The high level of removability of virus in the purification process of bio-drugs such as 5 logs removal draws the new concept of membrane structure. The novel structure is represented by the multi-layers, each of which shows the characteristics of a screen filter, resulting in the multi-steps filtration. In this review the preparation method of the membrane with multi-layers and its performance of virus removal and protein permeability are dealed with. In order to apply the me-mbrane in the actual purification process, the membrane should be validatable, that is, reproducible and predictable in virus removal. The combination of two type tests of a breakage and a non-breakage tests is employed in the manufacturing process of the membrane. The test for the confirmation of mean characteristic values such as mean pore size is an example of breakage tests and the pressure hold test is one of non-breakage tests. This combination makes the membrane validatable. The users of this membrane should carry out the integrity test developed for the membrane manufacturer. The target particle to be removed spread widely such as prion proteins and DNA. The mechanism of separation of fine particles has been clarified and then, the new separation method of diffusion using the membrane may be succesful in future.

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Membrane application to hemodialysis, plasma and cell separation is reviewed. Japan is leading in this field. Development and improvement of hemodialysis membranes are directed toward permeability of glomerular basement membrane and better biocompatibility. From this viewpoint, present polysufone membranes have advantages over other membranes, while further improvement is continuing. Use of the membranes to separate plasma is steadily increasing for therapeutic purpose, competing with centrifugation. Leukocyte reduction in blood transfusion has opened a new market for membrane or filter technology. New applications in cell separation are anticipated through development of cellular therapy and regenerative medicine.

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Membrane separation technology using the polymer has been applied above all. The artificial kidney is one of the things which industrially grew and succeeded most, the number of dialysis patients has exceeded 200000 in 2000 year-ends for the advance of hemodialysis.
Originally, a membrane means the biomembrane, and the organism maintains the life by the skillful membrane mechanism. It will be reasonable outcome to introduce the membrane separation technology into medical field, in the medical purpose to attempt the recovery of damaged biofunction.
Regrettably, the practical artificial membrane that has produced does not have the advanced function like the biomembrane. In the present state, that is applied in the medical field as an extension of membrane separation technology in the conventional industry field. In short, it is merely the physical separation membrane for the material separation using selective permeability by the interaction at most, of spatial size, between solute and membranogen material.
However, the peculiarity of using under the organism environment certainly must be considered in case of the medical application. The defense reaction of the organism works by the contact between blood and separation membrane which is foreign body for the organism. The degree of this reaction is called the biocompatibility, and they are important with the separation characteristics in the design of a membrane.

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Many kinds of membranes are widely used for medical device. This review focuses on blood glucose meter (MEDISAFE^®), leukocyte removal filters (IMUGARD^®, IMUFLEX^®), vitamin E-modified dialyzer (CLIRANCE^®-E, CLIRANCE^®-EE, CLIRANCE^®-PSE) and cell therapy device.
Current blood glucose meter (MEDISAFE^®) is convenience, because patients only put a blood droplet on test strip, and need not to wipe blood. Porous polysulfone-type membrane was used for test strip, which removed blood cells from whole blood and was penetrated by plasma. Two types of latest blood glucose meters are averable, one inform the rebel of blood glucose on voice for blind patients (MEDISAFE VOICE^®), and another need only one operation, that puncture, collect blood, and measure blood glucose (MEDISAFE^® ez). Porous polysulfone-type membrane was also used for them.
Leukocyte contamination in blood products have been shown to cause post-transfusion adverse effects. To eliminatethose effects, leukocyte number in products has been recommended to be less than 1-5×10⁶/bag, then, we have developed leukocyte removal filters, IMUGARD^® and IMUFLEX^®, which are made of porous polyurethane membrane. The mechanism of leukocyte reduction with porous membrane was studied using polyurethane membrane, and followings were found. Leukocytes are removed at a constant ratio against thickness of porous membrane.
There have been various reports on the effects of the vitamin-E modified dialyzer CLIRANCE^®-E/EE. These effects include a decrease oxidative stress and oxidative products. Therefore vitamin-E modified dialyzers are expected to reduce prolonged complications.
We have been developing a new filter device for MNC (mononuclear cell) separation using porous polyurethane membrane. This filter device has a transformable mechanism of compression-nonloaded state of the polyurethane membrane so that facilitates the object cell recovery from captured site. This filter shows over 90% of MNC recovery with over 95% of RBC (red blood cell), and about 90% of platelet removal from whole blood. This filter will be useful device for cell processing aim at the medical practices, such as cell therapy and reengineering therapy.

