Refine
Has Fulltext
- no (375) (remove)
Year of publication
Document Type
- Doctoral Thesis (375) (remove)
Keywords
- magnetic nanoparticles (2)
- microfluidics (2)
- 1,6,7,12-Tetraazaperylen (1)
- 2-deoxy-D-ribose-5-phoshphate aldolase (1)
- Aktuator (1)
- Aminolyse (1)
- Antifouling (1)
- Atemgas (1)
- Biomimetic (1)
- Biomimetics (1)
Institute
- Institut für Chemie (375) (remove)
Functional materials, also called "Smart Materials", are described by their ability to fulfill a desired task through targeted interaction with its environment. Due to this functional integration, such materials are of increased interest, especially in areas where the increasing micronization of components is required. Modern manufacturing processes (e.g. microfluidics) and the availability of a wide variety of functional materials (e.g. shape memory materials) now enable the production of particle-based switching components. This category includes micropumps and microvalves, whose basic function is the active control of liquid flows. One approach in realizing those microcomponents as pursued by this work, enables variable size-switching of water-filled microballoons by implementing a stimulus-sensitive switching motif in the capsule's membrane shell, while being under the influence of a constant driving force. The switching motif with its gatekeeper function has a critical influence on one or more material parameters, which modulate the capsule's resistance against the driving force in microballoon expansion process. The advantage of this concept is that even non-variable analyte conditions, such as concentration levels of ions, can be capitalized to generate external force fields that, under the control of the membrane, cause an inflation of the microballoon by an osmotically driven water influx. In case of osmotic pressure gradients as the driving force for the capsule expansion, material parameters associated with the gatekeeper function are specifically the permeability and the mechanical stiffness of the shell material. While a modulation of the shell permeability could be utilized to kinetically impede the water influx on large time scales, a modulation of the shell's mechanical stiffness even might be utilized to completely prevent the capsule inflation due to a possible non-deformability beneath a certain threshold pressure. In polymer networks, which are a suitable material class for the demanded capsule shell because of their excellent elasticity, both the permeability and the mechanical properties are strongly influenced by the crystallinity of the material. Since the permeability is effectively reduced with increasing crystallinity, while the mechanical stiffness is simultaneously greatly increased, both effects point in the same direction in terms of their functional relationship. For this reason and due to a reversible and contactless modulation of the membrane crystallinity by heat input, crystallites may be suitable switching motifs for controlling the capsule expansion. As second design element of reversible expandable microballoons, the capsule geometry, defined by an aqueous core enveloped by the temperature-sensitive polymer network membrane, should allow an osmotic pressure gradient across the membrane layer. The strength of the inflation pressure and the associated inflation velocity upon membrane melting should be controlled by the salt concentration within the aqueous core, while a turn in the osmotic gradient should furthermore allow the reversible process of capsule deflation. Therefore, it should be possible to build either microvalves and micropumps, while their intended action of either pumping or valving is determined by their state of expansion and the direction of the osmotic pressure gradient.. Microballoons of approximately 300 µm in diameter were formed via droplet-based microfluidics from double-emulsion templates (w/o/w). The elastomeric capsule membrane was formed by photo-crosslinking of methacrylate (MA) functionalized oligo(ε-caprolactone) precursors (≈ 3.8 MA-arms, Mn ≈ 12000 g mol-1) within the organic medium layer (o) via UV-exposure after droplet-formation. After removal of the toluene/chloroform mixture by slow extraction via the continuous aqueous phase, the capsules solidified under the development of a characteristic "mushroom"-like shape at specific experimental conditions (e.g. λ = 308 nm, 57 mJ·s-1·cm-2, 16 min). It could be furthermore shown that in dependency to the process parameters: oligomer concentration and curing-time also spherical capsules were accessible. Long curing-times and high oligomer concentrations at a fixed light-intensity favored the formation of "mushroom"-like capsules, whereas the contrary led to spherical shaped capsules. A comparative study on thin polymer network films of same composition and equal treatment proved a correlation between the film's crosslink density and their contraction capability, while stronger crosslinked polymer networks showed a stronger contraction after solvent removal. In combination with observations during capsule solidification via light-microscopy, where a continuous shaping from almost spherical crosslinked templates to "mushroom"-shaped and solidified capsules was stated, the following mechanism was proposed. In case of low oligomer contents and short curing-times, the contraction of the capsule shell during solvent removal is strongly diminished due to a low degree of crosslinking. Therefore, the solidifying shell could freely collapse onto the aqueous core. In the other case, high oligomer concentrations and long curing-times will favor the formation of highly crosslinked capsule membranes with a strong contraction capability. Due to an observed decentered location of the aqueous core within the swollen polymer network, an uneven radial stress along the capsule's circumference is exerted to the incompressible core. This lead to an uneven contraction during solvent removal and a directed flow of the core fluid into the direction of the minimal stress vector. In consequence, the initially thicker spherical cap contracts, whereas the opposing thinner spherical cap get stretched. The "mushroom"-shape over some advantages over their spherical shaped counterparts, why they were selected for the further experiments. Besides the necessity of a high density of crosslinking for the purpose of extraordinary elasticity and toughness, the form-anisotropy promotes a faster microballoon expandability due to a partial reduction of the membrane thickness. Additionally, pre-stretched regions of thin thickness might provide a better resistance against inflation pressure than spherical but non-stretched capsules of equal membrane thickness. The resulting "mushroom"-shaped microcapsules exhibited a melting point of Tm ≈ 50 - 60 °C and a degree of crystallinity of Xc ≈ 29 - 38 % depending on the membrane thickness and internal salt content, which is slightly lower than for the non-crosslinked oligomer and reasoned by a limited chain mobility upon crosslinking. Nonetheless, the melting transition of the polymer network was associated with a strong drop in its mechanical stiffness, which was shown to have a strong influence on the osmotic driven expansion of the microcapsules. Capsules that were subjected to osmotic pressures between 1.5 and 4.7 MPa did not expand if the temperature was well below the melting point of the capsule's membrane, i.e. at room temperature. In contrast, a continuous expansion, while approaching asymptotically to a final capsule size, was observed if the temperature exceeded the melting point, i.e. 60 °C. Microballoons, which were kept for 56 days at ∆Π = 1.5 MPa and room temperature, did not change significantly in diameter, why the impact of the mechanical stiffness on the expansion behavior is considered to be the greater than the influence of the shell permeability. The time-resolved expansion behavior of the microballoons above their Tm was subsequently modeled, using difusion equations that were corrected for shape anisotropy and elastic restoring forces. A shape-related and expansion dependent pre-factor was used to dynamically address the influence of the shell thickness differences along the circumference on the inflation velocity, whereas the microballoon's elastic contraction upon inflation was rendered by the inclusion of a hyperelastic constitutive model. An important finding resulting from this model was the pronounced increase in inflation velocity compared to hypothetical capsules with a homogeneous shell thickness, which stresses the benefit of employing shape anisotropic balloon-like capsules in this study. Furthermore, the model was able to predict the finite expandability on basis of entropy-elastic recovery forces and strain-hardening effects. A comparison of six different microballoons with different shell thicknesses and internal salt contents showed the linear relationship between the volumetric expansion, the shell thickness and the applied osmotic pressure, as represented by the model. As the proposed model facilitates the prediction of the expansion kinetics depending on the membranes mechanical and diffusional characteristics, it might be a screening