Templating-Assembly And Properties Of Polymer Capsules

Template-mediated polymer capsules have been found applications in various fields including synthetic chemistry, biotechnology, pharmaceutics, and diagnostics because of their tailored properties (e.g., size, composition, shell thickness, stability, and surface functionality), which have attracted particular interests of scientists. They have been becoming an interdisciplinary field among chemistry, biology and engineering. To fulfill more functionalities and applications of polymer capsules, in this thesis, novel polymer capsules using new templates and shell materials have been fabricated. The properties and functionalities of these capsules have also been explored. The outline and contents of this doctoral dissertation are as follows:Chapter 1 is a brief introduction of the research background of template-mediated polymer capsules in which assembly methods and applications of polymer capsules are reviewed. In this chapter, the details of the templating method especially layer-by-layer (LbL) assembly, including templates and shell materials, driving forces, pros and cons of LbL method, and the applications of capsules in encapsulation, microreactor, biomimetic mineralization, and drug release, are mainly demonstrated. Finally, the current and future research in polymer capsule field is concluded. The purpose and significance of this thesis are also demonstrated.In Chapter 2, the preparation of monodisperse polymer (polydopamine, PDA) capsules have been studied by a one-step interfacial polymerization of dopamine onto dimethyldiethoxysilane (DMDES) emulsion droplets and removal of the DMDES templates with ethanol. The results demonstrated that the diameters of the PDA capsules can be tailored from 400 nm to 2.4μm by varying either the DMDES emulsion condensation time or the emulsion concentration used for templating. Further, capsules with defined nanometer-scale shell thicknesses (ranging from～10 to 30 nm) can be prepared by adjusting the emulsion concentration. The shell thickness can be increased by repeated interfacial polymerization of dopamine, with three cycles yielding capsules with a shell thickness of up to 140 nm (for a 0.6% v/v suspension). The results also demonstrated that functional substances, such as organically-stabilized magnetic (Fe3O4) nanoparticles, quantum dots (CdSe/CdS), and hydrophobic drugs (thiocoraline), can be preloaded in the emulsion droplets, and following PDA coating and DMDES removal, these materials remain encapsulated in the polymer capsules. All of the unloaded and loaded PDA capsules were monodisperse and did not aggregate. This work not only enriches the chemistry of dopamine-based melanins (eumelanins), but also provides new avenues for the preparation of polymer capsules with defined size and shell thickness and for the encapsulation of a range of hydrophobic substances, leading to possible applications in devices, biotechnology, and drug delivery systems.In Chapter 3, multiwalled carbon-nanotube (MWCNT)-embedded microcapsules were fabricated by the stepwise deposition of polyelectrolytes and oxidized MWCNTs using the layer-by-layer (LbL) assembly technique based on electrostatic interaction. Electrochemical behaviors of the MWCNT-embedded microcapsules were studied by cyclic voltammetry (CV). Transmission electron microscopy (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), and confocal laser scanning microscopy (CLSM) were used to characterize the morphology of the microcapsules. The results revealed that MWCNTs were homogeneously assembled in the microcapsule shells to form a netlike structure. Mechanical properties of the MWCNT-embedded microcapsules were enhanced. CV measurements indicate that MWCNT-embedded microcapsules exhibit different electrochemical behaviors by changing surrounding conditions, such as pH and salt concentration. MWCNT-embedded microcapsules show a well-defined reversible voltammogram at-0.05 V. The peak potential decreased with increasing pH of support eclectrolyte. However, salt concentration in the support electrolyte has little influence on the peak current. The MWCNT-embedded microcapsules, combined with the electrochemical behaviors, are envisaged to be utilized in applications for biosensors and catalysis.In Chapter 4, magnetic microcapsules were constructed by fabricating nano-meter scaled C60-like "Keplerate" type{Mo72Fe30} with molecular formula [Mo72ⅥFe30ⅢO252(CH3COO)12Mo2O7(H2O)｝2｛H2Mo2O8(H2O)｝(H2O)91]·ca. 150H2O into nanocapsule shells using the LbL technique. The morphology of the obtained hybrid microcapsules were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Shell thickness of the {Mo72Fe3o}-embedded microcapsules can be tailored at the nanometer level more precisely than other nanoparticle-embedded capsules due to the homogeneous diameter and surface charges of{Mo72Fe30}. Interestingly, the{Mo72Fe30}-embedded microcapsules could be separated and aligned under a circumstance of magnetic field, though{Mo72Fe30} is a paramagnetic molecule. To our best knowledge, this is the first time to fabricate hybrid magnetic materials containing{Mo72Fe3o} using LbL technique. The obtained microcapsules can be a good candidate for bioseparation as well as targeted delivery.In Chapter 5, as well-known, more than 40% of active compounds identified through combinational screening programs are poorly water-soluble and are frequently abandoned for further development to drug products, as they can not be delivered using conventional formulation techniques, In this chapter, a general and facile approach of encapsulating water-insoluble compounds in polymer capsules was reported through mesoporous silica (MS) nanoparticle-mediated drug loading and subsequent generation of the polymer shell templated assembly using the layer-by-layer (LbL) technique. After removal of the MS particle, the water-insoluble compounds were retained in the polymer capsules. The drug-encapsulated capsules exhibited excellent colloidal stability in water. MTT experiments proved that the drug encapsulated in the capsules maintained their high cancer cell killing potency. Given the tunability of particle sizes and pore sizes of MS particles, as well as the versatility and controllability of the LbL technique, this novel approach constitutes a facile and promising route to translate water-insoluble compounds to relevant clinical applications.