|
|
: Viscoelasticity of bones - the methodology of measurement
Cihlář, Zdeněk ; Ďoubal, Stanislav (advisor) ; Kuchařová, Monika (referee)
Charles University in Prague, Faculty of Pharmacy in Hradec Králové Department of biophysics and physical chemistry Candidate: Mgr. Zdeněk Cihlář Supervisor: Prof. RNDr. Ing. Stanislav Ďoubal, CSc. Title of Thesis: Viscoelasticity of bones - the methodology of measurement The aim of the thesis was to verify the methodology of measuring the viscoelastic parameters of human bones using an apparatus enabling the measurement of dynamic characteristics. The method is based on measurement of deformation response of samples to short or rectangular impulse of force. The samples were obtained from femoral head. The methodology is therefore based on measuring of creep curves and impulse characteristics. Resulting damped oscillations were analysed. The transient and impulse characteristics in bending stress and twisting stress were obtained. Based on these characteristics, viscoelastic parameters of samples were determined (Young modulus, shear modulus and viscosity). The Poisson's number, indicating the ratio of transverse contraction to longitudinal extension of the material during deformation, was calculated using the values of Young's modulus and shear modulus. The measured values of the Young's modulus in bending stress vary in the range from 62MPa to 670MPa. The values of the shear stress modulus range...
|
|
|
Utilization of interfacial rheology to study of biological systems
Kachlířová, Helena ; Kalina, Michal (referee) ; Smilek, Jiří (advisor)
The aim of this bachalor thesis is to implement and optimization a relatively new method of interfacial rheology. The optimization of this method was realized on two types of interfaces, specifically liquid-liquid using immiscible systems water-chloroform and water-toluene, and water-air. The applicability of this method was tested by using real samples in form of surfactant septonex and biological system represented by protein (bovine serum albumin). The interfacial layers formed by septonex were purely viscous, where the rigidity of the layer increased slightly with concentration until reaching critical micellar concentration and then the rigidity decreased. In comparison with septonex, the interfacial film made of bovine serum albumin showed predominantly elastic behaviour.
|
|
|
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
|
|
|
Rheological characteristics of untreated and thermally modified wood under long-term loading in bending
Berková, Tereza ; Borůvka, Vlastimil (advisor) ; Ruman, Daniel (referee)
Heat-treatment belongs to the most ecological methods of wood preservation methods and increase of its natural stability in exposition to outdoor conditions. Research of mechanical properties opens new possibilities of thermowood usage in general.
Wood appertains to viscoelastic materials and due to long-term loading creeps. There currently rise both elastic deformation, deformation elastic in time and plastic deformation. Partially there are irreversible changes due to stress even after unloading.
This work presents first insight to the matters of thermowood rheology and inspects its behavior under long-term loading in bending. This paper compares ratio of these three types of deformation in untreated wood and thermally modified wood in seven different temperatures (140; 160; 180; 190; 200, 210°C). The samples were exposed to 600 hours applied loading covering 40% of ultimate stress (modulus of rapture). Test were performed under constant conditions in special creep units in conditioning kiln. Increasing deformation under constant load was analyzed by Burger rheological model.
The results show that samples treated under lower temperatures (140 and 160°C) exhibit greater creep than untreated wood. This result is positive for structural usage of wood. On the other hand the samples treated under higher temperatures levels (200 an 210°C) display deterioration of mechanical properties. This is due to changes in wood structures caused by heat-treatment.
The most important impact of this work goes to future research of this field. Next development has to apply for the best quality of samples and also select rather prismatic parallelism than transversal one. Also application of 40% ultimate stress loading appeared as too high and together with wood defects led to destruction of samples.
|
|
|
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.
