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Optimisation of polyethylene glycol hydrogels preparation by polymerisation and their subsequent characterisation
Fornůsek, Jakub ; Trudičová, Monika (referee) ; Smilek, Jiří (advisor)
The goal of this bachelor’s thesis was the optimization of the preparation of polyethyleneglycol hydrogels by radical polymerization and their subsequent characterization by the means of rheometry, swelling experiments and examination of transport properties through the absorption of an active substance and its subsequent desorption. To examine these hydrogels, UV photopolymerization was chosen due to its simplicity and reproducibility. As part of the optimalization, hydrogels were prepared under varying conditions and then characterised by the previously mentioned methods. The effect of the presence of the cross-linking agent ethylenglycol dimethacrylate on the properties of the resulting hydrogels was also investigated. These examined gels represent a new type of chemically cross-linked hydrogels, which are part of a basic research project applications by GAČR. From rheometric measurements, it was confirmed that a higher molecular weight of the measured sample corresponded to lower values of viscoelastic moduli. The effect of the cross-linking agent on these values was negligible. The mesh density played a significant role in swelling and transport experiments. As its value increased, the swelling capacity of the hydrogel decreased and therefore a smaller amount of water was absorbed. The presence of the cross-linking agent was also noticeable, as it contributed to a creation of higher density polymer networks.
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The utilization of atomic force miscroscopy to study of selected bacterial strain
Nováková, Simona ; Slaninová, Eva (referee) ; Smilek, Jiří (advisor)
The subject of the bachelor’s thesis was the study of selected bacterial strains by a selected method of atomic force microscopy. Thermophilic purple bacteria – Rhodoblastus acidophilus, Rhodobaca barguzinensis – were investigated. The main aim of this theses was focused on optimizing the usage of this microscopic method for imaging in an aqueous environment with the most appropriate fixation of sample. Focusing on bacterial strains demanded to preserve the viability of microorganisms and to observe optimal conditions for maintaining the native state during the measurement process. Furthermore, mechanical properties were evaluated – Young’s modulus and adhesion. The morphology of individual samples was compared for samples of the same species in different pH liquid environments and in environments with different concentrations of dissolved NaCl salt. The ability to produce PHA granules in purple bacteria was also targeted, however, due to the absence of first-class PHA synthase, PHA was not detected. The effects of different cultivation parameters such as different cultivation time or different pH of the environment were compared. Imaging of bacteria was carried out using the SNL-10 tip, which is suitable for bacterial samples in a liquid environment, and the measurement itself was carried out in QITM mode. A glass substance covered with a layer of Poly-L-lysin was used for immobilization. Finally, the mechanical properties were evaluated through Young’s modulus and adhesion for samples with various environmental factors.
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Investigation of transport processes in humic systems using computer modelling
Zeman, Matěj ; Sedláček, Petr (referee) ; Smilek, Jiří (advisor)
This bachelor’s thesis deals with issue of humic acid diffusion. The main goal of this work is to obtain a simple mathematical model that simulates the dialysis of a dye and humic acid and thus to investigate the bonding properties of humic acids as a sorption agent. This model was simplified enough to be used as a basis for the next modelling. The COMSOL Multiphysics program was used to create the model, especially the „Transport od Diluted Species“ and „Chemistry“ modules, which enable simulation of the mentioned processes. The results showed that it is possible to monitor dialysis over time using this model and at the same time the sorption properties of these substances can be observed.
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Preparation and characterisation of polysaccharide hydrogels
Kulíšková, Kateřina ; Kadlec, Martin (referee) ; Smilek, Jiří (advisor)
This bachelor thesis deals with the study of preparation and characterization of alginate hydrogels. It focuses mainly on the ionic crosslinking of alginate using divalent metal cations Ca2+, Cu2+, Zn2+, Ba2+, Fe2+ together with the trivalent cation Fe3+ in order to compare the crosslinking abilities of different oxidation states. The exogenous method was used for the preparation of alginate hydrogels and the prepared hydrogels were thus studied in the form of millimetre spheres. In the experimental part, optimization was performed to find out the optimum gelation time, which resulted in the crosslinking of the hydrogels throughout their volume. Ca2+ ions were used as a reference due to their wide application and the extensive experience with these ions at the faculty. The knowledge from the optimization was applied to the preparation of the other ions samples. The viscoelastic properties of the hydrogels were investigated by rheological measurements in the form of amplitude and squeeze tests. All ions, except Fe2+, were found to crosslink the hydrogels throughout the volume. Based on the complex modulus, the order of ions was determined according to the degree of crosslinking, The degree of crosslinking also has major impact on the degree of syneresis.
