University of Notre Dame/Interdisciplinary Center for the Study of Biocomplexity/Center News

Speaker: Dr. Huajian Gao
From: Max Planck Institute for Metals Research - Stuttgart, Germany
Date / Time / Room: Tuesday, November 1, 2005 / 3:30PM/Room 129 DeBartolo Hall

Title: Mechanics of Robust and Reversible Adhesion in Biology

Abstract:

Gecko and many insects rely on non-specific adhesion (van der Waals, capillary, etc) for survival. These animals have evolved specialized adhesive tissues with elaborate hierarchical

microstructures that allow them to manoeuvre on vertical walls or ceilings against gravity. It is interesting to observe that these bio-adhesion systems, even including specific adhesion between

receptors on cell membranes, all involve hierarchical, nonhomogeneous and strongly anisotropic materials design. We note that non-specific adhesion in biology must function robustly on rough surfaces and at the same time be easily releasable upon animal movement. How can an adhesion system designed for robust attachment simultaneously allow easy detachment? This question has

inspired our investigation of the mechanisms of robust and releasable adhesion based on interfacial failure mechanics. For single asperity contact, we show that optimal adhesion could be

achieved by a combination of size reduction and shape optimization. The smaller the size, the less important the shape and the more robust the adhesion. At this level, releasable adhesion can be achieved via asymmetric design of contact elements like gecko's seta. For large scale contact with rough surfaces, we consider the behavior of interfacial crack-like flaws between a hierarchically structured elastic nonhomogeneous anisotropic material and a rigid substrate. We show that robust adhesion can be achieved by a combination of graded elasticity, hierarchical energy dissipation and strength reduction, while strong elastic anisotropy of the adhesive tissue is the key to releasable adhesion. On the one hand, nonhomogeneous elastic properties and energy dissipation mechanisms associated with hierarchical structures can suppress the growth of interfacial cracks to achieve flaw tolerant adhesion at macroscopic length scales. On the other hand, strong elastic anisotropy allows the adhesion strength to vary strongly with the direction of pulling, resulting in an orientation-controlled fast switch between attachment and detachment. We conclude that robust and releasable adhesion requires an effective combination of material inhomogeneities, hierarchical structures and strong elastic anisotropy. These findings not only provide a theoretical foundation to understand adhesion systems in biology but also suggest possible strategies to develop novel adhesive materials for engineering applications.


	Speaker: Dr. Huajian Gao From: Max Planck Institute for Metals Research - Stuttgart, Germany Date / Time / Room: Tuesday, November 1, 2005 / 3:30PM/Room 129 DeBartolo Hall Title: Mechanics of Robust and Reversible Adhesion in Biology Abstract: Gecko and many insects rely on non-specific adhesion (van der Waals, capillary, etc) for survival. These animals have evolved specialized adhesive tissues with elaborate hierarchical microstructures that allow them to manoeuvre on vertical walls or ceilings against gravity. It is interesting to observe that these bio-adhesion systems, even including specific adhesion between receptors on cell membranes, all involve hierarchical, nonhomogeneous and strongly anisotropic materials design. We note that non-specific adhesion in biology must function robustly on rough surfaces and at the same time be easily releasable upon animal movement. How can an adhesion system designed for robust attachment simultaneously allow easy detachment? This question has inspired our investigation of the mechanisms of robust and releasable adhesion based on interfacial failure mechanics. For single asperity contact, we show that optimal adhesion could be achieved by a combination of size reduction and shape optimization. The smaller the size, the less important the shape and the more robust the adhesion. At this level, releasable adhesion can be achieved via asymmetric design of contact elements like gecko's seta. For large scale contact with rough surfaces, we consider the behavior of interfacial crack-like flaws between a hierarchically structured elastic nonhomogeneous anisotropic material and a rigid substrate. We show that robust adhesion can be achieved by a combination of graded elasticity, hierarchical energy dissipation and strength reduction, while strong elastic anisotropy of the adhesive tissue is the key to releasable adhesion. On the one hand, nonhomogeneous elastic properties and energy dissipation mechanisms associated with hierarchical structures can suppress the growth of interfacial cracks to achieve flaw tolerant adhesion at macroscopic length scales. On the other hand, strong elastic anisotropy allows the adhesion strength to vary strongly with the direction of pulling, resulting in an orientation-controlled fast switch between attachment and detachment. We conclude that robust and releasable adhesion requires an effective combination of material inhomogeneities, hierarchical structures and strong elastic anisotropy. These findings not only provide a theoretical foundation to understand adhesion systems in biology but also suggest possible strategies to develop novel adhesive materials for engineering applications.

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