tool for future material selections. In course of the microballoon expansion process, capsules of intermediate diameters could be isolated by recrystallization of the membrane, which is mainly caused by a restoration of the membrane's mechanical stiffness and is otherwise difficult to achieve with other stimuli-sensitive systems. The capsule's crystallinity of intermediate expansion states was nearly unchanged, whereas the lamellar crystal size tends to decreased with the expansion ratio. Therefore, it was assumed that the elastic modulus was only minimally altered and might increased due to the networks segment-chain extension. In addition to the volume increase achieved by inflation, a turn in the osmotic gradient also facilitated the reversible deflation, which was shown in inflation/deflation cycles. These both characteristics of the introduced microballoons are important parameter regarding the realization of micropumps and microvalves. The fixation of expanded microcapsules via recrystallization enabled the storage of entropy-elastic strain-energy, which could be utilized for pumping actions in non-aqueous media. Here, the pumping velocity depended on both, the type of surrounding medium and the applied temperature. Surrounding media that supported the fast transport of pumped liquid showed an accelerated deflation, while high temperatures further accelerate the pumping velocity. Very fast rejection of the incorporated payload was furthermore realized with pierced expanded microballoons, which were subjected to temperatures above their Tm. The possible fixation of intermediate particle sizes provide opportunities for vent constructions that allowed the precise adjustment of specific flow-rates and multiple valve openings and closings. A valve construction was realized by the insertion of a single or multiple microballoons in a microfluidic channel. A complete and a partial closing of the microballoon-valves was demonstrated as a function of the heating period. In this context, a difference between the inflation and deflation velocity was stated, summarizing slower expansion kinetics. Overall, microballoons, which presented both on-demand pumping and reversible valving by a temperature-triggered change in the capsule's volume, might be suitable components that help to design fully integrated LOC devices, due to the implementation of the control switch and controllable inflation/deflation kinetics. In comparison to other state of the art stimuli-sensitive materials, one has to highlight the microballoons capability of stabilizing almost continuously intermediate capsule sizes by simple recrystallization of the microballoon's membrane.
The increasing global population has led to a growing demand for cost-effective and eco-friendly methods of water purification. This demand has reached a peak due to the increasing presence of impurities and pollutants in water and a growing awareness of waterborne diseases. Advanced oxidation processes (AOPs) are effective methods to address these challenges, due to the generation of highly reactive radicals, such as sulfate radical (SO4•-), hydroxyl radical (•OH), and/or superoxide radical (•O2-) in oxidation reactions. Relative to conventional hydrogen peroxide (H2O2)-based AOPs for wastewater treatment, the persulfate-related AOPs are receiving increasing attention over the past decades, due to their stronger oxidizing capability and a wider pH working window. Further deployment of the seemingly plausible technology as an alternative for the well-established one in industry, however, necessitates a careful evaluation of compounding factors, such as water matrix effects, toxicological consequences, costs, and engineering challenges, etc. To this end, rational design of efficient and environmentally friendly catalysts constitutes an indispensable pathway to advance persulfate activation efficacy and to elucidate the mechanisms in AOPs, the combined endeavors are expected to provide insightful understanding and guidelines for future studies in wastewater treatment. A dozens of transition metal-based catalysts have been developed for persulfate-related AOPs, while the undesirable metal leaching and poor stability in acidic conditions have been identified as major obstacles. Comparatively, the carbonaceous materials are emerging as alternative candidates, which are characterized by metal-free nature, wide availability, and exceptional resistance to acid and alkali, as well as tunable physicochemical and electronic properties, the combined merits make them an attractive option to overcome the aforementioned limitations in metal-based catalytic systems. This dissertation aims at developing novel carbonaceous materials to boost the activity in peroxymonosulfate (PMS) activation processes. Functionalized carbon materials with metal particles or heteroatoms were constructed and further evaluated in terms of their ability to activate PMS for AOPs. The main contents of this thesis are summarized as follows: (1) Iron oxide-loaded biochar: improving stability and alleviating metal leakage Metal leaching constitutes one of the main drawbacks in using transition metals as PMS activators, which is accompanied by the generation of metal-containing sludge, potentially leading to secondary pollution. Meanwhile, the metal nanoparticles are prone to aggregate, causing rapid decay of catalytic performance. The use of carbons as supports for transition metals could mitigate these deficiencies, because the interaction between metals and carbons could in turn disperse and stabilize metal nanoparticles, thus suppressing the metal leaching. In this work, the environmentally benign lignin with its abundant phenolic groups, which is well known to serve as carbon source with high yields and flexibility, was utilized to load Fe ions. The facile low-temperature pre-treatment pyrolytic strategy was employed to construct a green catalyst with iron oxides embedded in Kraft-lignin-derived biochar (termed as γ-Fe2O3@KC). The γ-Fe2O3@KC was capable of activating PMS to generate stable non-radical species (1O2 and Fe (V)=O) and to enhance electron transfer efficiency. A surface-bound reactive complex (catalyst-PMS*) was identified by electrochemical characterizations and discussed with primary surface-bound radical pairs to explain the contradictions between quenching and EPR detection results. The system also showed encouraging reusability for at least 5 times and high stability at pH 3-9. The low concentration of iron in γ-Fe2O3@KC/PMS system implied that the carbon scaffold of biochar substantially alleviated metal leakage. (2) MOF-derived nanocarbon: new carbon crystals Traditional carbon materials are of rather moderate performance in activation PMS, due to the poor electron transfer capacity within the amorphous structure and limited active sites for PMS adsorption. Herein, we established crystalline nanocarbon materials via a simple NaCl-templated strategy using the monoclinic zeolitic imidazolate framework-8 (ZIF-8) sealed with NaCl crystals as the precursors. Specifically, NaCl captured dual advantages in serving as structure-directing agent during hydrolysis and protective salt reactor to facilitate phase transformation during carbonization. The structure-directing agent NaCl provided a protective and confined space for the evolution of MOF upon carbonization, which led to high doping amounts of nitrogen (N) and oxygen elements (O) in carbon framework (N: 14.16 wt%, O: 9.6 wt%) after calcination at a high temperature of 950 oC. We found that N-O co-doping can activate the chemically inert carbon network and the nearby sp2-hybridized carbon atoms served as active sites for adsorption and activation. Besides, the highly crystallized structure with well-established carbon channels around activated carbon atoms could significantly accelerate electron transfer process after initial adsorption of PMS. As such, this crystalline nanocarbon exhibited excellent catalytic kinetics for various pollutants. (3) MOF-derived 2D carbon layers: enhanced mass/electron transfer The two-dimensional (2D) configuration of carbon-based nanosheets with inherent nanochannels and abundant active sites residing on the layer edges or in between the layers, allowed the accessible interaction and close contact between the substrates and reactants, as well as the dramatically improved electron- and mass-transfer kinetics. In this regard, we developed dual-templating strategy to afford 2D assembly of the crystalline carbons, which found efficiency in reinforcing the interactions between the catalyst surface and foreign pollutants. Specifically, we found that the ice crystals and NaCl promoted the evolution of MOF in a 2D fashion during the freezing casting stage, while the later further allowed the formation of a graphitic surface at high calcination temperature, by virtue of the templating effect of molten salt. Due to the highly retained co-doping amounts, N and O heteroatoms created abundant active sites for PMS activation, the 2D configuration of carbon-based nanosheets enable efficient interaction of PMS and pollutants on the surface, which further boosted the kinetics of degradation.
