Thrombin generation and fibrin formation under flow on biomimetic tissue factor-rich surfaces

BACKGROUND

Blood flow regulates coagulation and fibrin assembly by controlling the rate of transport of zymogens, enzymes and plasma proteins to and from the site of an injury.

OBJECTIVE

The objective of this work was to define the hemodynamic conditions under which fibrin can form under flow on tissue factor (TF)-rich substrates.

METHODS

TF-coated silica beads (~ 800 nm) were patterned into 18-85-μm spots. Normal pooled plasma and factors VIII, IX and XI deficient plasmas were perfused over the beads coated with 0.08, 0.8 and 8 molecules-TF μm(-2) at shear rates of 50-1000 s(-1) . Fibrin deposition and thrombin generation were measured by fluorescence microscopy in a hydrodynamic focusing microfluidic device.

RESULTS AND CONCLUSIONS

Fibrin deposition was supported on patterned bead spots, but not planar TF substrates at the same surface TF concentration. There was a threshold spot size and a shear rate dependent TF concentration that was necessary to support fibrin polymerization. FVIII and FIX had minor effects on fibrin dynamics at 8 molecules-TF μm(-2) , but were essential at 0.8 molecules-TF μm(-2) . The absence of FXI influenced thrombin generation and fibrin deposition at both 0.8 and 8 molecules-TF μm(-2) . These results show that fibrin deposition requires perturbations in the flow field that protect reactions from dilution by flow under venous and arterial conditions. FVIII and FIX have a modest effect on fibrin deposition at high TF concentrations, but are necessary for fibrin deposition at low TF concentrations. FXI amplifies thrombin generation under flow at both low and high TF concentrations.

The validity and reliability of the Wing Subgroups Questionnaire

This study examined the validity and the internal and interrater reliability of the Wing Subgroups Questionnaire (WSQ), an assessment that classifies children with autism into one of three subtypes. Subjects were 42 students enrolled in multihandicapped special education classrooms. Results indicated that items pertaining to the active-but-odd and the aloof subtypes, and to typical development, demonstrated good consistency, whereas passive subtype items showed moderate consistency. Interrater reliability was good for all subtypes utilizing intraclass correlations, but it was moderate with regard to percentage agreement of subtype diagnosis. Interscale correlations were mostly low or negative, suggesting that the subtype scales are measuring distinct constructs. Significant differences among the subtypes were found on three measures of communication, three measures of social interaction, two measures of stereotypic behavior, and one measure of temper/aggression.

A trial of intra-arterial oxygen for the treatment of arterial disease in the legs

Images