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Structure-property relationships in poly(2-oxazoline)/poly(2-oxazine) based drug formulations
(2020)
According to estimates, more than 40% of all new chemical entities developed in pharmaceutical industry are practically insoluble in water. Naturally, the demand for excipients which increase the water solubility and thus, the bioavailability of such hydrophobic drugs is enormous. Poly(2-oxazoline)s (POx) are currently intensively discussed as highly versatile class of biomaterials. Although selected POx based micellar drug formulations exhibit extraordinarily high drug loadings > 50 wt.% enabling high anti-tumor efficacies in vivo, the formulation of other hydrophobic compounds has failed. This casts doubt on the general understanding in which a hydrophobic active pharmaceutical ingredient is dissolved rather unspecifically in the hydrophobic core of the micelles following the fundamental concept of “like dissolves like”. Therefore, a closer look at the interactions between all components within a formulation becomes increasingly important. To do so, a large vehicle platform was synthesized, loaded with various hydrophobic drugs of different structure, and the formulations subsequently characterized with conventional and less conventional techniques. The obtained in-depth insights helped to develop a more thorough understanding about the interaction of polymer and incorporated API finally revealing morphologies deviating from a classical core/shell structure. During these studies, the scarcely investigated polymer class of poly(2-oxazine)s (POzi) was found as promising drug-delivery vehicle for hydrophobic drugs. Apart from this fundamental research, the anti-tumor efficacy of the two APIs curcumin and atorvastatin has been studied in more detail. To increase the scope of POx and POzi based formulations designed for intravenous administration, a curcumin loaded hydrogel was developed as injectable drug-depot.
Detaillierte Einblicke in die Struktur von mit Wirkstoffen beladenen Polymermizellen sind rar, aber wichtig um gezielt optimierte Transportsysteme entwickeln zu können. Wir konnten beobachten, dass eine Erhöhung der Curcumin‐Beladung von Triblockcopolymeren auf Basis von Poly(2‐oxazolinen) und Poly(2‐oxazinen) schlechtere Auflösungseigenschaften nach sich zieht. Mitthilfe von Festkörper‐NMR‐Spektroskopie und komplementären Techniken ist es möglich, ein ladungsabhängiges Strukturmodell auf molekularer Ebene zu erstellen, das eine Erklärung für die beobachteten Unterschiede liefert. Dabei belegen die Änderungen der chemischen Verschiebungen und Kreuzsignale in 2D‐NMR‐Experimenten die Beteiligung des hydrophoben Polymerblocks an der Koordination der Curcumin‐Moleküle, während bei höherer Beladung auch eine zunehmende Wechselwirkung mit dem hydrophilen Polymerblock beobachtet wird. Letztere könnte elementar für die Stabilisierung von ultrahochbeladenen Polymermizellen sowie das Design von verbesserten Wirkstofftransportsystemen sein.
Based on previous results showing that thioether modification of gold nanoparticles (AuNPs), especially coating with a multivalent system, yielded in excellent colloidal stability, the first aim of this thesis was to prove whether functionalization of silver nanoparticles (AgNPs) with thioether also has a comparable or even enhanced stabilization efficacy compared with the gold standard of coating with thiols and, particularly, whether the multivalency of polymers leads to stable AgNPs conjugates. Herein, AgNPs coated with mono- and multivalent thiol- and thioether polymers were prepared to systematically investigate the adsorption kinetics onto the silver surface as well as the colloidal stability after exposure to different conditions relevant for biomedical application. Although the thioether-polymers showed a slower immobilization onto AgNPs, same or mostly even better stabilization was exhibited than for the thiol analogs.