Cardiovascular diseases are the main cause of death worldwide, and their prevalence is expected to rise in the coming years. Polymer-based artificial replacements have been widely used for the treatment of cardiovascular diseases. Coagulation and thrombus formation on the interfaces between the materials and the human physiological environment are key issues leading to the failure of the medical device in clinical implantation. The surface properties of the materials have a strong influence on the protein adsorption and can direct the blood cell adhesion behavior on the interfaces. Furthermore, implant-associated infections will be induced by bacterial adhesion and subsequent biofilm formation at the implantation site. Thus, it is important to improve the hemocompatibility of an implant by altering the surface properties. One of the effective strategies is surface passivation to achieve protein/cell repelling ability to reduce the risk of thrombosis.
This thesis consists of synthesis, functionalization, sterilization, and biological evaluation of bulk poly(glycerol glycidyl ether) (polyGGE), which is a highly crosslinked polyether-based polymer synthesized by cationic ring-opening polymerization. PolyGGE is hypothesized to be able to resist plasma protein adsorption and bacterial adhesion due to analogous chemical structure as polyethylene glycol and hyperbranched polyglycerol. Hydroxyl end groups of polyGGE provide possibilities to be functionalized with sulfates to mimic the anti-thrombogenic function of the endothelial glycocalyx.
PolyGGE was synthesized by polymerization of the commercially available monomer glycerol glycidyl ether, which was characterized as a mixture of mono-, di- and tri-glycidyl ether. Cationic ring opening-polymerization of this monomer was carried out by ultraviolet (UV) initiation of the photo-initiator diphenyliodonium hexafluorophosphate. With the increased UV curing time, more epoxides in the side chains of the monomers participated in chemical crosslinking, resulting in an increase of Young’s modulus, while the value of elongation at break of polyGGE first increased due to the propagation of the polymer chains then decreased with the increase of crosslinking density. Eventually, the chain propagation can be effectively terminated by potassium hydroxide aqueous solution. PolyGGE exhibited different tensile properties in hydrated conditions at body temperature compared to the values in the dry state at room temperature. Both Young’s modulus and values of elongation at break were remarkably reduced when tested in water at 37 °C, which was above the glass transition temperature of polyGGE. At physiological conditions, entanglements of the ployGGE networks unfolded and the free volume of networks were replaced by water molecules as softener, which increased the mobility of the polymer chains, resulting in a lower Young’s modulus.
Protein adsorption analysis was performed on polyGGE films with 30 min UV curing using an enzyme-linked immunosorbent assay. PolyGGE could effectively prevent the adsorption of human plasma fibrinogen, albumin, and fibronectin at the interface of human plasma and polyGGE films. The protein resistance of polyGGE was comparable to the negative controls: the hemocompatible polydimethylsiloxane (PDMS), showing its potential as a coating material for cardiovascular implants. Moreover, antimicrobial tests of bacterial activity using isothermal microcalorimetry and the microscopic image of direct bacteria culturing demonstrated that polyGGE could directly interfere biofilm formation and growth of both Gram-negative and antibiotic-resistant Gram-positive bacteria, indicating the potential application of polyGGE for combating the risk of hospital-acquired infections and preventing drug-resistant superbug spreading.
To investigate its cell compatibility, polyGGE films were extracted by different solvents (ethanol, chloroform, acetone) and cell culture medium. Indirect cytotoxicity tests showed extracted polyGGE films still had toxic effects on L929 fibroblast cells. High-performance liquid chromatography/electrospray ionization mass spectrometry revealed the occurrence of organochlorine-containing compounds released during the polymer-cell culture medium interaction. A constant level of those organochlorine-containing compounds was confirmed from GGE monomer by a specific peak of C-Cl stretching in infrared spectra of GGE. This is assumed to be the main reason causing the increased cell membrane permeability and decreased metabolic activity, leading to cell death. Attempts as changing solvents were made to remove toxic substances, however, the release of these small molecules seems to be sluggish. The densely crosslinked polyGGE networks can possibly contribute to the trapping of organochlorine-containing compounds. These results provide valuable information for exploring the potentially toxic substances, leaching from polyGGE networks, and propose a feasible strategy for minimizing the cytotoxicity via reducing their crosslinking density.
