Bioinspired 2D Isotropically Fatigue‐Resistant Hydrogels

Abstract

Engineering conventional hydrogels with muscle‐like anisotropic structures can efficiently increase the fatigue threshold over 1000 J m−2 along the alignment direction; however, the fatigue threshold perpendicular to the alignment is still as low as ≈100–300 J m−2, making them nonsuitable for those scenarios where isotropic properties are desired. Here, inspired by the distinct structure–properties relationship of heart valves, a simple yet general strategy to engineer conventional hydrogels with unprecedented yet isotropic fatigue resistance, with a record‐high fatigue threshold over 1,500 J m−2 along two arbitrary in‐plane directions is reported. The two‐step process involves the formation of preferentially aligned lamellar micro/nanostructures through a bidirectional freeze‐casting process, followed by compression annealing, synergistically contributing to extraordinary resistance to fatigue crack propagation. The study provides a viable means of fabricating soft materials with isotropically extreme properties, thereby unlocking paths to apply these advanced soft materials toward applications including soft robotics, flexible electronics, e‐skins, and tissue patches.

Ternary‐Porous Conjugated N‐Halamine Nanofibers/Graphene Aerogels for Rechargeable Degradation of Mustard Gas

“…The aligned open cells (10-15 µm), crumpled cell walls (1-5 µm), and microporous nanofibers (800-850 nm) constitute the three levels of the hierarchy of HNAs. The rGO sheets in the cell walls stack and overlap the nanofibers dominated by the π-π interactions, [19] and are bridged with randomly distributed nanofibrous ligaments. Significantly, the neighboring lamellas are partially wrinkled denoting favorable flexibility, which could serve as the substrate helping withstand the external stress during the deformation of the bulk.…”

Fatigue-free artificial ionic skin toughened by self-healable elastic nanomesh

“…Consequently, self-healing ionic skins even toughened by sacrificial or energy-dissipating components may resist crack propagation under monotonic load, but still, easily fail in cyclic loads which are unaffected by the complementary dissipation mechanisms 12 , 13 . Recent studies show that an elastomer’s fatigue threshold (the minimal fracture energy below which cracks cease to propagate under cyclic loading) may be largely enhanced by embedding high-energy hard domains in the matrix, such as nanocrystallites 12 , 14 , aligned lamellar/fibrillar structures 11 , 15 – 17 , and high-contrast segregated nanophases 18 – 20 . Yet, the incorporated hard domains are usually irreparable, and the only reported anti-fatigue polyampholyte hydrogels with healable hard phases exhibit a limited fatigue threshold ( Γ 0 ) of ∼150 J m −2 19 .…”

Poly(vinyl Alcohol) (PVA)-Based Hydrogel Scaffold with Isotropic Ultratoughness Enabled by Dynamic Amine–Catechol Interactions

“…Hydrogels and hydrogel-based composites are commonly applied as artificial scaffolds in a wide range of fields such as drug delivery, wound dressing, wearable electronics, and so forth. − Such applications are attributed to their similar physical properties to tissues, well-tolerated biocompatibility, and tunable mechanical properties in adapting to external stimuli. , However, compared to the biological load-bearing tissues (e.g., muscles) that are soft, resilient, and tough, the mechanical performance of the hydrogel-based materials is still less than satisfactory. , The high water content and sparse polymer network of the synthetic hydrogels make them naturally weak in mechanical strength. , Therefore, toughening strategies for hydrogels are always desirable . One of the effective strategies is to construct an anisotropic network within the hydrogel network mimicking the structure of muscles. ,− The resulting hydrogels exhibited a significant mechanical reinforcement along the alignment direction, which could be used as artificial tendons, while sacrificing the mechanical performance in the perpendicular direction. − For connective tissues such as the fibrous membranes of the articular capsule with fibers interwoven to resist excessive stretching and distension in multiple directions, the isotropic mechanical strength is highly demanding. , However, studies on soft and resilient scaffold materials with superior isotropic mechanical strength and biocompatibility are limited . One of the main difficulties is to design proper crosslinking strategies to enable the mechanical reinforcement of hydrogels in multiple directions while maintaining the structure for the transportation of relevant molecules (e.g., ions and nutrition ingredients) and the growth of cells.…”

“…14−16 For connective tissues such as the fibrous membranes of the articular capsule with fibers interwoven to resist excessive stretching and distension in multiple directions, the isotropic mechanical strength is highly demanding. 17,18 However, studies on soft and resilient scaffold materials with superior isotropic mechanical strength and biocompatibility are limited. 18 One of the main difficulties is to design proper crosslinking strategies to enable the mechanical reinforcement of hydrogels in multiple directions while maintaining the structure for the transportation of relevant molecules (e.g., ions and nutrition ingredients) and the growth of cells.…”