Laboratory for Atomistic and Molecular Mechanics, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA.
ACS Nano. 2011 Apr 26;5(4):3034-42. doi: 10.1021/nn200107u. Epub 2011 Mar 25.
The nuclear lamina, composed of intermediate filaments, is a structural protein meshwork at the nuclear membrane that protects genetic material and regulates gene expression. Here we uncover the physical basis of the material design of nuclear lamina that enables it to withstand extreme mechanical deformation of >100% strain despite the presence of structural defects. Through a simple in silico model we demonstrate that this is due to nanoscale mechanisms including protein unfolding, alpha-to-beta transition, and sliding, resulting in a characteristic nonlinear force-extension curve. At the larger microscale this leads to an extreme delocalization of mechanical energy dissipation, preventing catastrophic crack propagation. Yet, when catastrophic failure occurs under extreme loading, individual protein filaments are sacrificed rather than the entire meshwork. This mechanism is theoretically explained by a characteristic change of the tangent stress-strain hardening exponent under increasing strain. Our results elucidate the large extensibility of the nuclear lamina within muscle or skin tissue and potentially many other protein materials that are exposed to extreme mechanical conditions, and provide a new paradigm toward the de novo design of protein materials by engineering the nonlinear stress-strain response to facilitate flaw-tolerant behavior.
核纤层由中间丝组成，是核膜上的一种结构蛋白网格，可保护遗传物质并调节基因表达。在这里，我们揭示了核纤层物质设计的物理基础，使其能够在存在结构缺陷的情况下承受超过 100%应变的极端机械变形。通过一个简单的计算模型，我们证明这是由于纳米级机制，包括蛋白质展开、α到β的转变和滑动，导致了特征非线性力-伸长曲线。在更大的微尺度上，这导致机械能耗散的极度离域化，从而防止灾难性的裂纹扩展。然而，当在极端载荷下发生灾难性失效时，牺牲的是单个蛋白质丝，而不是整个网格。这种机制可以通过在应变增加时切线应力-应变硬化指数的特征变化来从理论上解释。我们的结果阐明了核纤层在肌肉或皮肤组织中的大伸长率，以及可能暴露在极端机械条件下的许多其他蛋白质材料，并通过工程非线性应力-应变响应来促进缺陷容限行为，为蛋白质材料的从头设计提供了一个新的范例。