Sulfamic acid/ N-Methyl-2-pyrrolidone (NMP) were selected as the reagents for the sulfation of polyGGE surfaces. Fourier transform attenuated total reflection infrared spectroscopy (ATR-FT-IR) was used to monitor the functionalization kinetics and the results confirmed the successful sulfate grafting on the surface of polyGGE with the covalent bond -C-O-S-. X-ray photoelectron spectroscopy was used to determine the element composition on the surface and the cross-section of the functionalized polyGGE and sulfation within 15 min guarantees the sulfation only takes place on the surface while not occurring in the bulk of the polymer. The concentration of grafted sulfates increased with the increasing reaction time. The hydrophilicity of the surface of polyGGE was highly increased due to the increase of negatively charged end groups. Three sterilization techniques including autoclaving, gamma irradiation, and ethylene oxide (EtO) sterilization were used for polyGGE sulfates. Results from ATR-FT-IR and Toluidine Blue O quantitative assay demonstrated the total loss of the sulfates after autoclave sterilization, which was also confirmed by the increased water contact angle. Little influence on the concentration of sulfates was found for gamma-irradiated and autoclaving sterilized polyGGE sulfates. To investigate the thermal influence on polyGGE sulfates, one strategy was to use poly(hydroxyethyl acrylate) sulfates (PHEAS) for modeling. The thermogravimetric analysis profile of PHEAS demonstrated that sulfates are not thermally stable independent of the substrate materials and decomposition of sulfates occurs at around 100 °C. Although gamma irradiation also showed little negative effect on the sulfate content, the color change in the polyGGE sulfates indicates chemical or physical change might occur in the polymer. EtO sterilization was validated as the most suitable sterilization technique to maintain the chemical structure of polyGGE sulfates.
In conclusion, the conducted work proved that bulk polyGGE can be used as an antifouling coating material and shows its antimicrobial potential. Sulfates functionalization can be effectively realized using sulfamic acid/NMP. EtO sterilization is the most suitable sterilization technique for grafted sulfates. Besides, this thesis also offers a good strategy for the analysis of toxic leachable substances using suitable physicochemical characterization techniques. Future work will focus on minimizing/eliminating the release of toxic substances via reducing the crosslinking density. Another interesting aspect is to study whether grafted sulfates can meet the need for anti-thrombogenicity.
Development of functionalized waterborne coatings for the production of multifunctional microapsules
(2022)
Under the in vivo condition, a cell is continually interacting with its surrounding microenvironment, which is composed of its neighboring cells and the extracellular matrix (ECM). These components generate and transmit the microenvironmental signals to regulate the fate and function of the target cells. Except the signals from the microenvironment, stimuli from the ambient environment, such as temperature changes, also play an important in modulating the cell behaviors, which are considered as regulators from the macroenvironment. In this regard, recapitulation of these environmental factors to steer cell function will be of crucial importance for therapeutic purposes and tissue regeneration. Although the role of a variety of environmental factors has been evaluated, it is still challenging to identify and provide the appropriate factors, which are required for optimizing the survival of cells and for ensuring effective cell functions.
Thus, in vitro recreating the environmental factors that are present in the extracellular environment would help to understand the mechanism of how cells sense and process those environmental signals. In this context, this thesis is aimed to harness these environmental parameters to guide cell responses. Here, human induced pluripotent stem cells (hiPSCs) and human keratinocytes (KTCs), HaCaT cells, were used to investigate the impact of signals from the microenvironment or stimuli from the macroenvironment.
Firstly, polydopamine (PDA) or chitosan (CS) modifications were applied to generate different substrate surfaces for hiPSCs and KTCs (Chapter 4 to Chapter 6). Our results showed that the PDA modification was efficient to increase the cell-substrate adhesion and consequently promoted cell spreading. While CS modification was able to decrease the cell-substrate adhesion and enhance the cell-cell interaction, which enabled the morphology shift from monolayered cells to multicellular spheroids. The quantitative result was acquired using the atomic force microscopy (AFM)-based single-cell force spectroscopy. The balance between the cell-substrate and cell-cell adhesion yielded a net force, which determined the preference of the cell to adhere to its neighboring cells or to the substrate. The difference in the adhesive behaviors further affected the cellular function, such as the proliferation and differentiation potential of both hiPSCs and HaCaT cells.
Next, the cyclic temperature changes (ΔT) were selected here to study the influence of macroenvironmental stimuli on hiPSCs and KTCs (Chapter 7 and Chapter 8). The macroenvironmental temperature ranging from 10.0 ± 0.1 °C to 37.0 ± 0.1 °C was achieved using a thermal chamber equipped with a temperature controller. This temperature range was selected to explore the responses of hiPSCs to the extreme environments, while a temperature variation between 25.0 ± 0.1 °C and 37.0 ± 0.1 °C was applied to mimic the ambient temperature variations experienced by the skin epithelial KTCs. The ΔT led to cell stiffening in both hiPSCs and HaCaT cells in a cytoskeleton-dependent manner, which was measured by AFM. Specifically, in hiPSCs, the cell stiffening was resulted from the rearrangement of the actin skeleton; in HaCaT cells, was due to the difference of the Keratin (KRT) filaments. Except for inducing cell hardening, ΔT also caused differences in the protein expression profiles in hiPSCs or HaCaT cells, compared to those without ΔT treatment, which might be attributed to the alterations in their cytoskeleton structures.
To sum up, the results of the thesis demonstrated how individual factors from the micro-/macro-environment can be harnessed to modulate the behaviors of hiPSCs and HaCaT cells. Engineering the microenvironmental cues using surface modification and exploiting the macroenvironmental stimuli through temperature control were identified as precise and potent approaches to steer hiPSC and HaCaT cell behaviors. The application of AFM served as a non-invasive and real-time monitoring platform to trace the change in cell topography and mechanics induced by the environmental signals, which provide novel insights into the cell-environment interactions.
‘Smart’ Janus emulsions
(2021)
Emulsions constitute one of the most prominent and continuously evolving research areas in Colloid Chemistry, which involves the preparation of mixtures or dispersions of immiscible components in a continuous medium. Besides conventional oil-in-water or water-in-oil emulsions, other emulsions of complex droplet morphologies have recently attracted significant research interests. Especially Janus emulsions, in which each droplet is comprised of two distinct sub-regions, have shown versatile potential applications. One of their advantages is the possibility of compartmentalization, which enables to play with two different chemistries in a single droplet. Though microfluidic methods are conventionally used to prepare Janus emulsions, their industrial applications are largely hindered by low throughput and extensive instrumentations. Recently, it has been discovered that simply one-pot moderate/high energy emulsification is also capable of developing Janus morphology, although their preparation and stabilization remain rather substantially challenging. This cumulative doctoral thesis focuses on the preparation and characterization of ‘smart’ Janus emulsions, i.e. Janus emulsions with special stimuli-responsive features. One-step moderate/high energy emulsification of olive and silicone oil in an aqueous medium was carried out. Special consideration was devoted to the interfacial tensions among the components to maintain the criteria of forming characteristic droplet architectures, in addition to avoiding multiple emulsion destabilization phenomena like imminent phase separation or even separated droplet formation. A series of investigations were conducted related to the formation of complexes of charged macromolecules and role of them as stabilizers to achieve stable Janus emulsions for a realistic timeframe (more than 3 months). The correlation between the size of the stabilizer particles and the droplet size of emulsion was established. Furthermore, it was observed that Janus emulsion gels with interesting rheological properties can be fabricated in the presence of suitable polyelectrolyte complexes. Janus emulsions that could be influenced by pH, temperature or magnetic field were successfully produced in presence of characteristic stimuli-responsive stabilizers. Afterwards, the effect of these changes was studied by different characterization techniques. The size and morphology could be tuned easily by changing the pH. The incorporation of iron oxide magnetic nanoparticles (synthesized separately by a co-precipitation method) to one component of the Janus emulsion was carried out so that the movement and orientation of the complex droplets in aqueous media could be controlled by an external magnetic field. Additionally, temperature-triggered instantaneous reversible breakdown of Janus droplets was also accomplished. The responses of the Janus droplets by the stimuli were well-documented and explained. Another goal of the present contribution was to exploit this special morphological feature of emulsions as a template for producing porous materials. This was demonstrated by the preparation of ultralight magnetic responsive aerogels, utilizing Janus emulsion gels. The produced aerogels also showed the capacity to separate toxic dye from water. To the best of our knowledge, this is the first example of investigation towards batch scale production of Janus emulsion with such special stimuli-responsive properties by a simple bulk emulsification method.