As multivalent thioether-poly(glycidol) (PG) is already proven as a promising candidate for AuNP modification and stabilization, the second aim of this thesis was to examine the stealth behavior of thioether-PG, side-chain functionalized with various hydrophobic (alkyl and cholesteryl) units, to gain a deeper understanding of AuNP surface functionalization in terms of protein adsorption and their subsequent cellular uptake by human monocyte-derived macrophages. For this purpose, citrate-stabilized AuNPs were modified with the amphiphilic polymers by ligand exchange reaction, followed by incubation in human serum. The various surface amphiphilicities affected protein adsorption to a certain extent, with less hydrophobic particle layers leading to a more inhibited protein binding. Especially AuNPs functionalized with PG carrying the longest alkyl chain showed differences in the protein corona composition compared to the other polymer-coated NPs. In addition, PGylation, and especially prior serum incubation, of the NPs exhibited reduced macrophage internalization.
As the use of mammals for in vivo experiments faces various challenges including increasing regulatory hurdles and costs, the third aim of this thesis was to validate larvae of the domestic silkworm Bombyx mori as an alternative invertebrate model for preliminary in vivo research, using AuNPs with various surface chemistry (one PEG-based modification and three PG-coatings with slightly hydrophobic functionalization, as well as positively and negatively charges) for studying their biodistribution and elimination. 6 h and 24 h after intra-hemolymph injection the Au content in different organ compartments was measured with ICP-MS, showing that positively charged particles appeared to be eliminated most rapidly through the midgut, while AuNPs modified with PEG, alkyl-functionalized PG and negatively charged PG exhibited long-term bioavailability in the silkworm body.
Zur Züchtung von Gewebe außerhalb des Körpers wird ein struktureller und biologischer Ersatz für die natürliche Extrazelluläre Matrix (ECM) benötigt, der durch künstliche Gerüst-struk¬tu¬ren, sogenannte Scaffolds, realisiert wird. Aktuell werden einige natürliche und synthe-tische biodegradierbare Polymere als Scaffold¬materialien verwendet, die jedoch alle noch signifi¬kante Nachteile aufweisen, weshalb verstärkt an Alternativen geforscht wird. Das Ziel dieser Arbeit war daher, auf Basis klassischer anorganisch-organischer Hybridpolymere, neuartige biodegradierbare Hybridpolymere zu synthetisieren, die ebenfalls durch einfache Variationen in ihrem strukturellen Aufbau gezielt modifiziert werden können. In diesem Zusammen¬hang sind Untersuchungen zur Erstellung grundlegender Struktur-Eigenschafts-beziehungen dieser sogenannten partiell degradierbaren Hybridpolymere von besonderer Bedeutung und daher ein wesentlicher wissen¬schaft¬licher Grundbestandteil dieser Arbeit, um dementsprechend anwendungs¬bezo¬gene Eigen¬schaften wie beispielsweise das E-Modul und die Degradationsrate definiert einstellen zu können.
In dieser Arbeit konnten ethanolische Sole aus TEOT und der metabolisierbaren α-Hydroxycarbonsäure Milchsäure (LA) in spinnfähige viskose Spinnmassen überführt werden und erstmalig über die Methode des Druckspinnens zu Mikrofasern prozessiert werden.
Die hybriden Fasern sind intrinsisch stabil. Über FTIR- und 13C-MAS-NMR-Untersuchungen konnte gezeigt werden, dass in der Faser der Koordinationsmodus von LA an Ti sowohl im mono- als auch im bidentaten Modus (Nomenklatur bezogen auf die Säureeinheit) vorliegt.
Die nähere Untersuchung des Degradationsverhaltens einer LA-Faser zeigte hauptsächlich die Freisetzung von Lactat und Ethanol innerhalb weniger Stunden. Danach kann kaum noch ein Massenverlust der Fasern nachgewiesen werden. Vermutlich ist die Degradationsgeschwindigkeit abhängig von der Sättigungskonzentration der wasserlöslichen Titanoxid-Spezies Ti(OH)4 und Ti(O)(OH)2. Die Löslichkeit dieser Verbindungen beträgt ca. 1 µmol/L. Die Freisetzung von Titanverbindungen an das Degradationsmedium konnte über ICP-Messungen und indirekt auch über NMR-Messungen der Degradationsprodukte in Lösung nachgewiesen werden. Nach ca. einer Woche in Lösung bildet sich der wasserlösliche metallorganische Komplex TiBALDH. Dieser Komplex zeigt keinen negativen Einfluss auf die Umwelt, so dass Zellkulturmedien, die in Kontakt mit den Fasermaterialien getreten sind, in Zukunft nach dem Autoklavieren gefahrlos entsorgt werden können.
