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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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Optimization of hydrogel carrier for assessment of antimicrobial activity of biocidal surfaces
Antálek, Adam ; Jančovičová, Viera (referee) ; Králová, Marcela (advisor)
This diploma thesis deals with the optimization of the composition and properties of hydrogels as carriers of microbial populations for the evaluation of the antimicrobial effects. There are standardized procedures for assessing antimicrobial surfaces, but they have shortcomings, such as the necessity of testing exclusively under laboratory conditions. In the presented work, a new evaluation methodology is proposed, which utilizes a modified resazurin test and hydrogels as platforms for bacterial seeding, enabling the assessment of the investigated antimicrobial surface. The composition and properties of hydrogel carriers were successfully optimized with respect to their swelling and mechanical properties, thereby improving recovery compared to standardized procedures. Tests on antimicrobial materials showed that the bacteria used on hydrogels continued to grow, rendering the use of composite hydrogels for this application impractical.
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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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Transport and mechanical properties of hybrid hydrogel networks based on gellan
Sokolínský, Jan ; Pekař, Miloslav (referee) ; Kalina, Michal (advisor)
This diploma thesis deals with the characterization of the mechanical and transport properties of gellan based hybrid hydrogels. As part of this work, the process of optimizing the preparation of gellan-poly(vinylalcohol) IPN hydrogel was first studied with an emphasis on the repeatability of the preparation due to the preservation of mechanical properties of the hydrogel. Then, both on the gellan hydrogels themselves and on selected IPN compositions, the effect of various additives was studied (specifically, the effect of the addition of a plasticizer and the effect of cross-linking by polyvalent ions). Based on these tests, a set of samples was selected, on which dynamic mechanical analysis, swelling and drying experiments were additionally measured. At the end of this diploma thesis, the transport properties of selected hydrogel compositions were also studied. The tests conducted in this thesis revealed that both the formation of a dual network and the addition of the mentioned additives allow us to influence the studied properties.
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Hydrogels modified by amphiphilic structures
Heger, Richard ; Sedlařík, Vladimír (referee) ; Kráčalík, Milan (referee) ; Pekař, Miloslav (advisor)
The submitted dissertation deals with the influence of amphiphilic structures on hydrogel properties. Additions of various amphiphilic substances associated with the formation of highly ordered structures affect the mechanical, transport and structural properties of hydrogels. The main inspiration for this type of work was living tissue, more precisely the extracellular matrix, which is often mimicked by hydrocolloids, and its high orderliness is responsible for its unique properties. The knowledge obtained from this tissue was applied to the hydrogel systems studied in this work. Various cross-linked hydrogel matrices (physically cross-linked agarose and gelatin, ionically cross-linked alginate and chemically cross-linked mixture of polyvinyl alcohol and chitosan) were suitable representatives for this work. These hydrogel systems were modified by the addition of various amphiphilic substances. The human body’s own phospholipid, lecithin, or variously charged more classic surfactants (CTAB, SDS and Triton X-100). Experimentally, this work is divided into three areas, the study of mechanical properties using rheology, the description of transport properties via release and flow experiments using various model drugs (rhodamine 6G, eosin B, amido black 10B, methylene blue and riboflavin), and morphological characterization using SEM. The characterization of hydrogel systems was supported by other techniques used in this work, such as drying and swelling experiments or gas sorption.
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New Areas of the Ultrasonic Application in Microelectronics Technology
Buršík, Martin ; Pietriková, Alena (referee) ; Králová,, Iva (referee) ; Szendiuch, Ivan (advisor)
Doctoral thesis deals with the deposition of special thixotropic materials for microelectronic technology. The aim of the work is the development of the new method optimizing the dosing process in order to achieve a print resolution of better than 100 microns. The work includes the development of a special dispensing head (UZD) using the influence of ultrasonic energy. These results demonstrate the possibility of a newly developed method that is able to print thixotropic materials with a resolution of 65 microns. Compared to other methods achieves these results with the commonly used materials for thick film technology with particle size up to 5 microns.
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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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Viscosimetry of hyaluronan-amphiphile systems
Trojan, Martin ; Běťák, Jiří (referee) ; Chytil, Martin (advisor)
This bachelor thesis investigates the interaction between the polysaccharide sodium hyaluronate (HA) and some amphiphilic molecules. As amphiphilic molecules the aminoacids lysine and 6 – aminocaproic acids were chosen. The presence of the carboxylic group on HA and the aminogroup on the aminoacids suggests electrostatic interaction between these two compounds. This supposal offers the possibility to modificate HA and uses it as a new type of a carrier of bioactive compounds, for example medicals. The HA of two molecular weights (1.75MDa and 70kDa) were chosen for the study of the interactions with the aminoacids. Solutions of HA and stock solutions of the aminoacids were prepared for their mutual mixing in the various volume ratios. The solutions and the mixtures were measured in three types of environment: pure water, 0.15M solution of NaCl and in phosphate buffer (PBS) of pH 6. The interactions were investigated by means of reometry. Our results show, the presence of interactions between HA and the aminoacids mainly in the system consisting the 1.75 MDa HA and lysine in water. As a result of the interactions, a decrease in the viscosity of the mixtures comparing to the HA solutions was observed.
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