Isao Kobayashi

Microscopic observation of emulsion droplet formation from a polycarbonate membrane

Real-time microscopic observations of the membrane emulsification process were performed using a novel membrane module and a microscope video system. The droplet growth and detachment processes from the membrane pores were analyzed from visual images taken during the experimental runs. A hydrophilic polycarbonate membrane with a mean pore size of 10 μm was employed. Microscopic observations of the oil droplet formation process from the membrane verified the continuous phase flow-driven droplet formation. This paper also describes the influences of the continuous phase flow velocity and the surfactant type on membrane emulsification. The use of anionic and nonionic surfactants resulted in successful membrane emulsification with no droplet coalescence at flow velocities greater than 0.1 m s−1. The droplet size of the resulting oil-in-water (O/W) emulsions decreased with an increase in the flow velocity, remaining almost constant at flow velocities greater than 0.4 m s−1. The emulsions prepared under these conditions had the average droplet sizes of about 20 μm and the coefficients of variation of 20–50%. In contrast, a cationic surfactant-containing system resulted in no droplet formation due to complete wetting of the membrane surface with the dispersed phase. An analysis of the surfactant–polycarbonate membrane interaction and contact angle measurements explained well the results that the membrane emulsification behavior critically depended on the type of surfactant used.

Effect of emulsifiers on the preparation of food‐grade oil‐in‐water emulsions using a straight‐through extrusion filter

This paper describes the preparation characteristics of food-grade soybean oil-in-water (O/W) emulsions using a novel straight-through extrusion filter, named a silicon straight-through microchannel (MC). Polyglycerol fatty acid ester (PGFE), polyoxyethelene sorbitan monolaurate (Tween 20), and sucrose fatty acid ester were tested as emulsifiers. Optical observations of the emulsification process exhibited that monodisperse oil droplets were stably formed from an oblong straight-through MC for PGFE and Tween 20. The effect of the emulsifier on the straight-through MC emulsification behavior is discussed. The selected PGFE- and Tween 20-containing systems enabled us to prepare monodisperse O/W emulsions with droplet diameters of 38—39 μm and coefficients of variation below 3% using an oblong straight-through MC with a 16 μm-equivalent channel diameter.

Formation of Biocompatible Nanoparticles via the Self‐Assembly of Chitosan and Modified Lecithin

The formation of biocompatible nanoparticles via the self-assembly of chitosan (CHI) and modified lecithin (ML) was studied. Stable nanoparticles in the size range of 123 to 350 nm were formed at over a wide molar mixing ratios of CHI/ML solutions (amino group/phosphate group) (NH(3) (+)/PO(3) (-)) and total polyelectrolyte (PE) concentrations (0.1 to 1 wt%) except at intermediate molar ratios when the surface charge was close to neutrality. Zeta-potentials of the nanoparticles were found to be independent of the total PE concentrations. Nanoparticles exhibited excellent stability at over an extended pH (pHs 3 to 6) and ionic strength range (< or = 500 mM NaCl concentration). The particle size and zeta-potential of the nanoparticles increased with the molecular weight of CHI. Transmission electron microscopy suggested that nanoparticles were generally spherical in shape with CHI constituting the exterior of its surface at high molar mixing ratios. Dextran-fluorescein isothiocyanate, bovine serum albumin, and Coomassie brilliant blue as models of nonionic, positively and negatively charged compounds were encapsulated within the nanoparticles at between 8.7% and 62.7% efficiency. The ability of the nanoparticle suspensions to be converted to lyophilized powder or concentrated suspension was also demonstrated.

Preparation of Monodisperse Food-Grade Oleuropein-Loaded W/O/W Emulsions Using Microchannel Emulsification and Evaluation of Their Storage Stability

