【公開日：2024.07.25】【最終更新日：2024.06.14】

課題データ / Project Data

課題番号 / Project Issue Number

23NM5291

利用課題名 / Title

to develop novel bio-inspired underwater adhesive

利用した実施機関 / Support Institute

物質・材料研究機構 / NIMS

機関外・機関内の利用 / External or Internal Use

内部利用（ARIM事業参画者以外）/Internal Use (by non ARIM members)

技術領域 / Technology Area

【横断技術領域 / Cross-Technology Area】（主 / Main）物質・材料合成プロセス/Molecule & Material Synthesis（副 / Sub）-

【重要技術領域 / Important Technology Area】（主 / Main）マテリアルの高度循環のための技術/Advanced materials recycling technologies（副 / Sub）次世代バイオマテリアル/Next-generation biomaterials

キーワード / Keywords

bio-inspired adhesive, polymer design, photochemistry,生分解性材料/ Biodegradable material,核磁気共鳴/ Nuclear magnetic resonance,資源代替技術/ Resource alternative technology,易循環型材料設計技術/ Recycling-friendly material design technology,資源循環技術/ Resource circulation technology

利用者と利用形態 / User and Support Type

利用者名（課題申請者）/ User Name (Project Applicant)

WANG SIQIAN

所属名 / Affiliation

物質・材料研究機構

共同利用者氏名 / Names of Collaborators in Other Institutes Than Hub and Spoke Institutes

ARIM実施機関支援担当者 / Names of Collaborators in The Hub and Spoke Institutes

服部晋也

利用形態 / Support Type

（主 / Main）機器利用/Equipment Utilization（副 / Sub）-

利用した主な設備 / Equipment Used in This Project

NM-001：NMR
NM-018：HPLC(質量分析計付き)
NM-019：ゲル浸透クロマトグラフィー装置群

報告書データ / Report

概要（目的・用途・実施内容）/ Abstract (Aim, Use Applications and Contents)

Caffeic acid (3,4-dihydroxycinnamic acid), a sort of plant polyphenol, was incorporated into the target polymer to achieve reusable tough adhesive, because the caffeic acid possesses bilateral characteristics: a marine mussel-inspired adhesive moiety from a catechol and reversible photo-crosslinkable moiety from a cinnamic acid. The caffeic acid-functionalized adhesive involves a two-step adhesion process: as first, the caffeic acid-functionalized polymer was applied on the adherend, followed by UV irradiation (peak wavelength of light-emitting diode (LED), l_P: 365 nm, UV_L) to form pre-applied adhesive layer (PAA) through cross-linking reactions among the caffeic acid moieties, which is non-sticky yet has excellent long-term shelf life more than two years, even under ambient stock condition. Second, by thermal activation of the PAA layer when needed, tough adhesion can repeatedly exhibit to a variety of adherends, including polytetrafluoroethylene (PTFE), polyethylene (PE), polypropylene (PP), and silicone rubber (Reuse-Many mode). Furthermore, the cyclic dimer of the caffeic acid moiety was decrosslinked by UV irradiation (l_P: 254 nm, UV_S), which allowed us to completely remove the adhesive residues from the adherends when it is no longer needed (Reset-On demand mode). Furthermore, by adding magnetic nanoparticles, the caffeic acid-functionalized polymer enables us to remote application under water by combination of UV_L irradiation with magnetic induction heating activation. Our research paves the way to rationally design bio-inspired adhesives that perform beyond nature, with plant-derived raw materials, ultimately leading to contribution to a sustainable circular economy.