Synthesis and Characterization of Upconversion Nanaparticles for Applications in Life Sciences
(2021)
Shape-Memory effects of thermoplatic multiblock copolymers with overlapping thermal transitions
(2021)
Die vorliegende Arbeit beschäftigt sich mit der Synthese von Disulfiden, der Thiol-Disulfid Metathesereaktion als Möglichkeit, Polymere zu funktionalisieren, und der Synthese von Polydisulfiden. Im ersten Teil der Arbeit wird die Aminolyse von RAFT-Polymeren und die Abhängigkeit der Polymer-Polymer Disulfidbildung von der Molmasse untersucht. Dabei wurde durch die Aufnahme von Reaktionskinetiken mittels Gel-Permeations-Chromatographie (GPC) festgestellt, dass je länger die Polymerketten sind, desto weniger Disulfid Polymerkopplung tritt auf. RAFT-Polymere werden oft genutzt, um die RAFT-Polymer Endgruppe nach der Polymerisation zu modifizieren oder in einer chemischen Reaktion zu funktionalisieren. Hier kann die Aminolyse in Anwesenheit von kurzkettigen Disulfiden, wie zum Beispiel Cystin, durchgeführt werden, um die Bildung von Polymer-Polymer Disulfiden vollständig zu unterdrücken und ein endgruppenfunktionalisiertes Polymer zu erhalten. Bei dieser Reaktion greift das bei der Aminolyse entstehende Polymerthiolat die kurzkettigen Disulfide an, und es kommt zur Bildung von funktionalisierten Polymeren. Es wurde ein Polyethylenglykoldisulfid eingesetzt, um ein amphiphiles Blockcopolymer zu erhalten. Als RAFT-Polymer wurde Polystyrol (PS) verwendet, und es konnte die Bildung von Polystyrol-Polyethylenglykol Copolymeren nachgewiesen werden. Das amphiphile Polymer bildet im wässrigen Medium Vesikel. Die Oberfläche der Vesikel konnte mittels der Thiol-Disulfid Metathese umfunktionalisiert werden. Die Aminolyse von PS RAFT-Polymeren mit einem Polylaktiddisulfid oder einem Polybenzylglutamatdisulfid ergab Polystyrol-block-Polyester und Polystyrol-block-Polyaminosäuren Copolymere. Im zweiten Teil der Arbeit liegt der Fokus auf der Synthese von Polydisulfiden und ihren thermischen Eigenschaften. Es wurden verschiedene Alkyldithiole synthetisiert und mittels Wasserstoffperoxid und Triethylamin polymerisiert. Dabei konnte gezeigt werden, dass die Polymere teilkristallin sind und dass der Schmelzpunkt und die Kristallinität der Polymere mit steigender Alkylkettenlänge zwischen den Disulfidbindungen zunehmen. Die Möglichkeit einer Polymerkettenerweiterung nach der Polymerisation ist mit diesem System gegeben. Die Abbaubarkeit der Polydisulfide konnte durch den Einsatz von Thiolen im basischen Milieu gezeigt werden.
This thesis focuses on the synthesis of novel functional materials based on plasmonic nanoparticles. Three systems with targeted surface modification and functionalization have been designed and synthesized, involving modified perylenediimide doped silica-coated silver nanowires, polydopamine or TiO2 coated gold-palladium nanorods and thiolated poly(ethylene glycol) (PEG-SH)/dodecanethiol (DDT) modified silver nanospheres. Their possible applications as plasmonic resonators, chiral sensors as well as photo-catalysts have been studied. In addition, the interaction between silver nanospheres and 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) molecules has also been investigated in detail.
In the first part of the thesis, surface modification on Ag nanowires (NWs) with optimized silica coating through a modified Stöber method has been firstly conducted, employing sodium hydroxide (NaOH) to replace ammonia solution (NH4OH). The coated silver nanowires with a smooth silica shell have been investigated by single-particle dark-field scattering spectroscopy, transmission electron microscopy and electron-energy loss spectroscopy to characterize the morphologies and structural components. The silica-coated silver nanowires can be further functionalized with fluorescent molecules in the silica shell via a facile one-step coating method. The as-synthesized nanowire is further coupled with a gold nanosphere by spin-coating for the application of the sub-diffractional chiral sensor for the first time. The exciton-plasmon-photon interconversion in the system eases the signal detection in the perfectly matched 1D nanostructure and contributes to the high contrast of the subwavelength chiral sensing for the polarized light.
In the second part of the thesis, dumbbell-shaped Au-Pd nanorods coated with a layer of polydopamine (PDA) or titanium dioxide (TiO2) have been constructed. The PDA- and TiO2- coated Au-Pd nanorods show a strong photothermal conversion performance under NIR illumination. Moreover, the catalytic performance of the particles has been investigated using the reduction of 4-nitrophenol (4-NP) as the model reaction. Under light irradiation, the PDA-coated Au-Pd nanorods exhibit a superior catalytic activity by increasing the reaction rate constant of 3 times. The Arrhenius-like behavior of the reaction with similar activation energies in the presence and absence of light irradiation indicates the photoheating effect to be the dominant mechanism of the reaction acceleration. Thus, we attribute the enhanced performance of the catalysis to the strong photothermal effect that is driven by the optical excitation of the gold surface plasmon as well as the synergy with the PDA layer.
