Naoki Nakajima

Bio: Naoki Nakajima is an academic researcher from Kyoto University. The author has contributed to research in topics: Ethylene glycol & Transplantation. The author has an hindex of 20, co-authored 68 publications receiving 1837 citations.

In vitro evaluation of cytotoxicity of diepoxy compounds used for biomaterial modification

Abstract: The toxicity of various diepoxy compounds used for biomaterials crosslinking was investigated with a cell culture method and compared with an in vivo method. The neutral red uptake by cells was used to count the number of cells still alive after contact with the diepoxy compounds, because this method was more sensitive in cell counting than the other four methods studied in this work. The amount of neutral red taken up by cells depended strongly on the activity of cells in comparison with other methods; only small amounts of neutral red were taken up when cells were in a low activity state even if they were still alive. The in vitro toxicity of diepoxy compounds evaluated by the neutral red method revealed a good correlation with that found by the in vivo Draize test. The in vitro cytotoxicity to a cell line of L929 was closely related to that of primary culture cells of the normal rabbit cornea epidermal cell. The toxicity of diepoxy compounds was lower as their chain was longer, probably because of the lower chemical reactivity. All the diepoxy compounds investigated in this study exhibited lower cytotoxicity than formaldehyde, glutaraldehyde, and a water-soluble carbodiimide.

Surface modification of magnesium by NaHCO3 and corrosion behavior in Hank's solution for new biomaterial applications

Abstract: The present study was carried out to improve the corrosion resistance of pure magnesium in Hank's Balanced Salt Solution (HBSS) through the surface modification. Three kinds of alkaline compounds, such as sodium hydrogen carbonate, sodium carbonate, and lithium hydroxide, were used for treatment. Only magnesium treated with aqueous sodium hydrogen carbonate solution gave a good corrosion resistance in HBSS solution at 25°C up to 75 days, while almost no effect in sodium carbonate and lithium hydroxide. It was likely that hydrogen carbonate ions were essential for the surface improvement of magnesium. X-ray diffraction patterns of modified magnesium showed new peaks of magnesium carbonate and others on the surface. New surface structure of needle-shaped crystals was observed by scanning electron microscopy (SEM). Both elemental mapping, and energy dispersive (EDX) techniques in SEM showed the precipitation of calcium magnesium phosphate (low crystallinity whitlockite:(Ca,Mg)3(PO 4 ) 2 ) on the surface of magnesium specimen. It could be concluded that surface modification with sodium hydrogen carbonate made it possible to apply metal magnesium in biomedical, dental, and other industrial usage.

Low cytotoxic tissue adhesive based on oxidized dextran and epsilon-poly-L-lysine.

Abstract: A novel adhesive hydrogel consisting of dextran and epsilon-poly(L-lysine) (dextran-PL) with multiple biomedical applications was developed. Periodate oxidation in aqueous media almost stoichiometrically introduces aldehyde groups in dextran molecules, and aldehyde dextran can react with the primary amino groups in epsilon-PL (ɛ-PL) at neutral pH to form a hydrogel. The gelation time of the hydrogel can be easily controlled by the extent of oxidation in dextran and of the acylation in ɛ-PL by anhydrides. The shear adhesion strength of dextran-PL was 10 times higher than that of fibrin glue, when wet collagen sheets were selected as test specimens. The cytotoxicity of aldehyde dextran and ɛ-PL were 1000 times lower than that of glutaraldehyde and poly(allylamine). The considerably low cytotoxicity of aldehyde dextran could be ascribed to its low reactivity with amine species when compared with glutaraldehyde. In contrast, a high reactivity of amino groups in ɛ-PL was observed when compared with glycine, L-lysine, and gelatin, which could be explained by their poor dissociation at neutral pH, thus leading to low cytotoxicity.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Tough adhesives for diverse wet surfaces

Abstract: Adhesion to wet and dynamic surfaces, including biological tissues, is important in many fields but has proven to be extremely challenging. Existing adhesives are cytotoxic, adhere weakly to tissues, or cannot be used in wet environments. We report a bioinspired design for adhesives consisting of two layers: an adhesive surface and a dissipative matrix. The former adheres to the substrate by electrostatic interactions, covalent bonds, and physical interpenetration. The latter amplifies energy dissipation through hysteresis. The two layers synergistically lead to higher adhesion energies on wet surfaces as compared with those of existing adhesives. Adhesion occurs within minutes, independent of blood exposure and compatible with in vivo dynamic movements. This family of adhesives may be useful in many areas of application, including tissue adhesives, wound dressings, and tissue repair.

Biodegradable Cellulose-based Hydrogels: Design and Applications

Abstract: Hydrogels are macromolecular networks able to absorb and release water solutions in a reversible manner, in response to specific environmental stimuli. Such stimuli-sensitive behaviour makes hydrogels appealing for the design of ‘smart’ devices, applicable in a variety of technological fields. In particular, in cases where either ecological or biocompatibility issues are concerned, the biodegradability of the hydrogel network, together with the control of the degradation rate, may provide additional value to the developed device. This review surveys the design and the applications of cellulose-based hydrogels, which are extensively investigated due to the large availability of cellulose in nature, the intrinsic degradability of cellulose and the smart behaviour displayed by some cellulose derivatives. Keywords: Hydrogels; cellulose; biodegradation. 1. Introduction Hydrophilic polymers can swell and absorb water without dissolving, provided that chemical or physical crosslinks exist among the macromolecular chains. The polymer network resulting from the crosslinks swells in the aqueous solvent, until the thermodynamic force of swelling is totally counterbalanced by the elastic, retractive force exerted by the crosslinks. This ‘solid-like solution’ of polymer and water resulting at equilibrium is known as a hydrogel. The amount of water retained by