Variations in the extensibility of fibrin fibers

Fibrin fibers, a major structural component of blood clots, are one of the most extensible natural fibers. However, the mechanisms responsible for their extensibility and their internal structure are not fully known.

Using an AFM we measured the extensibility of individual fibrin fibers. We found that conditions during fiber formation play a significant role in fibrin extensibility. Holding all else constant, fibrin fibers formed under lower thrombin concentrations were less extensible than fibers formed with higher thrombin concentrations. At a thrombin concentration of 0.01 U/ml the average fiber extensibility was 166 % +/- 56 % compared to 218 % +/- 56 % at 1 Ul/ml. More importantly, we found thrombin concentration alone was not the significant factor but the ratio of thrombin to fibrin concentration during formation determined extensibility.

The difference in extensible suggest changes in the internal structure and/or bond formations within the fiber. We support a model where fibers formed at higher thrombin to fibrin ratios have a lower internal protein density as shown by Domingues et al (Blood 2016). These less dense fibers form fewer connections in their alpha-C regions and are therefore able to extend further than their denser counterpart with more alpha-C interactions.