実験 / Experimental

I used ARIM instruments such as Nuclear Magnetic Resonance (NMR), Gel Permeation Chromatography (GPC), and Mass Spectrometry (MS) to characterize the structures of monomers and polymers synthesized in my research, facilitating better advancement of my research. The main experiments are used as follows: ¹H NMR (400 MHz) and ¹³C NMR (100 MHz) spectra were measured for CDCl₃ or DMSO-d solutions at 25 °C using a JNM-ECX 400 spectrometer (400 MHz-JEOL, Japan) (supported by ARIM institution), and the chemical shifts were reported in ppm with respect to the reference tetramethyl silane (SiMe₄, abbreviated as TMS). Gel permeation chromatography (GPC) was performed using Shodex GPC-101 equipped with a two-column system (Shodex KF-804L and Shodex KF-806L, Japan) (supported by ARIM institution) in THF at 25 °C and a 0.8 mL min⁻¹ flow rate. The instrument was calibrated by using polystyrene (PS) standards in the range of 2.6 to 96.4 kDa. High-resolution mass spectrometer (HRMS) spectra were measured for methanol solutions at 25 °C using a thermo scientific Q Exactive Plus spectrometer (Thermo Fisher Scientific Inc) (supported by ARIM institution).

結果と考察 / Results and Discussion

    Caffeic acid has dual functionality: adhesiveness from the catechol moiety and photo-reactivity from the cinnamoyl unit. We therefore designed a caffeic acid-functionalized adhesive polymer to be regarded as an analog of catechol and prepared a series of caffeic acid-functionalized copolymers of various molecular weights by the free radical polymerization of (E)-2-((3-(3,4-dihydroxyphenyl)acryloyl)oxy)ethyl acrylate and 2-ethylhexylmethacrylate in various ratios. The resulting caffeic acid functionalized polymers were characterized by proton nuclear magnetic resonance (¹H NMR) spectroscopy to confirm whether the caffeic acid moiety underwent photo-reversible [2+2] cycloaddition. This photo-cycloaddition reaction could be supported by ¹H-NMR spectroscopy. New signal peaks appeared in the chemical shift range 4.66–4.72 ppm upon UV_L irradiation (peak wavelength of lightemitting diode (LED), l_P: 365 nm), indicating that a cyclobutane group had formed. In addition, we realized that the formation of the photo-crosslinks affected the mechanical and thermal properties of Polymers. To determine the respective contributions of the catechol unit and the photo-crosslinking on adhesion and cohesion, we prepared Polymer without the photo-crosslinkable vinylene unit, without the hydroxyl groups with protected catechol hydroxyl groups, respectively. After UV_L irradiation, the adhesive strength of Polymer containing caffeic acid moiety was over approximately 95 times that of its adhesive strength before UV_L irradiation. Similarly, the adhesive strengths of polymers which contained photo-crosslinkable vinylene units but no catechols, increased by 7 times after UV_L irradiation that is much smaller, implying that catechol plays a critical role for adhesiveness. These results clearly indicate that cohesion by physical and chemical entanglement is essential for tough adhesion, as well as adhesion by non-covalent bonding between the catechol groups and the topmost surface of the adherend, as demonstrated by the mussel’s bioadhesive. Next, we confirmed that polymers containing caffeic acid moiety can be used as the photo-curable pre-applied adhesives, where adhesives in a viscous liquid form or dissolved in organic solvents when applied, transform into a hard yet non-sticky layer by UV_L irradiation. Notably, strong bio-inspired adhesives are often brittle, and need additional sacrificial weak interactions, such as hydrogen bonding, to enhance their toughness and bonding performance. In contrast, it was possible to maximize the toughness of the light-induced pre-applied adhesives system described herein by simply controlling its molecular weight and UV_L curing time. Here, HNMR, GPC and MS provided solid support for studying on characterization and properties of these adhesives.  

図・表・数式 / Figures, Tables and Equations

その他・特記事項（参考文献・謝辞等） / Remarks(References and Acknowledgements)

DOI（論文・プロシーディング）：10.1002/adfm.202215064

成果発表・成果利用 / Publication and Patents

論文・プロシーディング（DOIのあるもの） / DOI (Publication and Proceedings)

口頭発表、ポスター発表および、その他の論文 / Oral Presentations etc.

1. Oral presentation (No. 3J21), 72SPSJ

特許 / Patents

特許出願件数 / Number of Patent Applications：1件
特許登録件数 / Number of Registered Patents：1件