I am a member of the Membrane Society of Japan since the first meeting held on May 19, 1979. In this manuscript, I review my research on the relationship between structure/physical property and function in biomembrane. I introduce three major research projects. They are ‘study of temperature acclimation of cells”, ‘study of signal transduction of cells’ and ‘study of lipid rafts as phase-separated micro domain’.

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Redox polymers, aliphatic polymers bearing organic redox-active groups per repeating unit, are characterized by an ultimate population of the electron-releasing and -gaining site, which allows efficient redox-driven electron transport throughout the polymer membrane via self-exchange reactions. The high electron-transport reactivity of redox polymers provides very fast charge-propagation and reversible charge-storage in a rechargeable battery and photovoltaic cell. Redox polymers are emerging as a new class of electroactive organic materials useful for various kinds of wet-type energy storage and conversion devices.

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Reverse osmosis (RO) is one of the most effective and robust technologies for seawater desalination and wastewater reuse. However, RO uses so huge energy to produce fresh water that the high water production cost is one of the problems for RO process. There has been a growing interest in forward osmosis (FO). The FO process utilizes an osmotic pressure gradient generated by a highly concentrated solution (Draw Solution: DS) to allow water to diffuse through a semi-permeable membrane from a saline feed water (Feed Solution: FS), which has a relatively lower concentration than DS. A FO process consists of FO membranes, FO membrane modules, DS and a DS regeneration system. One of the primary obstacles hindering further development of FO processes is the lack of a suitable membrane designed specifically for osmotically driven membrane processes. A FO membrane requires high water permeability, low solute permeability and low structural parameter to reduce internal concentration polarization inside the membrane support layer. FO processes have potential applications to many desalination fields, such as landfill leachate, oil & gas wastewater, osmotic MBR, wastewater concentration, seawater desalination and pressure retarded osmosis.

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Application of membrane technology to water purification and wastewater treatment is being accelerated. The main obstacle for wider use of membrane technology is membrane fouling, which can be divided into two types depending on its reversibility: reversible (mostly cake layer) fouling and irreversible fouling. The former type of fouling can be cancelled by physical cleaning such as backwashing or air-souring, whereas the latter needs chemical cleaning to be cancelled. Most of full-scale membrane filtration units are operated with routine physical cleaning and control of irreversible fouling is therefore important. We have focused on characteristics of foulants causing irreversible fouling in membrane processes and have conducted many pilot-scale experiments using real drinking water source and municipal wastewater. Foulants extracted from the fouled membranes were subject to various analysis to investigate the characteristics of foulants. Analysis using Fourier transform infrared (FTIR) and 13C nuclear magnetic resonance (NMR) spectrum revealed that foulants that were responsible for irreversible fouling were mainly composed of polysaccharides and proteins regardless of type of application. It was also found that monosaccharide composition and amino acid composition in the foulants significantly varied depending on operational conditions of membrane processes. Detailed information on the foulants that cause irreversible fouling including their structures and origins is being revealed by advanced analytical techniques such as MALDI-TOF/MS. Once the structures of the foulants have been fully identified, it will be possible to specifically monitor the important foulants or microorganisms that produce them, which might enable effective control of membrane fouling. Also, extensive investigation of interactions between the important foulants and various membrane materials/structures should lead to the development of new anti-fouling membranes.

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Membrane Bio-Reactor (MBR) is a combined process of biological treatment and membrane separation. Kubota corporation addresses three approaches to reduce energy consumption of the current MBR system by 40% for energy saving MBR.
1) Evaluation of permeability of new membrane sheet and element
2) Control of air supply rate by monitoring permeability and improvement of membrane diffuser
3) Evaluation of Siphon filtration system instead of suction pump filtration system Comparing the permeability of current membrane sheet, it was validated that the new membrane sheet can be operated in the pilot plant at the higher average flux of 1.0 m³/(m²⋅d). It is under confirmation that air supply rate for cleaning membrane can be reduced by 50% compared to the current air supply rate by monitoring permeability and so on.
This research was supported by New Energy and Industrial Technology Development Organization (NEDO).

