Dialysis cells

As the direct communication is established between the pipette and the intracellular compartment in whole-cell configuration, the intracellular solution is rapidly dialyzed by the pipette solution, giving a control of the internal composition of the cell [29]. Nevertheless, as during the cell dialysis the intracellular material is extensively diluted this can be reflected by a run-down of the activity of some channels, whose normal function depends on the presence of some intracellular components, as for example, the calcium channel. The membrane potential of the cell in the whole-cell configuration is the same as that applied to the pipette, and negative currents are interpreted as cationic currents flowing into the cell, while positive currents represent outward cationic currents. 

Fiber dimensions have been studied for hemodialysis. When blood is circulated through the fiber lumen (m vivo), a significant reduction in apparent blood viscosity may occur if the flow-path diameter is below 100 p.m (11). Therefore, current dialy2ers use fibers with internal diameters of 180—250 p.m to obtain the maximum surface area within a safe range (see Dialysis). The relationship between the fiber cross section and the blood cells is shown in Figure 5. In many industrial appUcations, where the bore fluid is dialy2ed under elevated pressure (>200 kPa or 2 atm), fibers may burst at points of imperfection. Failure of this nature is especially likely for asymmetric fibers that display a large number of macro voids within the walls. 

Fig. 5. Scanning electron micrographs of hoUow fiber dialysis membranes. Membranes in left panels are prepared from regenerated cellulose (Cuprophan) and those on the right from a copolymer of polyacrylonitrile. The ceUulosic materials are hydrogels and the synthetic thermoplastic forms a microreticulated open cell foam with a tight skin on the inner wall. Pictures at top are membrane cross sections those below are of the wall region. Dimensions as indicated.

While it is easy to add materials to a fermentation, removal is difficult. Membrane devices have been placed in the fermenter or in external recycle loops to dialyze away a soluble component. Cells release wastes or metabolites that can be inhibitory these are sometimes referred to as staling factors. Their removal bv dialysis has allowed cell concentrations to reach ten to one hundred times that of control cultures. 

Lectins (proteins and/or glycoproteins of non-immune origin that agglutinate cells, from seeds of Robinia pseudoacacia), M 100,000. Purified by pptn with ammonium sulfate and dialysis then chromatographed on DE-52 DEAE-cellulose anion-exchanger, hydroxylapatite and Sephacryl S-200. [Wantyghem et al. Biochem J 237 483 1986.]... 

Figure 2.5 Possible technological solutions to bioprocess problems a) Fed-batch culture b) Continuous product removal (eg dialysis, vacuum fermentation, solvent extraction, ion exchange etc) c) Two-phase system combined with extractive fermentation (liquid-impelled loop reactor) d) Continuous culture, internal multi-stage reactor e) Continuous culture, dual-stream multi-stage reactor f) Continuous culture with biomass feedback (cell recycling). (See text for further details).

Several cytokines are in clinical use that support immune responses, such as IL-2, DFNs, or colony-stimulating factors. IL-2 supports the proliferation and effector ftmction of T-lymphocytes in immune compromised patients such as after prolonged dialysis or HIV infection. IFNs support antiviral responses or antitumoral activities of phagocytes, NK cells, and cytotoxic T-lymphocytes. Colony-stimulatory factors enforce the formation of mature blood cells from progenitor cells, e.g., after chemo- or radiotherapy (G-CSF to generate neutrophils, TPO to generate platelets, EPO to generate erythrocytes). 

Hollow fiber reactors [7] and dialysis reactors [8] avoid shear stress by separating cells and flowing media. In both reactors nutrient supply takes place by diffusion through the capillary wall or the dialysis membrane. 

Erythropoietin 166 amino acids glycosylated Mammalian cells Treatment of anaemia associated with dialysis and AZT/AIDS Approved for sale Without glycosylation protein is cleared very quickly from plasma... 

In the dialyzed batch start-up phase and the subsequent continuous operation a substantial increase in viable cell density and monoclonal antibody (MAb) titer was observed compared to a conventional suspension culture. The raw data, profiles of the viable cell density, viability and monoclonal antibody titer during the batch start-up and the continuous operation with a dialysis flow rate of 5 L/d are shown in Figures 17.6 and 17.7. The raw data are also available in tabular form in the corresponding input file for the FORTRAN program on data smoothing for short cut methods provided with the enclosed CD. 

The operation of the bioreactor was in the batch mode up to time t=2 2 h. The dialysis flow rate was kept at 2 Ud up to time t=91.5 h when a sharp drop in the viability was observed. In order to increase further the viable cell density, the dialysis flow rate was increased to 4 L/d and at 180 h it was further increased to 5 L/d and kept at this value for the rest of the experiment. 

Figure 17.7 Dialyzed Chemostat Viable cell density (raw and smoothed measurements) during initial batch start-up and subsequent dialyzed continuous operation with a dialysis flow rate of 5 L d [reprinted front the Journal of Biotechnology A Bioengineering with permission from J. Wiley],...

The cause of pruritus is unknown, although several mechanisms have been proposed. Vitamin A is known to accumulate in the skin and serum of patients with CKD, but a definite correlation with pruritus has not been established. Histamine may also play a role in the development of pruritus, which may be linked to mast cell proliferation in patients receiving hemodialysis. Hyperparathyroidism has also been suggested as a contributor to pruritus, despite the fact that serum PTH levels do not correlate with itching. Accumulation of divalent ions, specifically magnesium and aluminum, may also play a role in pruritus in patients with CKD. Other theories that have been proposed include inadequate dialysis, dry skin, peripheral neuropathy, and opiate accumulation.43... 

Peritoneal dialysis (PD) utilizes similar principles as hemodialysis in that blood is exposed to a semipermeable membrane against which a physiologic solution is placed. In the case of PD, however, the semipermeable membrane is the peritoneal membrane, and a sterile dialysate is instilled into the peritoneal cavity. The peritoneal membrane is composed of a continuous single layer of mesothelial cells that covers the abdominal and pelvic walls on one side of the peritoneal cavity, and the visceral organs, including the GI tract, liver, spleen, and diaphragm on the other side. The mesothelial cells are covered by microvilli that increase the surface area of the peritoneal membrane to approximate body surface area (1 to 2 m2). 

Hepatic steatosis usually is a result of excessive administration of carbohydrates and/or lipids, but deficiencies of carnitine, choline, and essential fatty acids also may contribute. Hepatic steatosis can be minimized or reversed by avoiding overfeeding, especially from dextrose and lipids.35,38 Carnitine is an important amine that transports long-chain triglycerides into the mitochondria for oxidation, but carnitine deficiency in adults is extremely rare and is mostly a problem in premature infants and patients receiving chronic dialysis. Choline is an essential amine required for synthesis of cell membrane components such as phospholipids. Although a true choline deficiency is rare, preliminary studies of choline supplementation to adult patients PN caused reversal of steatosis. 

Distribution of241 Am in a dialysis system containing sediment, phytoplankton, and detrital matter established that a substantial amount of americium accumulated in all three phases both in fresh and marine waters (NRC 1981). The adsorption process was not reversible and the longer the americium was adsorbed, the more difficult the chemical was to desorb. Appreciable amounts of americium have been shown to adsorb to bacterial cells such as those found in the Waste Isolation Pilot Plant in New Mexico (Francis et al. 1998). There is a potential that americium attached to biocolloids may facilitate its transport from the waste site. 

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