Fibrin Gel Structure Research Articles

Changes in functional activities of plasma fibrinogen after treatment with methylene blue and red light.

Methylene blue (MB) plus light treatment used for virus inactivation of human plasma units may lead to changes in the functional activities of fibrinogen. Single-donor units of fresh plasma were treated with 1.0 microM MB and a red light dose of 48 J per cm2. The effects of MB plus red light treatment on fibrinogen clottability, fibrin polymerization and gelation, clot stabilization, and fibrinolysis were studied. The concentration of clottable fibrinogen was unchanged during MB plus red light treatment, but a light-dose-dependent decrease of the concentration of functional fibrinogen was found. The initial release rate of fibrinopeptide A was slightly increased after MB plus red light treatment. Turbidity measurements of fibrin gel showed prolonged clotting time, lower fibrin fiber mass-to-length ratio, and slightly smaller fiber diameter. At a given clotting time, a gel with lower fibrin fiber mass-to-length ratio was produced. Clot stability and fibrinolysis remained normal. l-Histidine added to plasma before MB plus red light treatment normalized the thrombin-induced coagulation time in a dose-dependent way. MB plus red light treatment affected the polymerization and gelation phase of fibrin. A tighter fibrin gel structure was formed. No effect on stabilization of fibrin clot or fibrinolysis was found.

Structure of fibrin gels studied by elastic light scattering techniques: dependence of fractal dimension, gel crossover length, fiber diameter, and fiber density on monomer concentration.

The concentration dependence of the structure of fibrin gels, formed following fibrinogen activation by thrombin at a constant molar ratio, was investigated by means of elastic light scattering techniques. The scattered intensity distributions were measured in absolute units over a wave-vector range q of about three decades ( approximately 3x10(2)-3x10(5) cm(-1)). A set of gel-characterizing parameters were recovered by accurately fitting the data with a single function recently developed by us [F. Ferri et al., Phys. Rev. E 63, 031401 (2001)], based on a simple structural model. Accordingly, the gels can be described as random networks of fibers of average diameter d and density rho, entangled together to form densely packed and spatially correlated blobs of mass fractal dimension D(m) and average size (or crossover length) xi. As previously done for d, we show here that the recovered xi is also a good approximation of a weight average, namely, d approximately sqrt[<d2>(w)] and xi approximately <xi>(w). By varying the fibrinogen concentration c(F) between 0.034-0.81 mg/ml, gels with 100> or =xi> or =10 microm, 100< or =d< or =200 nm, 1.2< or =D(m)< or =1.4, and constant rho approximately 0.4 mg/ml were obtained. The power-law c(F) dependencies that we found for both xi and d are consistent with the model, provided that the blobs are allowed to partially overlap by a factor eta likewise scaling with c(F) (2> or =eta> or =1). Recasting the whole dataset on a single master curve provided further evidence of the similarity between the structures of all the gels, and confirmed the self-consistency of the model.

Growth kinetics and structure of fibrin gels.

The structure and kinetics of fibrin gels grown from fibrinogen solutions under quasiphysiological conditions, but in absence of Ca++, were investigated by means of elastic light scattering. By combining classical light scattering and low-angle elastic light scattering, an overall wave-vector range of about three decades was spanned, from q approximately 3 x 10(2) to q approximately 3 x 10(5) cm(-1). The scattered intensity distribution of the gels was measured in absolute units and fitted to a single function, which was able to reproduce accurately the data over the entire wave-vector range. From the fitting, it was possible to estimate the average diameter d of the fibrin fibers, the average crossover length xi of the gel, and establish the fractal nature of the gel structure, with a measure of its fractal dimension D(m). The measure of the intensity in absolute units also allowed the estimate of the density rho of the fibrin fibers and provided an independent measure of their size. The kinetics of formation of the gel was described in terms of a simple growth model: the scaffold of the network is formed very early in the course of the gelation process, at a "networking time," t(n), which is much smaller than the time required to form the final gel. At times t>t(n), the gel structure remains substantially unchanged and the successive growth consists only in a thickening of the gel fibers. Gels prepared under the same physical-chemical conditions, but at different fibrinogen concentrations, exhibited rather similar structures and kinetics, showing that the modalities of the gelation process are mainly governed by the solution conditions, and only secondarily by the fibrinogen concentration. For gels at fibrinogen concentration of approximately 0.24 mg/ml, the gel parameters were d approximately 130 nm, xi approximately 27 microm, D(m) approximately 1.3, and rho approximately 0.4 g/cm(3). Our d and rho values are in very good agreement with electron microscopy- and turbidity-derived literature data, respectively, while xi seems to be related to the mesh size of the initial scaffold formed at t(n), rather than to the mesh size of the final aged gel.

