Biosurfaces: Water Structure at Interfaces
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Science at surfaces and interfaces is central to many phenomena in the life sciences. For instance, the topography of the surface of a properly folded protein is almost always more important than its hydrophobic core for functions, such as catalysis, dimerization, or assembly. On a higher architectural hierarchy at cellular or tissue level, protein binding at the surface of cell membrane determines the cell physiology including proliferation, differentiation, and viability. This set of biosurfaces bears characteristics that are different from any other man-made surface in both complexity and scale. The surface of a protein contains a wide variety of functional groups, and the surface of cell membrane contains dynamic lipid bilayers imbedded with proteins, which is hardly resembled by any man-made surface such as palladium catalyst. Furthermore, most of the events occurring on these biosurfaces are at nanometer scale. For example, the functional assembly of ribosome executing protein synthesis and the focal adhesion mediating cell adhesion are both on the scale of 40–80 nm. For single protein catalysis, the active side is usually of a dimension larger than 1 nm. In contrast, most man-made surfaces function either at molecular level (catalysis) or at micrometer scale (lithography).
The importance of biosurfaces is both highlighted and revealed by the rapid development of biotechnology in recent years. In particular, a well-defined problem—bioinertness—first appears as a technological problem, and soon evolves into an intricate puzzle of fundamental science. In this article, the origin of this unique problem, the development of its solutions and the evolution of theories over a relative short span of time—less than 10 years—will be reviewed. Furthermore, the significance and implication of this problem and its solution will be discussed in the context of life sciences.