Cardiovascular prosthetic bypass grafts do not endothelialize spontaneously in humans, and so they pose a thrombotic risk. Seeding with cells improves thei r performance, particularly in small-caliber applications. Knitted tubular polyethylene- terephthalate (PET) vascular pros theses (6 mm) with commercial type I collagen (PET/Co) were modified in the lumen by the adsorption of laminin (LM), by coating with a fibrin network (Fb) or a combination of Fb and fibronectin (Fb/FN). Primary human saphenous vein endothelial cells were seeded (1.50 × 10 5 /cm 2 ), cultured for 72 h and exposed to laminar shear stress 15 dyn/cm 2 for 40 and 120 min. The control static grafts were excluded from shearing. The cell adherence after 4 h on PET/Co, PET/Co +LM, PET/Co +Fb and PET/Co +Fb/ FN was 22 %, 30 %, 19 % and 27 % of seeding, respectively. Comp ared to the static grafts, the cell density on PET/Co and PET/Co +LM dropped to 61 % and 50 %, respectively, after 120 min of flow. The cells on PET/Co +Fb and PET/Co +Fb/FN did not show any detachment during 2 h of shear stress. Pre-coating the clinically-used PET/Co vascular prosthesis with LM or Fb/FN adhesive protein assemblies promotes the adherence of endothelium. Cell retention under flow is improved particularly on fibrin-containing (Fb and Fb/FN) surfaces., J. Chlupáč ... [et al.]., and Obsahuje bibliografii a bibliografické odkazy
The gold standard material in bypass surgery of blood vessels remains the patient’s own artery or vein. However, this material may be unavailable, or may suffer vein graft disease. Currently available vascular prostheses, namely polyethylene terephthalate (PET, Dacron) and expanded poly tetrafluoroethylene (ePTFE), perform well as large-caliber replacements, but their long-term patency is discouraging in small-caliber applications (<6 mm), such as in coronary, crural or microvessel surgery. This failure is mainly a result of an unfavorable healing process with surface thrombogenicity, due to lack of endothelial cells and anastomotic intimal hyperplasia caused by hemodynamic disturbances. An ideal small-diameter vascular graft has become a major focus of research. Novel biomaterials have been manufactured, and tissue-biomaterial interactions have been optimized. Tissue engineering technology has proven that the concept of partially or totally living blood vessels is feasible. The purpose of this review is to outline the vascular graft materials that are currently being implanted, taking into account cell-biomaterial physiology, tissue engineering approaches and the collective achievements of the authors., J. Chlupáč, E. Filová, L. Bačáková., and Obsahuje seznam literatury
This paper presents the results of an experimental study to quantify the effects of bed slope and relative submergence on incipient motion of sediment under decelerating flows. Experiments were conducted in an experimental tilting-flume of 8 m long 0.4 m wide and 0.6 m deep with glass-walls. Three uniform sediments with median grain sizes of 0.95, 1.8 and 3.8 mm and three bed slopes of 0.0075, 0.0125 and 0.015 were used under decelerating flow. The main conclusion is that the Shields diagram, which is commonly used to evaluate the critical shear stress, is not suitable to predict the critical shear stress under decelerating flows.
The study on bedload transport behaviour is widely explored from the last few decades and many semiempirical or empirical equilibrium transport equations are developed. The phenomenon is a very complex due to its varied physical properties like velocity, depth, slope, particle size in the alluvial system. In practical applications, these formulae have appreciable deviation from each other in derivation and also their ranges of applications are different. Here, bedload transports have been categorized into moderate bedload transport and intense bedload transport depending upon the Einstein bedload transport parameter. Based on large database of different bedload measurements, a comparative analysis has been performed to ascertain prediction ability of different bedload equations based on various statistical criteria such as the coefficient of determination, Nash-Sutcliffe coefficient and index of agreement. It has been found that equations based on shear stress have worked better than other approaches (discharge, probabilistic and regression) for flume observations. and Výskum transportu splavenín počas posledného obdobia bol relatívne intenzívny; jeho výsledkom bolo množstvo empirických a poloempirických rovníc kvantifikujúcich rovnovážny transport splavenín. Je to zložitá problematika; je to tak v dôsledku meniacich sa fyzikálnych vlastností ako je rýchlosť, hĺbka, sklon, zrnitostné zloženie splavenín v aluviálnom systéme. Výsledky výpočtu z týchto rovníc sa významne líšia a líši sa tiež oblasť ich možnej aplikácie. V tejto štúdii je transport splavenín rozdelený na priemerný a intenzívny, podľa Einsteinovho parametra transportu splavenín. S využitím štatistických metód sme uskutočnili komparatívnu analýzu presnosti rozdielnych rovníc transportu splavenín. Pri analýze bola použitá rozsiahla databáza výsledkov meraní. Výsledkom je, že rovnice založené na informácii o tangenciálnom napätí dávajú lepšie výsledky ako tie, ktoré využívajú pre výpočet transportu splavenín prietoky, pravdepodobnostný prístup a regresie.