More porous fibrin gel structure obtained by interaction with Lys-plasminogen than with Glu-plasminogen

The effect of Glu1- and Lys78-plasminogen on the assembly and structure of fibrin gels was studied in purified fibrinogen-thrombin system and in plasminogen-free plasma, using turbidity, liquid permeation and three-dimensional (3D) confocal laser microscopy methods. In the purified fibrinogen system using the turbidity method, the final optical density of the fibrin gels increased with increasing concentrations of Lys-plasminogen. The fiber mass/length ratio mu increased with increasing concentrations of both Glu1- and Lys78-plasminogen, the effect of Lys78-plasminogen being much stronger. The permeability coefficient (Ks) analyzed with the permeation method revealed that fibrin gels formed in the presence of Lys78-plasminogen were more permeable (porous) than the control gels. The effect on the gel structure was inhibited by the fibrinolytic inhibitor epsilon-aminocaproic acid. The same results were obtained in plasma milieu for both mu and Ks as in the purified system, i.e. the gels became more porous with increasing concentrations of Lys78-plasminogen. 3D microscopy pictures of the gels verified the findings.

Fibrin gel as a three dimensional matrix in cardiovascular tissue engineering.

In tissue engineering, three-dimensional biodegradable scaffolds are generally used as a basic structure for cell anchorage, cell proliferation and cell differentiation. The currently used biodegradable scaffolds in cardiovascular tissue engineering are potentially immunogenic, they show toxic degradation and inflammatory reactions. The aim of this study is to establish a new three-dimensional cell culture system within cells achieve uniform distribution and quick tissue development and with no toxic degradation or inflammatory reactions. Human aortic tissue is harvested from the ascending aorta in the operation room and worked up to pure human myofibroblasts cultures. These human myofibroblasts cultures are suspended in fibrinogen solution and seeded into 6-well culture plates for cell development for 4 weeks and supplemented with different concentrations of aprotinin. Hydroxyproline assay and histological studies were performed to evaluate the tissue development in these fibrin gel structures. The light microscopy and the transmission electron microscopy studies for tissue development based on the three-dimensional fibrin gel structures showed homogenous cell growth and confluent collagen production. No toxic degradation or inflammatory reactions could be detected. Furthermore, fibrin gel myofibroblasts structures dissolved within 2 days in medium without aprotinin, but medium supplemented with higher concentration of aprotinin retained the three-dimensional structure and had a higher collagen content (P<0.005) and a better tissue development. A three-dimensional fibrin gel structure can serve as a useful scaffold for tissue engineering with controlled degradation, excellent seeding effects and good tissue development.

Racial and genetic determinants of plasma factor XIII activity.

