Catastrophic response surfaces

Sketch a response surface showing length (y,) as a function of force exerted (x,) on a rubber band that is stretched until it breaks. Give examples of other catastrophic response surfaces. [See, for example, Saunders (1980).]... 

A biologic surface that develops an endothelial cell surface is referred to as a neointima. If it is covered with blood components such as fibrin, it is called a pseudointima. In both cases, the surfaces are passive with respect to the blood to which they come into contact. A pseudointima, however, is typically unstable and subject to further ihrombic response. If the surface is damaged, as during surgical implantation, a catastrophic failure can result. This coupled with the difficulty of developing a complete endothelial layer caused one researcher to describe a device as physiologically tolerable rather than biocompatible or hemocompatible. 

As a practical example, take the use of a polymer in some biomedical apphcations such as an implant device, in which the polymer surface will continually contact blood or other body fluids. Classic surface studies using contact angle measurements, wetting phenomena. X-ray photoelectron spectroscopy, or other analytical techniques may indicate that the material should be biocompatible and not cause problems such as blood platelet deposition and clot formation and immune responses. Typical surface analyses, however, are not or cannot normally be carried out under conditions of use. Under such conditions, surface transitions and relaxations may occur with time that will transform the polymer surface into one that is no longer biocompatible from the standpoint of blood or other body fluid interactions. The result could be catastrophic for the recipient of the transplant or implant made of such material. 

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