Dialyzers hollow-fiber dialyzer

Hollow fiber dialyzers typically contain 1 -2 m2 of membrane in the form of fibers 0.1-0.2 mm in diameter. A typical dialyzer module may contain several thousand fibers housed in a 2-in.-diameter tube, 1-2 ft long. Approximately... 

In a hollow fiber dialyzer the blood flows down the bore of the fiber, providing good fluid flow hydrodynamics. An advantage of the hollow fiber design is that only 60-100 mL of blood is required to fill the dialyzer. At the end of a dialysis procedure hollow fiber dialyzers can also be easily drained, flushed with sterilizing agent, and reused. Dialyzer reuse is widely practiced, in part for economic reasons, but also because the biocompatibility of the membrane appears to improve after exposure to blood. 

The hollow-fiber dialyzer is the most effective design for providing low-volume, high efficiency devices with low resistance to flow. It is a composite of capillary, small, hollow... 

The performance of the hollow-fiber dialyzers depends on many fiber properties such as fiber dimension, surface area, porosity and water permeability. 

Salt is to be removed from a solution containing lOOg/Uter of salt and 200g/liter of rafBnose by dialysis in a hollow fiber dialyzer operating countercurrentiy. The overall mass-transfer coefficient for the salt was determined in the dialyzer with 200 cm /min feed flow rate and 500 cm /min pure water dialysate flow rate to be 0.0415 cm/min. If 90% of the salt is to be removed for the same feed and dialysate flow rates, what is the hollow fiber membrane area required Assume that the overall transport coefficient remains unchanged due to any changed conditions. (Ans. 14 860 cm. )... 

Example 11.2-2 Toxin removal vs. dialysate flow A hollow fiber dialyzer is 30 cm long, 3.8 cm in diameter, and contains a volume fraction of hollow fibers f of 0.2 which are 200 pm in diameter. The overall mass transfer coefficient k in these fibers is 3.6 10 " cm/ sec, and can be assumed independent of blood and dialysate flows. 

Where should it flow in a hollow fiber dialyzer ... 

The solution is dialyzed against the same buffer using a hollow fiber assembly, and then added onto a column of Affi-Gel Blue (50-100 mesh, 2 x 15 cm, Bio-Rad) prepared with the same buffer. The column is washed with the same buffer. Then luciferase is eluted with 50 mM Tris-HCl, pH 8.5, containing 5mM EDTA, 3 mM DTT, and 0.5 M NaCl (Hastings and Dunlap, 1986, state that it may be preferable to omit the Affi-Gel step because of difficulties encountered). 

D-glucosidase preparations were concentrated and dialyzed with an Amicon model DC-2 Hollow Fiber Ultraconcentrator equipped with HlPlO-20 or HlPlOO-20 cartridges. 

Hollow Fiber with Sorbent Walls. A cellulose sorbent and dialyzing membrane hollow fiber was reported in 1977 by Enka GlanzstolT AG. This hollow fiber, with an inside diameter of about A00 p m. has a double-layer wall The inner wall consists of Cuprophan cellulose and is very-thin. approximately 8 pm. The outer wall, which is ca 40-prn thick, consists mainly of sorbent substance bonded by cellulose. The advantage of such a fiber is that it combines the principles of hemodialysis w ith those of hernoperfusion. Two such fibers have been made one with activated carbon in the liber wall, and one with aluminum oxide, which is a phosphate binder. 

Kolf s first tubular dialyzer, shown in Figure 12.2, required several liters of blood to prime the system, a major operational problem. In the 1950s, tubular dialyzers were replaced with coil (spiral) devices, also developed by Kolf and coworkers. This coil system was the basis for the first disposable dialyzer produced commercially in the early 1960s. The blood volume required to prime the device was still excessive, however, and during the 1960s the plate-and-frame and hollow fiber devices shown in Figure 12.3 were developed. In the US in 1975, about 65 % of all dialyzers were coil, 20 % hollow fiber systems and 15 % plate-and-frame. Within 10 years the coil dialyzer had essentially disappeared, and the market was divided two-thirds hollow fibers and one-third plate-and-frame. By 1996, hollow fiber dialyzers had more than 95 % of the market. 

Figure 12.3 Schematic of hollow fiber and plate-and-frame dialyzers...

While both of these devices use hollow fiber membranes similar to the primary components of kidney dialyzer units, the difference between the two techniques lies in how the analyte undergoes mass transport into the device. Microdialysis sampling is a diffusion-based separation process that requires the analyte to freely diffuse from the tissue space into the membrane inner lumen in order to be collected by the perfusion fluid that passes through the inner lumen of the fiber. Ultrafiltration pulls sample fluid into the fiber lumen by applying a vacuum to the membrane (Figure 6.1). 

Parallel-plate hemodialyzers using flat membranes, with several compartments in parallel, separated by plastic plates, are now only available from Hospal Co (Crystal and Hemospal models). Blood circulates between two membranes and the dialysate between the other side of membrane and the plastic plate. These parallel-plate dialyzers have a smaller blood-pressure drop than hollow-fiber ones and require less anticoagulants as flat channels are less exposed to thrombus formation than fibers, but they are heavier and bulkier and thus less popular. A recent survey of the state-of-the-art in hemodialyzers is given in [13]. 

In Curacao, the major island of the Netherlands Antilles with a population of 130,000 inhabitants, distilled seawater from the water plant was used without further purification for hemodialysis for several decades. Unfortunately, two months before the planned installation of a water treatment system including a reversed osmosis (RO) in the dialysis center Diatel, a new distribution pipe supplying water to a dialysis center on the island was installed in 1996. To protect it from corrosion, this pipe was lined on the inside with a cement mortar. Because of the aggressiveness of the distilled water, calcium and Al leached from the cement mortar into the water used to prepare dialysate. At the time of replacement of the new conduit pipe, 29 patients were dialyzed in the dialysis unit. Patients were dialyzed three times per week during 3.5 to 4.5 hours using hollow fiber kidneys (Fresenius, F6 and F8). Untreated tap... 

An artificial kidney is a device that removes water and waste metabolites from blood. In one such device, the hollow fiber hemodialyzer, blood flows from an artery through the insides of a bundle of hollow cellulose acetate fibers, and dialyzing fluid, which consists of water and various dissolved salts, flows on the outside of the fibers. Water and waste metabolites—principally urea, creatinine, uric acid, and phosphate ions—pass through the fiber walls into the dialyzing fluid, and the purified blood is returned to a vein. 

A schematic diagram of the hollow fiber (or capillary) dialyzer, the most commonly used artificial kidney. The blood flows through many small tubes constructed of semipermeable membrane these tubes are bathed in the dialyzing solution. 

The dialysate solution is recirculated through the hemodialyzer system. In hospitals where multiple patients are treated, central dialysate supply systems are normally used. The flow rates of blood and dialysate through a hollow-fiber-type dialyzer are approximately 200-300 ml min-1 and 500 ml min-1, respectively. The more recently developed hemodialyzers have all been disposable that is, they are presterilized and used only once. Normally, a patient will undergo dialysis for 4—5 h per day, for three days each week. 

---