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Polyphosphazenes with Stimulated Degradation Submitted by M.Sc. Aitziber Iturmendi Submitted at POLYPHOSPHAZENES Institute of Polymer Chemistry Supervisor and First Examiner WITH STIMULATED Assoc. Univ.-Prof. Dr. Ian Teasdale Second Examiner Assoc. Univ.-Prof. Dr. Uwe DEGRADATION Monkowius Month Year May 2018 PATHWAYS Doctoral Thesis to obtain the academic degree of Doktorin der Naturwissenschaften in the Doctoral Program Naturwissenschaften JOHANNES KEPLER UNIVERSITY LINZ Altenberger Str. 69 4040 Linz, Austria www.jku.at DVR 0093696 STATUTORY DECLARATION I hereby declare that the thesis submitted is my own unaided work, that I have not used other than the sources indicated, and that all direct and indirect sources are acknowledged as references. This printed thesis is identical with the electronic version submitted. Linz, May 2018 iii The Amazing thing about life is that You choose what you allow into it You choose how things affect you You choose how you react Happiness is a Choice Make it It´s up to you v ACKNOWLEDGMENTS First of all, I want to thank Assoc. Univ.-Prof. Dr. Ian Teasdale. Thank you so much for giving me the opportunity to work in your team not only for 6 months, even for more than 5 years! Many thanks also for being my supervisor, my guide, my support (in and out of work) and why not part of my stress ;) I am grateful to Univ.-Prof. Dr. Oliver Brüggemann for providing me with all equipments I needed, the access to the labs and his support. I would like to thank also Assoc. Univ.-Prof. Dr. Uwe Monkowius for his help and guidance during my thesis. Sandra Rothemund, it was a pleasure to work with you. None of this work would have been possible without you, thank you for everything! I also want to thank all the colleagues at the ICP for your help and our moments together, and particullarly: - Wolfgang Gnong, for all our long talks, work discussions, and moments full of laughter and craziness! - Helena Henke, Tamara Aigner and Anne Linhardt, because it was a pleasure to work with you all, share lab experiences and discuss about polyphosphazenes. Particularly, thanks Helena for your help and friendship since I came to Linz. - Renate Herbrik and Andreas Schnölzer. Both of you helped me in every moment I needed, at work as well as out of it. Thank you so much for everything! Thanks also to Sabrina Theis, my project-partner, for your help and support especially with the photochemistry. I would like to thank also Assoc. Univ.-Prof. Dr. Wolfgang Schöfberger for his help with the NMR measurements, no matter the time they could take. I cannot forget Filipa Alves and Pascal Scholder. Thanks a lot for all our moments together (breaks, lunch times, beers...) and for being part of my family in Linz! Last but not least, I want to thank my friends and family. Thanks for your support, patience, love… Definitely, THANK YOU VERY MUCH for everything! vii ABSTRACT Degradable synthetic polymers are of great importance for many applications such as medical applications, as well as environmental reasons. Polymer degradation, based on the cleavage of covalent bonds, is nearly inevitable but it is time limited. Consequently, degradable polymers should be considered as polymers that degrade in specific conditions and within the timescale of the given application. Hence stimulated degradation pathways, in which the degradation process is initiated by an external trigger such as enzymatic, photochemical, and oxidative environments, are attractive tools to control the degradation of polymers. Poly(organo)phosphazenes are hybrid inorganic-organic polymers with a flexible backbone based on alternation of nitrogen and phosphorus atoms. The organic side groups, covalently bonded to the phosphorous atom, can protect the intrinsic hydrolytic backbone and tune the properties and degradation of the polymer. In this work a variety of degradable poly(organo)phosphazenes are described with different properties to make them water soluble but also porous cross-linked scaffolds. Moreover, pH, oxidation, and photochemical triggering systems can be applied to induce and promote the degradation of the polymers. Particularly, amino acid-based poly(organo)phosphazenes are presented with convenient hydrolytic degradation rates, making them attractive for many biomedical applications. Among the studied poly(organo)phosphazenes it has been shown that the degradation was promoted when the glycine amino acid was incorporated between the polymer backbone and the organic substituent. The work described in this thesis focuses on the synthesis of novel poly(organo)phosphazenes with triggered degradation pathways, that is, on stable polymers that degrade upon a certain stimulus. In the first part of the thesis a pH- triggered system is presented, in which degradation rates are