The unsafe use of needles propagates cross infections with bloodborne pathogens and reduces the positive impact of vaccinations on global health. While a plethora of needle-free injection devices exist, the reformulation of protein-based vaccines is largely empirical and costly, which presents a barrier to their widespread clinical application. This thesis contributes to the identification of approaches that facilitate rapid vaccine reformulation and enhance the immunogenicity of needle-free dry-powder vaccines with the help of novel antigen delivery platforms. We hypothesised that the thermodynamic stabilisation of diphtheria toxin mutant 197 (CRM197), a glycoconjugate vaccine carrier protein, may enhance its structural preservation during spray-freeze-drying (SFD), and that its formulation in either soluble, surface-adsorbed, or nanoparticle form impacts the elicited immune response. Differential scanning fluorimetry was used to study the effect of excipients on the thermal stability of CRM197. Dry-powder formulation of CRM197 used i) encapsulation into a thermodynamically stabilising excipient matrix by SFD, ii) surface-immobilisation via physisorption onto a novel potassium-doped hydroxyapatite (kHA) carrier microparticle formed by molten salt synthesis, and iii) chemical conjugation and surface presentation on amphiphilic block copolymer nanoparticles that were incorporated into SFD-powders (SFD-NP). The structural integrity of CRM197 was assessed by size separation in addition to various spectral and thermal analysis methods. The immunogenicity of dry-powder CRM197 formulations was subsequently tested in vivo. The results suggest that the thermodynamic stability of CRM197 in solution does not ensure its structural stability during SFD. While needle-free dermal vaccination with kHA-adsorbed CRM197 induced comparable antibody titres to conventional IM injection of alum-adjuvanted CRM197, needle-free SFD and SFD-NP powders were less immunogenic. The highest mean IgG titre and most balanced Th1/Th2 response was achieved with nanoparticle-conjugated CRM197 by IM, which outperformed the current clinical standard. Therefore, future vaccine design should combine thermodynamic and kinetic stability screening, and place special emphasis on the delivery and structural presentation of the antigen to the immune system.

Taking inspiration from nature, where composite materials made of a polymer matrix and inorganic fillers are often found, e.g. bone, shell of crustaceans, shell of eggs, etc., the feasibility on making composite materials containing chitosan and nanosized hydroxyapatite were investigated. A new preparation approach based on a co-precipitation method has been developed. In its earlier stage of formation, the composite occurs as hydrogel as suspended in aqueous alkaline solution. In order to get solid composites various drying procedures including freeze-drying technique, air-drying at room temperature and at moderate temperatures, between 50oC and 100oC were used. Physicochemical studies showed that the composites exhibit different properties with respect to their structure and composition. IR and Raman spectroscopy probed the presence of both chitosan and hydroxyapatite in the composites. Hydroxyapatite as dispersed in the chitosan matrix was found to be in the nanosize range (15-50 nm) and occurs in a bimodal distribution with respect to its crystallite length. Two types of distribution domains of hydroxyapatite crystallites in the composite matrix such as cluster-like (200-400 nm) and scattered-like domains were identified by the transmission electron microscopy (TEM), X-ray diffraction (XRD) and by confocal scanning laser microscopy (CSLM) measurements. Relaxation NMR experiments on composite hydrogels showed the presence of two types of water sites in their gel networks, such as free and bound water. Mechanical tests showed that the mechanical properties of composites are one order of magnitude less than those of compact bone but comparable to those of porous bone. The enzymatic degradation rates of composites showed slow degradation processes. The yields of degradation were estimated to be less than 10% by loss of mass, after incubation with lysozyme, for a period of 50 days. Since the composite materials were found biocompatible by the in vivo tests, the simple mode of their fabrication and their properties recommend them as potential candidates for the non-load bearing bone substitute materials. / Inspiriert von Natur, bei der Kompositmaterialien aus Polymermatrices und anorganischen Füllstoffen z.B. in Knochen, Krustentieren und Eierschalen vorzufinden sind, wurde die Herstellungsmöglichkeit von Kompositmaterial aus Chitosan und Hydroxyapatitdispersionen untersucht. Basierend auf einem Kopräzipitationsverfahren wurde eine neue Herstellungsmethode entwickelt, die als flexibler Zugang zu einem Spektrum von Komposittypen führt. In den frühen Phasen der Kompositbildung entsteht ein in der wässrigen alkalischen Lösung suspendiertes Hydrogel, das durch Filtration und Zentrifugation isoliert werden kann. IR und Ramanspektroskopie klären das Vorhandensein von Chitosan und Hydroxyapatit im Kompositmaterial. Hydroxyapatit ist als Nanopartikel der Größe von 15-50 nm in bimodaler Verteilung in der Chitosanmatrix dispersiert, und in durch Transmissionselektronenmikroskopie (TEM), X-Ray Diffraction (XRD) und Konfokaler Laserscanmikroskopie (CSLM) nachweisbaren 200-400 nm großen Clustern assembliert. NMR-Relaxationsmessungen an Hydrogelkompositmaterial decken die Existenz zweier Klassen vorkommenden Wassers im Netzwerk auf, gebundenes und freies Wasser. Mechanische Tests zeigen, dass die mechanische Festigkeit etwa eine Größenordnung unter der von massivem Knochen liegt, der Festigkeit von porösem Knochen aber gleichkommt. Enzymatische Abbauraten des Kompostimaterials sind als langsam einzuschätzen. Eine 50-tägige Einwirkzeit von Lysozym führte zu einem Abbau von 10 % der Kompositmasse. Die sich durch in vivo Tests herausstellende Biokompatibilität, die einfachen Herstellungsmöglichkeiten und die physikochemischen Eigenschaften empfehlen dieses Material als vielversprechenden Kandidaten für Knochenersatzmaterial in mäßig belasteten Bereichen.

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