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Preparation and characterization of polysaccharide hydrogel systems with gradient structure
Škutová, Patricie ; Krouská, Jitka (referee) ; Smilek, Jiří (advisor)
This bachelor thesis deals with the preparation of polysaccharide hydrogels with a diffusion gradient and their subsequent characterization in terms of viscoelastic properties, which are used to demonstrate the gradient structure. The main goal was to select a suitable method for the preparation of chitosan hydrogels with different molecular weights (168 kDa - 437 kDa). The biopolymer chitosan is a cationic polysaccharide that is suitable for use in biomedical applications due to its excellent biocompatible properties. First, concentration-uniform hydrogels without gradient structure were prepared, in which the influence of various parameters (chitosan molecular weight, chitosan concentration, sodium hydroxide concentration) was investigated. To prove the created gradient structure, the samples were subjected to the drying method (determination of the dispersion fraction) and determination of mechanical properties by oscillatory rheometry. Increased attention was paid to the search for a suitable preparation method for gradient chitosan hydrogels with higher molecular weight, which showed some problems with the already established method of preparation of hydrogels with gradient structure controlled by diffusion. From the results of the measurements obtained, it can be concluded that the viscoelastic properties of the hydrogels can be modified by changing the selected parameters and the method of preparation. By the controlled diffusion method, it was possible to prepare hydrogels with a gradual gradient of cross-linking density, which confirmed the assumption that the more cross-linked the layer, the higher the values of viscoelastic moduls and therefore the higher resistance to stress was confirmed.
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Biodegradable thermoplastics from renewable resources
Březinová, Štěpánka ; Kučera, František (referee) ; Petruš, Josef (advisor)
The theoretical part of diploma thesis summarizes the state of the art in the field of biodegradable thermoplastic materials, emphasizing polymeric materials made from renewable sources and the possibilities for their processing and for the modification of their useful properties. The experimental part of the thesis is focused on the preparation and characterization of biodegradable polymer blends based on thermoplastic starch (TPS) and poly(butylene adipate-co-terephthalate) (ECX). A suitable type of TPS was selected according to the rheological behavior of the melt for blending with ECX via extrusion technology. The degree of compatibility between TPS and ECX was evaluated by infrared spectroscopy (FTIR-ATR) and by examining the morphology of TPS/ECX blends using scanning electron microscopy (SEM). Affecting the mechanical properties, rheological behavior, and wettability of the prepared TPS/ECX was verified by testing the mechanical properties under tensile stress, determining the melt flow index (MFI), employing the oscillatory rheological test, and determining the maximum wettability. The experimentally obtained results show the possibility of optimizing the mechanical and rheological properties of TPS by blending with ECX. In terms of biodegradability, blends with a majority TPS content can be assumed to be more advantageous.
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The long-term stability and properties of a skin cream with addition of liposomes
Müllerová, Kristýna ; Pekař, Miloslav (referee) ; Enev, Vojtěch (advisor)
The aim of the thesis was to design a formulation and subsequently prepare a native skin cream and skin creams enriched with liposomal particles with encapsulated vitamin E. After preparation of the skin creams, their stability and rheological properties were studied at given time intervals during storage for 12 weeks. The stability of the prepared samples was determined using a LUMiSizer analytical centrifuge with STEP-Technology. Among the rheological properties, changes in the rate of structure recovery of the formulations were monitored, as well as changes in zero and infinite viscosity, which can be presented as changes in viscosity during product storage and changes in viscosity during application and spreading on the skin. All stability and rheological tests were performed for a temperature of 25 °C, which also corresponded to the storage temperature, and for a temperature of 37 °C, which approximately corresponds to the human body temperature. According to the results, the sample without the addition of liposomes showed the highest stability and the skin cream with the addition of 10 wt.% liposomes at 1 week of age showed the best spreadability. Next, the characterization of liposomal particles was performed. Finally, a sensory analysis was performed where the evaluators compared the fresh native skin cream, the native skin cream at 12 weeks of age, the fresh skin cream with the highest liposome content and the skin cream with the highest liposomal particle content at 12 weeks of age.
