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Coiled‐polymer‐fiber‐based artificial muscles can provide large contractile actuation stroke. However, it is a challenge to achieve high actuation load and high actuation stroke for artificial muscle simultaneously. Herein, a powerful coiled‐polymer‐fiber‐based artificial muscle with a "rigid‐and‐flexible" structure is fabricated by cotwisting rigid heterocyclic aramid (HA) fibers with flexible silver‐plated nylon (SPN) fibers. The artificial muscle based on coiled HA@SPN fibers can lift a load over 108 MPa with a fast response time of 0.6 s, which is 309 times heavier than the load that human muscle can lift, and generate a work density per temperature of 41.3 J (kg °C)−1. The coiled HA@SPN fiber muscle exhibits high actuation stability of over 30 000 cycles. The coiled HA@SPN fiber muscle can provide a contractile actuation stroke of up to 8.2% and generate an average gravimetric mechanical energy density of 702 J kg−1, which is 18.1 times that of human skeletal muscle (≈38.8 J kg−1). An average contractile power density of 1168 W kg−1 is obtained for coiled HA@SPN fiber muscle, which is 23.4 times that of human skeletal muscle (≈50 W kg−1). [ABSTRACT FROM AUTHOR]

Hydrogels with high strength, high modulus, and high toughness have great application potential in the field of artificial human load‐bearing tissues, but the preparation of materials with the above high performance is still a huge challenge. In this paper, a structural construction strategy of ordered‐to‐disordered (OTD) transition is proposed to obtain hydrogel fibers with high strength, high modulus, and high toughness. The structural construction strategy of OTD refers to the ordered‐to‐disordered transition of molecular segments in PVA polymer fibers through swelling and subsequent salting‐out treatment, while still maintaining the general order of the entire polymer chain. PVA molecular chain crystallites provide physical crosslinking to stabilize the structure. The results show that the elongation at break of the hydrogel fiber can reach 257%). The strength reaches 190.04 MPa, which is more than 4 times higher than that of human ligaments. The modulus reaches 137.31 MPa, which perfectly matches the human ligaments, and the toughness can reach 100.61 MJ m−3. In addition, it has stable mechanical properties in liquid environment and excellent biocompatibility, which has great application potential in the field of artificial ligaments. This OTD structural construction strategy provides a facile approach to achieving hydrogel fibers with desired mechanical properties. [ABSTRACT FROM AUTHOR]

To date, the main method in improving UV stability of aramid fibers is to coat ultraviolet screening agent on the surface of fibers. However, this method has a disadvantage that the coating tends to fall off when the fibers are exposed to an external force. In the present research, A diamine monomer 2-(4-aminophenyl)-5-aminobenzimidazole (PABZ) was introduced to modify poly ( p -phenylene terephthalamide) by copolymerization, and corresponding modified aramid fibers (PBIA fibers) were prepared. we found that PBIA fibers can form complex with hydrogen chloride (HCl) which would not lead to the obvious decrease in mechanical properties, and the decomplexation of HCl can only be achieved at high temperature (higher than 280 °C). At the same time, PBIA/HCl complex molecule showed intense fluorescence emission, and which can provide an effective way to dissipate the harmful UV energy, thus, the UV resistance of PBIA fibers can be improved. In addition, the HCl have the ability to quench the photoactive triplet state of PBIA fibers, which can also contribute to improve the UV resistance of PBIA fibers. After 48 h UV irradiation, the PBIA/HCl complex fibers almost remained their tensile performances (only about 3% loss in tensile strength), and UV irradiation did not bring the obvious deterioration in structure and performance of the complex fibers. On the contrary, for PBIA fibers, its chemical structure and physical properties all suffered to obvious damages (about 15% loss in tensile strength). The UV resistance of PBIA/HCl complex fibers is approximately 5 times higher than that of PBIA fibers. [ABSTRACT FROM AUTHOR]

For general composites, fiber can improve the strength of rubber matrix, but it will damage the original high deformation that affect the toughness. Therefore, to solve this problem, we propose a strategy of constructing rubber-helical fiber composite, which can not only improve the strength of rubber, but also maintain the original high deformation of rubber. Inspired by helical structure in nature, we convert straight fibers into helical fibers by winding. The helical fibers with spring characteristic have high strength and large deformation matching with rubber. The tensile strength and fracture toughness of the composite are 3.51 and 3.41 times those of the rubber matrix, respectively. When the aramid fiber was used instead of nylon fiber, the strength of the composite is 12.81 MPa, which is 17.8 times that of pure rubber matrix, and the mass fraction of the fiber is only about 1.60 %. Furthermore, by analyzing the reinforcement and toughening effect of helical fiber, we have determined that helical fiber plays the role of bearing stress and dispersing stress into three-dimensional space in composites. This work prepared a series of rubber-helical fiber composite to solve the conflict between the strength and toughness of rubber materials. Due to the characteristics of large deformation and high strength, the helical fiber has the effect of strengthening and toughening. [Display omitted] • Inspired by the natural helical structure, nylon helical fiber/silicone rubber composite was prepared as an example of helical fiber-rubber composite. • The high strength and toughness of composite relies on the special structure of helical fibers. • Unmodified composites possess high strength and toughness. • The strengthening mechanism of helical fiber is proposed, including interlocking structure and three-dimensional stress dispersion. [ABSTRACT FROM AUTHOR]

Thanks to the special helical structure, natural composites such as shell, wood, and bone have remarkable toughness, strength and damage tolerance. Herein, a bioinspired spiral nylon monofilament/epoxy composite is developed, which is a representative example of helical fiber/thermosetting composites. The relationship between toughness and strength of composites was studied by controlling parameters of the helical fibers. As a result, the impact resistance is regularly increased by the increase of pitch and the decrease of helix fiber angle. With a single-layer addition, the impact toughness of composites is increased by 150% without decreasing the mechanical strength and that is increased by 450% in the case of three-layer addition. The proposed toughening mechanism was verified by finite element analysis and dynamic mechanical analysis, which including 3D stress dispersion, the interlocking fibrous building interface, and energy absorption capacity of viscoelastic spring polymer. Furthermore, the toughness and strength of the composites is improved by 310% in single layer via surface modification of spiral fibers. The introduction of the three-dimensional spiral structure into the composite is demonstrated to be a unique strategy to overcome the trade-off between toughness and strength of high-performance composite materials. A spiral nylon monofilament/epoxy composite served as an example of helical fiber/thermosetting composites, which is inspired by the biological helical structure of natural composites, is manufactured. The novel change of fibers' structure can realize the three-dimensional dispersion of stress, which can greatly improve the impact strength of composites. [Display omitted] • A spiral nylon monofilament/epoxy composite served as an example of helical fiber/thermosetting composites is manufactured, inspired by the biological helical structure of natural composites. • The composites with high impact resistance relies on changes in the physical structure of fibers. • This toughening mechanism is proposed, including 3D stress dispersion, the interlocking fibrous building interface, and energy absorption capacity of viscoelastic spring polymer. • Interface modification and multilayer design play a better role in toughening. [ABSTRACT FROM AUTHOR]