New strategies for the encapsulation of biomaterials and hydrophobic low molecular weight substances

This thesis presents an approach to encapsulate protein crystals, for the first time. The encapsulation was achieved by the sequential adsorption of oppositely charged polyelectrolytes onto a charged protein crystal template, This extension of the so called layer-by-layer technique to crystalline proteins leads to their encapsulation in a nanoscale polymer multilayer capsule with a wall thickness of only 15 nm. The enzymes catalase and glucose oxidase were successfully encapsulated in their solid state with the polyelectrolyte system polyallylamine/polystyrene sulfonate. The loaded μm-sized capsules with enzymes leads to an entirely new class of μ-bioreactors. It was discovered that the activity of encapsulated enzymes is fully preserved in the capsules. The so produced μ-bioreactors are bearing the highest possible loading of a bio-compound per volume in nature. It was experimentally verified that the capsule wall is permeable for low molecular weight substances but impermeable for the macromolecular proteins. It was also demonstrated that encapsulated catalase in the interior of the capsule is protected from proteases in the surrounding media. This leads to a new strategy to stabilise biosensors and points towards new drug application strategies. Encapsulated glucose oxidase was used to construct a glucose biosensor by nanoengineered immobilisation of μ-bioreactor capsules onto an electrode surface. The layer-by-layer technique has been modified and employed to encapsulate water insoluble crystalline substances that bear no charge on their surface. Previously, these substances could not be encapsulated by the layer-by-layer technique. This limitation was overcome by introducing a surface charge to the substance particles by treatment with a surfactant, rendering them water dispersible and coatable with oppositely charged polyelectrolytes. Fluoresceine diacetate and pyrene were used as model substances for the encapsulation.; The presented approaches for the encapsulation of bio- and organic-crystalline materials demonstrate an alternative strategy to conventional encapsulation methods. They are applicable to a broad spectrum of substances including crystalline or solid biomaterials. The technologies have the potential to create novel core-shell materials with tailored functionalities and allow the incorporation of optical, magnetic, or biorecognition properties into the encapsulate. Three patents were filed to protect the intellectual properties of the presented technologies. (Abstract shortened by UMI.)...