High Throughput Screening of Fibrin Clots: Transport and Mechanics Measured by Microbeads

Correlations have been shown between cardiovascular disease and the blood clot properties measured by turbidity, permeability, elasticity, and electron or confocal microscopy. With the exception of turbidity, these techniques are low throughput and usually require large sample volumes. We are developing clinically relevant, high throughput compatible measurements of fibrin structure and mechanics. These methods use microbeads, where particles ~0.1 – 10 um are embedded in clots. We have measured the local elastic modulus of fibrin clots using a high throughput compatible technology that magnetically applies force to microbeads. In a single microplate preparation, with clots of concentrations 0.5, 1, and 3 mg/mL, we measured the stiffness G = 5.8, 12, and 42 (+/− 2, 5, and 20) Pa. Using prior technology for elasticity measurements, this experiment would have required 14 separate specimen preparations. To quantify clot structure, we have measured microbead transport due to passive diffusion. PEG-coated beads passively diffused over long distances in fibrin gels and continued diffusing for >24 hours. As expected, increasing fibrinogen concentration suppressed passive transport (from >36 um at 1 mg/mL to <18 um at 3 mg/mL over 15 minutes), and, as particle size increased from 200 nm to 1 um, transport dropped to zero. However, larger PEG-coated beads (2.8 um) transported long distances (> 100 um) through these clots when driven by applied magnetic forces. We conclude that microbead techniques show promise as high throughput alternatives to measuring permeability and elasticity in research and clinical fibrin clots.