Self-Encapsulation of Vaccine Antigens in PLGA Microparticles and Microneedles.

Abstract

There is an urgent need to reduce reliance on hypodermic injections for many protein-based therapies. Alternative approaches include developing controlled release formulations, which reduce dosing frequencies, and utilizing alternative delivery devices, such as microneedles. This thesis explores the development of controlled release microparticles made of poly(lactic-co¬-glycolic acid) (PLGA) that encapsulate stable/active proteins. These microparticles are then delivered via novel microneedle patches. This work has great implications for improving the utility and coverage of protein-based vaccines. PLGA microparticles are loaded with protein through a novel approach termed active self-healing encapsulation (ASE). This method loads proteins after microparticle fabrication, thus preventing protein exposure to a variety of stresses. ASE utilizes a protein trapping agent (Alhydrogel), along with the self-healing of microparticle surface pores to sequester and trap proteins inside the microparticles. The self-healing phenomenon was explored in detail, and was determined to be a viscoelastic response of the polymer to high surface tension when above the glass-transition temperature (Tg). The healing kinetics followed expected Williams-Landel-Ferry behavior, and Arrhenius plots generated activation energies consistent with polymeric creep. A mathematical model to predict healing times is also presented. The ASE technique afforded high loading (1.64% w/w) and encapsulation efficiencies up to 91% for the model protein Ovalbumin. In vitro controlled release was shown to be biphasic, with an initial release of soluble protein followed by a delayed release of Alhydrogel-complexed protein over the course of two months. Furthermore, a bulk batch of microparticles can be used to load many different proteins without needing to reformulate unique batches. A process was also designed to deliver protein-loaded microparticles via a microneedle patch. Microneedle patches can be easily self-applied, are easy to store/dispose, and are generally preferred by patients over traditional hypodermic needles. These patches, made of a dissolvable material, successfully delivered microparticles intradermally where they began antigen release. In animal models these patches generated a robust immune response that was as good as or better than conventional administration techniques. This thesis lays the ground work for a versatile system for delivering protein-based vaccines with reduced dosing requirements or limited need for hypodermic injections.