Fibrin is the main component of blood clots. The mechanical properties of fibrin are therefore of critical importance in successful hemostasis. One of the divalent cations released by platelets during hemostasis is Zn²⁺; however, its effect on the network structure of fibrin gels and on the resultant mechanical properties remains poorly understood. Here, by combining mechanical measurements with three-dimensional confocal microscopy imaging, we show that Zn²⁺ can tune the fibrin network structure and alter its mechanical properties. In the presence of Zn²⁺, fibrin protofibrils form large bundles that cause a coarsening of the fibrin network due to an increase in fiber diameter and reduction of the total fiber length. We further show that the protofibrils in these bundles are loosely coupled to one another, which results in a decrease of the elastic modulus with increasing Zn²⁺ concentrations. We explore the elastic properties of these networks at both low and high stress: At low stress, the elasticity originates from pulling the thermal slack out of the network, and this is consistent with the thermal bending of the fibers. By contrast, at high stress, the elasticity exhibits a common master curve consistent with the stretching of individual protofibrils. These results show that the mechanics of a fibrin network are closely correlated with its microscopic structure and inform our understanding of the structure and physical mechanisms leading to defective or excessive clot stiffness.

纤维蛋白是血凝块的主要成分。因此，纤维蛋白的机械特性对于成功止血至关重要。血小板在止血过程中释放的二价阳离子之一是 Zn ²⁺；然而，它对纤维蛋白凝胶的网络结构和由此产生的机械性能的影响仍然知之甚少。在这里，通过将机械测量与三维共聚焦显微镜成像相结合，我们表明 Zn ²⁺可以调整纤维蛋白网络结构并改变其机械性能。在 Zn ²⁺存在下，纤维蛋白原纤维形成大束，由于纤维直径的增加和总纤维长度的减少而导致纤维蛋白网络变粗。我们进一步表明，这些束中的原纤维彼此松散耦合，这导致弹性模量随着 Zn ^{2+ 的}增加而降低浓度。我们探索了这些网络在低应力和高应力下的弹性特性：在低应力下，弹性源于将热松弛拉出网络，这与纤维的热弯曲一致。相比之下，在高应力下，弹性表现出与单个原纤维的拉伸一致的共同主曲线。这些结果表明，纤维蛋白网络的力学与其微观结构密切相关，并告知我们对导致缺陷或过度凝块刚度的结构和物理机制的理解。