In the third part, the kinetic study on the adsorption of 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquino-dimethane (F4TCNQ) on the surface of Ag nanoparticles (Ag NPs) in chloroform has been reported in detail. Based on the results obtained from the UV-vis-NIR absorption spectroscopy, cryogenic transmission electron microscopy (cryo-TEM), scanning nano-beam electron diffraction (NBED) and electron energy loss spectroscopy (EELS), a two-step interaction kinetics has been proposed for the Ag NPs and F4TCNQ molecules. It includes the first step of electron transfer from Ag NPs to F4TCNQ indicated by the ionization of F4TCNQ, and the second step of the formation of Ag-F4TCNQ complex. The whole process has been followed via UV-vis-NIR absorption spectroscopy, which reveals distinct kinetics at two stages: the instantaneous ionization and the long-term complex formation. The kinetics and the influence of the molar ratio of Ag NPs/F4TCNQ molecules on the interaction between Ag NPs and F4TCNQ molecules in the organic solution are reported herein for the first time. Furthermore, the control experiment with silica-coated Ag NPs indicates that the charge transfer at the surface between Ag NPs and F4TCNQ molecules has been prohibited by a silica layer of 18 nm.
Advanced hybrid materials are recognized as one of the most significant enablers for new technologies, which holds true especially on the quest for sustainable energy sources and energy production schemes (e.g., semiconductor based photocatalytic materials). Usually, a single component is far from meeting all the demands needed for these advanced applications. Hybrid materials are composed of at least two components commonly an inorganic and an organic material on the molecular level, which feature novel properties exceeding the sum of the individual parts and might be the milestones of next-generation applications. This dissertation aims to provide novel combinations of the metal-free semiconductor graphitic carbon nitride (g-C3N4) with polymers to obtain materials with advanced properties and applications. Visible light constitutes the core of the present work as it is the only energy source utilized either in synthesis or in the application process. In the area of applications by combination of g-C3N4 and polymers, two different hybrids were thoroughly elucidated, i.e.. their design and construction as well as potential application in photocatalysis. Novel soft 3D liquid objects were formed via charge-interaction driven interfacial jamming between polyelectrolytes in aqueous environment and colloidal dispersions of g-C3N4 in edible sunflower oil. As such, stable liquid objects could be molded into specific shapes and utilized for photodegradation of organic dyes in water. Furthermore, the grafting of polymers onto g-C3N4 was investigated. Allyl-end functionalized polymers were grafted onto g-C3N4 by a photoinitiated process to yield g-C3N4 with versatile and improved properties, e.g. advanced dispersibility enabling processing via spin coating. As g-C3N4 produces radicals under visible light irradiation, which is of significant interest for polymer science, g-C3N4 containing polymer latex and macrogel beads (MGB) were synthesized by emulsion photopolymerization and inverse suspension photopolymerization, respectively. A well-controlled emulsion photopolymerization process via g-C3N4 initiation was designed, which features synthesis of well-defined and cross-linked polymer particles. Furthermore, the polymerization process was investigated thoroughly, indicating an ad-layer polymerization in early stages of the process. The utilization of functionalized g-C3N4 allowed the polymerization of various monomer types. Moreover, g-C3N4 was utilized as photoinitiator in hydrogel MGB formation. The formed MGB properties could be tailored via process design, e.g. stirring rate, cross-linker content and g-C3N4 content. Finally, MGBs were introduced as photocatalyst for waste water remediation, i.e. the degradation of Rhodamine B in aqueous solution was studied. The present thesis therefore builds a bridge between g-C3N4 and polymers and provides strategies for hybrid material formation. Furthermore, several potential applications are revealed with significant implications for photocatalysis, polymerization processes and polymer materials.
Magnetotactic bacteria comprise a heterogeneous group of Gram negative bacteria which share the ability to synthesise intracellular magnetic nanoparticles surrounded by a lipid bilayer, known as magnetosomes, which are arranged in linear chains. The bacteria exert a unique level of control onto the biomineralization of these nanoparticles, which is seen in the controlled size and shape they have. These characteristics have attracted great attention on understanding the process by which the bacteria synthesise the magnetosomes. Moreover, the magnetosome chain impart the bacteria with a net magnetic dipole which makes them susceptible to interact with magnetic fields and thus orient with the Earth’s magnetic field. This feature has attracted as well much interest to understand how the swimming motility of these microorganisms is affected by the presence of magnetic fields. Most of the studies performed in these bacteria so far have been conducted in the traditional manner using large populations of cells. Such studies have the disadvantage of averaging many different individuals with heterogeneous behaviours and fail to consider individual variations. In addition, in large populations each bacterium will be subjected to a different microenvironment that will influence the bacterial behaviour, but which cannot be defined using these traditional methods. In this thesis, different microfluidic platforms are proposed to overcome these limitations and to offer the possibility to study magnetotactic bacteria in defined environments and down to a single-cell resolution. First, a sediment-like microfluidic platform is presented with the purpose of mimicking the porous environment they bacteria naturally dwell in. The platform allows to observe via transmitted light microscopy that bacterial navigation in crowded environments is enhanced by the Earth’s magnetic field strengths (B = 50 μT) rather than by null (B = 0 μT) or higher magnetic fields (B = 500 μT). Second, a microfluidic system to confine single-bacterial cells in physically defined environments is presented. The system allows to study via transmitted light microscopy the interplay between wall curvature, magnetic fields and bacterial speed affect the motion of a confined bacterium, and shows how bacterial trajectories depend on those three parameters. Third, a microfluidic platform to conduct semi in vivo magnetosome nucleation with a single-cell resolution via X-ray fluorescence is fabricated. It is shown that signal arising from magnetosome full chains can be observed individually in each bacterium. Finally, the iron uptake kinetics of a single bacterium are studied via a fluorescent reporter through confocal microscopy. Two different approaches are used for this: one of the previously mentioned platforms, as well as giant lipid vesicles. It is observed how iron uptake rates vary between cells, as well as how these rates are consistent with magnetosome formation taking place within some hours. The present thesis shows therefore how microfluidic technologies can be implemented for the study of magnetotactic bacteria at different degrees, and the level of resolution that can be attained by going into the single- cell scale.
