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Dive into the research topics where Sosaku Ichikawa is active.

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Featured researches published by Sosaku Ichikawa.


Advanced Drug Delivery Reviews | 2013

Industrial lab-on-a-chip: Design, applications and scale-up for drug discovery and delivery

Goran T. Vladisavljevic; Nauman Khalid; Marcos A. Neves; Takashi Kuroiwa; Mitsutoshi Nakajima; Kunihiko Uemura; Sosaku Ichikawa; Isao Kobayashi

Microfluidics is an emerging and promising interdisciplinary technology which offers powerful platforms for precise production of novel functional materials (e.g., emulsion droplets, microcapsules, and nanoparticles as drug delivery vehicles- and drug molecules) as well as high-throughput analyses (e.g., bioassays, detection, and diagnostics). In particular, multiphase microfluidics is a rapidly growing technology and has beneficial applications in various fields including biomedicals, chemicals, and foods. In this review, we first describe the fundamentals and latest developments in multiphase microfluidics for producing biocompatible materials that are precisely controlled in size, shape, internal morphology and composition. We next describe some microfluidic applications that synthesize drug molecules, handle biological substances and biological units, and imitate biological organs. We also highlight and discuss design, applications and scale up of droplet- and flow-based microfluidic devices used for drug discovery and delivery.


Journal of Colloid and Interface Science | 2009

Effects of surfactant and electrolyte concentrations on bubble formation and stabilization.

Qingyi Xu; Mitsutoshi Nakajima; Sosaku Ichikawa; Nobutaka Nakamura; Poritosh Roy; Hiroshi Okadome; Takeo Shiina

As interest in the application of microbubbles grows, it is becoming increasingly important to understand the factors affecting their formation and properties in order to effectively generate microbubbles. This paper investigates the effect of surfactant concentration and electrolyte addition on the size distribution and stability of microbubbles. The anionic surfactant sodium dodecyl sulfate (SDS) was used as the surfactant. Minimum bubble diameter and maximum stability were achieved at surfactant concentrations above the CMC. The effect of the electrolyte addition was studied by adding sodium chloride (NaCl) at an SDS concentration below the critical micelle concentration (CMC). Addition of NaCl decreased bubble size and improved bubble preparation to a certain extent. The addition of salt at low concentrations did not affect the surface tension; however, the surface tension was reduced as salt concentration was increased and reached a constant value for NaCl concentrations above 0.25%. The presence of NaCl resulted in a significant decrease in zeta-potential, implying a reduction in the surface charge of SDS micelles. This result suggests that the presence of NaCl may improve the generation and stability of bubbles by enhancing the structures of the adsorption monolayer and interfacial film.


Bioscience, Biotechnology, and Biochemistry | 2005

Formation of Biocompatible Nanoparticles by Self-Assembly of Enzymatic Hydrolysates of Chitosan and Carboxymethyl Cellulose

Sosaku Ichikawa; Satoshi Iwamoto; Jun Watanabe

A simple preparation method for biocompatible nanoparticles in high concentration (0.5 wt %) by self-assembly of chitosan and carboxymethyl cellulose hydrolysates was developed. Chitosan and carboxymethyl cellulose were hydrolyzed beforehand with chitosanase and cellulase respectively to make fragments having lower molecular weights. Nanoparticles were spontaneously formed only by mixing the two hydrolysate solutions. The particle size distribution was relatively narrow, about 200 nm in mean size. The mean particle size decreased from 226 nm to 165 nm with decreasing molecular weight of chitosan hydrolysate from 9.5 to 6.8 kDa. The mixing ratio of chitosan and carboxymethyl cellulose hydrolysates also affected particle size. Changes in particle size are discussed in relation to a possible mechanism of polyionic complexation. The chitosan-carboxymethyl cellulose nanoparticles were stably suspended over 1 week even under low pH (pH 3.0), high ionic strength (NaCl 1 M), or low temperature (4 °C) conditions.


