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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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Study of transport processes using microrheological techniques in hydrogels
Píšová, Denisa ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
This diploma thesis is focused on the determintaion of viscoelastic properties of agarose hydrogels containing different polyelectrolytes by microrheological and macrorheological techniques. From microrheological techniques the dynamic light scattering was used. Firstly, the influence of different polyelectrolyte volume was studied. Then the effect of variously charged polyelectrolyte and ionic strenght on microrheological properties of agarose hydrogels were determined. Classic rheology was used to compare the results obtained using the DLS microrheology method. Finally, the results from macro- and microrheology were correlated with each other.
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Development of New Application Forms of Humic Substances for Agricultural and Environmental application
Kratochvílová, Romana ; Kráčalík, Milan (referee) ; Salaš, Petr (referee) ; Klučáková, Martina (advisor)
The new forms of superabsorbent polymers (SAP) on the base of acrylic acid were developed and studied in this thesis. The SAP are focused on agricultural and environmental applications. While they are applied to the soil, SAP can prevent water losing and they become a reservoir of humidity in case of dry season, moreover in combination with fertiliser they play role of controlled release medium. Eight various samples of SAP were experimentally prepared by networking of partially neutralized acrylic acid. Potassium peroxydisulfate was used as the initiator and N,N–methylenebisacrylamide as the crossing agent. Some of samples contained addition of second monomer of acrylamide. All of them were enriched by fertilisers – natural lignohumate or synthetic NPK or combination of both. The swelling characteristics of prepared samples were investigated in conditions of various ionic strength. The influence of xerogels’ particles size on swelling properties was also observed. The viscoelastic characteristics of hydrogel form of all SAP were determined by using of rotation rheometer. The changing of viscoelastic properties were studied in dependence on time, on freezing and on repeating swelling cycles. On top of that the controlled releasing ability of SAP was tested due to three modelling experiments. The biological activity of all polymer products was tested at the end of the thesis. All samples of SAP were incorporated into the artificial soil and the ability of the water retention in the soil was observed. The growing experiments were running by using of corn plants. The size and the mass of each plant were measured and branching of the root was objectively evaluated by programme Harmonic and Fractal Image Analyzer.
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Targeted modification of transport and structural properties of biomedical hydrogels
Bayerová, Zuzana ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
The presented diploma thesis deals with a targeted modification of the structural properties of hydrogels, which is closely related to the application properties of these materials (eg transport). Due to the desired pharmacological applications of the use of these materials for targeted drug release, hydrogels based on chitosan and polyvinyl alcohol as substances with good biocompatibility were selected for the study. The combination of these polymers ensured swelling (controlled by the presence of chitosan) and viscoelastic (influenced by the presence of polyvinyl alcohol) properties, which were characterized by a wide range of analytical and physicochemical methods (swelling, tensile strength, rheology, atomic force microscopy or specific surface area, etc.). Information on structural properties played a crucial role not only for a detailed description of the studied materials in terms of whether the structural properties can be changed in a targeted manner, but also served as an explanation for the different release of the active substance diclofenac from the hydrogel matrix. With regard to the literature search, the effect of pH and crosslinking was chosen to modify the properties. From the measured results it was found that even a slight change in pH has an effect on the transport or release of the active substance. The results obtained in this work may be useful in the formation of hydrogel matrices with drugs depending on the intended medical applications.
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Study on kinetic stability of suspension with magnetorheological properties
Vlachová, Kristýna ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
Sedimentation in magnetorheological (MR) fluids is undesirable for many technological applications. For this reason, several ways have been proposed to prevent sedimentation instability. This thesis deals specifically with the addition of a suitable additive. The topic was examined based on available literature and according to it was suggested a procedure for the experimental part. Two types of MR liquids with different composition and preparation method were prepared. The first suspensions included a water-in-oil emulsion as a carrier liquid and Span 80 and Tween 80 as additives. For the second MR fluids, the continuous phase was a blend of bearing oils and the suspension was stabilized with organoclay. In both cases, carbonyl iron particles with a diameter of 1,8–2,3 µm were used. The kinetic stability of the prepared MR fluids was monitored and compared using an analytical centrifuge.