|
|
|
Kinetics Studies of Collagen I Self-Assembly
Voldánová, Michaela ; Ondreáš, František (referee) ; Jančář, Josef (advisor)
Collagen, the most abundant protein of connective tissues, in various forms has a wide applications due to their diverse biological and chemical properties. One of the forms are collagen hydrogels, which are considered very suitable material for applications in tissue engineering, because they are able to provide biodegradable scaffolds that its properties correspond with living tissues. These systems are used for example as scaffold for targeted drug delivery with controlled release, in combination with cells can be used for the regeneration and reconstruction of tissues and organs. Heating the aqueous solution of collagen leads to spontaneous self-assembly process to variously distributed fibrillar structures, which are at a later stage of fibrillogenesis prerequisite for creating a three-dimensional supporting network, which is the basic building block of the gel. The resulting properties of the hydrogel depend not only on its structure, but also on the conditions which cause self-assembly process. Hydrogels were performed at 37 ° C and physiological pH. Studied structural variable was the concentration of collagen. So far, for the research of self-assembly were used spectrometric methods, which only provide information about kinetics of morphogenesis. In this work to study the kinetics of collagen I self-assembly were used rheological methods, which additionally give information about viscoelastic properties of the resulting material. The obtained experimental data confirmed two-step process of collagen I fibrillogenesis consisting of nucleation and growth process. Rheological hydrogels collagen behaved as a nonlinear yield-pseudoplastic. An attempt was made to molecular interpretation of the results. Using two-parametric Avrami equation was determined the rate of self-assembly for each concentration of collagen and the value of Avrami exponent determining the shape of produced units. The prepared hydrogels were subjected to increasing shear stresses (strain amplitude, shear rate). Larger amplitudes leads to collapse of the hydrogel structure, which is able to again partially regenerated.
|
|
|
Design of manufacturing technology for plastic hung
Popelka, Jan ; Kebrle, Ondřej (referee) ; Kandus, Bohumil (advisor)
The aim of my graduation theses is to work up the literature search of polymer processing. To give a short summary of their structure, characteristic and fabrication technique. Then to make a structural design of injection mold for producing the scheduled aim and motivate this design with requisite calculation for construction of the tool, a choice of injection machine and rundown of injection cycle. At the end of my work is this aim economically reviewed and compared with alternative form of structural design.
|
|
|
Passive microrheology of colloidal systems based on biopolymers.
Bjalončíková, Petra ; Burgert, Ladislav (referee) ; Mravec, Filip (advisor)
Diploma thesis was aimed to deal with evaluation of microrheology method in the research of biopolymer-protein. Used biopolymer was sodium hyaluronate and proteins were trypsin and chymotrypsin. For measuring of microrheology were used particles with different radius (0,5 m and 1 m). It was found, that both substances have viscous charakter. Passive microrheology is suitable for measuring the viscoelastic properties of biopolymers.
|
|
|
Effect of metal ions on the rheological behaviour of polyelectrolyte solutions
Lišková, Kateřina ; Běťák, Jiří (referee) ; Janeček, Jiří (advisor)
This diploma thesis is focused on two parts. The first one deals with rheological behavior of sodium carboxymethylcellulose (CMC-Na) solutions in the presence of sodium and calcium ions. The solutions of various concentrations were prepared by solubilization in aqueous solutions of NaCl or CaCl2. The effect of monovalent and bivalent ions on apparent viscosity and viscoelastic properties of these solutions was studied. It was found that in the case of low concentrations of CMC-Na in the sample (up to 0.5% w/w) the elastic character increases. At the same time the stiffness of the sample is higher with higher concentration of calcium ion in the solution. This increase might indicate the formation of gel network. On the other hand the viscosity of these solutions decreases with higher concentration of calcium ions. In case of solutions with concentration higher than 1.5% w/w changes of viscosity did not happen by influence of addition ions. Rheological behavior was compared also with solutions prepared without adding an electrolyte as well as with acid form of carboxymethylcellulose (CMC-H). In terms of second part the molecular dynamic simulations of hyaluronan tetramer both sodium and calcium in aqueous medium were performed. Structure and arrangement of water molecules in the surrounding of hyaluronan chain were studied. Structure was described by formalism of radial distribution functions. In the case of system containing sodium ions only, the obtained results are in accordance with earlier published data. Presence of calcium ions does not cause qualitative changes during the radial distribution functions in comparison with the system with sodium ions.
|
|
|
Influence of strain rate on stress-strain dependencies of aortic tissues
Slažanský, Martin ; Fuis, Vladimír (referee) ; Burša, Jiří (advisor)
The thesis deals with the influence of strain rate on stress-strain dependencies of aortic tissues to estimate the error of hyperelastic models, which are neglecting the viscoelastic effects that are typical for soft biological tissues. It was found by the experiment and the subsequent evaluation that in the range of the strain rate from 0,167 to 5,000 mm/s the influence of strain rate on stress-strain dependencies is negligible. The deviation by transition from experimental data to a constitutive model was significantly larger than the deviation between the data sets varying at different strain rates, which means that the use of stress-strain curves varying at different strain rates in given range of the strain rate has no effect on the resulting model. The best of analysis models that were examined in this thesis appears to be the Yeoh hyperelastic model using the FEM.
|
guest ::