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Gel-forming substances of natural cosmetics
Prokopová, Pavla ; Smilek, Jiří (referee) ; Pekař, Miloslav (advisor)
This bachelor thesis is focused on hydrogels preparation for natural cosmetics also it focused on those prepared hydrogels. The aim of the experimental part is to specify physical and chemical properties of hydrogels prepared from commercially available polysaccharides, which agree with conditionals of natural cosmetics standards. First phase of practical part was to prepare and optimize the preparation procedure of individual hydrogels and determine their optimal concentration for use in their characterization. The second phase was the actual preparation of samples for rheometric determination. The last stage was the rheometry itself. The four raw materials selected directly from the CPK Standards were xanthan gum, guar gum, tragacanth gum and gum arabic. The results clearly demonstrated that the best raw material for the preparation of natural hydrogel is xanthan gum. On the other hand, hydrogel from gum arabic is almost impossible to prepare.
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Polyvinyl alcohol hydrogels with gradient structure in crosslinking density
Ščotková, Romana ; Kalina, Michal (referee) ; Smilek, Jiří (advisor)
The presented thesis introduce one of the many possibilities for the physical preparation of PVA hydrogels with a gradient in the crosslinking density. Based on the research conducted, the main focus of which was the preparation methods of gradient hydrogels and the characterization of their properties, a cyclic freezing and thawing method was selected and optimized with a focus on the selected preparation parameters. The next step was to perform pilot experiments leading to the confirmation and characterization of the resulting gradient structure by selected instrumental techniques such as rheology, scanning electron microscopy or a method based on monitoring the loss of dispersion during drying of the samples. In addition to the confirmation of the gradient structure, one of the parameters studied was the effect of the addition of polysaccharide on the resulting mechanical properties. Gradient hydrogels with different molecular weights or biopolymer additions were compared in the second part of the experimental work based on diffusion experiments using methylene blue. At the end of the work, all the results obtained were discussed and additional measurements were proposed for a deeper understanding of the subject.
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Rheological characterization of polysaccharide gels with incorporated vesicles
Kalendová, Lucie ; Smilek, Jiří (referee) ; Venerová, Tereza (advisor)
This diploma thesis deals with the rheological characterization of polysaccharide gels with incorporated vesicular systems. Positively charged Ion Pair Amphiphile vesicles (IPA) consisting of cetrimethylammonium bromide, sodium dodecyl sulfate, dioctadecyldimethylammonium chloride and cholesterol were chosen for the incorporation. Other vesicles used for incorporation were oppositely charged liposomes made of phosphatidylcholine (DPPC), phosphatidic acid (PA) and cholesterol. The thesis is divided into two sections. The first one deals with preparation, characterization and stability control (temperature and time stability) of both vesicular systems by using dynamic light scattering (DLS). In this part, the vesicles’ stability was confirmed which made them perfect candidates for the following incorporation. The second part of the thesis describes the preparation and rheological characterization of selected gels. Three types of gels were prepared in total, specifically 1% and 2% gellan gum gels and 4% hyaluronic gel. All of them were studied in water, as well as in solutions of IPA vesicles or DPPC liposomes, both of same concentration (1 mmoll-). The subsequent rheological characterization including amplitude, frequency, and stress relaxation sweeps demonstrates there is no significant difference between reference gels and those containing vesicles. This indicates that vesicles used in this thesis were only freely stored in the gel networks, meaning the structure of the gels didn’t affect their transport properties. This is a significant information for using these systems in drug delivery.
