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Affiliation |
Engineering educational research section Applied Chemistry Program |
YAMASHITA Yusuke
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Degree 【 display / non-display 】
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博士（工学） ( 2025.9 鹿児島大学 )
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修士（工学） ( 2023.2 鹿児島大学 )
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学士（工学） ( 2021.3 鹿児島大学 )
Papers 【 display / non-display 】
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Yamashita Y., Ohzuno Y., Saito Y., Fujiwara Y., Yoshida M., Takei T.
Gels 9 ( 4 ) 280 2023.3
Authorship：Lead author, Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Gels
Moist wound healing is known to heal wounds faster than dry wound healing. Hydrogel wound dressings are suitable for moist wound healing because of their hyperhydrous structure. Chitosan, a natural polymer, promotes wound healing by stimulating inflammatory cells and releasing bioactive compounds. Therefore, chitosan hydrogel has great potential as a wound dressing. In our previous study, physically crosslinked chitosan hydrogels were successfully prepared solely by freeze-thawing of chitosan-gluconic acid conjugate (CG) aqueous solution without using any toxic additives. Furthermore, the CG hydrogels could be sterilized by autoclaving (steam sterilization). In this study, we showed that autoclaving (121 °C, 20 min) of a CG aqueous solution simultaneously achieved gelation of the solution and sterilization of the hydrogel. Hydrogelation of CG aqueous solution by autoclaving is also physically crosslinking without any toxic additives. Further, we showed that the CG hydrogels retained favorable biological properties of the CG hydrogels prepared by freeze-thawing and subsequent autoclaving. These results indicated that CG hydrogels prepared by autoclaving were promising as wound dressings.
DOI： 10.3390/gels9040280
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Yamashita Y., Ohzuno Y., Yoshida M., Takei T.
Macromol 4 ( 2 ) 376 - 386 2024.5
Authorship：Lead author, Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Macromol
Conventionally, chitosan hydrogels are acidic and contain toxic chemicals because chitosan is soluble only in acidic solvents and requires toxic additives such as chemical crosslinkers and polymerization agents to fabricate chitosan hydrogels. These properties prevent chitosan hydrogels from being used for medical applications. In this study, chitosan hydrogels were prepared by a simple and versatile process using urea hydrolysis by autoclaving (steam sterilization, 121 °C, 20 min). When autoclaved, urea hydrolyzes in an acidic chitosan aqueous solution, and ammonia is produced, which increases the pH of the solution, and chitosan becomes insoluble, leading to the formation of a chitosan hydrogel. The pH and osmotic concentration of chitosan hydrogels could be adjusted to be suitable for physiological conditions (pH: 7.0–7.5, and osmotic concentration: 276–329 mOsm/L) by changing the amount of urea added to chitosan solutions (chitosan: 2.5% (w/v), urea: 0.75–1.0% (w/v), pH: 5.5). The hydrogels had extremely low cytotoxicity without the washing process. In addition, not only pure chitosan hydrogels, but also chitosan derivative hydrogels were prepared using this method. The autoclaving technique for preparing low-toxic and wash-free sterilized chitosan hydrogels in a single step is practical for medical applications.
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Yamashita Y., Hosoya K., Fujiwara Y., Saito Y., Yoshida M., Matsune S., Okubo K., Takei T.
Gels 11 ( 1 ) 60 2025.1
Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：Gels
After endoscopic sinus surgery (ESS), nasal packing is often used to stop bleeding and promote wound healing. Because maintaining a moist environment is important to enhance wound healing, hydrogel-based wound dressings are effective to promote wound healing. Chitosan is used in the medical field because of its high hemostatic and wound healing properties. We developed a pH-neutral and non-toxic chitosan hydrogel, which was difficult to achieve using conventional methods. In this study, we show in animal experiments that the chitosan hydrogel (hydrogel particles) had higher wound healing properties than a commercially available solid wound dressing (dry state) composed of the same polymer. Additionally, we applied the injectable chitosan hydrogel particles as nasal packing materials to patients with bilateral chronic sinusitis undergoing ESS in a pilot clinical study. Concerning symptom scores, though the results narrowly missed statistical differences (p < 0.05), the average scores of our chitosan hydrogel were superior to those of a commercially available wound dressing (especially p = 0.09 for nasal bleeding). These findings suggest that the injectable chitosan hydrogel could be a viable option as a packing material following ESS.
DOI： 10.3390/gels11010060
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Guanidinylated nanochitins: guanidinylated chitin nanocrystals are dispersible at neutral pH Reviewed
Izawa H., Ando S., Sone K., Tajima W., Zewude D.A., Yamashita Y., Ifuku S.
Journal of Materials Chemistry B 14 ( 1 ) 144 - 152 2026.1
Language：English Publishing type：Research paper (scientific journal) Publisher：Journal of Materials Chemistry B
Despite nanochitins showing favorable biological effects, the colloid stability of positively charged nanochitins by virtue of the amino group is limited to acidic pH, which is different from biological conditions. Here, we show that guanidinylated chitin nanocrystals (GChNCs) are dispersible at neutral pH. The GChNCs are prepared by guanidinylation of partially deacetylated chitin nanocrystals (ChNCs) with 1-amidinopyrazole hydrochloride. The degrees of guanidinylation and acetylation of the GChNCs are 4.6% and 75.7%, respectively. A 1.0 wt% GChNC dispersion is prepared with 0.5 wt% acetic acid solution by sonication treatment. Although slight white turbidity is observed due to scattering, no visible macroscopic precipitates are observed. The average diameter of the GChNCs estimated by DLS analysis is 327.2 nm. When the GChNC dispersion is neutralized by adding 0.1 M NaOH solution, the transmittance of the GChNC dispersion is decreased by aggregation. However, the transmittance of the GChNC dispersion is higher than that of the ChNC dispersion, suggesting that the GChNC particles are less aggregated than the ChNC particles due to the positive charge by virtue of the high basicity of the guanidino group. Interestingly, we find that the GChNCs homogeneously disperse in 0.1 M HEPES buffer (pH 7.4) up to 0.5 wt% by sonication treatment, even though the average diameter of the GChNCs in the solution is 3.4-fold higher (1115.1 nm) than that prepared at pH 3.0. We additionally find no observation of this improved dispersibility of guanidinylated chitin nanofibers due to the guanidino group. This result indicates that the guanidinylation is effective in improving the dispersion of nanochitins with smaller aspect ratios, like ChNCs. Furthermore, we demonstrate that the dispersibility of GChNCs at neutral pH can be utilized for material development, where a gelatin–GChNF composite hydrogel displaying enhanced mechanical properties is successfully prepared by adding 10% (w/w) GChNCs.
DOI： 10.1039/d5tb01771h
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Low-Extrusion-Force Injectable Chitosan Gel Microparticles for Effective Wound Dressing in Endoscopic Sinus Surgery Reviewed
Yuji Nagase , Yusuke Yamashita , Takuma Yoshinaga , Yoshihiro Ohzuno , Masahiro Yoshida , Kei Hosoya , Masaki Kawabata , Masaru Yamashita , Shoji Matsune , Takayuki Takei
Eng 7 ( 1 ) 53 2026.1
Language：English Publishing type：Research paper (scientific journal)
DOI： 10.3390/eng7010053
DOI： 10.3390/eng7010053