Physical Chemistry and Soft Matter, Wageningen University and Research, Stippeneng 4, 6708WE Wageningen, Netherlands.
Phys Rev Lett. 2023 Mar 17;130(11):118203. doi: 10.1103/PhysRevLett.130.118203.
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.
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），但自然界已经开发出了相反的键：随着力的施加，它们的寿命会增加。虽然这种捕获键在单分子水平和粘附接触中已经得到了相当广泛的研究，但最近的工作表明，它们在肌动蛋白细胞骨架中也作为交联剂大量存在。然而，它们在这些网络中的作用和作用机制仍不清楚。在这里，我们提出了计算机模拟，展示了交联键是滑动键还是捕获键的聚合物网络对机械应力的响应。我们的结果表明，捕获键可能是保护动态网络免受断裂的必要条件，特别是对于在解键后可以自由扩散的移动连接体。虽然移动的滑动键会导致网络在高应力下非常脆弱，但移动的捕获键会在高应力区域聚集，从而稳定裂缝，导致更具延展性的断裂行为。这使得细胞能够在低应力下结合结构适应性，在高应力下保持机械稳定性。