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Tissue engineering is an interdisciplinary field that applies principles of engineering and the life sciences toward the development of biological substitutes that restore, maintain and improve the function of damaged tissues and organs. Isolated cells cannot form new tissues on their own. They require a specific environment, in which a supporting materials (i.e., artificial polymeric membranes in this review) act as a template and a natural environment in vitro.
The cell function depends on the matrices (i.e., the membranes) where the cells attach, e.g., whether the membranes contain the cell adhesion molecules (e.g., extracellular matrices, RGD, YIGSR, REDV and specific saccharides).
The key factors required for polymeric membranes used for the tissue engineering are discussed; chemical, physical and biological properties. The application of the tissue engineering using the porous membranes is reviewed such as nerve regeneration using nerve entubulation made of porous gel (nerve guide), bioartificial liver and biohybrid skin composed of fibroblast cells from neonatal foreskin, silicon rubber membrane and nylon mesh as the scaffold. The membrane science such as polymeric synthesis for the novel membranes, membrane formation theory and membrane characterization in the tissue engineering is significantly important for the development of the tissue engineering.

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The epithelial transport system is a thermodynamic system which is composed of membranes and fluid compartments. I regard membrane to be dissipative subsystem in which power dissipates, and fluid compartment to be capacitive subsystem in which power is stored. Each subsystem can be subdivided into elementary processes, and can be modeled by generalized capacitor, power transducer and resistor in a bond graph. For this modeling, I consider causality of dissipative process and devise a representation of power coupling in a dissipative subsystem. A membrane transport can be modeled by a combination of these subsystems. I can derive the phenomenological equation with concrete parameters from the model of the dissipative subsystem.

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An epoxy-group-containing monomer, glycidyl methacrylate (GMA), was grafted onto a porous hollow-fiber membrane made of polyethylene by immersion of the electron-beam-irradiated membrane in GMA/methanol and GMA/1-butanol solution. Subsequently, the produced epoxy group of the graft chain was converted into four kinds of chelate-forming groups capable of recovering an organic germanium compound, poly-trans- [(2-carboxyethyl) germanium sesquioxide] (p.t-CEtGeO). Breakthrough curves of p.t-CEtGeO during the permeation of a p.t-CEtGeO solution through the pores of the chelating porous hollow-fiber membranes were determined to compare the adsorption capacity; the membrane prepared by the reaction of the poly-GMA chain with 2-nitrilopropanol-2-nitriloisopropanol exhibited the highest adsorption capacity of p.t-CEtGeO at 34 mg per g of the membrane. The membrane prepared in 1-butanol has 1.5-fold greater adsorption capacity than that prepared in methanol. Breakthrough curves overlapped irrespective of the residence time of the p.t-CEtGeO solution across the membrane of 1.7 to 17 sec. High-speed recovery was realized due to negligible diffusional mass-transfer resistance of p.t-CEtGeO to the chelate-forming group of the graft chain.

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The Planova^® filter, which was introduced into the market by Asahi Kasei Corporation at 1987, removes virus from proteins, to increase the safety of plasma products and biotech products. It blocks the virus passage by a size-exclusion mechanism, based on its unique capillary-void structure and the multi-layer filtration mechanism. The target proteins are smaller than the membrane pores, and can therefore pass through the membrane.

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