Zudem sollte keines der detektierten Abbauprodukte in den abgegebenen Mengen toxisch auf den humanen Organismus bei in vivo-Anwendungen wirken. Lactat und Ethanol können im menschlichen Organismus verstoffwechselt werden. TIBALDH ist dem im menschlichen Serum nachweisbaren Titan(IV)citrat-Komplex strukturell sehr ähnlich. Aufgrund der Tatsache, dass die Bildung von TiBALDH ca. 1 Woche dauert, ist die vorherige Bildung des Titan(IV)citrat-Komplexes im humanen Organismus wahrscheinlich.
Weiterhin konnte das hybride Fasermaterial durch den Zusatz von basischen Stoffen neutralisiert werden und nach Vorkonditionierung der Fasern als nicht zytotoxisch eingestuft werden. Als Gegenionen wurde Ammonium, das biogene Amin Phenethylamin, die Aminosäure Phenylalanin und das Biopolymer CHI getestet. Für zukünftige Weiterentwicklungen können auch basische Wirkstoffe als Gegenionen herangezogen werden. Somit könnte das hybride Zellträgermaterial zusätzlich eine Drug-Delivery-Funktion erhalten.
Die LA-Fasern verhalten sich nach dem Verspinnen sehr flexibel. Bei einer Lagerung bei RT jedoch verspröden diese sehr schnell innerhalb von 3 d. Diese Materialeigenschaft wurde im zweiten Teil der Arbeit näher untersucht und optimiert.
Tempern des Fasermaterials bei 170 °C bewirkte eine Umlagerung der LA-Liganden zu AA-Liganden, aber keine Verbesserung der mechanischen Eigenschaften. Versuche einer getemperten LA-Faser mit CHI als Gegenion zeigte durchwegs positive Eigenschaften in den Zytotoxizitätstests und auf deren Oberfläche konnten Zellen der Zelllinien L929, 16HBE, HTB94 und MG63 erfolgreich kultiviert werden.
Durch die Verwendung anderer metabolisierbarer α Hydroxycarbonsäuren konnten Rückschlüsse auf die chemische Zusammensetzung der Fasern gezogen werden. Die Fasern scheinen aus wenig untereinander vernetzen Titan-oxo-carboxo-Clustern der Summenformel [Ti6O6(OR)6(Carboxylat)6] (mit R = H2+, H, Et oder „Ti6O6(OR)5(Carboxylat)6“) zu bestehen. Durch Variation der verwendeten Säuren konnten die Wechselwirkungen der Cluster untereinander verstärkt werden, so dass beispielsweise eine Faser mit MA bedeutend flexiblere Eigenschaften – auch bei einer Lagerung für 3d bei RT aufweist. Des Weiteren konnte durch Lagerung dieser Faser bei 4 °C der Versprödungsprozess für mind. 1 Monat gestoppt werden. Eine Lagerung von Medizinprodukten bei 4 °C stellt in Ländern mit ausreichender Infrastruktur kein Problem dar.
Aufbauend auf diesen Tatsachen und TGA-MS-Messungen konnte die These aufgestellt werden, dass sich zwischen den wenig untereinander vernetzten Titan-oxo-carboxo-Cluster direkt nach dem Verspinnen noch Wassermoleküle befinden. Diese Reste an Wasser verleihen – vermutlich aufgrund der Ausbildung von Wasserstoffbrückenbindungen – der Faser flexible Eigenschaften. Bei einer Lagerung bei RT entweichen diese Wasserreste und die Faser versprödet; bei einer Lagerung bei 4°C wird das Verdampfen des restlichen Wassers bedeutend verlangsamt.
