Hierarchical Self-assembly Of Hyperbranched Polymersomes And Their Applications In Cytomimetic Aggregation

Cytomimetic chemistry is a new promising research field generating in the end of the twenty century, belonging to the interdisciplinary research fields of chemistry, biology and material sciences. In this field, artificial membranes(vesicles) are used as building blocks to mimick the cellular structures and functions. Cell-cell aggregation plays crucial roles in living systems and exists in many biological processes, such as immune response, hemostasis, inflammation, embryogenesis, endothelial tissue, and neuron tissue, etc. As a part of cytomimetic chemistry, vesicle-vesicle aggregation mimicking cell-cell aggregation has attracted more and more attentions. Up to now, many scientists have done excellent work in this field and realized vesicle aggregation by using liposomes as building block and utilizing multivalent interactions of supramolecules as driving forces, mimicking the cell-cell aggregation. But there are still some problems as follow: Firstly, the size of vesicle is usually nanometer, which is much smaller than the cellular size. Secondly, the scale of obtained vesicle aggregates is also further smaller than that in nature. Thirdly, liposomes are widely used in the mimetism of cell aggregation, while polymersomes are less used. Finally, there are few reports about controllable or reversible vesicle aggregation. Focusing on abovementioned questions, this manuscript firstly introduced cell-sized hyperbranched polymersomes(BPs) into the field of cytomimetic aggregation and designed some new driving forces, including phase separation, host-guest interaction, click chemistry-induced covalent interaction, strong absorption interaction of dopamine, investigating aggregation behaviors of the hyperbranched polymersomes. The main results are shown as follows.1. Polymerization-like hierarchical self-assembly of hyperbranched polymersomesAmphiphilic hyperbranched multi-arm copolymers(HMAC) of HBPO-star-PEO and pH-responsible HBPO-star-PDMAEMA were synthesized by the cationic ring-opening polymerization and atomic transfer radical polymerization. Through the coassembly in aqueous solution, pH-responsible hybrid-arm hyperbranched polymersome(HABP) was prepared, and its hierarchical self-assembly behaviors were investigated under different pH conditions. This self-assembly process was characterized by optical microscopy(OM), fluorescent microscopy(FM), and laser-confocal scanning microscopy(LCSM). The mechanism was proved by LCSM and NOSEY spectra. In summary, with the pH increase, microphase separation of PDMAEMA segments occurred on the vesicular membranes, forming the “lipid raft”-like hydrophobic domain; at the same time, isotropic HABPs were transformed into anisotropic vesicles with binding sites. Driven by the hydrophobic interaction, anisotropic vesicle further aggregated into linear, branched, circular, hyperbranched and netty vesicle chains, as the processes of homopolymerization, grafting copolymerization, intermolecular cyclization, hyperbranched polymerization and crosslinked polymerization. Eventually, linear, branched, circular and netty microtubes were obtained after vesicle fusion.2. Macroscopic vesicle aggregation triggered by host-guest interactionCyclodextrin(CD), adamantane or azobenzene modified amphiphilic hyperbranched multi-arm copolymers(HMAC) were synthesized by the modifications of terminal-groups. Coassembly with the unlabeled HMACs, cyclodextrin modified BPs(CD-BPs), adamantane modified BPs(Ada-BPs), or azobenzene modified BPs(Azo-BPs) were prepared. Their structures and components were characterized by OM, FM and fluorescent spectrum(FL). Based on the host-guest interaction between CD and adamantane, macroscopic hyperbranched polymersomes aggregates were gained, mimicking the adheren junction. According to the OM and FM results, the aggregates were composed of three-dimensional(3D) densely packed vesicles. On the basis of FL and NOSEY spectra, host-guest interaction plays important roles in the aggregation process. Based on the light-responsible host-guest interaction between CD and azobenzene, light-induced reversible hyperbranched polymersomes aggregation system was constructed, mimicking the reversible cellular adheren junction. The driving force of reversible host-guest interaction was verified by addition of a competitive host molecules, UV/Vis and NOSEY spectra. Besides, the scale of the obtained vesicle aggregates could be regulated by the concentration of polymers and recognition units. With the decrease, the aggregates were changed from densely-packed BPs to linear BPs chains. Finally, vesicle fusion happened in these systems, which was characterized by OM, FM and FL.3. Click chemistry reaction-induced vesicle aggregation: controllable fusion and phase separationAlkynyl or azide units modified amphiphilic hyperbranched multi-arm copolymers(HMAC) were synthesized by the modifications of terminal-groups. Coassembly with the unlabeled HMACs, alkynyl modified BPs(Alk-BPs) and azide modified BPs(N3-BPs) were prepared. Their structures and components were characterized by OM, FM and FL. Mixing them together under the condition of click chemistry reaction, adheren junction mimetic hyperbranched polymersomes aggregation were obtained. According to the OM, NMR and FTIR results, this process was triggered by click chemistry reaction; besides, the packing scale of vesicle aggregation were in relation with concentration of functional groups. Besides, unexpected fusion phenomenon occurred in the aggregation process. Inspired by the desmosomes, azide units modified HMACs were synthesized, which could self-assemble in water to form azide-modified spherical micelle. Mixing it with Alk-BPs, large-scale and unfused hyperbranched polymersomes aggregates were prepared, which were verified by the OM, FM and FL. Regulating the molar ratios of alkynyl unit and azide unit, 3D densely packed vesicles could be changed into uniformly-dispersed vesicle. In addition, lateral microphase separation occurred in these click chemistry reaction-induced aggregation systems, which was related with the recognition units in the vesicular membranes. With the decrease, the microphase separation decreased.4. Three-components recognition interaction triggered vesicle aggregationThiol-modified amphiphilic hyperbranched multi-arm copolymers(HMAC) were synthesized by the transformation of functional groups. Through the hydration self-assembly, thiol-modified hyperbranched polymersome was prepared in water. Its hollow-lumen was detailly characterized by OM and FM. After the in-situ reduction, gold nanoparticles coated BPs were obtained. According to the UV/Vis, OM, SEM and TEM results, goad nanoparticles were uniformly dispersed onto the vesicular membranes, with an average diameter of 9.3 nm. Polydopamine coated multi-wall carbon nanotubes were prepared by the self-polymerization of dopamine. TEM image showed the thickness of polydopamine layer is 12.5 nm. Mixing them in the Tris buffer solution, large-scale hyperbranched polymersomes were successfully obtained. According to the diameter contrast before and after the aggregation, it is found that fusion phenomenon was avoided in this system.