Factor XIII (F XIII), a plasma transglutaminase, is essential for normal hemostasis and fibrinolysis. Plasma F XIII consists of two catalytic A (F XIIIA) and two non-catalytic B (F XIIIB) subunits. Activated F XIII is involved in the formation of fibrin gel by covalently crosslinking fibrin monomers. As the characteristics of the fibrin gel structure have been shown to be associated with the risk of coronary heart disease (CHD), F XIII activity may play a seminal role in its etiology. In this investigation, we determined plasma F XIII activity in two racial groups, including Asian Indians (n = 258) and Chinese (n = 385). Adjusted plasma F XIII activity was significantly higher in Indian men (142 vs. 110%; P<0.0001) and women (158 vs. 111%; P<0.0001) than their Chinese counterparts. As compared to Indians where the distribution of F XIII activity was almost normal, in Chinese it was skewed towards low activity. In both racial groups, bivariate and multivariate analyses showed strong correlation of F XIII activity with plasma fibrinogen and plasminogen levels. Race explained about 25% of the variation in F XIII activity even after the adjustment of significant correlates. We also determined the contribution of common genetic polymorphisms in the F XIIIA and F XIIIB genes in affecting plasma F XIII activity. Both loci showed significant and independent effects on plasma F XIII activity in Indians (F XIIIA, P< 0.01; F XIIIB, P<0.05) and Chinese (F XIIIA, P<0.0001; F XIIIB, P<0.13) in a gene dosage fashion. This study shows that both racial and genetic components play a significant role in determining plasma F XIII activity, and consequently it may affect the quantitative risk of CHD.

Fibrin gel structure in smokers and non-smokers in the northern Sweden MONICA study A pilot study

Objective: As the relationship between increased fibrinogen levels, including that in smokers, and cardiovascular complications is not fully understood we investigated the fibrin gel structure in a group of smokers and non-smokers. Design: Fibrin gel structure and levels of fibrinogen and triglycerides were analysed in samples from 24 middle-aged men (11 non-smokers, 13 smokers) and 27 middle-aged women (14 non-smokers, 13 smokers) of the Northern Sweden MONICA study. Methods: Fibrinogen was determined with a functional kinetic method. Fibrin gel structure was analysed by a permeability (flow) technique and the porosity of the gel expressed as permeability coefficient (Ks). Triglyceride levels were determined by an enzymatic method. Smoking status was validated by measurement of plasma cotinine. Results: Fibrin gel porosity (Ks) did not differ significantly between smokers and non-smokers. An inverse correlation was found between serum triglyceride levels and fibrin gel porosity. Conclusion: Thus we could not find any impairment of the fibrin gel porosity in smokers, which may be due to the low number studied. The relation of a tighter fibrin with elevated triglyceride levels may point to a pathogenetic mechanism whereby high triglyceride levels could promote atherothrombotic disease and confirms an earlier finding by us of a relation between these variables in healthy controls.

Fibrin gel structure in diabetic patients before and during treatment with acetylsalicylic acid: a pilot study

Objective : To investigate if treatment with a low daily dose of acetylsalicylic acid (ASA) may increase fibrin gel porosity in patients with diabetes mellitus. Design : A pilot-study. Setting : Out-patient clinic, Department of Endocrinology and Diabetology, Karolinska Hospital, Stockholm. Patients : 10 patients with type 1 diabetes. Interventions : Treatment with 75 mg ASA (Trombyl, Pharmacia & Upjohn, Uppsala, Sweden) once daily for 5 weeks. Venous blood samples were drawn before and at the end of the treatment period for determination of metabolic control, plasma fibrinogen level, and plasma fibrin gel structure. Main outcome measures: The long-term metabolic status was determined by fructosamine and glycosylated hemoglobin (HbA1c) in blood. The properties of the plasma fibrin gel structure, i.e. the permeability coefficient (Ks) and the fibre mass-length ratio (μ) formed in recalcified plasma on addition of thrombin were investigated. Results : The mean values of HbA1c and fructosamine were not significantly changed during, as compared to before, treatment with ASA. Plasma fibrinogen increased slightly ( p = 0.05), while fibrin gel porosity, as assessed by Ks and μ, increased significantly ( p < 0.05) in eight of the patients during treatment with ASA. The increase was most pronounced in three patients who at the same time improved HbA1c more than 10%. In contrast, Ks and μ decreased in two patients who experienced complications during the treatment. Conclusion : The results of this pilot study indicate that ASA may have positive effects on the fibrin gel porosity in patients with type 1 diabetes. However, long-term metabolic control seems also important, while the positive effects on fibrin gel structure seem abolished when inflammatory processes are present. Further studies are strongly needed to investigate factors influencing plasma fibrinogen and fibrin gel structure.

