Univ., Diss.--Regensburg, 2001.

Zugl.: München, University, Diss., 2009.

Tierärztl. Hochsch., Diss., 2003--Hannover.

No description available.

No description available.

No description available.

Acute myocardial infarction (AMI) is a leading cause of morbidity and mortality in the world (4). Restoration of coronary flow to the ischemic myocardium by interventions such as angioplasty, thrombolytic treatment or coronary bypass surgery is the current standard therapy for AMI (5). However, reperfusion of the ischemic myocardium may result in paradoxical cardiomyocyte dysfunction and worsen tissue damage, in a process known as “reperfusion injury” (6). Ischemic reperfusion (IR) injury may intensify pathological processes that contribute to the generation of oxyradicals, disturbances in cation homeostasis, and depletion of cellular energy stores, which may elicit arrhythmias, contractile dysfunction, and ultrastructural damage of the myocardium. These changes can lead to heart failure and ultimately sudden death. The exact mechanisms of IR injury are not fully known (7). Molecular, cellular, and tissue alterations such as cell death, inflammation, neurohumoral activation, and oxidat / Bioengineering

Conventional methods of cancer therapy have been severely limited by inefficient delivery of therapeutic doses without incidence of harsh and toxic side effects in normal tissues. Consequently, countless new methods for early detection and drug delivery have been investigated in the area of nanoparticles and hydrogels. Although many of these methods are promising, the complex nature of cancer increases the difficultly for the development of the perfect system. Cellulose nanocrystals (CNCs) have been studied widely for a variety of applications. Despite their advantages, investigations of their abilities in the biomedical field have not been explored. The goal of this project is to delve into the potential uses of CNCs in detection, targeted drug delivery, and potentiation of irreversible electroporation (IRE)-induced cell death in folate receptor (FR)-positive cancers. To accomplish this task we have prepared stable and reproducible CNCs from wood pulp via sulfuric acid hydrolysis. Furthermore, we have functionalized the surface of these nanoparticles and conjugated them with the targeting ligand folic acid (FA) and the fluorescent imaging agent fluorescein-5\'-isothiocyanate (FITC) to create FITC-CNC-FA; CNCs have also been conjugated with doxorubicin (DOX), a potent chemotherapeutic (DOX-ALAL-CNC-FA). We have determined FITC-CNC-FA's and DOX-ALAL-CNC-FA's ability to specifically target FR-positive cancer cells in vitro; meanwhile non-targeted CNCs (FITC-CNC) were shown unable to bind to these cell types. In addition, we have investigated FITC-CNC-FA's pharmacokinetic activity in vivo. To properly model the CNC conjugate's activity in vivo, a physiologically based pharmacokinetic (PBPK) model has been constructed. We have also examined CNCs' ability to potentiate a new technique for tumor ablation, IRE. Pre-incubation with FA-conjugated CNCs (CNC-FA) have shown an increase in cytotoxicity in FR-positive cancer cells induced by IRE. In addition, CNC-FA did not potentiate IRE-induced cytotoxicity in a FR-negative cancer cell type. For a more comprehensive understanding of CNC-FA's ability to potentiate IRE induced cytotoxicity, we optimized a 3D in vitro hydrogel system. Preliminary data suggest this method of experimentation will be more realistic to in vivo studies to be completed in the future. Together, these studies showcase CNCs as efficient and effective nano-carriers in tumor detection and treatment. / Ph. D.

Methods of guiding magnetic particles in a controlled fashion through the arterial system in vivo using external magnetic fields are explored. Included are discussions of applications, magnetic field properties needed to allow guiding based on particle characteristics, hemodynamic forces, the uniformity of field and gradients, variable tissue characteristics, and imaging techniques employed to view these particles while in transport. These factors influence the type of magnetic guidance system that is needed for an effective drug delivery system. This thesis reviews past magnetic drug delivery work, variables, and concepts that needed to be understood for the development of an in vivo magnetic drug delivery system. The results of this thesis are the concise study and review of present methods for guided magnetic particles, aggregate theoretical work to allow proper hypotheses and extrapolations to be made, and experimental applications of these hypotheses to a working magnetic guidance system. The design and characterization of a magnetic guidance system was discussed and built. The restraint for this system that balanced multiple competing variables was primarily an active volume of 0.64 cm3, a workspace clearance of at least an inch on every side, a field of 0.3T, and a local axial gradient of 13 T/m. 3D electromagnetic finite element analysis modeling was performed and compared with experimental results. Drug delivery vehicles, a series of magnetic seeds, were successfully characterized using a vibrating sample magnetometer. Next, the magnetic seed was investigated under various flow conditions in vitro to analyze the effectiveness of the drug delivery system. Finally, the drug delivery system was successfully demonstrated under limiting assumptions of a specific magnetic field and gradient, seed material, a low fluid flow, and a small volume. / Master of Science