Applied and Environmental Microbiology | 2010

Variation of Physiochemical Properties and Cell Association Activity of Membrane Vesicles with Growth Phase in Pseudomonas aeruginosa

Yosuke Tashiro; Sosaku Ichikawa; Motoyuki Shimizu; Masanori Toyofuku; Naoki Takaya; Toshiaki Nakajima-Kambe; Hiroo Uchiyama; Nobuhiko Nomura

ABSTRACT Pseudomonas aeruginosa and other Gram-negative bacteria release membrane vesicles (MVs) from their surfaces, and MVs have an ability to interact with bacterial cells. Although it has been known that many bacteria have mechanisms that control their phenotypes with the transition from exponential phase to stationary phase, changes of properties in released MVs have been poorly understood. Here, we demonstrate that MVs released by P. aeruginosa during the exponential and stationary phases possess different physiochemical properties. MVs purified from the stationary phase had higher buoyant densities than did those purified from the exponential phase. Surface charge, characterized by zeta potential, of MVs tended to be more negative as the growth shifted to the stationary phase, although the charges of PAO1 cells were not altered. Pseudomonas quinolone signal (PQS), one of the regulators related to MV production in P. aeruginosa, was lower in MVs purified from the exponential phase than in those from the stationary phase. MVs from the stationary phase more strongly associated with P. aeruginosa cells than did those from the exponential phase. Our findings suggest that properties of MVs are altered to readily interact with bacterial cells along with the growth transition in P. aeruginosa.


Biotechnology Progress | 2002

Factors affecting the composition of oligosaccharides produced in chitosan hydrolysis using immobilized chitosanases.

Takashi Kuroiwa; Sosaku Ichikawa; Osamu Hiruta; Seigo Sato; Sukekuni Mukataka

The hydrolysis reaction of chitosan using immobilized chitosanases with regard to the composition of its products and the yield of the intermediate target products, pentamer and hexamer of chitosan oligosaccharides, was investigated. Chitosanase was immobilized onto agar or agarose gel particles by the multipoint attachment method. In batch experiments, surface enzyme density, support particle size, temperature, agitator speed, and initial substrate concentration significantly affected the composition of the oligosaccharides produced. It was believed that these factors all related to the reaction rate and mass transfer rate at the surface of the support materials immobilizing the enzymes. These effects were summarized as a correlation with Damköhler number ( Da), defined as the ratio of the maximum reaction rate to the maximum mass transfer rate. The result showed that the reaction conditions that give a low value of Da provide a high yield of pentamer and hexamer oligosaccharides.


Langmuir | 2008

Temperature-sensitive nonionic vesicles prepared from Span 80 (sorbitan monooleate).

Keiichi Kato; Peter Walde; Norio Koine; Sosaku Ichikawa; Takashi Ishikawa; Ryo Nagahama; Takehiko Ishihara; Tetsuya Tsujii; Masachika Shudou; Yousuke Omokawa; Takashi Kuroiwa

Different types of nonionic vesicles were prepared from commercial Span 80 (also called sorbitan monooleate), as an inexpensive, biocompatible alternative to conventional phospholipid-based vesicles (liposomes). The vesicles were characterized by different techniques and comparison was made with vesicles formed from POPC (1-palmitoyl-2-oleoyl- sn-glycero-3-phosphocholine) or DOPC (1,2-dioleoyl- sn-glycero-3-phosphocholine). Dynamic light scattering measurements, electron microscopy analyses, and two types of fusion assays indicate that Span 80 vesicles are stable for at least 7 days at 4 or 25 degrees C, while storage at 42 degrees C causes irreversible vesicle fusion. This indicates that Span 80 vesicles are thermoresponsive with vesicle fusion occurring at elevated temperature. This property may be related to headgroup dehydration and is certainly not directly linked to the phase transition temperature (Tm) of the vesicles, since the Tm is below -30 degrees C, as determined by differential scanning calorimetry (DSC). The measured Tm value for Span 80 vesicles is lower than in the case of DOPC or POPC, correlating with a higher fluidity of Span 80 vesicles as compared to POPC or DOPC vesicles, as determined with DPH (1,6-diphenyl-1,3,5-hexatriene) as fluorescent membrane probe. High fluidity correlates with increased leakage of entrapped water-soluble dye molecules. Addition of cholesterol and soybean phosphatidylcholine lowers the extent of leakage, allowing a tuning of the bilayer permeability.


Journal of Bioscience and Bioengineering | 2002

Immobilization and stabilization of chitosanase by multipoint attachment to agar gel support.

