时间：2007年4月12日9:00am-10:am
地点：玉泉校区邵科馆211室
题目：热波动对生物膜粘附的稳定性的影响
(The Influence of Thermal Undulations on the Stability of Adhesion of a Biological Membrane)
报告人：美国布朗大学L. Ben Freund教授
Freund教授简介：
Freund教授是美国布朗大学H. L. Goddard University Professor。美国科学院院士，美国工程院院士，美国艺术与科学院院士，国际理论与应用力学联合会现任主席，PNAS（工程类）主编，Journal of the Mechanics and Physics of Solids上届主编，在断裂力学、固体中应力波、地震学、计算力学、位错理论、薄膜中的微结构演化等领域发表了190多篇文章，在动态断裂力学与薄膜材料方面有两本专论。Freund教授的当前研究领域是生物材料中的力学（包括cell adhesion, molecular transport in cell walls）和薄膜材料力学。
报告内容简介：
Fibroblasts and other tissue secreting cells have the ability to adhere to extracellular matrix and to migrate in the course of tissue generation. Adhesion occurs through specific bonding of large transmembrane protein molecules called integrins in the cell wall to ligands in the surrounding tissue. Integrins are mobile in the cell wall and diffuse randomly in a normal thermal environment. The mean density of integrins in the cell wall is normally too low for adhesion to occur casually upon contact. Instead, adhesions form gradually as a few integrins become immobilized in a small region. Such focal adhesion regions usually grow to about a micron or two in diameter.
Focal adhesions have been studied at a coarse scale by means of a number of experimental approaches. In a departure focusing on observations at such a scale, Arnold et al. [ChemPhysChem 5 (2004) 383] carried out experiments in which they were able to study the process of cell adhesion at the scale of individual binding sites. Among their observations was the discovery that there appeared to be an upper bound on spacing of integrin bond sites for tight adhesions to form. Furthermore, the critical value of this density was found to be essentially uniform among the four cell types examined. This naturally raises the question as whether or not this remarkable finding can be understood in terms of a fundamental physical phenomenon across the cell types. In this presentation, the question will be examined from the point of view of classical statistical mechanics with bonding being represented by a well in the potential energy landscape of the system. It will be shown that thermal fluctuations arising from immersion of the membrane in a heat bath can account for the appearance of a critical bond site spacing.