Better increase in fibrin gel porosity by low dose than intermediate dose acetylsalicylic acid.

To investigate the influence on plasma fibrin gel structure of low and intermediate doses of acetylsalicylic acid in healthy individuals. The influence of acetylsalicylic acid on thrombin formation, fibrinolytic capacity and plasminogen inhibitor-1 in plasma was also investigated. Nineteen subjects were treated with 75 mg and 11 with 320 mg acetylsalicylic acid daily; eight subjects received both doses. Fibrin gel structure was determined by a permeability technique yielding a porosity constant (Ks), and the thromboxane metabolite 11-dehydro-thromboxane B2 (TxM) was determined by an ELISA. Acetylsalicylic acid increased fibrin porosity by 65% at 75 mg (P<0.001, n=19), whereas lower increases were found at 320 mg (+22%, P<0.05, n=11). One week after withdrawal Ks had essentially returned to baseline (ns). Urinary thromboxane metabolites were suppressed during treatment (-61%, P<0.001 at 75 mg, n=19; -46%, P<0.01 at 320 mg, n=11). The intra-individual comparison showed similar results (Ks +92%, TxM -62% at 75 mg; Ks +5%, TxM -52% at 320 mg). Fibrinolytic capacity, plasminogen inhibitor-1 levels and thrombin generation (in platelet-poor citrated plasma) were not influenced. Low dose acetylsalicylic acid causes the greatest increase in fibrin gel porosity; this may well be of therapeutic importance.

Effect of zinc ions on fibrin network structure.

In addition to calcium, other physiologically important divalent cations (magnesium and zinc) are known to influence fibrin formation and structure. We have studied the effect of different concentrations (0-20 micromol/l) of zinc ions (Zn2+) in the absence and presence of calcium on the gel structure formed in purified fibrinogen-enzyme systems. For that purpose, we used turbidity measurement, liquid permeation and confocal three-dimensional microscopy of the gel as well as sodium dodecyl sulphate (SDS)-gel electrophoresis. The results of turbidity measurements indicated that the clotting time decreased with increasing concentrations of Zn2+. The fiber mass: length ratio (mu) values showed that the porosity of the gels increased in a concentration-dependent manner, i.e. at higher concentrations of Zn2+, larger pores with thicker fibrin fibers were formed. Three-dimensional microscopy data of the gels were in good agreement with the mu data. On SDS-gel electrophores of reduced fibrin, no cross-linking was observed in the presence of zinc ions only (without the addition of calcium ions), nor were D-D dimer bands observed in non-reduced plasmin digested fibrin samples in the presence of zinc ions only. The above results show that zinc changes the fibrin gel structure and that this effect appears to be independent of calcium.

Influence of fibrin structure on the formation and maintenance of capillary-like tubules by human microvascular endothelial cells.

