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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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Production of extracellular polysaccharides by extremophilic prokaryotes
Bystrická, Klaudia ; Smilek, Jiří (referee) ; Obruča, Stanislav (advisor)
Predložená diplomová práca sa zaoberá štúdiom biotechnologickej produkcie extracelulárnych polysacharidov (EPS) vybraných termofilných a halofilných mikroorganizmov. Po primárnom screeningu vybraných kultúr bola experimentálna časť tejto práce ďalej venovaná halofilnému archea Haloferax mediterranei. Cieľom tejto práce bola produkcia a charakterizácia polymérov a posúdenie biotechnologického potenciálu použitých extremofilných kultúr ako producentov EPS. Počas kultivácie H. mediterranei boli použité 3 základné média, ktoré boli následne optimalizované v prospech produkcie EPS. Získané precipitáty boli podrobené analýze pomocou GPC, FTIR a UHPLC-UV-ESI-MS/MS, na základe čoho bolo možné bližšie charakterizovať získaný produkt. Tieto experimenty dokázali, že so stúpajúcou koncentráciou NaCl v médiu, klesá výťažok polysacharidov a ich produkciu nepodporujú ani vysoké koncentrácie MgSO4 a KCl v médiu. Hlavnou komponentou polysacharidov vyprodukovaných H. mediterranei, je manóza, no v závislosti od použitého média môže obsahovať aj glukózu, galaktózu, ribózu alebo N-acetylglukosamin.
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The influence of humic acids methylation on the interaction of surface active agents
Bělušová, Anna ; Weidlich, Tomáš (referee) ; Smilek, Jiří (advisor)
The presented diploma thesis deals with the study of interactions between humic acids as the main component of soil organic matter with a model organic pollutant presented by cationic surfactant Septonex (which was expected to interact positively with humic acids due to its charge) through unconventional combination of dialysis and diffusion techniques realized in diffusion cells together with isothermal titration calorimetry capable of elucidating the nature of ongoing reactions from a thermodynamic point of view. The experiments were performed with a humic acid isolated by standard isolation procedure from Leonardite (1S104H) purchased from the International Society for Humic Substances, with humic acids isolated from lignite as well as modal chernozem. The aim of the submited diploma thesis is to assess the influence of carboxyl functional groups in the structure of humic acids to interactions with Septonex. For this reason, said samples of humic acids have been modified by selective methylation of their carboxyl functional groups, which can no longer participate in interactions with ionic substances. Results from diffusion cells and isothermal titration calorimetry confirmed the assumption that Septonex interacted with all types of unmodified humic acids more than with their methylated derivatives. Despite the available literature, it was surprising that the differences in the interaction of humic acids with Septonex were not diametrically different when comparing unmodified humic acids with their methylated derivatives. The extent of these interactions was assessed through the apparent equilibrium constant Kapp determined in the diffusion (dialysis) experiments and from the course of enthalpy curves from isothermal titration calorimetry. After the experiments and their evaluation, it can be concluded that humic acids and Septonex in their interactions, due to their structures, probably apply not only electrostatic interactions, especially through available carboxyl functional groups of humic acids and positively charged hydrophilic parts of Septonex molecules, but also a significant role have a hydrophobic effect, hydrogen bonds and Van der Waals forces.
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Reactivity-mapping studies on biopolymers in hydrogel forms
Smilek, Jiří ; Kislinger, Jiří (referee) ; Sedláček, Petr (advisor)
The diploma thesis is focused on the study of interactions between biopolymers and model probes in a hydrogel media utilizing diffusion processes. The main aim was to test and to optimize selected combination of diffusion methods (diffusion cells and unsteady diffusion) in study of interactions between biopolymers and organic dyes. Anionic (humic acids) and cationic (chitosan) representatives of biopolymers were utilized and methylene blue and methylene orange were used as a reactivity probe in the case of humic acids and chitosan, respectively. Another appreciable part of the work is represented by in-depth characterization of applied biopolymers and hydrogel samples by a wide range of analytical and physico-chemical methods (rheometry, UV-VIS, FT-IR etc.). Besides particular experimental results on studied systems, the diploma thesis provides both theoretical and practical background for subsequent applications of the innovative and full-automated method for reactivity mapping of biopolymers.
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Study on relaxation properties of hydrogels using rheological techniques
Lorenc, Pavel ; Klučáková, Martina (referee) ; Smilek, Jiří (advisor)
Submitted bachelor’s thesis deals with the study of relaxation and time stress of viscoelastic substances (hydrogels) using selected rheological techniques, especially with regard to oscillation tests. Hydrogels with different types of crosslinking were prepared and their properties were compared during the measurement. Agarose hydrogels (physically), alginate hydrogels (physicochemically), polyvinyl alcohol hydrogels (chemically) and hyaluronic acid hydrogels (ionically). In this bachelor's thesis, methods for measuring the relaxation properties of these hydrogels using a rheometer were designed and subsequently applied. We examined the relaxation properties of hydrogels using time-dependent tests that examined changes in amplitude over time. We performed a test that had 3 intervals, in which we monitored the response of hydrogels to the changes by changing the amplitudes of deformation with time. The relaxation properties of these hydrogels were studied, which showed significant differences in the behavior of hydrogels in measurements.By these methods, it was found that the structure of hydrogels and concentrations have an influence on relaxation. From the measured results, it was shown that the best relaxing properties have chemically crosslinked polyvinyl alcohol hydrogel, the lowest ability to relax was shown by physico-chemically crosslinked alginate hydrogel.The results from the measured data were finally compared, assessed and commented on the differences between the individual hydrogels.
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Preparation of magnetorheological fluids with high sedimentation stability
Oharek, Lukáš ; Kalina, Michal (referee) ; Smilek, Jiří (advisor)
The introduced bachelor thesis focuses on the current issue of stability of magnetorheological fluids in the gravitation field. To prepare stable magnetorheological fluid, influence of additives, particles modification and different carrier fluid are investigated. Regarding the increased viscosity of the carrier fluids, which negatively affect the magnetorheological effect, a magnetorheological fluid containing carbonyl iron particles, which were chemisorbed with non-ionic surfactant Tween 20 was prepared. Mineral oil and water emulsions were used as a carrier fluid, emulsifier Span 80 was used to stabilize the water-in-oil emulsion. Sedimentation stability is improved, at the same time the viscosity of the carrier fluid is increased.
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