Sosaku Ichikawa; Kazuya Takano; Takashi Kuroiwa; Osamu Hiruta; Seigo Sato; Sukekuni Mukataka

Highly stable chitosanase immobilized on an agar gel support was prepared by the multipoint attachment method. The optimum pH range was broadened to between 4 and 6, whereas for free chitosanase, the pH was only 5.6. The optimum temperature was also increased from 60 degrees C to 80 degrees C after the immobilization. The activity of immobilized chitosanase remained at 95% of its initial activity level after 225 h of incubation at 50 degrees C, whereas for free chitosanase, it decreased to 20% after 1 h of incubation. The immobilization markedly increased the thermostability of chitosanase. These changes in the reaction characteristics are favorable for the practical use of chitosanase in industrial processes. The effect of glycidol concentration in the activation of agar gel was also examined. The surface density of the aldehyde residue increased with increasing glycidol concentration. A maximal activity of 11.9 U/g-support was obtained when the glycidol concentration was 0.7 M. At concentrations higher than this, thermostability was almost the same. It was therefore proven that the optimal glycidol concentration in this system is 0.7 M. The effects of glycidol concentration on the activity and the thermostability of chitosanase are discussed in relation to the number of covalent bonds between the chitosanase and its support. Chitosan oligosaccharides were continuously produced using a column reactor packed with the immobilized chitosanase. The percentage of hydrolyzed chitosan after 28 reaction days was 44%. This was a slight decrease from the 48% observed on the first day. The total concentration of pentamer and hexamer ranged from 1.3 mg/ml to 1.5 mg/ml during the 28 reaction days. This was approximately 30% of the chitosan concentration in the supplied substrate solution.


Journal of Food Engineering | 1999

Solubility study of green tea extracts in pure solvents and edible oils

Victor Nwuha; Mitsutoshi Nakajima; Jihong Tong; Sosaku Ichikawa

Abstract The current study was aimed at the recovery of valuable bioactive components of green tea extracts (group of catechins) left over in industrial tea waste. The extraction and purification of green tea extracts (caffeine, (−)-epicatechin (EC), (+)-catechin (+C), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCg) and (−)-epicatechin gallate (ECg)) by use of 99.5%-ethanol and edible oils (oleic acid (OA) and sunflower oil (SFO)) were determined respectively. The solubility results were compared with the data obtained by the stability test after storing the samples for 14 days.


European Journal of Lipid Science and Technology | 2001

Characterization of phospholipid reverse micelles in relation to membrane processing of vegetable oils

R. Subramanian; Sosaku Ichikawa; Mitsutoshi Nakajima; Toshinori Kimura; Takaaki Maekawa

Studies were conducted to determine the critical micelle concentration (CMC) of phospholipids in vegetable oils and the size of reverse micelles to understand their rejection phenomenon in the membrane process. The CMC values of phosphatidylcholine (PC) in triolein and phospholipids in crude soybean oil were determined to be 440 and 1020 mg/kg, respectively, by using TCNQ (7,7,8,8-tetracyano-quinodimethane) solubilization technique. The surface tension measurements of these samples gave similar values of CMC. From small-angle X-ray scattering (SAXS) analysis, the size of the PC micelles was determined to be in the range of 3.56 to 4.70 nm. The characterization of reverse micelles formed in the oil system was found useful in enhancing the understanding of the possible rejection phenomenon of phospholipids by non-porous polymeric composite membranes used in our earlier studies on vegetable oils and in suggesting suitable types of membranes for the same.


Biotechnology and Bioengineering | 1998

Affinity extraction of proteins with a reversed micellar system composed of Cibacron Blue-modified lecithin.

Yan Sun; Sosaku Ichikawa; Shinji Sugiura; Shintaro Furusaki

Crude soybean lecithin was used as a novel surfactant to form reversed micelles in n-hexane. Cibacron Blue F-3GA (CB) was directly immobilized to the reversed micelles by a two-phase reaction. The reversed micellar system without CB showed low solubilizing capacity for low molecular weight proteins, lysozyme, and cytochrome c due to the weak electrostatic interactions. The introduction of CB significantly increased the solubilization of lysozyme because of its affinity binding to CB but showed no effect on the solubilization of cytochrome c since it did not bind to CB. Although bovine serum albumin had an affinity for CB, it was not extracted to the reversed micelles containing CB because its high molecular weight resulted in a significant steric hindrance effect. Thus the reversed micellar system had a high selectivity resulting from both biospecific and steric hindrance effects. The extraction yield of lysozyme decreased significantly with increasing ionic strength. Therefore, the back extraction of lysozyme was carried out using a stripping solution with an ionic strength of 0.865 mol/L. The overall recovery yield of lysozyme after back extraction could be increased to 87% by stripping for 2 h. The recovered lysozyme exhibited an activity equivalent to native lysozyme, and its secondary structure was also unchanged.

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Isao Kobayashi

National Agriculture and Food Research Organization

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Kunihiko Uemura

National Agriculture and Food Research Organization

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Toshiyuki Kanamori

National Institute of Advanced Industrial Science and Technology

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