Material-tissue interfaces: the role of surface properties and processes

The introduction of a foreign material into living tissue--intentionally as in biomedical applications (implants, protheses, drugs) or unintentionally as when minerals or fibers are inhaled--results in the creation of interfaces between the material and the surrounding tissue. This article identifies and discusses the possible role of material surface properties and molecular processes occurring at such interfaces. For kinetic and thermodynamic reasons, surfaces are different from the corresponding bulk of the material, and contain reactive (unsaturated) bonds, which in turn lead to the formation of surface reactive layers (e.g., surface oxides on metals) and adsorbed contamination layers. The encounter with the biological environment leads to further surface reactions modifying the surface, and to the adsorption of water, ions, and biomolecules, which are continuously exchanged. The exact nature of the dynamic, adsorbed water, ions, and biomolecule coating in turn influences the behavior of cells approaching the material surface, and hence the tissue response.