Fabrication And Biological Application Of Polysaccharide-based High-order Assemblies

Polysaccharides are a class of polymeric carbohydrates composed of monosaccharides.They are raw materials widely used in the biomedical field due to their abundance in nature and their good biocompatibility,biodegradability,unique biological functions such as cell recognition,protein targeting and so on.In this paper,two kinds of polysaccharide-based nanogels were prepared by Graft copolymerization Induced Self-assembly strategy?GISA?and used as the building blocks for high-order self-assembly.The high-order assemblies were fabricated through electrostatic interaction and polysaccharide-protein recognition respectively and their biological functions were explored as well.Firstly,a positively charged chitooligosaccharide/dextran-poly?methyl acrylate?nanogel?COS/Dex-ss-PMA NG,referred to as COS/Dex NG?was designed and prepared.The negatively charged polysaccharide,Hyaluronic Acid?HA?,was used to fabricate the high-order assembly?HA-NG?through the electrostatic interaction.The results showed that the size of nanogel can be controlled by N_MA/N_Glulu and high-order self-assembly of nanogels can only occur when the mass ratio of COS/Dex NG to HA(M_NG/M_HA)meets certain conditions.For COS/Dex NG with different size,the M_NG/M_HAA capable of inducing high-order self-assembly is not the same.Therefore,the size of HA-NG can be adjusted by controlling N_MA/N_Glulu and M_NG/M_HA to meet different application needs.For further study of the interaction between high-order assemblies and cells,COS/Dex NG₄ with N_MA/N_Glu of4:1 was fluorescently modified with the near-infrared fluorescent molecule Cy5.5.On this basis,a high-order assembly?HA-NG₄-Cy5.5?was constructed with M_NG/M_HA of 2:1.Cellular experiments showed that the high-order assembly had good biocompatibility,and active targeting of A549 cells which over-express CD44 could be achieved by specific binding between HA and CD44.Secondly,dextran-poly?methyl acrylate?nanogel?Dex-ss-PMA NG,referred to as Dex NG?was prepared via GISA.The specific recognition between the concanavalin A?Con A?and dextran was used to induce the high-order self-assembly of Dex NG,thereby getting the size controllable Con A-Dex NG.The particle size,structure and morphology of Con A-Dex NG were characterized by transmission electron microscopy,infrared spectroscopy,nuclear magnetic resonance spectroscopy and isothermal titration calorimetry.The mechanism of high-order self-assembly was discussed.In addition,the cytotoxicity of Con A and Con A-Dex NG on A549 cell was also investigated.The results showed that the sizes of the high-order assemblies are directly related to the mass ratio of Dex NG to Con A(M_NG/M_{Con A}).Free Con A had an inhibitory effect on A549 cells,and the process of high-order self-assembly did not affect the biological activity of Con A.In summary,this thesis uses electrostatic interaction and polysaccharide-lectin recognition to drive high-order self-assembly of polysaccharide-based nanogels.The results demonstrate the importance of non-covalent bonding for high-order self-assembly of polysaccharide nanomaterials,and obtain high-order assemblies composed of biomolecules such as polysaccharides and lectins.The scale of such assemblies is controllable and well dispersed.The study of biofunctionality and related assembly mechanisms have laid a solid foundation for subsequent biomedical applications.