Fibrin is a temporary matrix which not only covers a wound, but also provides a structure for invading cells during healing. Changes in the polymerization conditions before gelation of the clot affect the structure of fibrin and thus might influence the interaction with invading cells. Therefore we tested whether changes in the fibrin structure influence the formation of capillary-like tubular structures by human microvascular endothelial cells (hMVEC) in an in vitro angiogenesis model. Opaque [125I]fibrin structures prepared at pH 7.0, fibrin matrices at pH 7.4 and transparent [125I]fibrin structures prepared at pH 7.8 were neutralized (pH 7.4) before seeding hMVEC on top of them in confluent density. Endothelial cells were stimulated with a growth factor [basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF)165] and a cytokine [tumor necrosis factor (TNF)-alpha] to induce the u-PA/u-PA receptor-dependent formation of capillary-like tubular structures. The formation of these structures was quantified by determining the length of the invasive structures by image analysis and by measuring the accompanying [125I]fibrin degradation. Ingrowth of tubular structures proceeded at a faster rate in opaque matrices consisting of thick fibrin fibers as compared to transparent gels with fine fibrin fibers. The more rapid ingrowth of tubular structures in opaque fibrin gels induced by bFGF/TNF-alpha or VEGF165/TNF-alpha was accompanied by a larger extent of fibrin degradation. Both processes were inhibited by aprotinin and epsilon-aminocaproic acid indicating the involvement of plasmin. They were also inhibited by anti-u-PA or anti-u-PA receptor IgG, but not by anti-t-PA IgG, suggesting the involvement of cell-bound u-PA activity. However, in the opaque fibrin gels, the tubular structures dissolved upon prolonged incubation due to excessive fibrin degradation. Simulation of hMVEC with bFGF alone did not induce tubular structures, but ca used a high degree of t-PA- and plasmin-dependent fibrin lysis, and, after several days, a partial detachment of sheets of cells. Gradual inhibition of the excessive fibrin degradation by a series of aprotinin concentrations did not lead to tube formation in bFGF-treated cells. These data indicate that the formation and stability of tubular structures by hMVEC in fibrin is accompanied by controlled fibrinolysis and depends critically not only on cell-bound u-PA-dependent plasminogen activation, but also on the fibrin structure. Because the fibrin structure is largely influenced by the conditions in which fibrin has been polymerized, these conditions may have considerable impact on angiogenesis during wound healing and vascularization of tumour stroma.

Hyperfibrinogenemia and cardiovascular risk: possible strategies for intervention

Elevated plasma fibrinogen has been identified as an independent predictor of cardiovascular diseases. Although abundant evidence suggests a causal role of fibrinogen in the pathogenesis of atherothrombotic complications, this has not yet been proven. To overcome this dilemma, several strategies seem conceivable to intervene with hyperfibrinogenemia. Abstention from smoking and regular long-term endurance exercise significantly decrease fibrinogen. Treatment of chronic infections such as Helicobacter pylori, Chlamydia pneumoniae, or dental disease possibly influences cardiovascular risk indirectly by modifying fibrinogen levels. A number of drugs have been shown to reduce plasma fibrinogen besides their main therapeutic action; clinically, fibrates are by far the most important group. Other oral drugs with appreciable fibrinogen-lowering capacity include ticlopidine, pentoxifylline, beta-adrenergic blockers, ACE inhibitors, and several steroid hormones. Large clinical trials in patients post-myocardial infarction, with advanced periphonel arterial occlusive disease (POAD), and with diabetes mellitus, are under way, investigating in more detail the possible therapeutic efficacy of lowering fibrinogen on clinical endpoints. Aspirin might influence the physical properties of the fibrin gel structure, thereby rendering the clot more amenable to endogenous fibrinolysis. Chronic application of low dose urokinase or apheresis may be suitable in selected patient groups. Finally, a new approach consists in the interference with fibrinogen-dependent platelet aggregation through blockade of the glycoprotein IIb/IIIa-receptors.

