Browsing by Author "Akimoto, Jun"

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Controlling the electrostatic interaction using a thermal signal to structurally change thermoresponsive nanoparticles
(2019-09-20)
Akimoto, Jun
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Lin, Hsiu-Pen
;
Li, Yaw-Kuen
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Ito, Yoshihiro
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應用化學系
The negatively charged thermoresponsive polymers poly(benzyl methacrylate)-b-poly(acrylic acid)-b-poly(N-isopropylacrylamide) (PBzMA-b-PAAc-b-PIPAAm) were prepared by reversible-addition fragmentation chain transfer polymerization. The polymer formed core-shell polymeric micelles possessing a thermoresponsive corona composed of PAAc-b-PIPAAm below the lower critical solution temperature (LCST) of the PIPAAm chain. The nonionic thermoresponsive polymeric micelle composed of PBzMA-b-PIPAAm exhibited extensive intermicellar aggregation after the hydrophobic phase transition of the corona-forming PIPAAm chains. In contrast, insertion of the PAAc chain into the thermoresponsive micelle maintained its dispersibility above the LCST of PIPAAm because of the electrostatic repulsion between the micelles. The micelles with short PAAc chains suppressed the effect of the negative charge derived from PAAc below the LCST because of the extended PIPAAm chain on the micellar surface. In contrast, the negative charge property appeared due to collapse of the PIPAAm layer above the LCST. This thermoresponsive change in its electrostatic behavior enables the micelle to control the adsorption and desorption of oppositely charged molecules in response to the temperature change across the LCST.
Selective Control of Cell Activity with Hydrophilic Polymer-Covered Cationic Nanoparticles
(1970-01-01)
Lin, Hsiu-Pen
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Akimoto, Jun
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Li, Yaw-Kuen
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Ito, Yoshihiro
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交大名義發表
Cationic polymers exhibit high cytotoxicity via strong interaction with cell membranes. To reduce cell membrane damage, a hydrophilic polymer is introduced to the cationic nanoparticle surface. The hydrophilic polymer coating of cationic nanoparticles resulted in a nearly neutral nanoparticle. These particles are applied to mouse fibroblast (3T3) and human cervical adenocarcinoma (Hela) cells. Interestingly, nanoparticles with a long cationic segment decrease cell activity regardless of cell type, while those with a short segment only affect 3T3 cell activity at lower concentrations less than 500 mu g mL(-1). Most nanoparticles are located inside 3T3 cells but on the cell membrane of Hela cells. The short cationic nanoparticle shows negligible cell membrane damage despite its high accumulation on Hela cell membranes. Cell activity changed by hydrophilic polymer-coated cationic nanoparticles is caused by incorporated nanoparticle accumulation in the cells, not cell membrane damage. To suppress the cytotoxicity from the cationic polymer, cationic nanoparticle needs to completely cover with hydrophilic polymer so as not to exhibit the cationic effect and applies to cell with low concentrations to reduce the nonselective cytotoxicity from the cationic polymer.
Step-by-Step Assembled Enzyme-Polymer-Carbon Nanotubes for Solution-Processed Bioreactive Composites
(2019-07-01)
Lin, Hsiu-Pen
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Akimoto, Jun
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Li, Yaw-Kuen
;
Ito, Yoshihiro
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Kawamoto, Masuki
Protein-conjugated single-walled carbon nano tubes (SWCNTs) have received much attention for their diverse applications in molecular biology. Intrinsically water insoluble SWCNTs avoid conjugation with proteins, which leads to limited availability of biomolecule nanocarbon composites. Because protein functions are directly affected by assembled structures, the synthesis of heterogeneous composites with bioreactive responses is a great challenge. We demonstrate that step-by-step assembled enzyme/polymer/SWCNTs are obtained by using noncovalent-bonding methodologies in aqueous media. A multifunctional polymer containing aromatic, cationic, and redox-active units allows for a direct aqueous dispersion of SWCNTs through pi interactions and a subsequent charge attraction to the enzyme, which yields the ternary composites. The resulting composites show bioreactive responses in enzyme-conjugated SWCNT networks. The solution-processed glucose oxidase (GO(x))/polymer/SWCNT composite displays a high current density of 1420 mu A cm(-2) by enzymatic oxidation of glucose. Only 2.4 mu g of GO(x) is shown to be necessary for the enzymatic reaction with a sensitivity of 72 mu A mM(-1) cm(-2). This high sensitivity results from the assembled structure through noncovalent-bonding interactions. We demonstrate that the bioreactive composite allows energy conversion from a glucose-including beverage (cola) to electricity. Lactate oxidase-driven bioreactivity also takes place on the structurally organized composite. This step-by-step methodology would be beneficial for enzyme-assisted energy conversion nanocomposites.