Die vorliegende Dissertationsschrift mit dem Titel: „Ruthenium(II)- und Rhenium(I)-Komplexe des 1,6,7,12-Tetraazaperylens und seiner Dimethyl- und Tetramethylderivate“ von Matthias Kirste wurde unter der Leitung des Herrn Prof. Dr. Hans-Jürgen Holdt am Institut für Chemie der Universität Potsdam angefertigt. Die Arbeit beschäftigt sich mit Ruthenium(II)- und Rhenium(I)-Komplexen des großflächigen Liganden 1,6,7,12-Tetraazaperylen (tape) und seiner 2,11-Dimethyl-(dmtape)- und 2,5,8,11-Tetramethyl-(tmtape)-derivate. Es wurden die bekannten Herstellungen des tape- sowie des dmtape-Liganden verbessert und die Synthese des tmtape-Liganden neu entwickelt. Zudem gelang mit einer neu entwickelten chemischen Reaktion die Synthese des dianionischen 3,10-Disulfonato-1,6,7,12-tetraazaperylens. Mit dmtape und tmtape wurde jeweils ein neuer Ruthenium(II)-Komplex hergestellt. Die Komplexe wurden photophysikalisch und elektrochemisch charakterisiert. KT-DNS-Interkalationen wurden von einkernigen Ruthenium(II)-Komplexen mit jeweils tape-, dmtape- und tmtape als interkalative Einheit vermessen. Es zeigte sich, dass diese Komplexe mit einer hohen Bindungsaffinität in die doppelsträngige KT-DNS interkalieren. Aus den mononuklearen Ruthenium(II)-Komplexen gelang die Herstellung von heterodinuklearen RuIIReI-Komplexen, die charakteristische Signale in ihren UV/Vis-Absorptionsspektren zeigen und sehr leicht jeweils ein- sowie zweifach im Bereich von 70 mV bis -80 mV und -440 mV bis -600 mV vs. GKE reduzierbar sind. Diese dmtape- sowie tmtape-verbrückten heterodinuklearen RuIIReI-Komplexe ermöglichen eine Feinjustierung ihrer photophysikalischen und elektrochemischen Eigenschaften, wobei in dieser Arbeit mithilfe einer chemischen Reaktion eine gezielte Einstellung dieser Eigenschaften gezeigt werden konnte. Metallkomplexe mit solchen charakteristischen, leicht einstellbaren photophysikalischen sowie elektrochemischen Eigenschaften sind geeignete Sensor- und Elektronen-Shuttle-Moleküle besonders für bioanalytische Einsatzgebiete. Zudem könnten die vielen Einstellmöglichkeiten der elektronischen Struktur dieser Komplexe sehr interessant für katalytische Anwendungen sein.
The goal of regenerative medicine is to guide biological systems towards natural healing outcomes using a combination of niche-specific cells, bioactive molecules and biomaterials. In this regard, mimicking the extracellular matrix (ECM) surrounding cells and tissues in vivo is an effective strategy to modulate cell behaviors. Cellular function and phenotype is directed by the biochemical and biophysical signals present in the complex 3D network of ECMs composed mainly of glycoproteins and hydrophilic proteoglycans. While cellular modulation in response to biophysical cues emulating ECM features has been investigated widely, the influence of biochemical display of ECM glycoproteins mimicking their presentation in vivo is not well characterized. It remains a significant challenge to build artificial biointerfaces using ECM glycoproteins that precisely match their presentation in nature in terms of morphology, orientation and conformation. This challenge becomes clear, when one understands how ECM glycoproteins self-assemble in the body. Glycoproteins produced inside the cell are secreted in the extra-cellular space, where they are bound to the cell membrane or other glycoproteins by specific interactions. This leads to elevated local concentration and 2Dspatial confinement, resulting in self-assembly by the reciprocal interactions arising from the molecular complementarity encoded in the glycoprotein domains. In this thesis, air-water (A-W) interface is presented as a suitable platform, where self-assembly parameters of ECM glycoproteins such as pH, temperature and ionic strength can be controlled to simulate in vivo conditions (Langmuir technique), resulting in the formation of glycoprotein layers with defined characteristics. The layer can be further compressed with surface barriers to enhance glycoprotein-glycoprotein contacts and defined layers of glycoproteins can be immobilized on substrates by horizontal lift and touch method, called Langmuir-Schäfer (LS) method. Here, the benefit of Langmuir and LS methods in achieving ECM glycoprotein biointerfaces with controlled network morphology and ligand density on substrates is highlighted and contrasted with the commonly used (glyco)protein solution deposition (SO) method on substrates. In general, the (glyco)protein layer formation by SO is rather uncontrolled, influenced strongly by (glyco)protein-substrate interactions and it results in multilayers and aggregations on substrates, while the LS method results in (glyco)proteins layers with a more homogenous presentation. To achieve the goal of realizing defined ECM layers on substrates, ECM glycoproteins having the ability to self-assemble were selected: Collagen-IV (Col-IV) and fibronectin (FN). Highly packed FN layer with uniform presentation of ligands was deposited on polydimethysiloxane VIII (PDMS) by LS method, while a heterogeneous layer was formed on PDMS by SO with prominent aggregations visible. Mesenchymal stem cells (MSC) on PDMS equipped with FN by LS exhibited more homogeneous and elevated vinculin expression and weaker stress fiber formation than on PDMS equipped with FN by SO and these divergent responses could be attributed to the differences in glycoprotein presentation at the interface. Col-IV are scaffolding components of specialized ECM called basement membranes (BM), and have the propensity to form 2D networks by self-polymerization associated with cells. Col- IV behaves as a thin-disordered network at the A-W interface. As the Col-IV layer was compressed at the A-W interface using trough barriers, there was negligible change in thickness (layer thickness ~ 50 nm) or orientation of molecules. The pre-formed organization of Col-IV was transferred by LS method in a controlled fashion onto substrates meeting the wettability criterion (CA ≤ 80°). MSC adhesion (24h) on PET substrates deposited with Col-IV LS films at 10, 15 and 20 mN·m-1 surface pressures was (12269.0 ± 5856.4) cells for LS10, (16744.2 ± 1280.1) cells for LS15 and (19688.3 ± 1934.0) cells for LS20 respectively. Remarkably, by selecting the surface areal density of Col-IV on the Langmuir trough on PET, there is a linear increase between the number of adherent MSCs and the Col-IV ligand density. Further, FN has the ability to self-stabilize and form 2D networks (even without compression) while preserving native β-sheet structure at the A-W interface on a defined subphase (pH = 2). This provides the possibility to form such layers on any vessel (even on standard six-well culture plates) and the cohesive FN layers can be deposited by LS transfer, without the need for expensive LB instrumentation. Multilayers of FN can be immobilized on substrates by this approach, as easily as Layer-by-Layer method, even without the need for secondary adlayer or activated bare substrate. Thus, this facile glycoprotein coating strategy approach is accessible to many researchers to realize defined FN films on substrates for cell culture. In conclusion, Langmuir and LS methods can create biomimetic glycoprotein biointerfaces on substrates controlling aspects of presentation such as network morphology and ligand density. These methods will be utilized to produce artificial BM mimics and interstitial ECM mimics composed of more than one ECM glycoprotein layer on substrates, serving as artificial niches instructing stem cells for cell-replacement therapies in the future.
