Tendon-inspired anti-freezing tough gels

Abstract

Summary Hydrogels have gained tremendous attention due to their versatility in soft electronics, actuators, biomedical sensors, etc. Due to the high water content, hydrogels are usually soft, weak, and freeze below 0°C, which brings severe limitations to applications such as soft robotics and flexible electronics in harsh environments. Most existing anti-freezing gels suffer from poor mechanical properties and urgently need further improvements. Here, we took inspirations from tendon and coniferous trees and provided an effective method to strengthen polyvinyl alcohol (PVA) hydrogel while making it freeze resistant. The salting-out effect was utilized to create a hierarchically structured polymer network, which induced superior mechanical properties (Young's modulus: 10.1 MPa, tensile strength: 13.5 MPa, and toughness: 127.9 MJ/m 3 ). Meanwhile, the cononsolvency effect was employed to preserve the structure and suppress the freezing point to −60°C. Moreover, we have demonstrated the broad applicability of our material by fabricating PVA hydrogel-based hydraulic actuators and ionic conductors.

Hierarchically Anisotropic Networks to Decouple Mechanical and Ionic Properties for High-Performance Quasi-Solid Thermocells

“…Nevertheless, the mechanical stretching destroys some amorphous regions, which thus limits the fracture toughness. In contrast, unidirectional freezing is more gentle. − It is beneficial to prepare tailored nanostructures for gel networks but has not yet been demonstrated in quasi-solid thermocells.…”

Aligned Porous and Anisotropic Nanocomposite Hydrogel with High Mechanical Strength and Superior Puncture Resistance by Reactive Freeze-Casting

“…Thus, the range of applications for nanocomposite hydrogels is expanded. 36 To demonstrate the relative distribution of the nano segregates in the matrix with stretching, the small angle X-ray scattering (SAXS) analysis of s-BNCH at different strains was conducted. The 2D scattering patterns are shown in Figure S16 (Supporting Information).…”

“…Compared with the s-RPPH (1.1 MPa), the Parallel exhibits a remarkably enhanced tensile strength up to 10.22 MPa along the freezing direction and the Orthogonal could also reach 5.98 MPa (Figure a), indicating that the anisotropic and oriented structures in the nanocomposite hydrogels allow the mechanical property to be enhanced in the specific directions. Thus, the range of applications for nanocomposite hydrogels is expanded . To demonstrate the relative distribution of the nano segregates in the matrix with stretching, the small angle X-ray scattering (SAXS) analysis of s-BNCH at different strains was conducted.…”

Tough Hydrogel Electrolytes for Anti‐Freezing Zinc‐Ion Batteries

“…"Salting-out" ions, such as potassium ion (K + ) and acetate, are effective in toughening hydrogels via ionpromoted chain aggregation while maintaining the high water content. [34,53,59,60] Co-nonsolvency [61,62] also influences the chain aggregation, where adding cosolvent to the precursor promotes the formation of open-cell porous structures with densified polymer network; thus, enhancing both mass transport (10× lower overpotential compared to the less porous counterparts, Figure 2F) and strength (Figure 2B,C). The "salting-out" is achieved by an exemplary salt mixture: potassium acetate (KAc), which combines "salting-out" and anti-freezing abilities, mixed with zinc acetate (ZnAc 2 ), a compatible zinc ion (Zn 2+ )-containing salt.…”