increased at lower pH values. Then as potential stimulus also a known reactive oxygen species (ROS), H2O2 has been employed. ROS, generated in the organism as a consequence of aerobic life, can lead to various diseases when it is overproduced. Therefore, H2O2 has been used as an oxidative trigger leading to polymer degradation. As a third stimulus visible light has been applied which could be of particular interest also for many biological applications due to its mild and deeply penetrating wavelengths as well as spatial and temporal control. In the last part of the thesis degradable cross-linked scaffolds with ix highly interconnected pores are presented which provide special attraction for cell growth in tissue engineering applications. x KURZFASSUNG Abbaubare synthetische Polymere spielen auf Grund ihrer Eigenschaften nicht nur in der Umwelt, sondern auch in der Medizin eine bedeutende Rolle. Der Polymerabbau, der auf der Spaltung von kovalenten Bindungen basiert, ist zeitlich limitiert. Infolgedessen sollten abbaubare Polymere als Polymere betrachtet werden, die unter bestimmten Bedingungen und innerhalb des Anwendungszeitrahmens abbauen. Daher sind stimulierte Abbauprozesse von großer Wichtigkeit, wobei externe Triggers als hervorragende Werkzeuge eingesetzt werden können, die entweder enzymatisch, photochemisch oder oxidativ das Polymer kontrolliert abbauen. Poly(organo)phosphazene sind anorganisch-organische Hybridpolymere mit einem flexiblen Rückgrat, das auf abwechselnden Stickstoff- und Phosphoratomen basiert. Die organischen Seitenketten, die kovalent an das Phosphoratom gebunden sind, können einerseits das hydrolytisch labile Rückgrat schützen, und anderseits die Eigenschaften und den Abbau des Polymers beeinflussen. Diese Arbeit beschreibt eine Auswahl an abbaubaren Poly(organo)phosphazenen mit unterschiedlichen Eigenschaften, um sie wasserlöslich oder zu porösen vernetzen Gerüsten zu machen. Darüber hinaus können pH-, oxidations- und photochemisch- triggernde Systeme angewandt werden um den Abbau der Polymere zu induzieren und zu fördern. Insbesonders werden aminosäurebasierende Poly(organo)phosphazene mit geeigneten hydrolytischen Abbauraten präsentiert, die dadurch attraktiv für viele biomedizinische Anwendungen sind. Unter den untersuchten Poly(organo)phosphazenen konnte man erkennen, dass der Polymerabbbau durch den Einbau der Aminosäure Glycin zwischen Polymerrückgrat und organischem Substituenten begünstigt wird. Der Fokus dieser Arbeit liegt auf der Synthese von neuartigen Poly(organo)phosphazenen mit getriggerten Abbauprozessen, also auf stabilen Polymeren, die durch einen bestimmten Stimulus abbauen. Im ersten Teil dieser Forschungsarbeit wird ein pH-getriggertes System präsentiert, bei welchem die Abbaurate bei niedrigeren pH Werten gesteigert wird. Im zweiten Ansatz wurde eine bekannte reaktive Sauerstoffspezies (ROS), H2O2, als möglichen Stimulus angewandt. ROS, das im Organismus in Folge von aerobem Leben erzeugt wird, kann durch Überproduktion zu verschiedenen Krankheiten führen. Daher wurde H2O2 als oxidativer Trigger zum Abbau des Polymers eingesetzt. Als dritter Stimulus wurde Licht im xi sichtbaren Bereich verwendet. Aufgrund der tiefdringen Wellenlänge des Lichts, sowie die räumlich und zeitliche Kontrolle, kann dieser Stimulus besonders im biologischen Anwendungsbereiche interessant sein. Im letzten Teil dieser Arbeit werden abbaubare quervernetzte Gerüste mit stark miteinander verbundenen Poren präsentiert, welche besonders attraktiv für das Zellwachstum in Tissue Engineering ist. xii OVERVIEW This thesis is divided in the following main chapters: Chapter 1 outlines the importance of degradable polymers in diverse applications. Furthermore, it introduces the field of polyphosphazenes with a concise summary about common synthesis routes, highlights the particular interest of water-soluble polymers and explains the possible degradation mechanism. Chapter 2 emphasizes the synthesis of novel poly(organo)phosphazenes with triggered degradation rates, that is, synthesis of polymers with good hydrolytic stability that undergo degradation only upon certain stimuli: Chapter 2.1 presents the synthesis of water-soluble polyphosphazenes with tunable degradation rates. By incorporation of some amino acid groups between the polymer backbone and the water-solubilizing group the degradation is tailored, as well as increased at lower pH-values. Preliminary cell viability studies prove the biocompatibility and non-toxic nature of these polymers. Chapter 2.2 shows the selective degradation of some polyphosphazenes upon oxidation. The polyphosphazenes with self-immolative side groups undergo degradation upon H2O2 exposure while in absence of it are hydrolytically stable. Moreover, the polymers without the self-immolative
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