Rabbi Md Foysal, Koenderink Gijsje H, Mulla Yuval, Kim Taeyoon
Weldon School of Biomedical Engineering, Purdue University, 206 S. Martin Jischke Drive, West Lafayette, IN 47907, USA.
Department of Bionanoscience, Kavli Institute of Nanoscience Delft, Delft University of Technology, Delft 2629HZ, the Netherlands.
Acta Biomater. 2025 Jul 1;201:372-384. doi: 10.1016/j.actbio.2025.06.004. Epub 2025 Jun 3.
Semiflexible polymer networks are ubiquitous in biological systems, including a scaffolding structure within cells called the actin cytoskeleton. The polymers in these networks are interconnected by transient bonds. For example, actin filaments in the cytoskeleton are physically connected via cross-linker proteins. The mechanical and kinetic properties of the cross-linkers significantly affect the rheological properties of the actin cytoskeleton. Here, we employed an agent-based model to elucidate how the force-dependent behaviors of the cross-linkers determine the material properties of passive networks without molecular motors and the force generation of active networks with molecular motors. The cross-linkers are assumed to behave either as a slip bond, whose dissociation rate increases with forces, or as a catch-slip bond, whose dissociation rate decreases with forces at low force level but increases with forces at high force level. We found that catch-slip-bond cross-linkers can simultaneously increase both the stress and the strain at the yield point. Through a systematic variation in the force dependence of the catch-slip bonds, we identified the specific parameter regimes that enable network reinforcement and enhanced extensibility simultaneously. Specifically, we found that a sufficiently large force threshold for the catch-slip transition is essential for maintaining dynamic force-bearing elements that turnover continuously-a mechanism not achievable with slip bonds. Additionally, we demonstrate that such force-dependent redistribution of the catch-slip bonds substantially enhances internal contractile forces generated by a motor in active networks. STATEMENT OF SIGNIFICANCE: Polymer networks are ubiquitous in industrial and biological systems. The polymers in these networks are often interconnected by transient bonds. The transient bonds behave as a slip bond whose dissociation rate is proportional to forces or as a catch-slip bond whose dissociation rate decreases with increased force (catch) at low force level but increases with increased force (slip) at high force level. In this study, we computationally tested different types of catch-slip bonds to define how the material properties of polymer networks are fine-tuned by each property of molecular bonds. We found that catch-slip bonds can increase both stress and strain at a yield point, which is impossible to achieve without the catch-slip bonds.
半柔性聚合物网络在生物系统中无处不在，包括细胞内一种名为肌动蛋白细胞骨架的支架结构。这些网络中的聚合物通过瞬态键相互连接。例如，细胞骨架中的肌动蛋白丝通过交联蛋白进行物理连接。交联剂的力学和动力学性质显著影响肌动蛋白细胞骨架的流变性质。在这里，我们采用基于主体的模型来阐明交联剂的力依赖行为如何决定无分子马达的被动网络的材料性质以及有分子马达的主动网络的力产生。假设交联剂表现为滑动键，其解离速率随力增加，或者表现为捕捉 - 滑动键，其解离速率在低力水平下随力减小，但在高力水平下随力增加。我们发现捕捉 - 滑动键交联剂可以同时增加屈服点处的应力和应变。通过系统改变捕捉 - 滑动键的力依赖性，我们确定了能够同时实现网络增强和增强可扩展性的特定参数范围。具体而言，我们发现捕捉 - 滑动转变的足够大的力阈值对于维持持续更新的动态受力元件至关重要——这是滑动键无法实现的机制。此外，我们证明这种捕捉 - 滑动键的力依赖重新分布显著增强了主动网络中马达产生的内部收缩力。重要性声明：聚合物网络在工业和生物系统中无处不在。这些网络中的聚合物通常通过瞬态键相互连接。瞬态键表现为解离速率与力成正比的滑动键，或者表现为捕捉 - 滑动键，其解离速率在低力水平下随力增加（捕捉）而减小，但在高力水平下随力增加（滑动）而增加。在本研究中，我们通过计算测试了不同类型的捕捉 - 滑动键，以确定聚合物网络的材料性质如何通过分子键的每种性质进行微调。我们发现捕捉 - 滑动键可以增加屈服点处的应力和应变，没有捕捉 - 滑动键则无法实现这一点。
