Membrane technology can be investigated from various viewpoints. This article briefly summarizes permeation properties and characterization methods in gas and liquid phase. First, permeation properties through charged nanofiltration membranes are introduced in terms of rejection of electrolytes of various valence types and ion separation of mixed electrolytes. Pore size evaluation by nanopermporometry and modified Gas translation model is introduced for nano–sized and subnano–sized pores, respectively, followed by process simulation of single and multi-modules and application to membrane reactors. Finally, generalized solution–diffusion model, which enables comprehensive understanding of reverse osmosis, pervaporation and vapor permeation, is introduced.

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Pharmacokinetics is an academic field that attempts to understand the mechanisms underlying the fate of drugs in the body after administration, including absorption, distribution, metabolism, and excretion processes. The biomembrane transport is an important factor determining these processes either directly or indirectly. In this article, I would like to introduce how I started my research on membrane transport and how I encountered The Membrane Society of Japan. In addition, as an example of membrane transport research, I will briefly explain the studies on the organic ion transport in the renal tubular epithelial cell membranes and on the kidney–specific accumulation of aminoglycoside by receptor–mediated endocytosis.

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Membrane symposium is one of the most important events of Japanese Membrane Society. It was held in Kyoto for a long time. Since I lived in Kyoto, I have a deep attachment to this Membrane symposium. My first attendance in this symposium is in 1994. After that, I attended in this symposium every year except for my 1 year staying in USA. Here, I overview my research activities based on the topics presented in Membrane symposium. The research topics that I did are Gas separation membrane, Porous membrane preparation by phase separation, Membrane fouling reduction, Membrane with channel material, Forward osmosis (FO) process and Organic solvent reverse osmosis (OSRO).

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Transdermal drug delivery is receiving a growing concern to alternate conventional drug administration techniques such as oral administration or needle–stick based administration methods. In this review article, we proposed a patch system based on a solid–in–oil nanodispersion technique as a simple and efficient delivery method of drugs, especially protein and peptide vaccines, through the skin. The skin is an attractive route for vaccination because there are many immune cells. We have developed the solid–in–oil nanodisperison technique to deliver pharmaceutical bioactives efficiently through the skin. Solid–in–oil nanodispersions are nanosized drug carriers designed to overcome the skin barrier. Drug administration using a patch is user–friendly and can improve patient compliance. Protein and peptide antigen drugs were efficiently delivered across the intact skin using the solid–in–oil nanodispersions. The technique is potent transcutaneous immunization method without needles.

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Exchangeable apolipoproteins such as apoA–I and apoE function in lipid transport as structural components of lipoprotein particles, cofactors for enzyme, and ligands for cell–surface receptors. Both apoA–I and apoE contain amphipathic α– helical repeats that can adopt a helix bundle conformation in the N–terminal domain, with the separate C–terminal domain being primarily responsible for lipid binding. Interaction with lipid membranes induces changes in the conformation of the N–terminal domain in apoA–I and apoE, providing molecular insights into how these apolipoproteins interact with lipids on cell surfaces and lipoprotein particles. A hereditary amyloidogenic mutation in apoA–I destabilizes the N–terminal helix bundle structure and facilitates amyloid fibril formation by the N–terminal fragment of apoA–I in solution as well as on lipid membranes. Here, I briefly review my research on the structure and function of apolipoproteins based on lipid–apolipoprotein interaction.

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In response to a request to write about the history of my membrane technology research, I decided to write a three–part series. I started my research on membrane technology in 1974, about 50 years ago. It was around the time when membranes were not commercially available in Japan, and seawater desalination using reverse osmosis was just beginning to be put into practical use in the United States. Since then, I have researched various things about membranes, so I can’t write everything in three articles. Of course, there are some studies that did not produce good results and were forgotten. Therefore, instead of writing about the research conducted in chronological order, I divided the research themes broadly and decided to write about each of them. In this first installment, I will write about membrane fouling and transport equations for membrane permeation, which are areas in which I have conducted experiments and analyzed myself. Concerning fouling of membranes, I showed flux behavior by fouling when sewage treated water is treated with reverse osmosis and I demonstrated that the gel layer concentration was not constant, which was believed to be constant in the gel layer model. Moreover, I explained that the characteristic phenomena of fouling could be explained only by osmotic pressure. These discoveries were the first in the world at the time, but are now common knowledge and are written in every textbook. As for the transport equation, I proved the effectiveness of the 3–parameter transport equation as an alternative to the 2–parameter transport equation proposed by my teacher, Professor Shoji Kimura, and proposed a pore model that connects the parameters and the membrane pore structure.

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Contamination of portable water source with organic micropollutants have increasingly recognized as a potential risk for the human health. Such contaminants include pesticide, herbicide, medicines, PFAS (per– and polyfluoroalkyl substance) and so on. These organic micropollutants could be removed by conventional spiral wound nanofiltration (NF) technology, however, it often requires extensive pretreatment, thus had to increase greenhouse gas emission in the entire treatment process while solving human health issue. In order to solve this dilemma, direct nanofiltration (dNF) technology has been developed. The hollow fiber dNF membrane, with the patented polyelectrolytes based layer by layer technology, was tested with actual surface water that contains micropollutants. For most of the micropollutants including PFAS, the dNF permeate showed below detection limits, which was not possible with conventional hollow fiber UF/MF technology due to their larger pore size. The same dNF membrane was operated in a commercial plant in Dumai, Indonesia for humic acid removal. The membrane have exhibited stable operation for one and half a year.

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