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Recently, membrane processes have been often applied to the water treatment system. In the end of 2010, total water treatment amount by membrane process was 1,290,000 m³/day and the water purification plants with membrane filtration reached to 737 plants. At early stage, membrane filtration processes were applied to water purification plants with small scale. However, at present large-scale membrane filtration plants with about hundred thousands m³/day have been operated. Many water purification plants are nowadays in renewal date. Therefore, water purification systems with membrane filtration attract much attention and the further spread of these systems is anticipated in future.

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Bile salts have potent detergent properties and damage hepatocytes by affecting the integrity of cellular membranes, which is important in liver disease. However, it is not fully understood how the canalicular membrane of hepatocytes acquires resistance against bile salts. ABCB4 mediates the secretion of phospholipids, preferentially phosphatidylcholine, from hepatocytes into the canalicular lumen in the presence of bile salts in an ATP-dependent manner. The biliary phospholipids in mixed micelles reduce the detergent activity of bile salts and protect the membranes of cells. In the liver, phosphatidylethanolamine (PE) is converted to phosphatidylcholine (PC) by PE N-methyltransferase (PEMT). The enzymatic activity and substrate specificity of PEMT are regulated by the N-terminal region localized in the endoplasmic reticulum lumen. PEMT expression enhances the cellular resistance against conjugated bile salts, which may be attributable to the alterations in the phospholipid composition and membrane structure. Therefore, ABCB4 and PEMT should play a crucial role in the resistance of hepatocytes against bile salt-induced cytotoxicity and in cholestasis and hepatocellular injury.

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In human erythrocytes, the 80-kDa isoform of protein 4.1R, 4.1R⁸⁰, maintains mechanical membrane stability and deformability as a result of multiple protein-protein interactions. 4.1R⁸⁰ binds to transmembrane proteins glycophorin C (GPC) and band 3 via its 30-kDa N-terminal FERM (Four one-Ezrin-Radixin-Moesin) domain (referred to as “R30” in the present study) and to spectrin and actin via a 10-kDa domain. Although the sites in R30 responsible for interaction with transmembrane proteins have been extensively studied, the identity of these sites has been challenged recently. Antibodies, in particular monoclonal antibodies (mAbs), are powerful tools not only for immunochemical studies but also for functional analyses such as the monitoring of the dynamic interactions of R30 with its binding partners. In the present study, we have generated mouse mAbs against recombinant R30 protein, and characterized their respective recognition epitopes in R30 using various recombinant proteins. Four representative clones, #5, #7, #9, #13 recognized the Y¹³¹DPELHGVDYVSDFKLAPN (pep8.1), Q¹⁵⁰ TKELEEKVMELHKSYR (pep8.2), M¹HCKVSLLDDTVYECVVE (pep4) and Q²⁴⁷EQYESTIGFKLPSYRA (pep13) epitopes, respectively. These sequences are located in the N-,α- and C-lobe structure of R30, respectively. IAsys-based in vitro binding analyses enabled us to demonstrate that the binding of R30 to pH 11-treated inside-out-vesicles (IOVs) was reduced by two combinations of mAbs (#5 and #9 or #7 and #9) but not by any of the mAbs alone and to confirm that the GPC binding site of R30 was located at or near pep8.1 and pep8.2 in the α- lobe of R30. Our study validates that this novel panel of mAbs constitutes a powerful tool for various types of analyses of 4.1R.

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In the past 30 years or more, Nitto Denko have started to develop spiral wound type reverse osmosis (RO) new thin composite membrane technology to apply to high efficiency water purification process such as brackish water and seawater desalination. Recently Nitto Denko released the new RO products with LD Technology™ for difficult industrial wastewater applications and reclamation of high quality water from municipal sewage for reuse applications. The advanced spiral wound element with LD Technology™, is based on a new idea of biofouling retardation in the spacer material and its improved structure. Therefore, in order to achieve low pressure drop performance of feed water channel, the RO element has the effective spacer of antibacterial property to control biofouling from the combination spacers. LD Technology™ consists of the innovative thicker spacer with a great improvement in geometry design and biostatic effect.

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