Die Faser mit den flexibelsten Eigenschaften konnte letztendlich durch die Verwendung des zweizähnigen Carboxylat-Liganden MalA erhalten werden.
Zusammenfassend konnte in dieser Arbeit ein neuartiges faserförmiges Material auf Basis von Titan-oxo-carboxo-Clustern produziert werden, welches großes Potential besitzt als Zellträgermaterial Anwendung zu finden. Aufbauend auf den hier gewonnenen Ergebnissen können die mechanischen Eigenschaften weiter optimiert und die Anforderungen des gewünschten Zielgewebes feinjustiert werden. Zudem besteht die Möglichkeit dem Material Drug-Delivery-Eigenschaften zu verleihen. Somit könnte das Scaffold aus Mikrofasern neben den bereits integrierten chemischen und physikalischen Stimuli (die Oberflächenfunktionalitäten und die Oberflächentopographie der Fasern) auch durch freigesetzte Wirkstoffe Zellen zur gewünschten Differenzierung anregen.
The detection of smallest mechanical loads plays an increasingly important role in many areas of advancing automation and manufacturing technology, but also in everyday life. In this doctoral thesis, various microparticle systems were developed that are able to indicate mechanical shear stress via simple mechanisms. Using a toolbox approach, these systems can be spray-dried from various nanoscale primary particles (silica and iron oxide) to micrometer-sized units, so-called supraparticles. By varying the different building blocks and in combination with different dyes, a new class of mechanochromic shear stress indicators was developed by constructing hierarchically structured core-shell supraparticles that can indicate mechanical stress via an easily detectable color change. Three different mechanisms can be distinguished. If a signal becomes visible only by a mechanical load, it is a turn-on indicator. In the opposite case, the turn-off indicator, the signal is switched off by a mechanical load. In the third mechanism, the color-change indicator, the color changes as a result of a mechanical load. In principle, these indicators can be used in two different ways. First, they can be incorporated into a coating as an additive. These coatings can be applied to a wide range of products, including food packaging, medical devices, and generally any sensitive surface where mechanical stress, such as scratches, is difficult to detect but can have serious consequences. Second, these shear stress indicators can also be used directly in powder form and for example then applied in 3D-printing or in ball mills. A total of six different shear stress indicators were developed, three of which were used as additives in coatings and three were applied in powder form. Depending on their composition, these indicators were readout by fluorescence, UV-Vis or Magnetic Particle Spectroscopy. The development of these novel shear stress indicator supraparticles were successfully combined molecular chemistry with the world of nano-objects to develop macroscopic systems that can enable smart and communicating materials to indicate mechanical stress in a variety of applications.
In the framework of this thesis, new UV-patternable organic-inorganic hybrid polymers with higher refractive indices than reported in the literature for photonic applications were developed and studied with respect to their chemical structure, their optical properties, and their ability of being patterned by 1PP and 2PP. Particularly with 2PP, one could create 3D structures using the novel hybrid materials. The materials were prepared from hydrolysis and polycondensation reactions of · organo-alkoxysilanes and titanium alkoxide precursors, modified with and without CL and organo-alkoxysilanes precursors, and · organo-alkoxysilanes, titanium alkoxide and organophosphorus precursors. The major scope of this work was to increase the refractive index of ORMCER® materials based on only organo-alkoxysilanes. Thus, the parameters which influence the refractive index were investigated thoroughly. In particular, the synthesis parameters such as the introduction of titanium alkoxide and its concentration, the organo-alkoxysilanes, the catalyst concentration, the solvent used, but, also the processing parameters such as, the UV exposure dose, initiator concentration, and developer were investigated.