W/O/W emulsion is an emerging system in developing new functional and low-calorie food products. The aim of this study is to produce food-grade monodisperse water-in-oil-in-water (W/O/W) emulsions loaded with a hydrophilic bioactive oleuropein. W/O/W emulsions were prepared via high-pressure homogenization and subsequent microchannel (MC) emulsification. The internal aqueous phase was a 5-mM sodium phosphate buffer containing d(+)-glucose (5xa0wt.%) and oleuropein (0.1–0.7xa0wt.%). The oil phase consisted of soybean oil and tetraglycerin monolaurate condensed ricinoleic acid esters (TGCR; 3–8xa0wt.%). The external aqueous phase was a 5-mM sodium phosphate buffer containing d(+)-glucose (5xa0wt.%) and decaglycerol monolaurate (1xa0wt.%). Oleuropein-loaded submicron W/O emulsions with average droplet diameters as small as 0.15xa0μm and monomodal droplet size distributions were prepared by high-pressure homogenization when applying high TGCR concentrations of 5–8xa0wt.% and low oleuropein concentrations of 0.1–0.3xa0wt.%. Monodisperse oleuropein-loaded W/O/W emulsions with average W/O droplet diameters of around 27xa0μm and coefficients of variation of below 5xa0% were successfully prepared when using a silicon MC array plate with wide channels of 5-μm depth and 18-μm width. The monodisperse W/O/W emulsions prepared at high TGCR concentrations and low oleuropein concentrations were the most stable during 40xa0days of storage. The adsorption behavior of oleuropein at the internal aqueous–oil interface was relevant to W/O/W emulsions microstructure and stability. The results are believed to provide useful information for successfully preparing stable monodisperse W/O/W emulsions loaded with hydrophilic functional compounds. The surface activity of the loaded material seems to be a key parameter in optimizing the formulation of W/O/W food emulsion.

EXTRACTION OF PALLADIUM(II) AND PLATINUM(IV) AS CHLOROCOMPLEX ACIDS INTO BASIC ORGANIC SOLVENTS

ABSTRACT Solvent extraction of platinum(IV) and palladium(II) with tri-n-octylamine(TOA) in o-xylene from 4.0M (Na,H)(Cl, HSO4) has been investigated at 298K in order to compare with similar extraction by trioctylphosphine oxide(TOPO). The dependence of the distribution ratio of platinum(IV) and pal 1adium(II) on TOA, hydrogen ion and chloride ion concentrations suggests the dominant extracted species of these metals would be 2:1 for proto-nated amine : chlorocomplex anion and the extraction should be essentially anion exchange reaction. The extraction constants (Kex = D[H+(T0A)C1xa0]xa02[C1xa0]2), were evaluated as 106-3 and 105.8 for platinum(IV) and pal ladium(II), respectively. The anion exchange with protonated TOPO salt represented by H(T0P0)2 +C1xa0 is less than that with protonated TOA salt by a factor of one order.

Relief of Arsenate Toxicity by Cd-Stimulated Phytochelatin Synthesis in the Green Alga Chlamydomonas reinhardtii

In most photosynthetic organisms, inorganic arsenic taken up into the cells inhibits photosynthesis and cellular growth. In a green alga, Chlamydomonas reinhardtii, 0.5xa0mM arsenate inhibited photosynthesis almost completely within 30xa0min. However, in cells acclimated with a sublethal concentration (0.05 to 0.1xa0mM) of Cd, the inhibition of photosynthesis at 30xa0min after the addition of arsenate was relieved by more than 50%. The concentrations of arsenic incorporated into the cells were not significantly different between the Cd-acclimated and the non-acclimated cells. The Cd-acclimated cells accumulated Cd and synthesized phytochelatin (PC) peptides, which are known to play an important role in detoxification of heavy metals in plants. By the addition of an inhibitor of glutathione (an intermediate in the PC biosynthetic pathway) biosynthesis, buthionine sulfoximine, cells lost not only Cd tolerance but also arsenate tolerance. These results suggest that glutathione and/or PCs synthesized in Cd-acclimated cells are involved in mechanisms of arsenate tolerance.

Formulation and stability assessment of ergocalciferol loaded oil-in-water nanoemulsions: Insights of emulsifiers effect on stabilization mechanism

In the study, we investigated the effect of emulsifiers with different stabilizing mechanisms on the formulation and stability of ergocalciferol loaded oil-in-water (O/W) emulsions. O/W emulsion stabilized by modified lecithin (ML; electrostatic stabilization), sodium caseinate (SC; electrosteric stabilization) or decaglycerol monooleate (MO-7S; steric stabilization) were formulated using high-pressure homogenization. The Sauter mean diameter (d3,2) of emulsions produced by ML, SC and MO-7S were 126±1, 127±4 and 138±3nm, respectively. The stability of resulting emulsions was evaluated when they exposed to different environmental stresses and during 30days of storage at 25 and 55°C. Results showed that the emulsions prepared by MO-7S or ML were stable against a wide range of pH (2-8), while SC-stabilized emulsions showed instability with extensive droplet aggregation at pH4 or and 5. Only ML-stabilized emulsions showed droplet growth due to coalescence when treated at high NaCl concentration (300-500mM). In the absence of glucose, SC-stabilized O/W emulsions showed better freeze-thaw stability, in comparison to those formed with ML or MO-7S emulsifiers. The emulsion produced by ML was found to be stable to droplet aggregation at heating temperatures (80-120°C) for 1h. All the O/W emulsions stored at 25°C showed good physical and chemical stability. However, the chemical stability of ergocalciferol in emulsion system decreased in order of ML>MO-7S≫SC during storage at 55°C for a period of 30days. These findings provide valuable information for the development of nanoemulsion-based delivery system applied in food and beverage products.

