Colloidosomes are microcapsules whose shells consist of colloid particles, which are coagulated by a stabiliser or fused by sintering. In recent years, they have attracted considerable attention because of their potential applications in a range of industries, such as food, bioreactors and medicine. However, traditional particulate polymer shell colloidosomes leak low molecular weight encapsulated materials due to their intrinsic shell permeability, and this problem will limit their applications in pharmaceutical industries. In this thesis, we report aqueous core colloidosomes coated with a silver or gold shell, which make the capsules impermeable. The shells can be ruptured using ultrasound. The silver shells are prepared by making an aqueous core capsule with a particulate polymer shell and then adding AgNO3, surfactant and L-ascorbic acid to form a second shell. The gold coated colloidosomes are prepared by making an aqueous core capsule with a particulate polymer shell and then adding HAuCl4, surfactant and L-ascorbic acid. We propose to use the metal coated capsules as drug carriers to load an anticancer drug, doxorubicin. After triggering by ultrasound, encapsulated drug, broken fragments and possibly some drug attached on the surface of the capsules may all kill cancer cells. For silver coated colloidosomes, at 10 capsules/cell, they have a low cytotoxicity, showing a cell viability of more than 90% during the first 24 h and more than 60% after 72 h. Increasing the number of capsules, the cytotoxicity of the silver shells increases heavily. Compared with silver ones, the gold shells show less toxicity to cells. We also used the capsules to load an antibiotic kanamycin and triggered to release the drug and kill E.coli. In addition, we set up a targeting model by modifying the colloidosomes using 4,4'-dithiodibutyric acid and attaching them with proteins - rabbit Immunoglobulin G (IgG). Label-free Surface Plasmon Resonance biosensor was used to test the specific targeting of the functional silver or gold shells with rabbit antigen. The results demonstrate that a new type of functional metal coated colloidosome with non-permeability, ultrasound sensitivity and immunoassay targeting could be applied to many medical applications.

This thesis present a study of thermo-gelling polycaprolactone (PCL) dispersion which consist of a mixture of PCL microspheres (MSs) and thermo-responsive, graft cationic copolymer. The PCL microspheres are solid or colloidosomes (hollow). This study aims toward an injectable colloidal cell delivery system. The thermo-responsive copolymer used in this study is a new family of cationic graft copolymer. The cationic graft copolymer consisted of cationic poly(N,N-dimethylaminoethyl methacrylate) backbone and poly 2-(2-methoxyethoxy) ethyl methacrylate (PMA) side chains. A series of new cationic graft copolymers were synthesized with different PMA arm length and grafting density. A representative copolymer showed good cell viabililty. The solid PCL MSs were prepared using solvent evaporation method. The MSs were mixed with the thermo-responsive graft copolymer. At room temperature the mixture were liquid-like and gelled at body temperature (37 ˚C). This indicates that the mixture systems were injectable. The injectable route offers a minimal invasive route to fill defect void inside the body. Furthermore, a porous morphology was evident for the mixed gels at 37 ˚C and the porosity could be altered using different composition of the mixed components. The mixed system showed self-healing properties for low volume fraction of PMA. The mixed system particle gel was more ductile in electrolyte but showed similar morphology to the mixed system particle gels prepared in water. This part of the study was carried out using PCL MSs prepared by cetyltrimethylammonium bromide (CTAB) as surfactant. A brief study using polyvinyl alcohol (PVA) as the surfactant showed that the PCL MSs had similar diameter and gel morphology which suggests that the model systems studied using CTAB may be applicable to the PVA system. Microencapsulation attracts interest due to its ability to deliver and control release actives and also its application in many fields. Colloidosomes are one of the microcapsules/microspheres used for microencapsulation. In this study a two step, facile and scaleable colloidosome preparation method was introduced. The PCL colloidosome shell consisted of partially fused small nanoparticles. The PCL colloidosomes were birefringence under cross polarised light due to the stress applied during solvent evaporation. A brief study showed that the mixture system of colloidosomes and thermo-responsive graft copolymer are able to gel at 37 ˚C.

Stimulus-responsive colloidosomes which completely dissolve upon a mild pH change are developed. pH-Responsive nanoparticles that dissolve upon a mild pH increase are synthesized by a nanoprecipitation method and are used as stabilizers for a double water-in-oil-in-water Pickering emulsion. These emulsions serve as templates for the production of pH-responsive colloidosomes. Removal of the middle oil phase produces water-core colloidosomes that have a shell made of pH-responsive nanoparticles, which rapidly dissolve above pH 7. The permeability of these capsules is assessed by FRAP, whereby the diffusion of a fluorescent tracer through the capsule shell is monitored. Three methods for tuning the permeability of the pH-responsive colloidosomes were developed: ethanol consolidation, layer-by-layer assembly and the generation of PLGA-pH-responsive nanoparticle hybrid colloidosomes. The resulting colloidosomes have different responses to the pH stimulus, as well as different pre-release permeability values. Additionally, fundamental studies regarding the role of particle surface roughness on Pickering emulsification are also shown. The pH-responsive nanoparticles were used as a coating for larger silica particles, producing rough raspberry-like particles. Partial dissolution of the nanoparticle coating allows tuning of the substrate surface roughness while retaining the same surface chemistry. The results obtained show that surface roughness increases the emulsion stability of decane-water systems (to almost twice), but only up to a certain point, where extremely rough particles produced less stable emulsions presumably due to a Cassie-Baxter wetting regime. Additionally, in an octanol-water system, surface roughness was shown to affect the type of emulsion generated. These results are of exceptional importance since they are the first controlled experimental evidence regarding the role of particle surface roughness on Pickering emulsification, thus clarifying some conflicting ideas that exist regarding this issue.