Over the years, hydrogels have been developed and used for a huge variety of different applications ranging from drug delivery devices to medical products. In this thesis, a poly(2-methyl-2-oxazoline) (POx) / poly(2-n-propyl-2-oxazine) (POzi) bioink was modified and analyzed for the use in biofabrication and targeted drug delivery. In addition, the protein fibrinogen (Fbg) was genetically modified for an increased stability towards plasmin degradation for its use as wound sealant. In Chapter 1, a thermogelling, printable POx/POzi-based hydrogel was modified with furan and maleimide moieties in the hydrophilic polymer backbone facilitating post-printing maturation of the constructs via Diels-Alder chemistry. The modification enabled long-term stability of the hydrogel scaffolds in aqueous solutions which is necessary for applications in biofabrication or tissue engineering. Furthermore, we incorporated RGD-peptides into the hydrogel which led to cell adhesion and elongated morphology of fibroblast cells seeded on top of the scaffolds. Additional printing experiments demonstrate that the presented POx/POzi system is a promising platform for the use as a bioink in biofabrication. Chapter 2 highlights the versatility of the POx/POzi hydrogels by adapting the system to a use in targeted drug delivery. We used a bioinspired approach for a bioorthogonal conjugation of insulin-like growth factor I (IGF-I) to the polymer using an omega-chain-end dibenzocyclooctyne (DBCO) modification and a matrix metalloprotease-sensitive peptide linker. This approach enabled a bioresponsive release of IGF-I from hydrogels as well as spatial control over the protein distribution in 3D printed constructs which makes the system a candidate for the use in personalized medicine. Chapter 3 gives a general overview over the necessity of wound sealants and the current generations of fibrin sealants on the market including advantages and challenges. Furthermore, it highlights trends and potential new strategies to tackle current problems and broadens the toolbox for future generations of fibrin sealants. Chapter 4 applies the concepts of recombinant protein expression and molecular engineering to a novel generation of fibrin sealants. In a proof-of-concept study, we developed a new recombinant fibrinogen (rFbg) expression protocol and a Fbg mutant that is less susceptible to plasmin degradation. Targeted lysine of plasmin cleavage sites in Fbg were exchanged with alanine or histidine in different parts of the molecule. The protein was recombinantly produced and restricted plasmin digest was analyzed using high resolution mass spectrometry. In addition to that, we developed a novel time resolved screening protocol for the detection of new potential plasmin cleavage sites for further amino acid exchanges in the fibrin sealant. / Hydrogele wurden im Laufe der Jahre für eine Vielzahl von Anwendungen, von der Verabreichung von Medikamenten bis hin zu medizinischen Produkten, entwickelt und eingesetzt. In dieser Arbeit wurde eine Poly(2-methyl-2-oxazolin) POx) / Poly(2-n-propyl-2- oxazin) (POzi) Biotinte modifiziert und für den Einsatz in der Biofabrikation und für die gezielte Verabreichung von Medikamenten analysiert. Außerdem wurde das Protein Fibrinogen (Fbg) gentechnisch verändert, um seine Stabilität gegenüber dem Plasminabbau in seiner Funktion als Wundkleber zu erhöhen In Kapitel 1 wurde ein thermogelierendes, druckbares Hydrogel auf POx/POzi-Basis mit Furan- und Maleimid-Funktionen im hydrophilen Polymerrückgrat modifiziert, was die Reifung der Konstrukte nach dem Druck durch Diels-Alder-Chemie bewirkt. Die Modifizierung ermöglichte eine langfristige Stabilität der Hydrogele in wässrigen Lösungen, was für Anwendungen im Bereich der Biofabrikation oder im Tissue Engineering erforderlich ist. Darüber hinaus haben wir RGD-Peptide in das Hydrogel integriert, was zur Zelladhäsion und einer verlängerten Morphologie von Fibroblasten, die auf den Gelen ausgesät wurden, führte. Weitere Druckexperimente zeigen außerdem, dass das POx/POzi-System eine vielversprechende Plattform für den Einsatz als Biotinte in der Biofabrikation ist. Kapitel 2 unterstreicht die Vielseitigkeit der POx/POzi-Hydrogele, indem das System für die gezielte Abgabe von Medikamenten angepasst wird. Wir verwendeten einen von der Natur inspirierten Ansatz für eine biorthogonale Konjugation vom Insuline-like Growth Factor I (IGF- I) an das Polymer unter Verwendung einer Dibenzocyclooctin-Modifikation des Polymers am Ende der Omega-Kette und eines Matrix-Metalloproteasen-empfindlichen Peptid-Linkers. Dieser Ansatz ermöglichte eine bioresponsive Freisetzung von IGF-I aus Hydrogelen sowie eine räumliche Kontrolle über die Proteinverteilung in 3D-gedruckten Konstrukten, was das System zu einem Kandidaten für den Einsatz in der personalisierten Medizin macht. Kapitel 3 gibt einen allgemeinen Überblick über die Notwendigkeit von Wundversiegelungsmitteln und die derzeit auf dem Markt befindlichen Generationen von Fibrinklebern einschließlich der Vorteile und Herausforderungen. Darüber hinaus werden Trends und potenzielle neue Strategien zur Lösung aktueller Probleme und zur Erweiterung der Toolbox für künftige Generationen von Fibrinklebern aufgezeigt. In Kapitel 4 werden die Konzepte der rekombinanten Proteinexpression und des Molecular Engineering auf eine neue Generation von Fibrin Wundklebern angewandt. In einer Proof-of- Concept-Studie haben wir ein neues rekombinantes Fbg Expressionsprotokoll und eine Fbg Mutante entwickelt, die weniger anfällig für einen Abbau durch Plasmin ist. Gezielte Lysine in Plasmin-Schnittstellen in Fbg wurde entweder durch Alanin oder Histidin in unterschiedlichen Teilen des Moleküls ausgetauscht. Das Protein wurde rekombinant hergestellt und eine verminderte Schnittrate wurde mittels hochauflösender Massenspektrometrie gezeigt. Zusätzlich haben wir ein neues zeitaufgelöstes Screening-Protokoll entwickelt, mit dem sich neue potenzielle Plasmin-Spaltstellen für weitere Aminosäurenaustausche in Fibrin-Klebern auflösen lassen.