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Effect of different type and crosslinking density of polyethylene glycol hydrogels on transport and sorption properties
Janáková, Kristýna ; Pekař, Miloslav (referee) ; Krouská, Jitka (advisor)
The main goal of this work was to study the transport and sorption properties of polyethylene glycol (PEG) hydrogels with different types and densities of cross-linking. Before characterizing these properties it was necessary to optimize the preparation of selected hydrogels including the study of mechanical properties using rheological measurements. A significant part of the work, therefore, consists of the optimization of PEGDA-thiol hydrogels created from 4-arm polyethylene glycol-thiol (PEG-4SH) and polyethylene glycol diacrylate PEGDA by step-growth polymerization. To compare the transport and sorption properties of another type of crosslinking, PEGDA hydrogels were prepared using radical polymerization. In the transport experiments, the sorption and desorption of the Rhodamine 6G dye were monitored using free diffusion. Molecular absorption spectrometry (UV/VIS) was used to characterize the course of these experiments. The structure of these gels was compared using scanning electron microscopy.
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Characterization of Mechanical Properties of semi-IPN Hydrogels Based on Poly(vinylalcohol)
Přibyl, Jiří ; Pekař, Miloslav (referee) ; Kalina, Michal (advisor)
This diploma thesis deals with the issue of mechanical properties of semi-IPN hydrogels based on poly(vinylacohol). The prepared poly(vinylalcohol) hydrogels were modified by the addition of sodium alginate, dextran, DEAE-dextran, chitosan, and poly(ethyleneglycol). The mechanical properties were studied by various methods, such as the oscillatory amplitude rheological test, dynamic mechanical analysis, swelling experiments and drying characteristics. Microcalorimetry was used to study the interactions between poly(vinylalcohol) and biopolymers in solution using the ITC method and the morphology of prepared hydrogels was visualized using cryo-SEM. The main concept for semi-IPN hydrogels is that there is minimal influence on the mechanical properties but leads to the modification of the binding sites present in the hydrogel structure, which has a high potential in transport properties. From the experimental results, the effects of each biopolymer on the mechanical properties were determined. The obtained results showed that the additions of biopolymers do not have a significant impact on the mechanical properties of PVAl hydrogels, but in the case of swelling experiments, there is a significant influence of the number of freezing/thawing cycles, ionic strength of the environment, and the used biopolymer.
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Simulation of nonlinear response of construction materials and problem of identitifaction of material parameters
Hokeš, Filip ; Kala, Zdeněk (referee) ; Krejsa,, Martin (referee) ; Kala, Jiří (advisor)
The issue of parameter idenetification within numerical simulations can be considered a necessary step in the use of mathematical models, such as complex material models of building materials utilized in finite element method. The problem is particularly epmhasized in the case of anisothropic materials but also in the case of concrete, which behaves differently in tension and compression and which shows different response under rapid-dynamic and long-term loading. Correct capture of the concrete response in the computation requires usage of plasticity theory, damage theory, visco-elasticity and visco-plasticity or their mutual combinations. It results in development of material models and rheological schemes with large amount of parameters that are not commonly available in standards. The disseration presents application of meta-heuristic algorithm Particle Swarm for parameter identification. The success of the method is demonstrated in a pair of cases, first on the identification of elastoplastic material model parameters from stress strain diagram and then to identify the values of stiffness constants and viscosities of the rheological scheme from a creep curve.
