Viscoelastic methods (VEM) made available the bedside assessment of blood clotting. Unlike standard laboratory tests, the results are based on the whole blood coagulation and are available in real time at a much faster turnaround time. In combination with our new knowledge about pathophysiology of the trauma-induced coagulopathy, the goal-oriented treatment protocols have been recently proposed for the initial management of bleeding in trauma victims. Additionally, the utility of viscoelastic monitoring devices has been proved even outside this setting in cardiosurgical patients or those undergoing liver transplantation. Many other situations were described in literature showing the potential use of bedside analysis of coagulation for the management of bleeding or critically ill patients. In the near future, we may expect further improvement in current bedside diagnostic tools enabling not only the assessment of secondary hemostasis but also the platelet aggregation. More sensitive assays for new anticoagulants are underway. Aim of this review is to offer the reader a multidisciplinary overview of VEM and their potential use in anesthesiology and critical care.

• Klíčová slova
• coagulation, point-of-care testing, thrombosis, transfusion, trauma-induced coagulopathy, viscoelastic methods,
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

A new method to estimate the selected viscoelastic parameters of foods using damped vibration analysis is presented for the evaluation of fruits and baked products. A flat disk is attached to the flat sample surface using a laser rangefinder that measures the sample thickness in advance, and it is locked by a trigger. Next, the trigger is released to allow the probe to press the sample through the force of gravity. The damped vibration of the probe caused by the deformation of the food is measured by monitoring the displacement of the probe via a linear encoder. The bulk modulus and viscosity are estimated using the fractional Zener model and mass. Young's modulus (E) is estimated independently by determining the maximum velocity of the probe using Hooke's law. Poisson's ratio (ν), and the shear modulus and viscosity are calculated by employing the estimated E and bulk modulus. The bulk modulus, bulk viscosity, shear modulus, shear viscosity, and E of apples were found to be higher than those of bananas. The bulk modulus, bulk viscosity, E, and shear modulus for white bread were lower than those for pound cake, but the ν values were higher, whereas those of sponge cake were intermediate. After drying the baked products for 1 day, most of the parameters of the samples increased, but the value of ν for white bread decreased. The proposed free-falling device estimated the four viscoelastic coefficients, Poisson's ratio, and Young's modulus of the food sample in less than 1 s.

• Klíčová slova
• apple, baked food, banana, damped vibration, free-falling probe,
• MeSH
• modul pružnosti MeSH
• pružnost * MeSH
• viskozita MeSH
• Publikační typ
• časopisecké články MeSH

This study investigated an effect of different ways of the preparation of insoluble hyaluronan material on its mechanical and viscoelastic properties. Hyaluronan (NaHy) of molecular weight Mw=500,000 g mol(-1) was modified with N-(3-dimethylaminopropyl-N'-ethylcarbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS), to be able absorb liquid without changing its mechanical properties. The modified, water insoluble NaHy materials were prepared in different geometry; as modified films and modified cylinders with exact dimensions. The occurrence of modification was confirmed by FT-IR (Fourier transform infrared spectroscopy) and (1)H NMR (proton nuclear magnetic resonance) spectroscopy and swelling test. The determined mechanical and viscoelastic properties of unmodified and modified hyaluronan revealed the high dependency of elasticity changes depending on the gel processing method. Moreover, NaHy gels in the cylindrical form with the sponge-like structure predominant them as a convenient geometry for application in a humid environment.

• Klíčová slova
• Carbodiimide, Hyaluronan, Mechanical properties, Modification, Viscoelastic properties,
• MeSH
• ethyldimethylaminopropylkarbodiimid chemie   MeSH
• hydrogely chemie   MeSH
• kyselina hyaluronová chemie   MeSH
• pevnost v tahu MeSH
• protonová magnetická rezonanční spektroskopie MeSH
• pružnost * MeSH
• spektroskopie infračervená s Fourierovou transformací MeSH
• sukcinimidy chemie   MeSH
• viskozita MeSH
• voda MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• ethyldimethylaminopropylkarbodiimid MeSH
• hydrogely MeSH
• kyselina hyaluronová MeSH
• N-hydroxysuccinimide MeSH Prohlížeč
• sukcinimidy MeSH
• voda MeSH

