We tested what to our knowledge is a new computational model for fibrin fiber mechanical behavior. The model is composed of three distinct elements: the folded fibrinogen core as seen in the crystal structure, the unstructured α-C connector, and the partially folded α-C domain. Previous studies have highlighted the importance of all three regions and how they may contribute to fibrin fiber stress-strain behavior. Yet no molecular model has been computationally tested that takes into account the individual contributions of all these regions. Constant velocity, steered molecular dynamics studies at 0.025 Å/ps were conducted on the folded fibrinogen core and the α-C domain to determine their force-displacement behavior. A wormlike chain model with a persistence length of 0.8 nm (Kuhn length = 1.6 nm) was used to model the mechanical behavior of the unfolded α-C connector. The three components were combined to calculate the total stress-strain response, which was then compared to experimental data. The results show that the three-component model successfully captures the experimentally determined stress-strain behavior of fibrin fibers. The model evinces the key contribution of the α-C domains to fibrin fiber stress-strain behavior. However, conversion of the α-helical coiled coils to β-strands, and partial unfolding of the protein, may also contribute.

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Studies suggest that patients with deep vein thrombosis and diabetes often have hypercoagulable blood plasma, leading to a higher risk of thromboembolism formation through the rupture of blood clots, which may lead to stroke and death. Despite many advances in the field of blood clot formation and thrombosis, the influence of mechanical properties of fibrin in the formation of thromboembolisms in platelet-poor plasma is poorly understood. In this paper, we combine the concepts of reactive molecular dynamics and coarse-grained molecular modeling to predict the complex network formation of fibrin clots and the branching of fibrin monomers. The 340-kDa fibrinogen molecule was converted into a coarse-grained molecule with nine beads, and using our customized reactive potentials, we simulated the formation and polymerization process of a fibrin clot. The results show that higher concentrations of thrombin result in higher branch-point formation in the fibrin clot structure. Our results also highlight many interesting properties, such as the formation of thicker or thinner fibers depending on the thrombin concentration. To the best of our knowledge, this is the first successful molecular polymerization study of fibrin clots to focus on thrombin concentration.

The mechanical and fatigue behavior of neat poly(lactic acid) (PLA) films and PLA films reinforced with 5 wt% nanoclay particles has been examined using various analytical procedures. The results showed that for the films tested in this study, PLA-5 wt% samples were more susceptible to crazing at the same maximum fatigue stress as the neat PLA samples, as evidenced by results from light transmission experiments. Optical microscopy results confirmed this observation. In addition, under fatigue loading conditions, the neat PLA samples displayed almost the same fatigue resistance (number of cycles to failure) at 3 and 30 Hz, while the PLA-5 wt% samples showed a shift in the number of cycles to failure to higher values at a frequency of 30 Hz. Using the linear regression curves from the S– N data (stress vs. number of cycles to failure), time-to-failure curves were generated to show the difference between the neat PLA and PLA-5 wt% samples when tested at frequencies of 3 and 30 Hz. Based on these results, it is known that the nanoclay particles served to increase the fatigue resistance at the higher frequency of 30 Hz, when compared to the neat PLA sample.