The most commonly used artificial organ is the artificial kidney using dialysis membrane, a machine that performs a treatment known as hemodialysis. This process cleanses the bodies of renal failure patients by dialysis, filtration and adsorption which are simple physicochemical processes. Dialysis membranes account for the largest volume of artificial membranes, far outstripping other fields. Worldwide, the consumption of dialysis membranes has reached some 300 million square meters a year. More than 70% of the dialysis membranes in use are made of polysulfone. This paper describes dialyzers and dialysis membranes so far developed for blood purification.

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Removal rate of renal toxic substances in a dialyzer depends on the mass transfer rate through a dialysis membrane and in the dialysate-side boundary films. To increasing dialysis fluid-side mass transfer rate, the most important factors are jacket structure and hollow fiber shape, so newly developed dialyzers with improved jacket structure and hollow fiber shape that optimize dialysis fluid flow have been made available on the market in recent years.
The overall mass transfer resistance is the sum of the resistances due to the membrane itself and the thin boundary film that is formed in the fluids on both sides of the membrane (Series Boundary Film Resistance Model). The boundary film mass transfer coefficient for a fluid flowing within a straight tube has been obtained theoretically. Colburn's equation converted to mass transfer by analogy with the theoretical approximation equation that yields the boundary film coefficient of heat transmission when laminar flow occurs in a straight tube, can be used to calculate the boundary film transfer in laminar mass transfer.
In the present study, mass transfer correlation equations between Sherwood number (Sh) containing dialysis fluidside mass transfer film coefficient and Reynolds number (Re) were formed for newly developed dialyzers. The exponents of Re were 0.62 for APS-15S whereas approximately 0.5 for the newly developed dialyzers. The dialysis fluid-side mass transfer film coefficients of the newly developed dialyzers were higher than those of the conventional dialyzer. Based on the mass transfer correlation equations, introduction of short taper, full baffle of dialyzer jacket and further wave-shaped hollow fiber improves the dialysis fluid flow.

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The patients in a chronic kidney failure are generally treated with a hemodialyzer as a substitute for their kidney. The antithrombogenicity is highly required to the hollow fiber membrane inside a hemodialyzer. To improve that of the polysulfone (PSf) membrane which is mainly used, a hydrophilic polyvinylpyrrolidone (PVP) polymer is blended to it.
We focused on the mobility of the bound water to the hydrophilic polymer, and found a new hydrophilic polymer (NV polymer) which was more antithrombogenic than PVP polymer. Applying the NV polymer to the PSf membrane surface in the nanometer order, we created an extremely antithrombogenic hollow fiber membrane for hemodialysis, which made the number of the platelet adhesion less than a hundredth compared with a conventional PSf membrane with PVP polymer.

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Many synthetic polymer dialysis membrane materials like polysulfone (PSf) and polyester-polymer alloy (PEPA) are hydrophobic polymers. Hence in preparing the membranes, a hydrophilic modifier of polyvinylpyrrolidone (PVP) should be added to hydrophilize them in order to suppress plasma protein adsorption on their surfaces. In the present study, we evaluated both PVP distributions and surface characteristics of dialysis membranes and films from a nanoscale perspective. We determined adsorbability between plasma proteins immobilized on the probe and PVP containing PSf films from the force-curve measurement by atomic force microscopy (AFM). The adsorption of albumin was inhibited by the presence of PVP on film surfaces more significantly than that of more hydrophobic fibrinogen. Furthermore, we performed nanoscale functional-group analysis of dialysis membranes made from PSf and PEPA by using near-field infrared microspectroscopy (NFIR). NFIR is a useful analysis technique for obtaining submicroscale to nanoscale chemical information. The nanoscale NFIR analysis showed heterogeneous distribution of PVP on the membrane surfaces and difference in the PVP homogeneities of different dialysis membranes.

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The fluid and solute transfer performances of dialyzers have been improved as a result of advances in membrane and device technology. To date, many types of dialyzers with high performance membranes have been developed. In some of these dialyzers, the pressure drop in the blood and dialysate streams occurs in a countercurrent manner, inducing internal filtration/back filtration (IF/BF). Namely, filtration from the blood through the membrane and to the dialysate occurs in the upstream of the blood flow and back filtration from the dialysate to the blood occurs in the downstream.
Recently, several types of dialyzer with enhanced internal filtration have been introduced for clinical application as a means of improving the efficiency of solute removal, and the enhanced internal filtration in these dialyzers has increased the convective transport of the solute besides the diffusive transport. The internal filtration flow rates (Q_IF) of the dialyzer, however, have never been evaluated precisely. During our studies, blood flow velocity in a cross-sectional plane of a dialyzer was measured by pulse Doppler ultrasonography to evaluate Q_IF. An in vitro study using bovine blood was carried out to determine the profile of local blood flow velocity with a probe slider that enables the probe to move in parallel along a dialyzer. The Doppler ultrasonography is a useful method for bedside monitoring of Q_IF in several dialyzers, because it is noninvasive to the patient and produces reliable data with higher reproducibility.