INTRODUCTION: Major liver resections are associated with high morbidity and mortality. The main causes of this fact include a significant blood loss which may be associated with this surgical procedure. Hemocoagulation disorder, diagnosed by standard laboratory tests, is very frequent in the postoperative period and often requires the administration of blood derivatives. Several recent studies, however, have questioned the presence of such coagulopathy when viscoelastic methods are used to assess the coagulation process. The studies have concluded that that the coagulation disorder only exists at a laboratory level, the coagulation process itself being unaffected, and no therapeutic intervention is therefore needed. The use of viscoelastic methods may play a crucial role in deciding whether or not to correct the assumed coagulation disorder. METHOD: Our study was designed as a prospective observational study. Data were collected in the Surgical Intensive Care Unit during one year (1 January - 31 December 2016). The study included 18 patients who underwent major liver resection. When coagulation disorder was diagnosed using standard coagulation tests in the postoperative period, we performed a ROTEM examination. The results of the standard and ROTEM examination were then compared. RESULTS: Out of the total of 18 patients enrolled in the study, a coagulopathy was diagnosed in 15 cases (83%) using standard coagulation tests. In these patients, we performed rotational tromboelastometry (ROTEM) which did not show any coagulation disorder. CONCLUSION: Our study has demonstrated that when viscoelastic methods are used to evaluate the function of blood clotting in patients after major hepatic surgery, no coagulopathy has been found as opposed to the evaluation with standard blood clotting tests. Unnecessary transfusions of blood derivatives can be avoided as well as all risks linked to their administration. Viscoelastic methods of coagulation assessment (ROTEM, TEG) help provide a detailed insight into the coagulation process and our observations have shown that they should play a significant role in the postoperative assessment of patients following major hepatic resections.Key words: ROTEM - viscoelastic methods - coagulopathy.

• MeSH
• koagulopatie * MeSH
• krvácení MeSH
• lidé MeSH
• nemoci jater * chirurgie   MeSH
• prospektivní studie MeSH
• tromboelastografie * MeSH
• vyšetření krevní srážlivosti MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• pozorovací studie MeSH

This paper deals with the solution of the model equations, which describes the propagation of the surface Love-type waves in a waveguide structure consisting of a lossy isotropic inhomogeneous layer placed on a viscoelastic homogeneous substrate. The paper points to the possibility of using the triconfluent Heun differential equation to solve the model equation. The exact analytical solution within the inhomogeneous layer is expressed by the triconfluent Heun functions. The exact solutions are general in the sense that only the internal parameters of the triconfluent Heun functions can change the spatial dependencies of the material parameters in the inhomogeneous layer's thickness direction. Based on the comparison, the limits of the WKB method applicability are discussed. It is further demonstrated that substrate losses affect the dispersion characteristics only to a small extent. Using examples in which the surface layer is represented by functionally graded materials, it was shown that the distance between the modes can be influenced through those materials.

• Publikační typ
• časopisecké články MeSH

This study presents a microindentation system which allows spatially resolved local as well as bulk viscoelastic material information to be obtained within one instrument. The microindentation method was merged with dynamic mechanical analysis (DMA) for a tungsten cone indenter. Three tungsten cone indenters were investigated: tungsten electrode, tungsten electrode + 2% lanthanum, and tungsten electrode + rare earth elements. Only the tungsten electrode + 2% lanthanum indenter showed the sinusoidal response, and its geometry remained unaffected by the repeated indentations. Complex moduli obtained from dynamic microindentation for high-density polyethylene, polybutylene terephthalate, polycarbonate, and thermoplastic polyurethane are in agreement with the literature. Additionally, by implementing a specially developed x-y-stage, this study showed that dynamic microindentation with a tungsten cone indenter was an adequate method to determine spatially resolved local viscoelastic surface properties.

• Klíčová slova
• complex modulus, dynamic indentation, dynamic mechanical analysis, spatial resolution, tungsten cone indenter,
• Publikační typ
• časopisecké články MeSH

This study was conducted to determine the effect of 1-stage homogenization (OSH) and 2-stage homogenization (TSH) and the addition of polysaccharides [κ-carrageenan (CR) or furcellaran (FR) at levels ranging from 0.000 to 1.000% (wt/wt)] on the physicochemical, viscoelastic, and mechanical vibration damping properties of processed cheese sauces (PCS) after 30 d of storage (6 ± 2°C). The basic chemical properties (pH, dry matter content) were similar for all tested samples. Viscoelastic measurements indicated that PCS rigidity was directly proportional to increasing CR or FR concentration and to the application of homogenization. The interactions between the application of homogenization and the concentration of polysaccharides used were also significant. Compared with OSH, TSH did not lead to any further increase in the rigidity. The preceding results were also supported by data obtained from a nondestructive method of mechanical vibration damping. No changes in water activity were observed in any PCS sample. Overall, the addition of FR or CR appeared to be highly suitable for increasing the emulsion stability of PCS. If PCS products with softer consistency are desired, then a concentration of CR/FR ≤0.250% (wt/wt) could be recommended together with OSH/TSH. For products for which a firmer PCS consistency is required, the addition of CR in concentrations of ≥0.500% (wt/wt) or FR in concentrations of ≥1.000% (wt/wt) together with OSH is recommended. Finally, as the concentration of polysaccharides increased, a darker PCS color was observed.

