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LUBRICATION THEORY IN HIGHLY COMPRESSIBLE POROUS MEDIA: SKIING, TIP-TOEING AND SENSING YOUR WAY ACROSS THE ENDOTHELIAL GLYCOCALYX

Sheldon Weinbaum
Department of Biomedical Engineering, The City College of New York, CUNY

Xiaobing Zhang
Departments of Biomedical and Mechanical Engineering, The City College of The City University of New York 138th Street at Convent Avenue, New York, NY10031, USA

Yuefeng Han
Departments of Biomedical and Mechanical Engineering, The City College of The City University of New York 138th Street at Convent Avenue, New York, NY10031, USA

Stephen Cowin
Departments of Biomedical and Mechanical Engineering, The City College of The City University of New York 138th Street at Convent Avenue, New York, NY10031, USA

Resumo

In this paper we shall provide an overview of the endothelial surface layer (ESL) or glycocalyx in several roles, as a transport barrier, as a porous hydrodynamic interface in the motion of red and white cells in microvessels and as a mechanotransducer of fluid shearing stresses to the actin cortical cytoskeleton of the endothelial cell (EC). These functions will be examined from a new perspective, the quasi-periodic ultrastructural model proposed in (Squire et al., 200 I) for the three-dimensional organization of the ESL and its linkage to the submembranous scaffold. We shall show that the core proteins in the bush-like structures comprising the matrix have a flexural rigidity, E1, that is sufficiently stiff to serve as a molecular filter for plasma proteins and as an exquisitely designed transducer of fluid shearing stresses. However, E1 is inadequate to prevent the buckling of these protein structures during the intermittent motion of red cells or the penetration of white cell microvilli. In these cellular interactions the viscous draining resistance of the matrix is essential for preventing adhesive molecular interactions between proteins in the endothelial membrane and circulating cellular components.