Department of Mechanical Engineering, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
Soft Matter. 2018 Feb 28;14(9):1530-1539. doi: 10.1039/c7sm02300f.
A challenging problem in designing nanocomposites is to engineer nanoparticle interfaces that have tunable cohesive strength and rate-responsive behavior, for which inspiration can be taken from biological systems. An exemplary bio-interface is the Chaperone-Usher (CU) pili, such as type 1 expressed by bacteria Escherichia coli. The pili have unique biomechanical properties that enhance the ability of bacteria to sustain attachment to surfaces under large stresses, such as constant force extensibility, logarithmic velocity-uncoiling force dependence, and adhesive tips with catch bond behavior that exhibit longer bond life-times at greater force levels. Although biophysics of the pili under strain or stress is well-studied for anti-infective applications that aim to compromise pili adhesion, utilizing the biomechanical properties of the pili in material design applications is yet to be explored. In this work, we modeled the elongation of a single CU pilus with catch bond tip adhesin and examined its toughness response using Monte Carlo simulations. We showed that the pilus can act as a "molecular seat belt" that exhibits low toughness when pulled slowly and high toughness when pulled rapidly. Furthermore, we found that systematically varying the catch bond and shaft parameters leads to tunable seat belt behavior at the interface, where the sharpness of the transition from the low toughness to the high toughness regime and the velocity at the start of the transition can be dictated by molecular design parameters. Lastly, we tested the performance of CU pilus in slowing down a fast particle, and reveal that pili can effectively stop micron size projectiles with high initial velocities. The molecular seat belt mechanism presented here provides insight into how nanocomposite interfaces can be engineered to create molecular networks with linkers that switch on or off depending on strain rate.
设计纳米复合材料的一个挑战性问题是设计具有可调内聚强度和响应速度的纳米颗粒界面，这方面可以从生物系统中获得灵感。一个典型的生物界面是伴侣蛋白- usher (CU) 菌毛，例如大肠杆菌表达的 type 1。菌毛具有独特的生物力学特性，增强了细菌在大应力下维持附着在表面的能力，例如恒力延伸性、对数速度-解旋力依赖性以及具有捕获键行为的粘性尖端，在更高的力水平下表现出更长的键寿命。尽管菌毛在应变或应力下的生物物理学已被很好地研究，用于旨在破坏菌毛粘附的抗感染应用，但利用菌毛的生物力学特性在材料设计应用中尚未被探索。在这项工作中，我们用带有捕获键尖端黏附素的单根 CU 菌毛建模，并使用蒙特卡罗模拟研究了其韧性响应。我们表明，菌毛可以作为一种“分子安全带”，在缓慢拉伸时表现出低韧性，在快速拉伸时表现出高韧性。此外，我们发现系统地改变捕获键和轴参数会导致界面处的安全带行为可调，其中从低韧性到高韧性的转变的尖锐度和转变开始时的速度可以由分子设计参数来决定。最后，我们测试了 CU 菌毛在减缓高速粒子方面的性能，并揭示了菌毛可以有效地阻止具有高初始速度的微米大小的射弹。这里提出的分子安全带机制提供了一种思路，即如何设计纳米复合材料界面，以创建具有根据应变速率开关的链接器的分子网络。
