Super-strong intelligent fiber that "adheres upon contact with water"

A team led by Pei-Yi Wu and Sheng-Tong Sun at Donghua University reported a strong hydrogel fiber material with water-induced adhesion properties that resolves the structural contradiction of simultaneously achieving mechanical strength and self-adhesion. The fiber exhibits reversible humidity-responsive characteristics, maintaining high strength in a dry state and rapidly transforming into a highly adhesive state upon contact with water. This water-activated self-adhesive behavior is completely reversible, providing new insights for the design of high-performance adhesive materials in fields such as intelligent capture and micro-soft robots. The article was was recently published as an open access research article in CCS Chemistry, the flagship journal of the Chinese Chemical Society.

Background information:
Many viewers of Spider-Man are likely impressed by the incredible webs—incredibly strong yet capable of precisely adhering to and capturing their targets. In the real world, spider silk can indeed quickly become sticky in wet environments to trap flying insects, while remaining strong and resilient in dry conditions to support its mesh structure. However, in materials science, integrating the seemingly contradictory properties of high mechanical strengthand self-adhesion (the former requiring low chain mobility, the latter requiring high chain mobility) into a single man-made material has always been a significant challenge. Inspired by spider silk, the research team envisioned using wateras a "switch" to disrupt the physical cross-linking within strong fibers through hydration, thereby releasing mobile polymer chains and creating adhesiveness on the surface. This strategy holds promise for resolving the inherent conflict between the stiffness and adhesiveness of fiber materials.

Highlights of this article:
This study designed a copolymer hydrogel, P(DMAPS-co-NMA), and continuously fabricated micron-sized fibers using pultrusion spinning. These fibers possess a unique nano-confined phase-separated structure: the "strength unit" (PNMA units) tightly aggregates through hydrogen bonds in the dry state, forming nano-confined clusters that endow the fibers with ultra-high mechanical strength; the "adhesion unit" (PDMAPS units) acts as a matrix, highly hydrophilic and hygroscopic, imparting surface adhesion to the fibers. In ambient conditions, the fiber's internal structure is compact, the material is very hard and tough, and has almost no adhesiveness. However, under high humidity conditions, water molecules disrupt the hydrogen bonds of the PNMA clusters and the dipole interactions of the PDMAPS matrix, causing the fiber to soften instantaneously and release a large number of freely moving PDMAPS suspension chains, generating strong adhesion. Furthermore, this process is completely reversible ; when the moisture evaporates, the fiber returns to its strong and tough state, achieving a cyclical switching between "adhesion and detachment."

Under ambient conditions (25°C, 50% RH), the hydrogel fiber exhibits a Young's modulus as high as 1.3 GPa (comparable to engineering plastics) and a fracture energy of 228.5 kJ m⁻², demonstrating excellent resistance to crack propagation and impact. When activated and cured by water, the fiber rapidly absorbs water, softens, and becomes sticky. Its interfacial toughness (i.e., adhesion strength) after curing on a glass substrate reaches 1689 J m⁻², a value even exceeding that of VHB commercial tape (~1442 J m⁻²) . With its intelligent switching capability between "toughness" and "adhesion," this fiber shows great potential for applications such as intelligent capture. It requires no heating or electricity, relying solely on changes in ambient moisture to achieve object grasping and release, making it energy-efficient and highly effective. Through a series of characterization methods (AFM, low-field NMR, two-dimensional correlation infrared, etc.), this paper further reveals the microscopic response mechanism of water-induced adhesion.

Summary and Outlook:
This study, by mimicking the natural intelligence of spider silk, designed a novel hydrogel fiber with a layered nanostructure, successfully resolving the structural design contradiction between material stiffness and adhesion. This super-strong fiber, which "adheres upon contact with water," not only provides a new paradigm for the design of high-performance adhesive materials, but its unique intelligent response characteristics and scalable fabrication advantages also make it promising for applications in micro soft robots, intelligent grasping devices, and reversible adhesives.

The findings were published as a Research Article in CCS Chemistry. Liu Zhen, a master's student at the College of Chemistry and Chemical Engineering, Donghua University, is the first author of the paper, with Professor Wu Peiyi and Researcher Sun Shengtong as co-corresponding authors. This work was supported by the National Natural Science Foundation of China (NSFC) Key Project, among other funding.

---

About the journal: CCS Chemistry is the Chinese Chemical Society’s flagship publication, established to serve as the preeminent international chemistry journal published in China. It is an English language journal that covers all areas of chemistry and the chemical sciences, including groundbreaking concepts, mechanisms, methods, materials, reactions, and applications. All articles are diamond open access, with no fees for authors or readers. More information can be found at https://www.chinesechemsoc.org/journal/ccschem.

About the Chinese Chemical Society: The Chinese Chemical Society (CCS) is an academic organization formed by Chinese chemists of their own accord with the purpose of uniting Chinese chemists at home and abroad to promote the development of chemistry in China. The CCS was founded during a meeting of preeminent chemists in Nanjing on August 4, 1932. It currently has more than 120,000 individual members and 184 organizational members. There are 7 Divisions covering the major areas of chemistry: physical, inorganic, organic, polymer, analytical, applied and chemical education, as well as 31 Commissions, including catalysis, computational chemistry, photochemistry, electrochemistry, organic solid chemistry, environmental chemistry, and many other sub-fields of the chemical sciences. The CCS also has 10 committees, including the Woman’s Chemists Committee and Young Chemists Committee. More information can be found at https://www.chinesechemsoc.org/.