Starting off with solubility experiments of possible precursors, the present study reveals the whole development of a sol gel processing route for transparent p type semiconductive thin films with delafossite structure right to the fabrication of functional p-n junctions. The versatile sol formulation could successfully be modified for several oxide compositions, enabling the synthesis of CuAlO2, CuCrO2, CuMnO2, CuFeO2 and more. Although several differences in the sintering behaviour of powders and thin films could be observed, the powder experiments significantly contributed to the clearification of the intricate phase development during thermal annealing and also to optimization of the annealing sequence for thin film processing. Two different ternary systems turned out to be the most promising candidates for p-TCO application: Copper aluminum oxide for its high optical transmittance and copper chromium oxide for its low synthesis temperature, which allowed thin film deposition on low-cost borosilicate substrates. In order to combine the advantages of these two systems, the quaternary oxide composition CuAl1-xCrxO2 was investigated. With a higher optical transmittance than CuCrO2, a lower synthesis temperature than CuAlO2 and a lower resistivity than both parent systems, the optimum composition of the quaternary oxide is reached for x = 0.50. Compared to physical vapour deposition techniques, the undoped thin films presented here still need to make up some deficites in their optoelectronic performance. Although the best sol-gel samples are able to compete with RF sputtered samples or sampes deposited by PLD in transmittance, their resistivity is almost two orders of magnitude higher. The most probable reasons for this are the characteristic imperfections of sol-gel thin films like porosity and small crystallite size, which create barriers like grain boundaries and bottlenecks like barely connected particles. By additional effort such shortcomings can be repelled to a certain extend, but nevertheless the density of undoped sol-gel material always stays behind its pendants processed by physical vapour deposition.[246] Furthermore, such additional endeavour is likely to annihilate the advantage of sol-gel technique in processing costs. Extrinsic doping is a common method to decrease the resistivity of delafossite materials. Partially replacing the trivalent cations by divalent ones creates additional holes and thus generates additional charge carriers for p-type semiconductivity. This can improve the conductivity of delafossites by up to three orders of magnitude. Due to the compositorial flexibility of sol-gel processing, dopants could be introduced easily in this study by soluble precursors. However, improving the conductivity of CuAlO2 and CuAl0.5Cr0.5O2 via this method failed. Actually, this seems to be due to the fact that instead of being incorporated into the delafossite phase the dopant ions form intransparent phase impurities like spinels, which interfere with optical transmittance of the thin films. On the contrary, doping had a positive effect on the conductivity and the optical transmittance of copper chromium oxide, with magnesium being the most effective dopant. The resistivity could be decreased by more than three orders of magnitude, but in order to achieve this, much higher Mg concentrations than by other thin film deposition methods were necessary. This indicates a low doping efficiency in sol gel processed thin films, but also the ability of sol gel processing to incorporate more magnesium into the oxide than any other processing method. The extensive substitution of the chromium ions also increases the optical transmittance and allows sol gel processed thin films to draw level with thin films deposited by sputtering methods or PLD. Finally, the applicability of the delafossite thin films was proven by the asymmetric current voltage characteristics of heterojunctions between ITO and the delafossites. Shunting problems of the metallic contacts, on the other hand, reveal structural deficites of the delafossites, which should be the subject of further investigations.
The introduction of novel bioactive materials to manipulate living cell behavior is a crucial topic for biomedical research and tissue engineering. Biomaterials or surface patterns that boost specific cell functions can enable innovative new products in cell culture and diagnostics. This study aims at investigating the interaction of living cells with microstructured, nanostructured and nanoporous material surfaces in order to identify distinct systematics in cell-material interplay. For this purpose, three different studies were carried out and yielded individual effects on different cell functions.
