Medium exchange

Bath-type heat exchangers can be either direct or indirect. In a direct bath exchanger, the heating medium exchanges heat directly with the fluid to be heated. The heat source for bath heaters can be a coil of a hot heat medium or steam, waste heat exhaust from an engine or turbine, or heat from electric immersion heaters. An example of a bath heater is an emulsion heater-treater of the type discussed in Volume 1. In this case, a fire tube immersed in the oil transfers heat directly to the oil bath. The calculation of heat duties and sizing of fire tubes for this type of heat exchanger can be calculated fom Chapter 2. 

The core of double membrane stirrer perfusion bioreactors is a stirrer on which two microporous hollow fiber membranes are mounted, one of them being hydrophobic and used for bubble-free aeration, the second of them being hydrophilic and used for cell-free medium exchange [15]. This system has been reported to provide viable cell densities of 20 million cells per miUiliter for more than two months [106]. Although Lehmann et al. [15] have described the scale-up of this system to the 20-L and 150-L scale, it has been most commonly employed at the bench-scale. 

We have exposed non-confluent ceU cultures with 50,000 cells/mL attached to the cell culture bottle and introduced a medium exchange for 1 h. The medium was exchanged with pH from 2, 3, 4, 5 and 9, 10, 11, 11.3. We have observed acute changes and after a period of 1 h, the pH-conditioned medium was withdrawn and replaced by a tissue culture medium. The overall conclusion of these experiments show that pH must be returned to less than 9 and higher than 5 within less than 60 min and preferably within 30 min. This is achieved by the results are given in Fig. 6.14. 

The feasibility of amperometric sucrose and mercury biosensors based on the immobilization of invertase, glucose oxidase, and muta-rotase entrapped in a clay matrix (laponite) was investigated by Mohammadi et al. [31]. In this work, the effect of pH of a tri-enzymatic biosensor in which the optimum pH of the three enzymes is different (Invertase, pH 4.5 Glucose oxidase, pH 5.5 and Mutarotase, pH 7.4) [41] was studied. The pH effect on the biosensor response was analyzed between pH 4 and 8 and the highest activity was found at pH 6.0. In order to improve the selectivity of the invertase toward mercury and to avoid silver interference, a medium exchange technique was carried out. The biosensor was exposed to mercury in an acetate buffer solution at pH 4 while the residual activity was evaluated with phosphate buffer solution at pH 6 [41]. 

For cells growing continuously in suspension, the subculture process can be performed similarly to the method used for microbial cultures. Trypsin treatment is not required and subculture is faster and less traumatic for the cells. Total medium exchange is not generally performed for these cultures since it would require a centrifugation step. Culture maintenance can be performed by dilution with fresh medium after adequate cell growth. 

Gargas et al. (1994) employed a three compartment model describing the urinary excretion of chromium (Aitio et al. 1988) to estimate the bioavailability of chromium(III) from chromium(in) picolinate in volunteers ingesting capsules containing 400 pg. The model contained 3 compartments, a fast-exchange compartment receiving 40% of absorbed chromium with a half-life of 7 hours, a medium-exchange... 

Cells are often maintained in spinner or shake flasks by periodic replacement of spent medium (with or without replacement of suspended cells) with fresh medium. Values for ix pp, x and can be obtained for these systems by treating them as batch reactors during the intervals between feedings. The cell concentration at the beginning of each interval can be measured directly or calculated from the value before medium exchange and the fraction of medium replaced. Taking samples between medium exchanges will improve the accuracy of the results obtained. 

It can be shown that growth and death of the uninfected cells can be neglected due to medium exchange, limited space on microcarriers and fast progression of infection. Therefore, only infection is considered for description of the uninfected cell s behavior ... 

Hegewisch-Becker, S., Faltz, C., and Hossfeld, D. K. (1996) Prolongation of medium exchange is associated with a decrease in function but not expression of the P-glycoprotein pump in leukaemic cells. Eur. J. Haematol. 56,12-22. 

Pfaller W, Felder E, Koppelstaetter C, Abbot SE, Westwick J. Epiflow a new cell culture system utilising continuous medium exchange and continuous supply with respiratory gases. ATLA 1999b 27 423 (Abstract). 

Surface silanol groups of silica aquasols stabilized in an alkaline medium exchange protons for the alkaline ion such as Na+, K+, or NH4+ (Figure 13). The surface silanol groups can be esterified, as in silica organosols, or silanized (silylated) (Figure 14). Derivatization of the silica surface is the basis for the use of silica in analytical and process chromatography. 

Particle separation methods based on the effects on suspended particles of exposure to an ultrasonic standing-wave field have been reported [51]. Carrier medium exchange in a laminar flow microchannel has also been achieved using... 

Petersson F, Nilsson A, Jonsson H, Laurell T (2005) Carrier medium exchange through ultrasonic particle switching in microfluidic channels. Anal Chem 77 1216-1221... 

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