Physiological environment

SAMs of tliiolates on gold are generally resistant to strong acids or bases [175, 178 and 179], are not destroyed by solvents [180] and can witlistand physiological environments [181, 182 and 183]. However, tliey also show some degradation if exposed to tire ambient atmosphere for sufficiently extended periods [184]. 

TPEs are gaining and will capture more ground in the multimiUion-dollar medical supply and artificial organs market as replacement materials for thermosets with aU the performance advantages and low processing costs. However, TPEs have to be specially made for such applications, particularly to withstand the physiological environment in vivo. 

A major challenge in providing electrical power for implantable devices is the isolation of toxic or bio-incompatible materials. As the size of the device decreases to a centimeter or millimeter scale, the parts responsible for isolation, such as canisters and seals, begin to determine the size of the device. An alternative is to design an electrochemical system that is compatible with the physiological environment and can take advantage of chemical species available in that environment, specifically the... 

The development of cardiac assist devices and other instrumentation and components which come in contact with the cardiovascular system requires materials which will perform in a physiological environment. One particularly difficult application is the diaphragm for blood pumps, which requires an elastomer to undergo cyclic deformation and/or flexing while in contact with blood. 

The majority of CYP enzymes are located in a hydrophobic environment in the endoplasmic reticulum of cells, although cytosolic enzymes also exist, such as CYP101. In order to mimic the physiological environment of CYP enzymes, a number of groups have used phospholipids to construct biosensors such as DDAB, dimeristoyl-L-a-phosphatidylcholine (DMPC), dilauroylphosphatidylethanolamine (DLPE) and distearoylphosphatidylethanolamine (DSPE). Phospholipid layers form stable vesicular dispersions that bear structural relationship with the phospholipid components of biologically important membranes. By this way a membranous environment is created that facilitates electron transfer between the enzyme s redox center and the electrode. 

Bouhuys, A. Breathing Physiology, Environment and Lung Disease. New York Gnme and Stratton, 1974. 511 pp. 

The protection of microelectronics from the effects of humidity and corrosive environments presents especially demanding requirements on protective coatings and encapsulants. Silicone polymers, epoxies, and imide resins are among the materials that have been used for the encapsulation of microelectronics. The physiological environment to which implanted medical electronic devices are exposed poses an especially challenging protection problem. In this volume, Troyk et al. outline the demands placed on such systems in medical applications, and discuss the properties of a variety of silicone-based encapsulants. 

The physiological pH value is not the pH value experienced by the in vivo system. The in vivo protein is optimally active in a pH range present in a localized volume (or, compartment) that is different than the pH range of the larger physiological environment. 

Sodium nitroprusside is the only clinically used metal complex of NO, so that its reactions provide an indication of the types of reactivity that metallonitrosyl complexes might be expected to have in physiological environments (see Fig. 1). The in vivo activation of nitroprusside depends on its reduction to [Fe(CN)5NO], which then releases cyanide to give [Fe(CN)4NO] which in turn releases NO and additional CN to yield Fejl,) and [Fe(CN)g] [75]. [Fe(CN)5(NO)] is paramagnetic (g, = 1.9993, g, = 1.9282, g = 2.008,... 

Perfusion is not a modern technique, since it was already employed in 1912 [ 11 ] to keep small pieces of tissue viable for extended microscopic observations. It was a result of the observation that in vivo cells are continuously supplied with blood, lymph or another body fluid to keep them in a constant physiological environment, supporting cell concentrations as high as 10 cells/mL [9]. 

Transition-metal based compounds constitute a discrete class of chemotherapeutics, widely used in medicine as antitumor agents.56 Several ruthenium complexes enable the body to catalyze oxidation and reduction reactions, depending on the physiological environment, and have attracted much interest as alternative antitumor drugs in the treatment of cancer cells resistant to cisplatin in cancer... 

The ability to make small alterations in structure allows us to explore the types of events that occur in the final stages of evolution and that fine-tune an enzyme to its physiological environment. Starting from the final structure, which is presumably optimal for the native environment, we can work backward by inducing mutations that make the enzyme less active. We can first detect the types of changes in activity on mutation. 

Clearly, proteins can adhere to surfaces by electrostatic mechanisms, particularly at low ionic strength where the electrostatic field of the surface and the protein is much more extended. Indeed, this is the basis of ion exchange chromatography, so widely used for the separation, purification, and characterization of proteins. However, by the time one reaches the 0.15 M salt concentration of the physiologic environment, general electrostatic processes are no longer dominant. 

Hoffman129 and Baier 13° have reviewed most of the hypotheses and mechanisms suggested for blood compatibility in general and for the role of protein adsorption in particular. The safest statement one can make is that protein adsorption is indeed important in the blood compatibility process, in the compatibility of soft contact lenses, in the stability and acceptance of intraocular lenses, in the soft tissue foreign body reaction 131), and in virtually all situations where solid surfaces come into contact with physiologic environments. 

It is also safe to say that, because of the great complexity of proteins, even of the simplest, most well-characterized proteins, such as insulin, lysozyme, and myoglobin, and because of the very wide range of proteins present in most physiologic environments, very simplistic hypotheses and mechanisms are generally not very applicable. 

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