Influence of surface treatment on the smectic ordering within porous glass

The influence of the surface treatment on the Sm-A-N phase transition of the 8CB (octylcyanobiphenyl) liquid crystal confined to controlled pore glass (CPG) matrices is studied. The characteristic linear size of voids in the chosen CPG matrix is 0.2 &mgr;m. The voids' surface was either nontreated or silane treated enforcing tangential or homeotropic anchoring, respectively. In both cases the x-ray measurements reveal a qualitative change of the temperature dependence of the smectic order-parameter correlation length in comparison to the bulk sample. In addition, the apparent smectic pretransitional ordering is observed for the silane-treated sample. A theoretical description based on the Landau-de Gennes type approach is developed to explain the experimental data. The surface positional anchoring strength of the silane-treated sample is estimated to be of the order of 10(-4) J/m(2) and at least 100 times weaker for the nontreated case.

Finger-like lysing patterns of blood clots.

One-dimensional modeling of fibrinolysis (Senf, 1979; Zidansek and Blinc, 1991; Diamond and Anand, 1993) has accounted for the dissolution velocity, but the shape of the lysing patterns can be explained only by two- or three- drug-induced blood clot dissolution patterns obtained by proton nuclear magnetic resonance imaging, which can be described by the enzyme transport-limited system of fibrinolytic chemical equations with diffusion and perfusion terms (Zidansek and Blinc, 1991) in the reaction time approximation if the random character of gel porosity is taken into account. A two-dimensional calculation based on the Hele-Shaw random walk models (Kadanoff, 1985; Liang, 1986) leads to fractal lysing patterns as, indeed, is observed. The fractal dimension of the experimental lysing patterns changes from 1.2 at the beginning of the experiments to a maximum of approximately 1.3 in the middle and then decreases toward one when the clot is recanalized.

Lysing patterns of retracted blood clots with diffusion or bulk flow transport of plasma with urokinase into clots--a magnetic resonance imaging study in vitro.

Fresh retracted clots are known to be poorly lysable by fibrinolytic agents. We have studied whether lysis of retracted clots could be enhanced by bulk transport in comparison to pure diffusion of plasma containing urokinase (400 IU/ml) into the clots. Cylindrical retracted blood clots were occlusively glued by a polyester into plastic tubes and put in contact with plasma through the clot bases. One group of clots (perfused clots, n = 10) was placed under a pressure difference of 6 kPa (60 cm H2O) which resulted in an average plasma flow of 0.97 +/- 0.34 microliters/min through the clot during the first hour. Another group of clots (non-perfused clots, n = 10) was incubated in the lytic plasma without a pressure difference. Clot sizes were measured during lysis by magnetic resonance imaging (MRI). Channels representing lysed areas penetrated into perfused clots with a velocity of 5.4 +/- 1.6 mm/h (n = 10), whereas the boundaries of non-perfused clots subsided with a velocity of less than 0.1 mm/h. Eight of the 10 perfused clots were recanalized after 8 h and the sizes of the perfused group were reduced to 64.0 +/- 10.7% of the initial values. The relative sizes of non-perfused clots after 8 h remained significantly higher: 95.0 +/- 1.3%, p < 0.005. In a separate experiment good agreement was obtained between the measured clot sizes by MRI and the residual radioactivity of 125I-fibrin in the clot.(ABSTRACT TRUNCATED AT 250 WORDS)

Dependence of blood clot lysis on the mode of transport of urokinase into the clot--a magnetic resonance imaging study in vitro.

Magnetic resonance imaging was employed to study the dependence of clot lysing patterns on two different modes of transport of urokinase into whole blood clots. In one group of clots (nonperfused clots, n1 = 10), access of urokinase to the fibrin network was possible by diffusion only, whereas in the other group (perfused clots, n2 = 10) bulk flow of plasma containing urokinase was instituted through occlusive clots by a pressure difference of 3.7 kPa (37 cm H2O) across 3 cm long clots with a diameter of 4 mm. It was determined separately that this pressure difference resulted in a volume flow rate of 5.05 +/- 2.4 x 10(-2) ml/min through occlusive clots. Perfused clots diminished in size significantly in comparison to nonperfused ones already after 20 min (p less than 0.005). Linear regression analysis of two-dimensional clot sizes measured by MRI showed that the rate of lysis was more than 50-times faster in the perfused group in comparison to the nonperfused group. It was concluded that penetration of the thrombolytic agent into clots by perfusion is much more effective than by diffusion. Our results might have some implications for understanding the differences in lysis of arterial and venous thrombi.

The influence of transport parameters and enzyme kinetics of the fibrinolytic system on thrombolysis: mathematical modelling of two idealised cases.

Experimental data obtained by magnetic resonance imaging and photographing clot dissolution in vitro have shown that whole blood clots dissolve almost two orders of magnitude faster when urokinase is introduced into the clot by pressure induced permeation than when its access is limited to diffusion. In view of these findings, two mathematical models have been developed that quantitatively link the enzymatic and transport properties of the fibrinolytic system to the velocity of thrombolysis. Without a pressure gradient across the thrombus, the plasminogen activator molecules diffuse into the thrombus through the blood-thrombus boundary plane. The blood-thrombus boundary slowly moves inwards due to thrombolysis that is spatially restricted to a relatively narrow zone. The velocity of thrombolysis is primarily limited by the diffusion constants of the plasminogen activator and plasmin. In contrast, when plasminogen activator is rapidly distributed along the thrombus by pressure induced bulk flow, lysis occurs at each segment of the thrombus after a lag period that is due to plasmin activation and sufficient fibrin degradation. The lag time is determined primarily by the catalytical properties of the plasminogen activator and plasmin. The mathematical models with the observations of the clot boundaries during lysis permit the characterization of plasmin action on the fibrin network.

Proton NMR study of the state of water in fibrin gels, plasma, and blood clots.

A proton NMR relaxation and pulsed field gradient self-diffusion study of water in fibrin gels, plasma, and blood clots has been performed with special emphasis on the effect of the sol-gel and shrinkage transitions. Deuteron NMR in fibrin gels was also studied to supplement the proton data. It is shown that a measurement of the water proton or deuteron T1/T2 ratio allows for a determination of the bound water fraction in all these systems. The change in the T1/T2 ratio at the shrinkage transition further allows for a determination of the surface fractal dimension of the gel if the change in the volume of the gel is known. The self-diffusion coefficient of water in these systems, which determines the transport properties of the gel, is found to be proportional to the free water fraction in both the nonshrunken and shrunken state.