Compressive nanomechanics of opposing aggrecan macromolecules
Compressive nanomechanics of opposing aggrecan macromolecules
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DOI：
10.1016/j.jbiomech.2005.09.007
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发表时间：
2006-01-01
影响因子：
2.4
通讯作者：
Ortiz, Christine
中科院分区：
文献类型：
--
作者：
Dean, Delphine;Han, Lin;Ortiz, Christine
在这项研究中，我们测量了在接近生理条件下对立的聚合蛋白大分子之间的纳米级压缩相互作用，以阐明组织水平软骨生物力学行为的分子起源。将胎牛骨骺软骨聚集蛋白分子化学末端移植到平面基底、标准纳米原子力显微镜（AFM）探针尖端（r -尖端类似于50 nm）和更大的胶体探针尖端（r -尖端类似于2.5 μ m）。为了评估相反的聚集层之间的正常纳米力学相互作用力，使用接触模式AFM对带有微接触印刷聚集层的衬底进行了成像，并测量了聚集层的高度（以及变形）作为溶液离子强度（IS）和施加法向载荷的函数。然后，利用高分辨率力谱技术，在0.001-1 M NaCl溶液中，测量了尖端和衬底上相对聚合体之间的纳米尺度压缩力与尖端-衬底分离距离的关系。纳米尖端可以测量2-4聚合体的分子刚度，而胶体尖端可以探测更大的组装体（类似于10(4)个分子）的纳米力学性能。当使用密集堆积的胶体尖端时，胶凝蛋白的压缩刚度比使用含有少量胶凝蛋白的纳米尖端时要高得多，这表明横向相互作用对正常纳米力学性能的重要性。在0.1 M NaCl条件下，当聚集体密度为40 mg/ml（生理密度为20 ~ 80 mg/ml）时，测得的应力（近生理离子强度）急剧增加，对应于平均gag间距为4 ~ 5德拜长度（4 ~ 5 nm）；这一特征间距与相反聚集蛋白分子的GAG链之间显著静电相互作用的开始一致。将纳米力学数据与基于泊松-玻尔兹曼模型的预测进行比较，进一步阐明了静电和非静电相互作用对压缩中聚合体刚度的影响机制。本研究最重要的方面包括：结合两种不同长度尺度的实验，使用微接触印刷来量化聚合体变形和相应的纳米尺度压缩应力与应变曲线，使用不同功能的尖端来深入了解变形的分子机制，以及实验数据与基于静电相互作用双层分量的三个日益完善的泊松-玻尔兹曼（P-B）理论模型的预测的比较(c) 2005 Elsevier Ltd.。版权所有。
In this study, we have measured the nanoscale compressive interactions between opposing aggrecan macromolecules in near-physiological conditions, in order to elucidate the molecular origins of tissue-level cartilage biomechanical behavior. Aggrecan molecules from fetal bovine epiphyseal cartilage were chemically end-grafted to planar substrates, standard nanosized atomic force microscopy (AFM) probe tips (R-tip similar to 50 nm), and larger colloidal probe tips (R-tip similar to 2.5 mu m). To assess normal nanomechanical interaction forces between opposing aggrecan layers, substrates with microcontact printed aggrecan were imaged using contact mode AFM, and aggrecan layer height (and hence deformation) was measured as a function of solution ionic strength (IS) and applied normal load. Then, using high-resolution force spectroscopy, nanoscale compressive forces between opposing aggrecan on the tip and substrate were measured versus tip-substrate separation distance in 0.001-1 M NaCl. Nanosized tips enabled measurement of the molecular stiffness of 2-4 aggrecan while colloidal tips probed the nanomechanical properties of larger assemblies (similar to 10(4) molecules). The compressive stiffness of aggrecan was much higher when using a densely packed colloidal tip than the stiffness measured for using the nanosized tip with a few aggrecan, demonstrating the importance of lateral interactions to the normal nanomechanical properties. The measured stress at 0.1 M NaCl (near-physiological ionic strength) increased sharply at aggrecan densities under the tip of similar to 40 mg/ml (physiological densities are similar to 20-80 mg/ml), corresponding to an average inter-GAG spacing of 4-5 Debye lengths (4 5 nm); this characteristic spacing is consistent with the onset of significant electrostatic interactions between GAG chains of opposing aggrecan molecules. Comparison of nanomechanical data to the predictions of Poisson-Boltzmann-based models further elucidated the regimes over which electrostatic and nonelectrostatic interactions affect aggrecan stiffness in compression. The most important aspects of this study include: the incorporation of experiments at two different length scales, the use of microcontact printing to enable quantification of aggrecan deformation and the corresponding nanoscale compressive stress vs. strain curve, the use of tips of differing functionality to provide insights into the molecular mechanisms of deformation, and the comparison of experimental data to the predictions of three increasingly refined Poisson-Boltzmann (P-B)-based theoretical models for the electrostatic double layer component of the interaction (c) 2005 Elsevier Ltd. All rights reserved.