63. Protection by the fibrin gel structure of certain histidines essential for polymerization against photo-oxidation

63. Protection by the fibrin gel structure of certain histidines essential for polymerization against photo-oxidation

49. Hyperfibrinogenemia and cardiovascular risk: possible strategies for intervention

Summary Elevated plasma fibrinogen has been identified as an independent predictor of cardiovascular diseases. Although abundant evidence suggests a causal role of fibrinogen in the pathogenesis of atherothrombotic complications, this has not yet been proven. To overcome this dilemma, several strategies seem conceivable to intervene with hyperfibrinogenemia. Abstention from smoking and regular long-term endurance exercise significantly decrease fibrinogen. Treatment of chronic infections such as Helicobacter pylori, Chlamydia pneumoniae , or dental disease possibly influences cardiovascular risk indirectly by modifying fibrinogen levels. A number of drugs have been shown to reduce plasma fibrinogen besides their main therapeutic action; clinically, fibrates are by far the most important group. Other oral drugs with appreciable fibrinogen-lowering capacity include ticlopidine, pentoxifylline, beta-adrenergic blockers, ACE inhibitors, and several steroid hormones. Large clinical trials in patients post-myocardial infarction, with advanced periphonel arterial occlusive disease (POAD), and with diabetes mellitus, are under way, investigating in more detail the possible therapeutic efficacy of lowering fibrinogen on clinical endpoints. Aspirin might influence the physical properties of the fibrin gel structure, thereby rendering the clot more amenable to endogenous fibrinolysis. Chronic application of low dose urokinase or apheresis may be suitable in selected patient groups. Finally, a new approach consists in the interference with fibrinogen-dependent platelet aggregation through blockade of the glycoprotein IIb/IIIa-receptors.

Gemfibrozil Reduces Thrombin Generation in Patients with Combined Hyperlipidaemia, without Influencing Plasma Fibrinogen, Fibrin Gel Structure or Coagulation Factor VII

A double-blind, placebo-controlled, cross-over study was conducted in 21 men with combined hyperlipoproteinaemia to examine if lipid-lowering treatment with gemfibrozil (10-12 weeks) affects blood coagulation and fibrin gel structure at rest or during mental stress. Gemfibrozil lowered plasma triglycerides by 57 +/- 4%, whereas high density lipoprotein (HDL) cholesterol increased by 22 +/- 5%. Gemfibrozil lowered the triglyceride content of low density lipoprotein (LDL). Gemfibrozil reduced the plasma concentrations of thrombin-antithrombin complex (TAT) and prothrombin fragment F1 + 2 (F1 + 2), both at rest and during mental stress. However, there were no effects of gemfibrozil treatment on the plasma concentrations of fibrinogen, factor VII antigen, activated factor VII (VIIa) or activated factor XII (XIIa), or on fibrin gel structure. Acute mental stress per se did not influence coagulation factors, reaction products or fibrin gel structure, or their responses to the study drug. Thus, gemfibrozil reduced thrombin generation in men with combined hyperlipoproteinaemia, without influencing the plasma levels of fibrinogen, VIIa and XIIa, or fibrin gel structure. Attenuation of thrombin generation may contribute to the primary-preventive effects of gemfibrozil on coronary heart disease.

Proneness to Formation of Tight and Rigid Fibrin Gel Structures in Men with Myocardial Infarction at a Young Age

The native fibrin gel structure formed in vitro from plasma samples was examined by liquid permeation of hydrated fibrin gel networks in 38 unselected men who had suffered a myocardial infarction before the age of 45 years and in 88 age-matched population-based control men. Both the fibrin gel porosity (permeability coefficient, Ks) and the calculated fiber mass-length ratio varied considerably within the two groups, but were generally lower in the patients. Ks was 8.3 +/- 5.2 cm2 x 10(9) (mean +/- SD) in the patient group and 12.5 +/- 5.7 cm2 x 10(9) among controls (p < 0.001). The corresponding figures for fiber mass-length ratio were 13.1 +/- 7.7 and 16.5 +/- 7.5 Dalton/ cm x 10(-13), respectively (p < 0.01). Around 50% of the patients had Ks values below the 10th percentile of the control group. A strong inverse correlation was seen between plasma plasminogen activator inhibitor-1 (PAI-1) activity and Ks (r = -0.603, p < 0.001) or fiber mass-length ratio (r = -0.565, p < 0.001) in the patient group. Corresponding weaker associations of PAI-1 with fibrin gel properties were also present in the control group. In addition, inverse relationships of very low density lipoprotein (VLDL) triglyceride concentrations to Ks (r = -0.362, p < 0.001) and fiber mass-length ratio (r = -0.283, p < 0.01) were found among the controls. Proneness to formation of tight and rigid fibrin gel networks with abnormal architecture in vitro is in vivo associated with myocardial infarction at a young age. Impaired fibrinolytic function secondary to a raised plasma PAI-1 activity level is associated with abnormal fibrin gel structure.

