Preparation Of Functionalized Polymersomes And Their Applications In Biomedical Field

In the past decade, polymersomes have attracted extensively interest and attention based on their intriguing physicochemical property, nano-and micron-sized dimensions and functions, as well as tremendous potential applications in biomedicine and biotechnology. Unlike liposomes self-assembled from low molecular weight lipids, polymersomes are in general prepared from macromolecular amphiphilic block copolymers. Polymersomes exhibit unique features highlighted with high stability, tunable membrane properties, biocompatibility, and capacity of loading and transporting hydrophilic as well as hydrophobic species.The studies focused on membrane’s functionalization, hydrophobic loading and size control for polymersomes based on amphiphilic block copolymer PEO-b-PBD have been conducted. Polymersomes have been successfully prepared as multifunctional nano-carriers which are capable of loading hydrophilic as well as hydrophobic species and fast conjugating bioactive molecules on the surface of polymersomes. A mechanism of membrane fusion for the internalization of polymersomes has been proposed and the investigations with different experiments have been performed. Moreover, near-infrared fluorescence probes based on polymersomes self-assembled by PEO-b-PBD have been successfully applied for multispectral in vivo imaging to detect tumor foci. This dissertation can be further categorized into some parts as discussed below:1. Polymersomes based on amphiphilic block copolymers PEO-b-PBD have been successfully prepared as multifunctional nano-carriers Polymersomes have been prepared by the means of "’film rehydration" with amphiphilic block copolymers PEO-b-PBD. Biotin-avidin system has been conjugated with polymersomes to perform membrane’s functionalization. The functionalized polymersomes are convenient for conjugation of targeting molecules or bioactive species to form a versatile targeting platform. Meanwhile, hydrophobic dyes Nile Red and DAF have been loaded into the hydrophobic membrane of polymersomes to form fluorescence emissive polymersomes with high stability and the emission spectra for Nile Red and DAF have been investigated before/after the encapsulation. Finally, vesicles with a hundreds nanometer order of magnitude have been achieved by the convenient method of sonication, freeze thaw and filtration facilitating the preparation and utilization of nano-sized polymersomes. Thus, polymersomes have been successfully prepared as multifunctional nano-carriers which are capable of loading hydrophilic as well as hydrophobic species and fast conjugating bioactive molecules on the surface of polymersomes.2. A mechanism of membrane fusion for internalization of polymersomes has been first proposed and explored by atomic force microscopy, FRET and specific endocytic inhibitors. It is demonstrated that there is a formed fusion area located on the surface of cells treated with NR-P and Nile Red are released into plasma membrane and the internalization of NR-P is an energy-dependent process and lipid raft-mediated endocytosis may play a major role in this process. Therefore, it is proposed that the interaction between polymersomes and cells begin with membrane fusion and followed by lipid raft-mediated endocytosis. The mechanism of membrane fusion for the internalization of polymersomes and the investigation with different experiments indicate that the mechanism of membrane fusion is different from the ordinary manner of uptake for nanoparticles in cells, which offer a new thought for the interactions between nano-carriers and cells.3. Near-infrared fluorescent probes based on polymersomes have been successfully applied to NIR fluorescence imaging to carry out in vivo tumor detection. Two polymersome-based NIR fluorescent probes have been prepared through the self-assembly of amphiphilic block copolymers PEO-b-PBD and hydrophobic near-infrared dyes (DiD and DiR), which were modified with different targeting ligands (anti-CEA antibody and anti-EGFR antibody), respectively. After simultaneous injection of these two probes into the tumor-bearing mice via tail vein, multispectral near-infrared fluorescence images have been obtained. The results indicate that two intensive fluorescent signals were detected well co-localized at the tumor foci. In addition, the results of signal-to-background ratios show that there are significant accumulation and tumor/skin contrast for polymersomes-based probes. This method may have great potentials for improving the diagnostic and therapeutic specificity and accuracy in cancer diagnosis and treatment.