While most chemical bonds weaken under the action of mechanical force (called slip bond behavior), nature has developed bonds that do the opposite: their lifetime increases as force is applied. While such catch bonds have been studied quite extensively at the single molecule level and in adhesive contacts, recent work has shown that they are also abundantly present as crosslinkers in the actin cytoskeleton. However, their role and the mechanism by which they operate in these networks have remained unclear. Here, we present computer simulations that show how polymer networks crosslinked with either slip or catch bonds respond to mechanical stress. Our results reveal that catch bonding may be required to protect dynamic networks against fracture, in particular for mobile linkers that can diffuse freely after unbinding. While mobile slip bonds lead to networks that are very weak at high stresses, mobile catch bonds accumulate in high stress regions and thereby stabilize cracks, leading to a more ductile fracture behavior. This allows cells to combine structural adaptivity at low stresses with mechanical stability at high stresses.

中文翻译：

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交联剂的流动性控制着粘合网络的断裂行为

虽然大多数化学键在机械力的作用下会减弱（称为滑动键行为），但自然界已经形成了相反的键：它们的寿命随着力的施加而增加。虽然在单分子水平和粘合剂接触中已经对这种捕获键进行了相当广泛的研究，但最近的工作表明它们也大量作为交联剂存在于肌动蛋白细胞骨架中。然而，它们在这些网络中的作用和运作机制仍不清楚。在这里，我们展示了计算机模拟，展示了与滑移键或捕捉键交联的聚合物网络如何响应机械应力。我们的研究结果表明，可能需要捕获结合来保护动态网络免受断裂，特别是对于在解除绑定后可以自由扩散的移动连接器。虽然移动滑动键导致网络在高应力下非常脆弱，但移动捕捉键在高应力区域积累，从而稳定裂缝，导致更具延展性的断裂行为。这允许细胞将低应力下的结构适应性与高应力下的机械稳定性结合起来。