Dialysis fiber

To treat hollow dialysis fibers the fluorine gas was passed through the inside ofthe capillaries (Figure 17.3). By flow stream measurements the exact amount of gas that entered the capillaries could be determined. The treatment time and the fluorine concentration was measured to determine possible effects on the main biocompatibility properties.7,8... 

Tetrodotoxin (TTX) a voltage-dependent Na+-channel blocker was infused directly into the prefrontal cortex through the dialysis fiber. TTX significantly decreased ACh spontaneous release by more than 40%, but the exposure to 100 mM potassium released similar amounts of ACh in the absence and in the presence of 0.5 pM TTX (figure 2). However, H3 receptor-induced inhibition is... 

The influence of bicuculline on immepip-induced inhibition of 100 mM potassium-evoked release of ACh from the cortex of freely moving rats. Bicuculline was infused into the prefrontal cortex through the dialysis fiber 20 min before S2 and maintained during S2 stimulation. Immepip was infused, alone or with bicuculline, 10 min before S2 and maintained during S2. Shown are the means S.E. 

This glucose sensor relies on macromolecules trapped at one terminus (the distal end) of an optical fiber for signal generation. The macromolecules, FITC-labeled dextran and rhodamine-labeled concanavalin A (Rh-ConA), are trapped by a hollow dialysis fiber that fits snugly over the end of the optical fiber, as shown in Figure 7.8(a). A competitive equilibrium is set up between glucose and FITC-dextran, both of which bind to Rh-ConA ... 

The emission intensity of FITC is monitored at 520 nm as the analytical signal. When FITC-labeled dextran is bound to Rh-ConA, the rhodamine label quenches the 520-nm emission, so that the intensity measured is at a minimum. In the presence of the analyte (glucose), which diffuses across the dialysis fiber at the tip of the optical fiber, FITC-dextran is displaced from Rh-ConA by glucose, and emission intensity at 520-nm increases. This sensor allows glucose quantitation at concentrations up to 5 mM, and has a relatively slow response due to equilibration of the macromolecular reactions. 

Fig. 11. In-vivo glucose load with a healthy volunteer. Points plotted on the graph (+) are the glucose concentrations measured with a blood glucose analyser and (-) are the peaks of temperature change. The dialysis fiber (10 mm) was inserted subcutaneously. The perfusion rate was 3 pl/min...

The use of individual capillary membranes (often called dialysis fibers or hollow fibers) makes it possible to work with the small volumes needed for bioanalytical chemistry. The capillary geometry makes it easy to move microliter samples continuously and provides for a more rapid collection rate. 

Ultrafiltration probes (Fig. 2) consist of one or more hollow dialysis fibers connected to a single microbore, nonpermeable outflow tube. The outflow tube is connected to the source of negative pressure, either a roller pump or a Vacutainer. The probes come in various configurations with different numbers of fibers and different fiber lengths. Ultrafiltration probes tend to be larger than microdialysis probes. Typically there are one to three fibers, each 2 to 12 cm in length. The choice of a probe depends on the size of the implantation site and the desired flow rate. With an ultrafiltration probe, membrane surface area (and therefore probe size) affects the flow rate. A subcutaneously implanted probe with three 12-cm fibers would yield a flow rate of 1 jul/min, which would be suitable for subcutaneous implantation in a 200-g rat or any larger animal. For subcutaneous implantation in a mouse, a probe with one or three 2-cm fibers would be appropriate. 

FIG. 2. An ultrafiitiation probe consists of hollow dialysis fibers attached to microbore outflow tubing (A). Negative pressure is generated either by i ing a peristaltic pump (B) or by attaching a needle hub and using a Vacutainer (C). 

Janie, E. M., and Kissinger, P. T. (1993). Microdialysis and ultrafiltration sampling of small molecules and ions from in vivo dialysis fibers. AACC TDM/Toxicol. 14(7), 159. 

Figures 12.1.14-12.1.16 show a variety of shapes which have been observed. These include nanospheres, assemblies of cylindrical aggregates, and nanofibers." Nanospheres were obtained by the gradual removal of solvent by dialysis, fibers were produced by a series of processes involving dissolution, crosslinking, and annealing. Figure 12.1.17 sheds some light on the mechanism of aggregate formation. Two elements are clearly visible from micrographs knots and strands. Based on studies of carbohydrate amphiphiles, it is concluded that knots are formed early in the process by spinodal decomposition. Formation of...

A microdialysis sampling has been used for multivessel dissolution testing of isoniazide tablets. The dialyzer is produced using regenerated hollow cellulose dialysis fibers, and the detection is at 254 nm. 

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