Page 401 - Academic Press Encyclopedia of Physical Science and Technology 3rd Chemical Engineering

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Encyclopedia of Physical Science and Technology EN009K-419 July 19, 2001 20:57

336 Membranes, Synthetic, Applications

FIGURE 47 Schematic representation of the complex multifunctions enabled in a dual membrane bioreactor for
hydridoma cell culturing (Integra Biosciences AG, Wallisellen, Switzerland).

exclusively for producing high-value compounds—such A. Hemodialysis, Hemofiltration
as pharmaceuticals—whose market potential can support
A major physiological function of the kidney is to remove
the cost of developing new processes, their use has ex-
toxic metabolic wastes and excess fluids from the blood
panded to include processing of lower-value commodities
stream.Thisfunctionmaybeimpairedthroughchronicde-
and even wastes through creative integration of proven,
generation or as a result of injury. Hemodialysis is the most
increasingly reliable membrane unit operations.
commonly prescribed means of blood purification for end-
stage renal disease. The worldwide dialysis patient popu-
lation approached 1 million at the end of the 20th century.
VII. BIOMEDICAL APPLICATIONS In hemodialysis, blood from the patient flows on one
side of a membrane and a specially prepared dialysis so-
The use of synthetic membranes for medical therapy be- lution is fed to the other side. Waste material in the blood
gan with artificial kidney systems. For the better part of such as urea, excess acids, and electrolytes diffuse into
the 20th century, hemodialysis has been used as an im- the dialysate; the blood is then returned to the patient, as
portant life-support process for patients with renal dys- shown in Fig. 48. A patient typically undergoes dialysis
function. Today this procedure is practiced worldwide, three times per week in sessions lasting several hours each.
representing the single largest commercial membrane ap- Modern dialysis systems combine sophisticated monitor-
plication on the basis of consumption and revenue. Other ing and control functions to ensure safe operation. Regen-
blood treatment processes involving membranes have also erated cellulose was the first material used in hemodialysis
been developed over time, such as hemofiltration, plasma- membranes because of its biocompatibility and low cost;
pheresis, blood oxygenation, and various extracorporeal it remains the most popular choice. Subsequently, high-
therapies. In parallel, artificial organ concepts have been permeability dialysis membranes derived from cellulose
reduced to practice that include synthetic membranes as esters, modified polysulfone, or polyacrylonitrile copoly-
key components; some are nearing completion of clinical mers have also gained wide acceptance because of the
trial and poised to begin benefiting patients. shorter sessions they make possible.