Die vorgelegte Arbeit besteht aus drei Teilprojekten, der Realisierung eines Multiparametersensors (Temperatur, pH-Wert und Sauerstoffkonzentration), der Konzipierung und Untersuchung eines optischen Atemgassensors und Untersuchungen zur Anwendung des Konzeptes der Sauerstofflöschung in der Immuntechnologie. Zur Realisierung des Multiparametersensors wurden die einzelnen Sensorfarbstoffe, sofern notwendig, synthetisiert und anschließend einzeln unter Laborbedingungen charakterisiert. Im weiteren Verlauf wurde ein Versuchsaufbau konzipiert mit dem es möglich ist, alle verwendeten Sensorfarbstoffe mit einer Anregungsquelle anzuregen. Dabei erfolgte die Detektion der Parameter Temperatur und Sauerstoffkonzentration mittels Phasenmodulationsspektroskopie und die pH-Wert-bestimmung mittels stationärer Fluoreszenzspektroskopie. So konnte ein Multiparametersensor konzipiert werden, mit dem es möglich ist, die drei genannten Parameter simultan, in Echtzeit und ohne externe Temperaturmessung zu detektieren. Im Rahmen der Entwicklung eines optischen Atemgassensors konnte zunächst eine neue Sensorform entwickelt werden. Durch diese neue Sensorform, welche sich durch sehr kurze Ansprechzeiten auszeichnet, ist es möglich den Sauerstoffgehalt in der Exspirationsluft sehr detailreich zu erfassen. Durch freiwillige Selbstversuche mit dem Atemgassensor konnte eine Korrelation mit einer etablierten Untersuchungsmethode hergestellt werden. Während der Untersuchungen zur Anwendung des Konzeptes der Sauerstofflöschung in der Immuntechnologie konnte zunächst ein Modell entwickelt werden, welches die Wechselwirkung zwischen Antikörper und synthetisiertem Farbstoff, welcher als Antigen fungierte, beschreibt. Nachdem weiterhin eine Wechselwirkung zwischen Antikörper und Antigen in einfachen Medien, wie PBS-Pufferlösung, gezeigt werden konnte, gelang dies auch in komplexen Medien wie bovinem Serum, Kuhmilch oder Speichelflüssigkeit. So konnte ein System entwickelt werden, mit dem es möglich ist Antikörper-Antigen-Wechselwirkungen in komplexen biologischen Medien zu verfolgen.
In recent years the development of renewable energy sources attracted much attention due to the increasing environmental pollution induced by burning fossil fuels. The growing public interest in reducing greenhouse gases and the use of pollution-free energies (bio-mass-, geothermal-, solar-, water- or wind energy) paved the way for scientific research in renewable energies. [1] Solar energy provides unlimited access and offers high applicational flexibility, which is needed for energy consumption in a modern society. The scientific interest in photovoltaics (PV) nowadays focuses on discovering new materials and improving materials properties, aiming for the production of highly efficient solar cells. Lately, a new type of absorber material based on the perovskite type structure reached power conversion efficiencies of more than 24%. [2] By varying the chemical composition the electronic properties as e.g. the band gap energy can be tuned to increase the absorption range of this absorber material. This makes them in particular attractive for use in tandem solar cells, where silicon and perovskite absorber layers are combined to absorb a large range of the vible light (28.0% efficiency). [2] However, perovskite based solar cells not only suffer from fast degradation when exposed to humidity, but also from the use of toxic elements (e.g. lead), which can result in long-term environmental damage. Therefore, the aim of this study was to determine the fundamental structural and optoelectronical properties of highly interesting hybrid perovskite materials, the MAPbX3 solid solution (MA=CH3NH3; X=I,Br,Cl) and the triple cation (FA1-xMAx)1-yCsyPbI3 solid solution (FA=HC(NH2)2). The study was performed on powder samples by using X-ray diffraction, revealing the crystal structure and solubility behavior of all solid solutions. Moreover the temperature-dependent behavior was studied using in-situ high resolution synchrotron X-ray diffraction and combinatorial thermal analysis methods. The influence of compositional changes on the band gap energy variation were observed using spectroscopic methods as photoluminescence and diffuse reflectance spectroscopy. The obtained results have shown that for the MAPb(I1-xBrx)3 solid solution a large miscibility gap in the range of 0.29 ( ± 0.02) ≤ x ≤ 0.92 ( ± 0.02) is present. This miscibility gap limits the suitable compositional range for use in thin film solar cells of mixed halide compounds. From the temperature-dependent in-situ synchrotron X-ray diffraction studies the complete T-X-phase diagram was established. Studies on the MAPb(Cl1-xBrx)3 solid solution revealed that MAPb(Cl1-xBrx)3 forms a complete solid solution series. For the triple cation (FA1-xMAx)1-yCsyPbI3 solid solution the aim was to study the formation of the d-modification in FAPbI3, which is undesired for solar cell application. This can be overcome by stabilizing the favored high temperature cubic a-modification at ambient conditions. By partial substituting the formamidinium molecule by methylammonium and cesium the stabilization of the cubic modification was successful. The solubility limit of FA1-xCsxPbI3 solid solution was determined to be x=0.1, while a full miscibility was observed for the FA1-xMAxPbI3 solid solution. For the triple cation (FA1-xMAx)1-yCsyPbI3 solid solution a solubility limit of cesium was observed to be y=0.1. The optoelectronic properties were investigated, revealing a linear change of band gap energy with chemical composition. It is demonstrated that the stabilized triple cation compound with cubic perovskite-type crystal structure shows enhanced stability of approximately six months. Furthermore, a short insight into lead-free perovskite-type materials is given, using germanium as non-toxic alternative to lead. For germanium based perovskites a fast decomposition in air was observed, due to the preferred formation of GeI4 in oxygen atmosphere. In-situ low temperature synchrotron X-ray diffraction measurements revealed a yet unknown low temperature modification of MAGeI3. [1] WESSELAK, Viktor; SCHABBACH, Thomas; LINK, Thomas; FISCHER, Joachim: Handbuch Regenerative Energietechnik. Springer, 2017 [2] NREL: Best Research-Cell Efficiencies. https://www.nrel.gov/pv/assets/pdfs/best-research-cell-efficiencies-190416.pdf. – 25.04.2019