Preparation And Self-Assembly Of Polysaccharide Surfactant

Biocompatible surfactants and their self-assembly have attracted considerable research interests in the field of the material chemical engineering in recent years. The biocompatible functional materials prepared through self-assembly on the basis of amphiphilic molecules have shown significant potentials in the application in drug controlled release, bio-imaging, intelligent switch, and so on. In this study, biodegradable and biocompatible polysaccharide amphiphilic block copolymers have been synthesized, and applied as the surfactants in the preparation of the drug carrier nanoparticles (NPs) and fluorescent NPs, which could be tuned in morphology and size, by Flash Nanoprecipitation (FNP). Moreover, the photo-reversible hydrogel based on annular amphiphilic polysaccharide (cyclodextrin, CD) has been prepared by the "Host-Guest" self-assembly, and systematic investigations have been done on the relationship between its structure and properties. The main research content is listed as follows:1. Firstly, the amino-terminated Dextran (Dex-NH2) was synthesized by reductive amination reaction. Secondly, by the ring-open polymerization reaction through L-lactide, D,L-lactide, D,L-lactide and glycolide, as well as ε-caprolactone respectively, PLLA (poly (L-lactic acid)), PDLLA (poly (D,L-lactic acid)), PLGA (poly(lactic-co-glycolic acid), and PCL (polycaprolactone) have been polymerized. After modification on their end groups, PLLA-acryloyl, PDLLA-acryloyl, PLGA-acryloyl and PCL-CHO were obtained. Lastly, through the Michael addition reaction of acryloyl group and amino group, and through reductive amination reaction of aldehyde group and amino group, the polysaccharide amphiphilic block copolymers Dex-b-PLLA, Dex-b-PDLLA, Dex-b-PLGA as well as Dex-b-PCL were synthesized.2. The Dex-b-PLLA-β-carotene NPs were prepared with Flash Nanoprecipitation (FNP) by using the polysaccharide amphiphilic block copolymer Dex-b-PLLA as the surfactants and the β-carotene as the model drug. It was found that the sizes of NP could be tuned by solvent ratios and stream velocities, and the NP sizes decreased over time (the "anti-Ostwald" phenomenon) was observed during the preservation.3. The Aggregation-Induced Emission (AIE) fluorescent NPs have been prepared by FNP. It was found that the NP sizes and the fluorescent properties of AIE NPs could be tuned with the solvent ratio and the stream velocity. In the observation of the microstructure of the AIE fluorescent NPs based on the polysaccharide amphiphilic block copolymer through TEM, a large number of nanoscale rod particles were found.4. In the systematic study on the AIE fluorescent NPs prepared by FNP based on the polysaccharide amphiphilic block copolymer, it was found that the Dex-b-PDLLA concentration could tune the morphology of AIE fluorescent NPs. Specifically, with the increase of Dex-b-PDLLA concentration, the morphology of AIE fluorescent NPs changed from sphere particles to rod particles. Moreover, the glass-transition temperature of hydrophobic block of polysaccharide amphiphilic block copolymer could tune the morphology of fluorescent NPs by FNP. The morphology of AIE fluorescent NPs formed based on Dex-b-PCL were sphere, of which the glass-transition temperature of hydrophobic block of Dex-b-PCL was much lower than the room temperature; while the rod fluorescent NPs were obtained, of which the glass-transition temperature of hydrophobic block of Dex-b-PDLLA, Dex-b-PLLA, and Dex-b-PLGA are higher than the room temperature.5. Photo-reversible hydrogel were prepared by "Host-Guest" self-assembly of annular amphiphilic polysaccharide a-cyclodextrin (a-CD) grafted PAA (poly (acrylic acid)) and azobenzene (Azo) grafted PAA. The morphology of this hydrogel under visible light is Gel, while after irradiation of 365 nm UV, the conformation of Azo converts from trans to cis and the cis-Azo cannot form inclusion complex, and then the Gel converts to be Sol. After visible light irradiation again, the Azo come back to trans conformation and trans-Azo can form inclusion complex with a-CD again, and then the Sol converts back to Gel. The reversible Sol-Gel transition of hydrogel could be tuned by visible light and UV irradiation. The zero-viscosity of hydrogel increased with the increase of azobenzene substitution degree, polymer mass concentration and tethered chain length.