Cell migration processes are controlled by sensitive interaction with external cues such as topographic structures of the cell's environment. The first part of this study presents systematically controlled assays to investigate the effects of spatial density and local geometry of micron scale topographic cues on amoeboid migration of Dictyostelium discoideum cells in quasi-3D pillar fields with systematic variation of inter-pillar distance and pillar lattice geometry. We can extract motility parameters in order to elucidate the details of amoeboid migration mechanisms and consolidate them in a two-state contact-controlled motility model, distinguishing directed and random phases. Specifically, we find that directed pillar-to-pillar runs are found preferably in high pillar density regions, and cells in directed motion states sense pillars as attractive topographic stimuli. In contrast, cell motion in random probing states is inhibited by high pillar density, where pillars act as obstacles for cell motion. In a gradient spatial density, these mechanisms lead to topographic guidance of cells, with a general trend towards a regime of inter-pillar spacing close to the cell diameter. In locally anisotropic pillar environments, cell migration is often found to be damped due to competing attraction by different pillars in close proximity and due to lack of other potential stimuli in the vicinity of the cell. Further, we demonstrate topographic cell guidance reflecting the lattice geometry of the quasi-3D environment by distinct preferences in migration direction.
We further investigate amoeboid single-cell migration on intrinsically nano-structured, biodegradable silica fibers in comparison to chemically equivalent plain glass surfaces. Cell migration trajectories are classified into directed runs and quasi-random migration by a local mean squared displacement (LMSD) analysis. We find that directed movement on silica fibers is enhanced in a significant manner by the fibers' nanoscale surface-patterns. Further, cell adhesion on the silica fibers is a microtubule-mediated process. Cells lacking microtubules detach from the fibers, but adhere well to glass surfaces. Knock-out mutants of myosin II migrating on the fibers are as active as cells with active myosin II, while the migration of the knock-out mutants is hindered on plain glass.
We investigate the influence of the intrinsically nano-patterned surface of nanoporous glass membranes on the behavior of mammalian cells. Three different cell lines and primary human mesenchymal stem cells (hMSCs) proliferate readily on nanoporous glass membranes with mean pore sizes between 10 nm and 124 nm. In both proliferation and mRNA expression experiments, L929 fibroblasts show a distinct trend towards mean pore sizes > 80 nm. For primary hMSCs, excellent proliferation is observed on all nanoporous surfaces. hMSC on samples with 17 nm pore size display increased expression of COL10, COL2A1 and SOX9, especially during the first two weeks of culture. In upside down culture, SK MEL-28 cells on nanoporous glass resist the gravitational force and proliferate well in contrast to cells on flat references. The effect of paclitaxel treatment of MDA MB 321 breast cancer cells is already visible after 48 h on nanoporous membranes and strongly pronounced in comparison to reference samples.
The studies presented in this work showed novel and distinct effects of micro- and nanoscale topographies on the behavior of various types of living cells. These examples display how versatile the potential for applications of bioactive materials could become in the next years and decades. And yet this variety of different alterations of cell functions due to topographic cues also shows the crucial part of this field of research: Carving out distinct, robust correlations of external cues and cell behavior is of utmost importance to derive definitive design implications that can lead to scientifically, clinically and commercially successful products.
A series of polypeptoid homopolymers bearing short (C1–C5) side chains of degrees of polymerization of 10–100 are studied with respect to thermal stability, glass transition and melting points. Thermogravimetric analysis of polypeptoids suggests stability to >200 °C. The study of the glass transition temperatures by differential scanning calorimetry revealed two dependencies. On the one hand an extension of the side chain by constant degree of polymerization decrease the glass transition temperatures (Tg) and on the other hand a raise of the degree of polymerization by constant side chain length leads to an increase of the Tg to a constant value. Melting points were observed for polypeptoids with a side chain comprising not less than three methyl carbon atoms. X-ray diffraction of polysarcosine and poly(N-ethylglycine) corroborates the observed lack of melting points and thus, their amorphous nature. Diffractograms of the other investigated polypeptoids imply that crystalline domains exist in the polymer powder.