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Alternative crosslinking methods for sodium alginate resulting in hydrogels with suitable application properties
Kouřilová, Ludmila ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
This diploma thesis is focused on the preparation of alginate gels with the potential to influence their final application properties (transparency, syneresis, viscoelastic properties, etc.). Based on literature review, a total of three gelation strategies leading to the gelation of sodium alginate were selected, namely ionotropic gelation by external gelation method, ionotropic gelation by internal gelation method, and alginate crosslinking with phytic acid, which is capable of forming both ionic bonds and intramolecular hydrogen bonds. Subsequently, the preparation of alginate gels was optimized, their mechanical properties were characterized, and finally, the influence of several factors (polymer concentration, amount of crosslinking agent, gelation time, addition of sucrose, etc.) on the resulting properties of the prepared gels was monitored. Within the scope of the thesis, it was demonstrated that the resulting properties of sodium alginate-based gels are influenced not only by the polymer concentration, the amount of crosslinking agent used, gelation rate, or syneresis, but in the case of ionotropic gelation by external gelation, for example, also by the type of anion used. An interesting part of the thesis is also the optimization of determining the mechanical properties of alginate gels through compression tests. During these tests, the sample is compressed between two rheometer sensors, and the mechanical response of sample to the applied force is measured. It is one of the most easily conceivable rheometric tests.
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Micro/macro-scale investigation of the viscoelastic properties of hydrogel materials
Obrusníková, Klára ; Pekař, Miloslav (referee) ; Smilek, Jiří (advisor)
Tato diplomová diplomová práce byla zaměřená na srovnání mezi mikroreologickými metodami a makroreologickým přístupem, zejména při charakterizaci hydrogelů. Dynamický rozptyl světla, fluorescenční korelační spektroskopie a optická pinzeta byly vybrány jako mikroreologické techniky, zatímco oscilační reometrie sloužila jako makroreologický nástroj. Výsledky z dynamického rozptylu světla a fluorescenční korelační spektroskopie pro hydrogely agarózy a gellanu byly porovnány s reometrií a mezi sebou. Hodnoty viskoelastických modulů získané z mikroreologických měření byly výrazně nižší než ty získané pomocí makroreologie. Jak dynamický rozptyl světla, tak fluorescenční korelační spektroskopie nabízejí širší škálu měřitelných frekvencí než reometrie, ale obě metody mají své limitace při charakterizaci hydrogelů. U dynamického rozptylu světla dochází k odrazu světla od gelové sítě, což způsobuje šum a zhoršuje kvalitu získaných výsledků. Fluorescenční korelační spektroskopie, přes svou vyšší specifitu, vykazuje jen velmi malé rozdíly mezi vzorky různých koncentrací. Optická pinzeta je na Fakultě chemické novou metodou, a byla provedena pouze kalibrační měření. Tuhost optické pasti, důležitá hodnota pro kalibraci optické pinzety, byla stanovena pro roztoky glycerolu.
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Controlled modification of tips usable for selected measurement modes of atomic force microscopy
Lišková, Kateřina ; Szabová, Jana (referee) ; Smilek, Jiří (advisor)
This master's thesis deals with the modification of tips commonly used in atomic force microscopy and their following utilization for determining the mechanical properties of selected hydrogel systems at the local level. For targeted modification, a method of micro-particle fixation on a cantilever was chosen, which was successfully modified using melamine resin particles. Initially, the mechanical properties of a selected representative of physically cross-linked hydrogels (agarose polysaccharide) were measured, which were evaluated based on the Young's modulus of elasticity, adhesive force, and work. The obtained results were compared with values measured using two commercially available cantilevers differing in both shape and basic parameters such as spring constant and resonance frequency. Subsequently, the influence of the setpoint force applied to the sample by the cantilever was verified. The usability of modified cantilevers was also tested on a selected representative of ionically cross-linked hydrogels (sodium alginate cross-linked with multivalent ions). Within the experimental part of the master's thesis, it was verified that the use of cantilevers with a higher contact area leads to more reliable results in terms of reliability and reproducibility, considering that the final value of the Young's modulus includes not only the contribution of the polymer chain but also the pores. When determining mechanical values, it is important to specify not only the cantilever used and its properties but also all other experimental parameters, the change of which may affect the final values of the Young's modulus determined at the micro level by atomic force microscopy.
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