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Correlation between the onset of beadless character of nanofibrous webs and rheological characteristics of electrospun polymer solutions
Zelenková, Jana ; Peer, Petra ; Filip, Petr
An overwhelming majority of applications of nanofibrous webs requires sufficiently smooth character of nanofibres surface. This character is apart other parameters strongly influenced by a concentration of chosen polymeric material in the solvents. Qualitative attributes roughly depend on the prepared concentration, specifically whether it belongs to one of the four basic regions: dilute, semidilute unentangled, semidilute entangled and concentrated. A concentration separating the latter two regions is often taken as a zero-th approximation indicating an onset of beadless nanofibrous webs. The present contribution uses as a more precise indicator behaviour of so-called phase angle relating viscous and elastic moduli, in other words mutual participation of viscous and elastic components. To this aim three frequently used polymers were used: copolymer of poly(vinylidene fluoride) and hexafluoropropylene (PVDF-co-HFP), poly(ethylene oxide) (PEO) and poly(vinyl butyral) (PVB). For materials exhibiting first a constant behaviour or moderate decrease in a phase angle for lower concentrations, an approximation of the starting concentration is given by a concentration value where a phase angle curve starts to decrease, apparently reflecting a more progressive viscoelastic nature. As shown, such approximation provides relatively very good approximation enabling to eliminate a traditional trial-and-error method.
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Polysaccharide gels in medical applications
Svitačová, Denisa ; Kadlec, Martin (referee) ; Venerová, Tereza (advisor)
This bachelor thesis deals with the performance of hydrogels containing polysaccharides, their characterization and reproducibility of the preparation of these gels, which is described in the literature. Based on the research, suitable polysaccharides, namely guar and gellan gum, were selected. Subsequently, an article was selected, the procedure of which was reproduced. Calcium chloride was used as a crosslink agent in the mixture of guar gum and gellan solution. Problems appear in the reproducibility of the article which did not allow the exact repetition of the hydrogel preparation procedure described in the article. Based on the findings, an optimized range of mixtures with various other gelling agents was developed. The individual prepared materials were suitably characterized by rheological tests. Specifically, amplitude tests, the results of which proved the formation of a three-dimensional network in their structure, and thus the formation of hydrogels. Frequency tests were used to determine their mechanical properties.
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Transport Properties of Gellan Hydrogels
Sokolínský, Jan ; Sedláček, Petr (referee) ; Kalina, Michal (advisor)
This bachelor thesis deals with the characterization of mechanical and transport properties of gellan based hydrogel systems. As gellan gum is a biopolymer, hydrogels based on this biopolymer are suitable candidates for use in the pharmaceutical industry and medical applications. The characterization of mechanical properties was realized by rheological analysis and by drying scales, transport properties were characterized by diffusion experiments in combination with the detection using UV-VIS spectrometry. The result of this work is a comparation and commentary of the measured data, in order to provide an overview of the properties of physical gellan gum hydrogels. It was found out that by changing the concentration of the biopolymer and by a suitable selection of the dispersion medium, transport, and mechanical properties of the physical gellan gum hydrogels can be modified.
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Corelation of transport and viscoelastic properties of hydrogels with diffusion gradient
Ščotková, Romana ; Sedláček, Petr (referee) ; Smilek, Jiří (advisor)
The aim of the presented bachelor thesis was to prepare hydrogels with diffusion gradient and to demonstrate the gradient structure of hydrogels in terms of viscoelastic and transport properties. With regard to potential biomedical applications, the cationic polysaccharide chitosan was selected for the preparation, especially for its antimicrobial and biocompatible properties. The resulting gradient hydrogels were subsequently characterized by oscillation tests to observe the differences using different concentrations and molecular weights of chitosan, crosslinking agent concentrations, dispersion environments for chitosan dissolution, and different gel crosslinking times. The samples were also subjected to drying experiments to confirm the gradient structure formed. The ability of the hydrogels to transport the active species was confirmed by visually evaluating the permeation of the anionic dye (bromothymol blue) during the gelation process. From the results obtained during the experimental part of the bachelor thesis it can be concluded that the viscoelastic properties of hydrogels can be modified by changing selected parameters during the preparation itself. It was also confirmed the assumption that with better mechanical properties of hydrogels there is a deterioration of transport properties. By controlled diffusion method, it was possible to prepare a hydrogel with a gradual gradient of crosslinking density, thus modifying the viscoelastic and transport properties.
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