, and it was found that the particle size decreased with the decrease of pH,until completely dissolved. The amphiphilic glycopolymers aggregated to large size with pH increasing. In addition, treating curcumin as hydrophobic drug model, we explored the encapsulation of the amphiphilic glycopolymers with curcumin, drug loading and release properties at different pH conditions. The result showed that curcumin was released faster with pH decrease. DNA gel electrophoresis showed that stable complexes were formed when the weight ratio of amphiphilic glycopolymers to plasmid DNA was 2:1. All the amphiphilic glycopolymers exhibited rather low cytotoxicity, and certain transfection efficiency in HepG2 cells. The amphiphilic glycopolymers have a potential to be used as drug and gene co-delivery carrier. |
PDF Full Text Request