FAR-FROM-EQUILIBRIUM PHENOMENA IN BIOADHESION PROCESSES

This review is concerned with the physical chemistry of processes occu rring during bioadhesion, i.e. when living cells approach and contact other cells, or when living cells approach and contact nonliving or so lid surfaces. A good deal is known at present about biological membran e composition, pointing towards a heterogeneous composition of this me dium. There is now a clear need to detailed, specific and quantitative understanding of interactions between biological membranes. Experimen ts and theory begin to converge in order to provide a better understan ding of the cell functions depending on these interactions: anchorage, spreading, locomotion, differentiation, activation of immune response and so on. In this review, equilibrium processes are first recalled a nd interpreted by several models (mechanical or thermodynamical models ). Far-from-equilibrium processes are then described, for mammalian ce lls or more precisely for red blood cells. These processes are interpr eted in terms of the interfacial instability theory, taking into accou nt the role of external contraints leading to dissipative structures. Examples of such far-from-equilibrium processes are the appearance of nonuniform morphologies due to the bridging of surface polymers, the c lustering of surface receptors following a surface reaction between ce ll receptors and fixed binding sites on a substrate, etc. The approach remains always macroscopic, but opens vistas to correlate with molecu lar approaches. Several important and challenging research directions regarding non-equilibrium processes in bioadhesion are the relation be tween adhesion and fusion, the metabolic regulation controlled or indu ced by adhesion, the process of reversible/irreversible adhesion and s eparation etc. The importance of integrated studies combining the effo rts of different disciplines (biology, chemistry, physics, computer sc ience etc.) is stressed throughout this review and will provide new an swers to fundamental problems.