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According to the statistical survey carried by the Japanese Society for Dialysis Therapy at the end of 2010, the number of dialysis patients had reached to 297,126. The mean age was 66.2, and aging of this population had been progressed. Also, diabetes mellitus consists of 43.5% of all the primary diseases. Dialysis patients with complications are increasing in number, and more patients are in needs for assistance.
This trend will burden onto the medical personnel more heavily, so there is growing apprehension that medical errors and accidental infections may increase. The safety requirements are becoming higher, so it is desired to secure patients' safety and to improve medical personnel's environment.
In recent years, the water treatment systems to purify dialysis fluid and the fully automated dialysis system has developed to increase safety and save labor. These systems are effective to lighten the burden in current medical setting.
Purifying the dialysis fluid gives more treatment options. Mass substitution hemodiafiltration (HDF) therapy, including online HDF, is enabled, so it leads to the improvement of clinical symptoms.
The systems for dialysis therapy equip various membranes, such as RO membranes, UF membranes, and dialyzers. This report explains the utilization of each system.

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Hemodialysis is by far the most popular treatment modality for kidney disease patients in which blood and washingsolution (called dialysate)are separating flowing on either side of the separation membrane in order to remove wastesubstances mainly due to concentration gradient. This treatment, however, requires not only membrane devices (dialyzers)but also electric power source, computer-controlled high-tech dialysis machine, more than 120 L ofdialysate, and cannot be performed when the crisis occurs. We have been developing a wearable blood purificationsystem by combining membrane and other devices. The first system included particles of adsorbent dispersed inagar gel and it removed toxic substances as long as 1 week; however, the direct contact of blood with agar mayinduce bioincompatible reactions. The second and third systems included an ultrafilter and an adsorbent that connected to the outside loop of the ultrafilter with various returning points of ultrafiltrate. Ultrafiltration naturallyoccurs due to pressure gradient from blood compartment to the outer lumen of the membrane and the ultrafiltratereturns back to the main blood stream by virtue of the connection. Both systems showed the solute removal performances with satisfactory results. Moreover, this system may be further developed to the system with no electricpower source, water, or pump that can be available even under the crisis.

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Polypyrrole/acetylcellulose composite membranes, the solute-separation property of which is controllable, were prepared by electrochemical polymerization of pyrrole in a ultrafiltration membrane of acetylcellulose. The polymerization was carried out with two supporting electrolytes (NaClO₄ and sodium p-toluenesulfonate) under a galvanostatic condition. The difference of the supporting electrolytes influenced the solute-separation property of the formed composite membranes.
The separation property of the membranes was evaluated by the rejection of various molecular weights of polyethylene glycol as model solutes. The composite membranes separated the solutes with the molecular weight from a few hundreds to a few thousands. They changed their molecular weight cut-off by electrochemical doping and dedoping of electrolyte anions (dopants) to the polypyrrole component. In the composite membranes, the pores in the active layer of the acetylcellulose membrane component were likely to be filled with polypyrrole molecules. It was considered that the changes of the molecular weight cut-off were due to blockage of the pores by incorporation of the dopant anions into the polypyrrole molecules.
The composite membranes also changed finely the values of the solute rejection by adjusting the applied doping potential when the dopant anion with suitable molecular weight was selected (for example, 1-naphtalenesulfonate anion). Therefore, the composite membranes in the present study were recognized as the functional separation membranes, the solute-separation property of which is externally controllable.

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Decentralized water treatment and supply system with membrane technology has been rapidly spread in Japan, especially in groundwater purification by private sector. It is called “Groundwater Membrane Filtration System”, and the system includes all the components to manage water treatment and supply like public waterworks from water source to water tap. In addition, purified groundwater (treated water) has qualified water level to meet Japanese legal quality standard as drinking water, and treated water is blended with municipal water at user's storage tank. This combined water supply system is quite effective to prevent lack of drinking water in case of disaster, so that the groundwater membrane filtration system has attracted attention as one of the countermeasures for disaster. This paper describes the features of Wellthy's groundwater membrane filtration system, introducing the actual situation of installed system in the Great East Japan Earthquake.

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