• Klíčová slova
• furcellaran, homogenization, processed cheese sauce, rheological properties, κ-carrageenan,
• MeSH
• karagenan MeSH
• manipulace s potravinami metody   MeSH
• polysacharidy MeSH
• reologie MeSH
• sýr * analýza   MeSH
• thyreotropin MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• karagenan MeSH
• polysacharidy MeSH
• thyreotropin MeSH

The goal of the experiment was to develop an identification method capable of objective detection of changes of viscoelastic properties of skin with a scar remaining after a modified radical mastectomy. We compared the intact skin and the skin with a scar, a scar before and after physiotherapy. We used two methods. The first one is based on measurements of the local dynamic deformation response of the skin and the second one is the matrix identification of static deformation that identifies properties of the whole tested region of the explored tissues. We identified the skin stretchability, shiftability against deeper layers and deeply analysed both the methods. In some patients, we found statistically proven difference. In all these cases the measurement methods have detected changes of the observed tissue condition. We found both methods to be potentially applicable after further improvements as a diagnostic tool, which can contribute to the improvement of postoperative care of patients.

• MeSH
• biologické modely * MeSH
• jizva diagnóza   patofyziologie   terapie   MeSH
• kůže * MeSH
• lidé MeSH
• mastektomie modifikovaná radikální MeSH
• pooperační komplikace diagnóza   patofyziologie   terapie   MeSH
• pooperační péče přístrojové vybavení   metody   MeSH
• pružnost MeSH
• reologie přístrojové vybavení   metody   MeSH
• techniky fyzikální terapie * MeSH
• zatížení muskuloskeletálního systému MeSH
• Check Tag
• lidé MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• klinické zkoušky MeSH
• práce podpořená grantem MeSH

An accurate material representation of polymeric interlayers in laminated glass panes has proved fundamental for a reliable prediction of their response in both static and dynamic loading regimes. This issue is addressed in the present contribution by examining the time-temperature sensitivity of the shear stiffness of two widely used interlayers made of polyvinyl butyral (TROSIFOL BG R20) and ethylene-vinyl acetate (EVALAM 80-120). To that end, an experimental program has been executed to compare the applicability of two experimental techniques, (i) dynamic torsional tests and (ii) dynamic single-lap shear tests, in providing data needed in a subsequent calibration of a suitable material model. Herein, attention is limited to the identification of material parameters of the generalized Maxwell chain model through the combination of linear regression and the Nelder-Mead method. The choice of the viscoelastic material model has also been supported experimentally. The resulting model parameters confirmed a strong material variability of both interlayers with temperature and time. While higher initial shear stiffness was observed for the polyvinyl butyral interlayer in general, the ethylene-vinyl acetate interlayer exhibited a less pronounced decay of stiffness over time and a stiffer response in long-term loading.

• Klíčová slova
• dynamic shear test, dynamic torsional test, ethylene-vinyl acetate, generalized Maxwell model, laminated glass, polymer, polyvinyl butyral, rheometer,
• Publikační typ
• časopisecké články MeSH

In this work, advanced polymer nanocomposites comprising of polyvinyl alcohol (PVA) and nanodiamonds (NDs) were developed using a single-step solution-casting method. The properties of the prepared PVA/NDs nanocomposites were investigated using Raman spectroscopy, small- and wide-angle X-ray scattering (SAXS/WAXS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). It was revealed that the tensile strength improved dramatically with increasing ND content in the PVA matrix, suggesting a strong interaction between the NDs and the PVA. SEM, TEM, and SAXS showed that NDs were present in the form of agglomerates with an average size of ~60 nm with primary particles of diameter ~5 nm. These results showed that NDs could act as a good nanofiller for PVA in terms of improving its stability and mechanical properties.

• Klíčová slova
• mechanical properties, morphology, nanocomposite, nanodiamond, poly (vinyl alcohol),
• Publikační typ
• časopisecké články MeSH