ABSTRACT
The Biomembrane Force Probe ..................................................................................................................... 638 15.3 Model Systems for Extended Bioadhesion ................................................................................................................. 638
15.3.1 Surface Forces and Adhesion Energy Measurement Techniques.................................................................. 638 15.3.1.1 Surface Force Apparatus ................................................................................................................ 638 15.3.1.2 Vesicle Micromanipulation ............................................................................................................ 639
15.3.2 Adhesion of Surfaces Coated with a Compact Layer of Adhesion Sites...................................................... 640 15.3.2.1 Theory ............................................................................................................................................ 640
15.3.3 Electrostatic Nanotitration of Weak Biochemical Bonds .............................................................................. 643 15.3.4 Surfaces Bearing Mobile Adhesion Sites ...................................................................................................... 645
15.4 Adhesion of Living Cells ............................................................................................................................................ 649 15.4.1 Living Cells: An Active Material .................................................................................................................. 649 15.4.2 Adhering Spherical Shells.............................................................................................................................. 649 15.4.3 Adhering Elastic Spheres ............................................................................................................................... 651 15.4.4 Experimental Characterization of the Mechanical Properties of Living Cells .............................................. 652 15.4.5 Application of Adhesion Measurements to Biologically Relevant Problems ............................................... 653
References ................................................................................................................................................................................ 654
Adhesion between inert materials has long been described, both experimentally and theoretically. A much less explored domain is the adhesion of biological matter such as living cells. In general, the latter is triggered by a signal while the former just depends on more static physicochemical features. In contrast to inert materials, the adhesion of cells always relies on receptor=ligand (often named key=lock) interactions which consist of molecules from one cell that recognize those of another cell. This molecular recognition always results from known physicochemical interactions (van der Waals forces, electrostatic forces, hydrophobic interactions, hydrogen bonds, etc.) combined with a particular geometry of the molecules. In spite of these complications, several physical methods allow the investigation of this biological adhesion either by studying simplified models with a limited number of parameters, or by studying a single bond between cell adhesion molecules, or by investigating realistic biological systems such as cells for which it is still possible to obtain a physical description. In living matter, interactions and bonds are unceasingly formed and broken between various molecules or organized aggregates and cells (Alberts, 1998). These interactions occur either spontaneously or after a signal which triggers production of the molecular species corresponding to the programmed biological phenomenon. Cell adhesion is involved in a large number of biological
et al., 1994). A majority of cells can divide and multiply only when they adhere to other cells or tissues. The adhesion between cells if often a way to exchange signals, for instance mediated by a cross talk between different families of cell adhesion molecules. The first stages of inflammation correspond to several different cell adhesion processes after an external microorganism is detected (Alberts et al., 2002). As a consequence, white blood cells start having a weak adhesion to the vessel walls that restricts their movement to rolling along the wall. This first adhesive contact due to selectins and their ligand triggers another process, which increases the adhesion and blocks the cell in a fixed position. Then, other adhesion processes drive the white blood cells across the vessel walls by letting them pass between the cells that make up the wall. Eventually, the white blood cells reach the microorganism and adhere to them to destroy them. There is an increasing interest in understanding biological adhesion in views of designing new antiinflammatory drugs, new biomaterials, understanding some processes linked to metastasis proliferation, and also control the properties of numerous materials nowadays designed to have increasing sophisticated functions.