Plasminogen activator activity and plasma-coagulum lysis measured by use of optimized fibrin gel structure preformed in microtiter plates

We introduce a new fibrin plate assay performed in microtiter plates. By means of spectroscopic studies we optimized the structure of the fibrin gel and then used the optimized fibrin gel to determine plasminogen activator activity. Plasminogen activator solutions were applied on top of the fibrin gel, and the absorbance of the gel was recorded at 405 nm. After incubation for 17 h at 25 degrees C, the absorbance was measured again. The difference in absorbance was proportional to the concentration of plasminogen activator, such that the dose-response curves were linear when the difference in absorbance was plotted as a function of the logarithmic concentration of plasminogen activator. We assayed both tissue-type and urokinase-type plasminogen activator activity. The intraassay CV was < 4.7% (n = 20); the interassay CV was < 3.1% (n = 15). Using the optimized procedure, we modified the assay for determination of plasma-coagulum lysis time in human plasma. We established a reference interval for lysis time in apparently healthy subjects of 75 to 201 ks. Patients with deep vein thrombosis showed significantly (P = 0.013) higher values.

Ultrasound Increases Flow through Fibrin Gels

Ultrasound accelerates fibrinolysis in vitro and in animal models of thrombosis. Since transport of fibrinolytic enzymes into clots by permeation may be an important determinant of the rate of fibrinolysis, we examined the effect of ultrasound on permeation through fibrin gels in vitro. Gels of purified fibrin were prepared in plastic tubes, and the rate of pressure-mediated fluid permeation was measured. Exposure to 1 MHz ultrasound at 2 W/cm2 and a duty cycle of 5 msec on, 5 msec off resulted in a significant (p = .005) increase in flow through the gel of 29.0 +/- 4.2% (SEM). The ultrasound-induced flow increase was intensity-dependent, increasing from 17.0 +/- 1.2% at 1 W/cm2 to 30.1 +/- 1.9% at 2.3 W/cm2. Increased flow was not due to heating, detachment of fibrin from the tube wall or fragmentation of the gel resulting in channeling. However, degassing the fluid by autoclaving significantly reduced the ultrasound-induced increase in flow. We conclude that exposure of fibrin gels to ultrasound increases pressure-mediated permeation. This effect may be related to cavitation-induced changes in fibrin gel structure, and could contribute to the accelerated fibrinolysis observed in an ultrasound field.

Fibrinogen structure, activation, polymerization and fibrin gel structure

Fibrinogen structure, activation, polymerization and fibrin gel structure

The effect of plasma antithrombin concentration on thrombin generation and fibrin gel structure

Congenital deficiency of antithrombin (AT) is associated with thrombotic events and AT consumption occurs in some severe disorders and after treatment with heparin. The aim of this study was to investigate whether variations in the level of plasma AT modify thrombin generation and the fibrin formation process after the intrinsic coagulation mechanism is triggered. Normal plasma was depleted of AT by immunoadsorption on CNBr-Sepharose coupled with the anti-AT-IgG fraction of antiserum. The AT-depleted plasma was reconstituted with AT (between 0.3 and 1.5 AT units per ml). Thrombin generation was measured as the development of thrombin-antithrombin complexes (TAT). The lag phase preceding fibrin formation depended on the concentration of AT. The short lag phase was seen in completely AT-depleted plasma and the long in plasma with 1.5 AT units per ml. TAT generation, determined in parallel consecutive samples, showed that the rate at which thrombin was generated was inverse to the AT concentration in plasma. The network structure of hydrated fibrin gels in the clotted plasma was studied by measuring the wavelength dependence of gel turbidity. The mass/length ratio value, -i.e. the thickness of fiber strands and porosity of the gel increased with increasing AT concentrations. It is concluded that plasma AT regulates the rate of prothrombin-thrombin conversion, the clotting time and the consequently network structure of the fibrin gel.