Biological tissues, surface behavior

In microfiuidic devices the measurement of the wall shear stress is challenging in general. For a direct measurement, methods commonly used such as oil film interferometry or liquid crystal coatings cannot be applied since already the thin layer of oil alters the fluids behavior at the wall. Shear stress sensors, like micro-piUars, surface mounted and elevated hot wires, and Preston tubes, might be applicable in macroscopic flows but not for microscale flow investigations. The first reason is their size, which is often larger than the whole microfiuidic channel or structure on the surface. Furthermore, in some cases like the studies on endothelial cells mentioned above, the wall is a biological tissue that cannot be altered or replaced. Secondly, the sensors would... 

For a tissue substitute to function properly, many biological aspects of the tissue and component cells must be understood. Some aspects include the extracellular matrix, cell-specific gene expression and surface markers, cell growth parameters, population arrangement and behavior, and the immune system. 

Diquat and paraquat applied to aquatic systems were eflFective in controlling pond flora and did not directly aflFect pond fauna (45, 67). The absence of herbicidal activity to aquatic fauna was attributed to inactivation by adsorption on bottom muds and the subsequent lack of biological availability (45). The phytotoxic eflFects to pond flora probably occurred through absorption into the plant tissues of herbicides adsorbed on leaf surfaces. Other details concerning the behavior of diquat and... 

It is clear that future efforts to improve the host tissue responses to implant materials will focus, in large part, on controfling cell and tissue responses at implant interfaces. This goal will require continued acquisition of fundamental knowledge of cell behavior and cell response to specific materials characteristics. It is likely that a better understanding of the cellular-derived extracellular matrix-implant interface wiU offer a mechanism by which biologic response modifiers such as growth and attachment factors or hormones may be incorporated. Advancements of this type will likely shift the focus of future research from implant surfaces which as osseoconductive (permissive) to those which are osseoinductive (bioactive). 

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