Fibrin plate

UK is a serine protease that activates plasminogen to plasmin. Plasmin dissolves the fibrin in blood clots. The attachment of UK to the islet surface was expected to dissolve blood clots that surrounded the islets in the liver thus, IBMIR could be inhibited in the initial stages. A fibrin plate-based assay was performed to assess the... 

Quantification of coagulation factors is notoriously difficult, because of the interrelations among the various components of the coagulation cascade, the broad range of normal values, and considerable inter-laboratory variability (52). This variability is illustrated by a WHO study of users of combined oral contraceptives, conducted on several continents, which showed statistically significant differences among clinical centers in prothrombin time, fibrin plate lysis, plasminogen, and activated partial thromboplastin time (SEDA-16, 464). Effects also vary between different populations, users of different doses, users of different products, and tests performed at different periods of the medication cycle (63,69). 

Figure 11 Fibrinolytic activity in rabbit plasma (estimated on fibrin plates) after i.v. injection of 50,000 IU/kg urokinase (U) or benzoyl-urokinase (BU) or guanidinobenzoyl-urokinase (GBU). (From Ref. 38.)...

An important aspect of pharmaceutical enzymes is the choice of an appropriate substrate and its appropriate concentration. The substrate should correspond to the specificity of the enzyme and should be relevant to the physiological activity, as far as possible. Fortunately, in some cases the substrate and conditions of the assay are closely related to the situation in which the enzyme is thought to act therapeutically. However, the precise quantification of enzyme activity in a reproducible manner, which is the main purpose in pharmaceutical control, is often difficult to reconcile with such conditions. Thus, the fibrin plate method... 

Initially, fibrinolytic activity is measured by both plasminogen-rich and plasminogen-free fibrin plates [46,47]. When an individual earthworm is cut into pieces and placed on a plasminogcn-rich fibrin plate, fibrinolytic activity can be detected at the anterior portion of the earthworm [3]. The average fibrinolytic activity of the 6-isozyme mixture is about 100 CU (plasmin unit) and 250 IU (urokinase unit) [3,24]. Although the fibrin plate is usually used to measure the activity, it is a time-consuming process (18 24 hr) indeed. 

Recently, an assay using chromophoric substrate (Chromozym TH) was developed [7], When Chromozym TH is added, the absorbance at 405nm will increase, and the linear section from 15 to 30 sec is used to calculate the activity (international unit, one unit is defined as the specific activity required to convert 1 pM substrate/min/mg of enzyme), Fig. (7). The increasing absorbance is resulted from the p-nitroanilide released off the substrate during hydrolyzation. As compared with the fibrin plate method, this chromogenic assay is more rapid, convenient and reproducible. The specificity of the assay, however, is lower than that of fibrin-plate method because the chromogenic substrate could be hydrolyzed by some other proteases, for instance thrombin. 

Assays Fibrin plate Cliromophoric procedure Light Scattering... 

Fig. 11 Islets with immobilized urokinase (UK-islets) were tested for the ability to dissolve fibrin, (a) Fibrin in the plate gel medium was dissolved by UK-islets (clear areas). Fifty islets were applied to each spot, and the plate was observed after incubation at 37 °C for 14 h. (1) untreated islets (2) UK-islets treated with oligo(dT)2o-PEG-lipid (C16), just after preparation (3) UK-islets treated with oligo(dT)2o-PEG-lipid (C16) lost activity after 2 days in culture (4) UK-islets treated with oligo(dT)20-PEG-lipid (C18), just after preparation and (5) UK-islets treated with oligo (dT)20-PEG-lipid (C16) lost activity after 2 days in culture, (b) Morphology of UK-islets after 1 and 7 days of culture...

See color plate.) The coagulation cascade. The formation of fibrin strands is the result of a sequential activation of a number of enzymes. The hemostatic balance is maintained by endogenous inhibitors such as AT, HC-II, and TFPI. Abbreviations AT, antithrombin TFPI, tissue factor pathway inhibitor. 

It appears as a thick syrup, soluble in H9O and in alcohol, and strongly alkaline in reaction. Even in dilute aqueous solution it prevents the coagulation of albumin and redissolves coagulated albumin and fibrin. It is a. strong base attracts carbon dioxid from the air forms with HCl a salt, soluble in alcohol, which crystallizes in plates and needles, very much resembling in appearance those of cholesterin. Its chloroplatinate is purified with difficulty its chloraurate readily. Solutions of its chlorid differ... 

However, Biirker has returned to this conception. According to him, coagulation of the blood is intimately related to the decomposition of the plates. All the conditions which influence thrombin, and consequently coagulation, such as temperature, contact, chemical products, act equally on the transformation of the plates. Sodium metaphosphate, magnesium sulphate, ammonium oxalate, all of which hinder coagulation, also preserve the blood components. This decomposition of the plates would take place under the action of a trypsin contained in the blood. Once these particles are destroyed, coagulation would appear. The quantity of fibrin formed is then in direct proportion to the... 

It is perhaps inadvisable to pretend that fibrin comes only from the transformation of the plates. It appears, however, from a certain number of observations that we shall present later that these organized components of the blood actually play a part in coagulation, but only in the elaboration of the active substance, and not of the fibrin which is precipitated. Therefore they will not be considered at this point. 

The work of Hammarsten and Arthus has established the fact that calcium salts are indispensable in the transformation of fibrinogen into fibrin. This discovery changed completely the direction of investigations and led to different interpretations. According to A. Schmidt, coagulation of blood is caused by secretions arising from the leucocytes and the plates. The substance secreted is not in reality an enzyme, but is pro-throm-... 

Fig. 1.11 a Fibrin gel after polymerization in a 6-well plate, b-d Scanning election microscopy (SEM) images demonstrating the nano-fiber network structure of the fibrin, which enables the gentle embedding of cells, with a vascular smooth muscle cell (SMC) shown in d immediately after the gelation of the fibrin within a web-like network surrounded by cell culture medium. Reproduced from Ref. [86] Jockenhoevel and Flanagan... 

Plate II. Organized fibrin thrombus showing bacteria. Grocott stain, 400 X. 

The natural materials are often derived from skin such as, for example, collagen, gelatin, fibrin, hyaluronic acid, chondroitin sulfate and also acellular dermis from cadaveric skin origin. But materials from other origins are also widely used, such as bacterial polyesters (Valappil et al., 2007), cellulose (Teeri et al., 2007), chitosan, alginate, dextran, etc. A lot of constructs based on natural products can be found in different forms such as membrane, plate, sheet, fiber, sponge, and hydrogel. 

Cells showed high viability after printing, which was equivalent to that of manually plated cells, cells printed within 1 nun from the border of VEGF releasing fibrin gel showed GF-induced changes in their morphology... 

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