Membrane biocompatibility

Membrane-based separation, lactic acid production and, 14 120 Membrane biocompatibility, in hemodialysis, 26 823—824 Membrane bioreactors, 16 26 Membrane-bound enzymes, 10 338 Membrane cell process, 9 620 Membrane cells... 

Ion-selective electrodes with a liquid membrane are more reliable than ion-selective electrodes with a solid membrane because of the uniformity of the active material partition in the membrane. For the construction of biosensors the maximum reliability is obtained by using graphite paste as the support. As of the present, for in vivo tests only sensors based on plastic membranes have been used. The main problem associated with using them for in vivo tests is the biocompatibility of the materials.147 149 The membrane biocompatibility, the matrix biocompatibility, and the electroactive material biocompatibility are important factors. The matrix biocompatibility is assured by the biocompatibility of the polymer and by the biocompatibility of the plasticizer. The ratio between the quantity of polymer and quantity of plasticizer affects the response of electrochemical sensors because the matrix of the solid membrane electrodes plays the same role as does the solvent in liquid membrane electrodes. 

For hemodialysis membranes, biocompatibility is the primary requirement. It is known that surface properties such as surface roughness play important roles in determining membrane biocompatibihty. It has also been reported that for a given material, smoother surfaces are more biocompatible [64]. Hence, the sinfaces of three different commercial hollow fibers were studied by AFM to compare their roughness parameters. Figures 4.42 and 4.43 show AFM images of inner and outer surfaces, re-... 

This volume has been organized into four sections, namely, biosensors, biosensor polymers and membranes, biocompatibility and biomimet-ics, and immobilization and stabilization methods. This book should be useful to biochemists, chemists, and chemical engineers doing or planning to do research and development work in diagnostics, specifically biosensors and dry chemistries. Polymer scientists should also find this voliune worthwhile to read. 

Inadequate membrane biocompatibility elicits a variety of responses, including activation of the coagulation and complement system, activafion of platelets and leukocytes, production of cytokines and free oxygen radicals, and accumulation of bradykinin. Although they initiate locally, these responses cause systemic changes to the blood and the body behavior. They may also change the surface and transport properties of the membranes used. However, it should be recalled that the treatment of bio(in)compatibility is not solely related to the biomaterials used but rather depends also on the blood fluid dynamics in the membrane device and the whole extracorporeal blood circulation loop, as well as on how blood is handled in extracorporeal circulation. 

The presence of polymer, solvent, and ionic components in conducting polymers reminds one of the composition of the materials chosen by nature to produce muscles, neurons, and skin in living creatures. We will describe here some devices ready for commercial applications, such as artificial muscles, smart windows, or smart membranes other industrial products such as polymeric batteries or smart mirrors and processes and devices under development, such as biocompatible nervous system interfaces, smart membranes, and electron-ion transducers, all of them based on the electrochemical behavior of electrodes that are three dimensional at the molecular level. During the discussion we will emphasize the analogies between these electrochemical systems and analogous biological systems. Our aim is to introduce an electrochemistry for conducting polymers, and by extension, for any electrodic process where the structure of the electrode is taken into account. 

Applicability in biological ion assay is an important factor for biocompatible potentio-metric ion sensors. Attempts were made to determine Na" " concentrations in human blood sera by using silicone-rubber membrane Na+-ISFETs based on (5) [Fig. 17(a)] [29]. The found values for Na concentration in undiluted, 10-fold diluted, and 100-fold diluted serum samples are in good agreement with the Na" " calibration plots. Even in the undiluted serum samples, only a slight potential shift was observed from the calibration. This indicates that the calixarene-based silicone-rubber-membrane Na+-ISFETs are reliable on serum Na assay. For comparison with the silicone-rubber membrane, Na -ISFETs with corresponding plasticized-PVC membrane containing (2) or (5) were also tested for the Na assay. The found values of Na" " concentration... 

The flow behavior in miniaturized hemodialyzer modules with two types of biocompatible membrane materials, SMC and SPAN, was investigated by using doubly distilled water as the flowing fluid in both compartments, subsequently termed membrane side (M) and dialysate side (D), respectively (Figure 4.6.1 (c, d)) [12], SMC stands for Synthetically Modified Cellulose and SPAN for Special PolyAcryloNitrile-based copolymer (Akzo Nobel, Membrana GmbH), both types representing standard membrane material. The capillaries made from this hollow... 

With either type of dialysis, studies suggest that recovery of renal function is decreased in ARF patients who undergo dialysis compared with those not requiring dialysis. Decreased recovery of renal function may be due to hemodialysis-induced hypotension causing additional ischemic injury to the kidney. Also, exposure of a patient s blood to bioincompatible dialysis membranes (cuprophane or cellulose acetate) results in complement and leukocyte activation which can lead to neutrophil infiltration into the kidney and release of vasoconstrictive substances that can prolong renal dysfunction.26 Synthetic membranes composed of substances such as polysulfone, polyacrylonitrile, and polymethylmethacrylate are considered to be more biocompatible and would be less likely to activate complement. Synthetic membranes are generally more expensive than cellulose-based membranes. Several recent meta-analyses found no difference in mortality between biocompatible and bioincompatible membranes. Whether biocompatible membranes lead to better patient outcomes continues to be debated. 

However, some researchers have preferred to develop hydrophobic sensitizers and, indeed, it needs to be recognized that some degree of hydrophobicity is advantageous to facilitate the penetration of biological membranes. In these cases a delivery vehicle is required, and this must be biocompatible, and provide a suspension which is stable up to the point at which the natural transport system (e.g., albumin or lipoprotein or both) takes over. 

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