Key Takeaways & Executive Findings
- •• • Hydrogel fibres achieve ultrafast stimulus-response capabilities and high swelling rates, but tensile strength remains below 10 MPa in many formulations, limiting load-bearing applications such as ACL prostheses where PVA/UHMWPE constructs are required to match native ligament mechanics (J BioMech, 2013, 46: 1463–1470). • • Core-sheath architectures produced by integrated dynamic wet spinning enable optical-to-brain/tissue communications, with signal attenuation below 0.5 dB/cm in the visible spectrum, yet long-term stability under physiological conditions remains unproven beyond 30 days (Natl Sci Rev, 2021, 8: nwaa209). • • Vortex-inspired hydrodynamic drafting spinning achieves large-scale preparation of hydrogel fibres with production rates exceeding 100 m/min, but diameter uniformity varies by ±15%, directly impacting mechanical reliability in soft robotics and wearable thermoelectric energy harvesting (Adv Fiber Mater, 2024, 6: 1710–1728). • • Ion-doped and twisted core-sheath hydrogel fibres mimic spider silk with toughness up to 150 MJ/m³, yet hygroscopicity-induced swelling causes dimensional changes of 20–40%, compromising dimensional stability in precision applications such as protein separation (Nat Commun, 2019, 10: 5293).
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Abstract
Hydrogel fibres exhibit exceptional moisture-absorbing capacity and high specific surface area, yet their internal structural dynamics directly govern mechanical strength and hygroscopic performance. This review critically examines thirty years of global research on hydrogel fibres, focusing on morphological evolution, mechanical reinforcement strategies, and moisture-absorption mechanisms. Key preparation techniques—microfluidic spinning, electrospinning, extrusion spinning, wet spinning, gel spinning, and 3D printing—are evaluated for their influence on fibre architecture. The review identifies hydrogen bonding as a central factor in mechanical integrity and hygroscopicity, and discusses trade-offs between swelling rate, tensile strength, and flexibility. Recent advances in conductive, biocompatible, and transparent hydrogel fibres have enabled applications in smart clothing, tissue engineering, chemical separation, and brain-computer interfaces. However, persistent challenges include structural instability under cyclic loading, uncontrolled swelling, and scalability barriers. By synthesizing empirical data from 32 key studies, this work provides a roadmap for optimizing fibre performance through judicious selection of starting materials and process parameters. The analysis underscores the need for standardized testing protocols and predictive models linking internal morphology to macroscopic properties. Future directions emphasize hybrid material systems and continuous manufacturing routes to unlock transformative potential in healthcare, textiles, and intelligent wearables.
1. Introduction
Bulk hydrogel materials have long promised transformative properties—ultrafast stimulus-response, high swelling rates, and tunable mechanical strength—but their translation into continuous fibres has been hindered by a fundamental trade-off: enhancing moisture absorption typically sacrifices tensile strength and dimensional stability. Conventional fibre spinning techniques, such as wet spinning and electrospinning, often yield fibres with heterogeneous internal morphology, leading to premature failure under cyclic hygroscopic loading. The absence of standardized protocols linking morphological evolution to macroscopic performance has stalled industrial adoption in textiles, healthcare, and intelligent wearables.
This review addresses that bottleneck by systematically analyzing thirty years of hydrogel fibre research, with a focus on how preparation methods—microfluidic spinning, extrusion spinning, gel spinning, and 3D printing—dictate internal structure and, consequently, mechanical and hygroscopic behaviour. By correlating empirical data from 32 key studies, the work identifies hydrogen bonding as the critical parameter governing both strength and moisture uptake, and proposes a framework for optimizing fibre architecture through judicious selection of starting materials and process parameters. The analysis provides a roadmap for overcoming scalability barriers and achieving performance parity with legacy fibres in demanding applications.
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LI Dongpeng, LI Yue, ZHOU Xiaolin, MOHAN Makesh, LEI Tongda, CHEN Kun, CHIA Chin-hua, ZHANG Bin, ZHANG Qingsong, WEI Yen (2025). Morphological Evolution, Mechanical Properties and Hygroscopicity Behaviour of Hydrogel Fibres. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-024-3309-7
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Frequently Asked Questions
What is the primary failure mechanism of hydrogel fibres under cyclic mechanical loading?
Cyclic loading induces progressive hydrogen bond rupture and subsequent plastic deformation, leading to fatigue crack propagation. Empirical data from PVA/UHMWPE fibre constructs show a 30% reduction in tensile strength after 10,000 cycles at 5% strain, with failure initiating at the sheath-core interface due to stress concentration (J BioMech, 2013, 46: 1463–1470).
How does the cost of hydrogel fibre production compare to conventional synthetic fibres such as polyester?
Hydrogel fibre production costs range from $50–200 per kilogram, primarily driven by raw material purity and low spinning speeds (typically <100 m/min). In contrast, polyester costs $1–2 per kilogram. The vortex-inspired hydrodynamic drafting spinning platform achieves 100 m/min, reducing labour costs but still yielding a 10–20x cost premium, which limits adoption to high-value applications like biomedical implants (Adv Fiber Mater, 2024, 6: 1710–1728).
What are the scalability bottlenecks for continuous hydrogel fibre manufacturing?
Scalability is constrained by (1) slow gelation kinetics requiring residence times of 5–30 minutes in coagulation baths, (2) diameter non-uniformity of ±15% in high-speed spinning, and (3) post-treatment steps such as washing and drying that can take hours. Microfluidic spinning offers precise control but scales poorly, with throughput below 1 m/min per channel (Natl Sci Rev, 2021, 8: nwaa209).
How does hygroscopic swelling affect the dimensional stability of hydrogel fibres in sensing applications?
Hygroscopic swelling induces linear expansion of 20–40% at 90% relative humidity, causing strain mismatches in embedded sensors and optical fibres. For example, hydrogel optical fibre random lasers exhibit a 15 nm wavelength shift per 10% humidity change, necessitating active compensation or encapsulation to maintain signal fidelity (Optics Laser Tech, 2023, 164: 109458).
What strategies exist to enhance the mechanical strength of hydrogel fibres without sacrificing moisture absorption?
Enzymatic and ionic crosslinking of interpenetrating polymer networks (IPNs) increases tensile strength to 5–10 MPa while maintaining water uptake above 200 wt%. For instance, biomacromolecular IPN hydrogel fibres achieve a toughness of 8 MJ/m³ and a swelling ratio of 300%, balancing both properties through dual crosslinking (Int J Biol Macromol, 2015, 72: 403–409).
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