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Microrheology of Biocolloids
Hnyluchová, Zuzana ; Omelka, Ladislav (referee) ; Kráčalík, Milan (referee) ; Pekař, Miloslav (advisor)
The main aim of the doctoral thesis was study of passive microrheological techniques as advanced methods for characterisation of viscoelastic properties of soft material. These techniques are able to provide certain advantaged or additional information on classical rheology. Several techniques from the wide range of passive microrheological group such as one particle video – microrhelogy with IDL data procesing, microrheology based on light scattering – DLS or FCS microrheology have been applied in practice during my PhD studies. New Matlab script has been also invented to simply obtain information about viscosity of low volume samples. Aplicability of techniques were studied on several various bicolloids such as solutions or gels of hyaluronic acid, on study of properties at the interfaces or on gelation proces studies of agarose. Obtained data were compared classical rheology results. Suitability of each technique for investigated systems or appropriate reccomendations for further measurements were didcussed based on obtained data. Main advantages and limites of passive microrheology techniques were also described in comparison wih classical rheology method.
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Rheology as a powerful tool for the complex characterization of hydrogels
Kadlec, Martin ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
This diploma thesis investigates the suitability of relaxation tests as a part of complex characterization of hydrogel materials using classical rheology methods. With respect to the current research, creep and three interval thixotropy tests were taken into account. For them, general optimization was done aiming to find an ideal parameter settings. The optimization was performed using physically crosslinked agarose (AG) hydrogel and the tuned tests were also applied to two more samples: hyaluronan (HyA) and polyvinyl alcohol (PVAl) gel. These materials were selected due to their mutually different crosslinking principle. The experiments showed, the AG gel proved to have the best ability to recover after deformation of all studied samples. On the other hand, the HyA gel relaxed the worst. Although the final results of both tests were comparable, the regeneration process itself was different. Hence, the complex relaxation characteristics cannot be described using one of the performed tests alone and both the creep and three interval thixotropy tests have great importance in the scope of complex relaxation behaviour. The obtained results may lead to more precise description of deformation and relaxation, which are frequent phenomena occurring during treatment and application of hydrogel materials.
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Utilization of advanced rheological techniques for the study of biological systems
Krňávková, Šárka ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
A new method for determining viscoelastic properties on the interfacial interface called interfacial rheology was intoduced and investigated. Measured data were compared with data from tanziometer for model system of surfactant. Three concentration renge of surfactant, namely SDS (anionic), TTAB (cationic) and Tween (nonionic), were measured. From the measured data the influence of structure, critical micellar concentration and charge on the viscoelastic properties of the interfacial interface was determined. Furthermore, this new method was used for biological systems and specifically for biofilms of two bacterial strains. First, the viscoelastic properties of biofilms on the agar were determined, and the viscoelastic properties dependence on temperature
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Interfacial rheology as the effective tool to description of interfacial behaviour of biofilms
Kachlířová, Helena ; Kráčalík, Milan (referee) ; Smilek, Jiří (advisor)
The aim of this diploma thesis is to optimize a method of interfacial rheology for testing the interfacial behaviour of biofilms on the liquid-air interface and after that use the method for studying the biofilm formation under optimal and stress conditions. For studying the biofilm formation, Kombucha was used. It is a microbial culture forming a cellulose biofilm on the interface. As the stress conditions, reduction of sucrose concentration, change of pH and change of ionic strength was used. Next, the ability of regeneration of biofilm formed on the interface was studied. The biofilm formation was occured in all cases except of increasing ionic strength. As expected, the best biofilm biofilm growth was observed under optimal condition, which means a sucrose concentration 100 g/l.
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Physical hydrogels based on biopolymers and surfactants
Velcer, Tomáš ; Lehocký, Marián (referee) ; Kráčalík, Milan (referee) ; Pekař, Miloslav (advisor)
This doctoral thesis studies the properties and behaviour of phase-separated hydrogels. These can be prepared by interaction of polyelectrolytes with oppositely charged surfactants. Negatively charged polysaccharide hyaluronan and cationic surfactant carbethopendecinium bromide (Septonex), whose properties, behaviour and utilization are described in the first two chapters of theoretical part, were selected for this role. Hyaluronan is naturally-occuring in living organisms and is known for his specific targeting to the tumour cells. Septonex is used as antiseptic and disinfectant. Experimental part of this work is focused on examination of the structure and behaviour of these types of hydrogels especially from rheological point of view. The crucial part of this study was to establish mechanical properties and their dependence on environment. This led to design further studies. Structural analysis was held using the methods of ATR-FTIR, ionic chromatography and ICP-OES helping to measure the inner content of entry materials in the gels and supernatants respectively. The last chapter deals with antimicrobial activity. The results of this study indicate a potential usage of these substances in the field of medical applications.
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