AbstractsBiology & Animal Science

Purpose: The increasing interest in new generation vaccines is based upon utilising highly purified proteins and peptides as antigens. However, a disadvantage of these subunit vaccines is that they are often poorly immunogenic. Therefore there is a need to develop new formulation strategies which can generate the desired immune responses and are both safe and efficacious. One important formulation strategy involves incorporating antigens in polymeric nanoparticles, while another formulation strategy involves the dispersion of antigens in a sustained release carrier with the aim of increasing the size of the immune response generated and perhaps avoiding the need for multiple immunisations. In this thesis the aim was to combine these two approaches by dispersion of polymeric nanoparticles loaded with the antigen into a sustained release delivery systems (a self gelling microemulsion). Two polymeric nanoparticles (poly(ethylcyanoacrylate), PECA and chitosan nanoparticles, CNP) were dispersed in self gelling microemulsion (ME) templates. Ovalbumin (Ova) and Quil A were used as model antigen and adjuvant respectively. Biocompatible microemulsions were developed by establishing pseudoternary phase diagrams and these were then characterised at 37 ˚C. Lamellar liquid crystalline gel regions were found adjacent to the microemulsion regions in the phase diagrams. Upon addition of water or body fluids a phase transition from microemulsions to liquid crystalline systems may occur, which may make these systems suitable for sustained antigen delivery, as the rate of diffusion within the liquid crystalline phase is slower as compared to liquid vehicles. The study investigated the influence of the oil and water composition of the microemulsions on viscosity and release of antigen dispersed in the microemulsion in molecular form and incorporated into nanoparticles from the microemulsions and liquid crystalline gels. The ability of these formulations to generate immune responses towards Ova was also investigated in vivo. Methods: The ME components consisted of isopropyl myristate, lecithin, ethanol, water and either decyl glucoside (DG) or capryl-caprylyl glucoside (CCG). The selected microemulsions had a surfactant: water (S:W) ratio of 9:1 and a surfactant: oil (S:O) ratio of 5.2: 4.8. Formulations were loaded with fluorescently labelled Ova (FITC-Ova) and used as polymerisation templates for the preparation of PECA nanoparticles by interfacial polymerisation. CNP were prepared separately by a precipitation/coacervation method facilitated by sodium sulphate. The viscosity of one phase and two phase liquid crystalline gels (with and without nanoparticles incorporated) was determined using a cone and plate rheometer. A fluorometric assay was used to determine entrapment and in vitro release of FITC-Ova. An HPLC method was used to determine entrapment of Quil A in PECA nanoparticles and CNP. Self-gelling microemulsion templates containing Ova and Quil A either free or incorporated in nanoparticles were subsequently investigated in…