Recent lab-on-chip developments for novel drug discovery

Microelectromechanical systems (MEMS) and micro total analysis systems (μTAS) revolutionized the biochemical and electronic industries, and this miniaturization process became a key driver for many markets. Now, it is a driving force for innovations in life sciences, diagnostics, analytical sciences, and chemistry, which are called ‘lab‐on‐a‐chip, (LOC)’ devices. The use of these devices allows the development of fast, portable, and easy‐to‐use systems with a high level of functional integration for applications such as point‐of‐care diagnostics, forensics, the analysis of biomolecules, environmental or food analysis, and drug development. In this review, we report on the latest developments in fabrication methods and production methodologies to tailor LOC devices. A brief overview of scale‐up strategies is also presented together with their potential applications in drug delivery and discovery. The impact of LOC devices on drug development and discovery has been extensively reviewed in the past. The current research focuses on fast and accurate detection of genomics, cell mutations and analysis, drug delivery, and discovery. The current research also differentiates the LOC devices into new terminology of microengineering, like organ‐on‐a‐chip, stem cells‐on‐a‐chip, human‐on‐a‐chip, and body‐on‐a‐chip. Key challenges will be the transfer of fabricated LOC devices from lab‐scale to industrial large‐scale production. Moreover, extensive toxicological studies are needed to justify the use of microfabricated drug delivery vehicles in biological systems. It will also be challenging to transfer the in vitro findings to suitable and promising in vivo models. WIREs Syst Biol Med 2017, 9:e1381. doi: 10.1002/wsbm.1381

Efficient preparation of giant vesicles as biomimetic compartment systems with high entrapment yields for biomacromolecules.

The ‘lipid‐coated ice‐droplet hydration method’ was applied for the preparation of milliliter volumes of a suspension of giant phospholipid vesicles containing in the inner aqueous vesicle pool in high yield either calcein, α‐chymotrypsin, fluorescently labeled bovine serum albumin or dextran (FITC‐BSA and FITC‐dextran; FITC=fluorescein isothiocyanate). The vesicles had an average diameter of ca. 7–11u2005μm and contained 20–50% of the desired molecules to be entrapped, the entrapment yield being dependent on the chemical structure of the entrapped molecules and on the details of the vesicle‐formation procedure. The ‘lipid‐coated ice droplet hydration method’ is a multistep process, based on i) the initial formation of a monodisperse water‐in‐oil emulsion by microchannel emulsification, followed by ii) emulsion droplet freezing, and iii) surfactant and oil removal, and replacement with bilayer‐forming lipids and an aqueous solution. If one aims at applying the method for the entrapment of enzymes, retention of catalytic activity is important to consider. With α‐chymotrypsin as first model enzyme to be used with the method, it was shown that high retention of enzymatic activity is possible, and that the entrapped enzyme molecules were able to catalyze the hydrolysis of a membrane‐permeable substrate which was added to the vesicles after their formation. Furthermore, one of the critical steps of the method that leads to significant release of the molecules from the water droplets was investigated and optimized by using calcein as fluorescent probe.

Effect of esterified oligosaccharides on the formation and stability of oil-in-water emulsions.

Hydrophobically modified oligosaccharides were prepared by an enzyme-catalyzed reaction of maltodextrin/xylo-oligosaccharide and palmitic acid. Maltodextrin with dextrose equivalent (DE) of 16 palmitate (DE16_P) and 9 palmitate (DE9_P), as well as xylo-oligosaccharide palmitate (Xylo_P), were used. The effect of the concentration (10-50% (w/w)) and type of esterified oligosaccharides on the Sauter mean diameter and droplet-size distribution, the rate of coalescence (Kc), and the creaming properties of O/W emulsions were investigated. Esterified oligosaccharides (EO) adsorbed to the surface of the oil droplets. EO formed polydisperse O/W emulsions with particle sizes between 12 and 70 μm, depended on concentration of EO. The Sauter mean diameter, Kc, and the creaming index decreased markedly, with increasing concentration of EO. The type of ester minimally affected the Sauter mean diameter at each ester concentration. DE9_P inhibited coalescence and creaming more efficiently than other EO, mainly due to the higher viscosity of the continuous phase.