New strategies for the encapsulation of biomaterials and hydrophobic low molecular weight substances
by Dieter Wilhelm Trau
xv, 169,  leaves : ill. (some col.) ; 30 cm
Encapsulation technologies for a broad spectrum of substances have been developed in the last decades. Encapsulated substances find an increasing number of applications in the fields of biotechnology, medicine, sensors and cosmetics. More and more, encapsulated substances are becoming a part of everybody's daily life. Encapsulation can add new properties to substances and can increase the quality of products....[ Read more ]
Encapsulation technologies for a broad spectrum of substances have been developed in the last decades. Encapsulated substances find an increasing number of applications in the fields of biotechnology, medicine, sensors and cosmetics. More and more, encapsulated substances are becoming a part of everybody's daily life. Encapsulation can add new properties to substances and can increase the quality of products.
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 second part of this thesis demonstrates a new method for the encapsulation of poorly water soluble organic substances. Many substances that are of significance in medicine, for example crystalline materials of low molecular weight drugs, have limited water solubility. Their application in an aqueous medium often represents a substantial problem. 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. In addition, hollow polymeric shells were produced by dissolving the solid core, giving direct proof for the successful encapsulation. It was demonstrated that the shell thickness and the particle size is fully controllable by varying the number of layers, the layer material and the dispersion process. This new method leads to an encapsulate which is applicable in an aqueous phase for pharmaceutical, medical or cosmetic applications.
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. The encapsulation processes were investigated and the encapsulates were characterised by a full range of analytical methods, e.g. light- and electron-microscopy, permeability experiments, zeta potential measurements and bio-functionality tests. Three patents were filed to protect the intellectual properties of the here presented technologies.