Publications by authors named "Naruki Kurokawa"

4 Publications

  • Page 1 of 1

Fabrication of Gd-DOTA-functionalized carboxylated nanodiamonds for selective MR imaging (MRI) of the lymphatic system.

Nanotechnology 2021 Mar 3. Epub 2021 Mar 3.

Department of Mechanical Engineering, Keio University Faculty of Science and Technology Graduate School of Science and Technology, 3-14-1 Hiyoshi Kohoku-ku, Yokohama, 223-8542, JAPAN.

Magnetic resonance imaging (MRI) contrast agents with the particle diameter of around 3-10 nm hold the potential to be selectively uptaken by lymphatic vessels and be filtered in the kidney for final excretion. However, there are no existing MRI contrast agents based on gadolinium (Gd) complexes within the size of this range, and thus the selective imaging of the lymphatic system has not yet been achieved. In our previous report, we succeeded in fabricating nano-scale MRI contrast agents by complexing ordinary contrast agents (Gd-diethylenetriaminepentaacetic acid (DTPA)) with carboxylated nanodiamond (CND) particles to conquer this problem. However, DTPA has recently been reported to release Gd ions in the course of time, leading to the potential danger of severe side effects in the human body. In this study, we utilized cyclic-chained DOTA as an alternative chelating material for DTPA to fabricate CND-based MRI contrast agents for the selective lymphatic imaging. The newly fabricated contrast agents possessed the diameter ranging from 3 nm to 10 nm in distilled water and serum, indicating that these particles can be selectively uptaken by lymphatic vessels and effectively filtered in the kidney. Furthermore, the DOTA-applied CND contrast agents exhibited stronger MRI visibility in water and serum compared to DTPA-applied CND contrast agents. These results indicate that DOTA-applied CND contrast agents are promising materials for the selective MR imaging of lymphatic systems.
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http://dx.doi.org/10.1088/1361-6528/abeb9cDOI Listing
March 2021

Thermophysical Property Measurements of Tetrabutylphosphonium Oxalate (TBPOx) Ionic Semiclathrate Hydrate as a Media for the Thermal Energy Storage System.

Front Chem 2020 16;8:547. Epub 2020 Jul 16.

Department of Mechanical Engineering, Keio University, Tokyo, Japan.

With increasing global power demand, thermal energy storage technology could play a role ensuring a sustainable energy supply in power generation from renewable energy sources and power demand concentration. Hydrates have high potential as phase change materials (PCMs) for the use as a thermal energy storage medium. To develop thermal energy storage technology using a hydrate-based material, further investigation of thermophysical properties and the selection of a suitable hydrate are required. Tetrabutylphosphonium oxalate (TBPOx) ionic semiclathrate hydrate contains oxalic acid in salt form, as a guest compound, which is classified as carboxylic acid group with low environmental impact. In the present study, the phase equilibrium temperature and the dissociation heat of TBPOx hydrate were measured. The highest equilibrium temperature of the solid hydrate formed was 9.4°C at the mass fraction 0.35 of TBPOx in aqueous solution. The largest dissociation heat was 186.0 ± 0.5 kJ·kg at the mass fraction of 0.35. Comparing with other PCMs with close phase equilibrium temperatures, TBPOx hydrate is superior in safety and sustainability. These results indicate that TBPOx hydrate would be suitable as the thermal storage medium for the general air conditioning systems.
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http://dx.doi.org/10.3389/fchem.2020.00547DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7378790PMC
July 2020

SANS study on the nano-crystalline network structure of elastic physical gels made of syndiotactic polypropylene.

Soft Matter 2019 Jul;15(27):5521-5528

Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan.

The structure-property relationship of an elastic physical gel, obtained by simply quenching syndiotactic polypropylene (sPP)/decahydronaphthalene solution with liquid nitrogen, was investigated based on small-angle neutron scattering (SANS) analysis. The SANS analysis revealed that sPP nanocrystals with a constant radius of 4-5 nm existed in the sPP gels regardless of the sPP concentration, whereas the correlation length of the nanocrystals drastically decreased from ∼130 to ∼20 nm upon increasing the sPP concentration from 2 to 12 wt%. The volume fraction and the number density of the sPP nanocrystals increased monotonously with the increase in the sPP concentration. The rheological properties and the melting behavior of the quenched sPP gels were highly consistent with the number density of the nanocrystals calculated from the SANS analysis, strongly suggesting that the sPP nanocrystals actually worked as crosslinking points by inducing elasticity in the quenched sPP gels.
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http://dx.doi.org/10.1039/c9sm00582jDOI Listing
July 2019

Strong, Resilient, and Sustainable Aliphatic Polyester Thermoplastic Elastomers.

Biomacromolecules 2017 Jun 3;18(6):1845-1854. Epub 2017 May 3.

Department of Chemistry, University of Minnesota , Minneapolis, Minnesota 55455-0431, United States of America.

Thermoplastic elastomers (TPEs) composed of ABA block polymers exhibit a wide variety of properties and are easily processable as they contain physical, rather than chemical, cross-links. Poly(γ-methyl-ε-caprolactone) (PγMCL) is an amorphous polymer with a low entanglement molar mass (M = 2.9 kg mol), making it a suitable choice for tough elastomers. Incorporating PγMCL as the midblock with polylactide (PLA) end blocks (f = 0.17) results in TPEs with high stresses and elongations at break (σ = 24 ± 2 MPa and ε = 1029 ± 20%, respectively) and low levels of hysteresis. The use of isotactic PLA as the end blocks (f = 0.17) increases the strength and toughness of the material (σ = 30 ± 4 MPa, ε = 988 ± 30%) due to its semicrystalline nature. This study aims to demonstrate how the outstanding properties in these sustainable materials are a result of the entanglements, glass transition temperature, segment-segment interaction parameter, and crystallinity, resulting in comparable properties to the commercially relevant styrene-based TPEs.
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http://dx.doi.org/10.1021/acs.biomac.7b00283DOI Listing
June 2017