1 wileyonlinelibrary.com recoverability and self-healing property, due to their intrinsic structural heterogeneity and/or lack of effi cient energydissipation mechanisms, [ 13 ] which greatly limit their uses for other applications requiring highly mechanical properties such as cartilage, tendon, muscle, and blood vessel.Many efforts have been made to develop tough hydrogels with new microstructures and toughening mechanisms, such as double network hydrogels, [ 14 ] nanocomposite hydrogels, [ 15 ] sliding-ring hydrogels, [ 16 ] macromolecular microsphere composite hydrogels, [ 17 ] tetrapolyethylene glycol hydrogels, [ 18 ] hydrophobically associated hydrogels, [ 19,20 ] and dipole-dipole or hydrogen bonding enhanced hydrogels. [ 21,22 ] Among them, double network (DN) hydrogels have demonstrated their excellent mechanical properties. The existing knowledge of DN gels from synthesis methods, network structures, to toughening mechanisms mainly comes from chemically cross-linked DN gels. [ 23 ] Both networks with contrasting structures in DN gels are separately crosslinked by covalent bonds, [ 24 ] and the interpenetration of two contrasting networks makes the chemically linked DN gels both tough and soft, as evidenced by stiffness (elastic modulus of 0.1-1.0 MPa), strength (failure tensile stress of 1-10 MPa, strain 1000%-2000%, failure compressive stress 20-60 MPa, strain 90%-95%), and toughness (tearing fracture energy of 10 2 -10 3 J m −2 ). [ 23 ] Chemically linked DN gels have comparable toughness to cartilage and rubber. The toughening mechanisms are largely based on "sacrifi cial bonds" that break from the fi rst network to effectively dissipate energy, protect the second network, sustain stress, and store elastic energy, thus to reinforce the gels. However, the fracture of the fi rst network also causes irreversible and permanent bond breaks, making the gels very diffi cult to be repaired and recovered from damages and fatigues. [ 25 ] Thus, the internal fracture process of the fi rst network is considered to be critical for toughness enhancement, because relatively large damage zones formed in the fi rst network allow for more accumulated damage before macroscopic crack propagation occurs throughout whole networks. [ 26,27 ] Double network (DN) hydrogels with two strong asymmetric networks being chemically linked have demonstrated their excellent mechanical properties as the toughest hydrogels, but chemically linked DN gels often exhibit negligible fatigue resistance and poor self-healing property due to the irreversible chain breaks in covalent-linked networks. Here, a new design strategy is proposed and demonstrated to improve both fatigue resistance and self-healing property of DN gels by introducing a ductile, nonsoft gel with strong hydrophobic interactions as the second network. Based on this design strategy, a new type of fully physically cross-linked Agar/hydrophobically associated polyacrylamide (HPAAm) DN gels are synthesized by a simple one-pot method. Agar/ HPAAm DN gels exhibit excellent mech...

Genetically encoded protein scaffolds often serve as templates for the mineralization of biocomposite materials with complex yet highly controlled structural features that span from nanometres to the macroscopic scale. Methods developed to mimic these fabrication capabilities can produce synthetic materials with well defined micro- and macro-sized features, but extending control to the nanoscale remains challenging. DNA nanotechnology can deliver a wide range of customized nanoscale two- and three-dimensional assemblies with controlled sizes and shapes. But although DNA has been used to modulate the morphology of inorganic materials and DNA nanostructures have served as moulds and templates, it remains challenging to exploit the potential of DNA nanostructures fully because they require high-ionic-strength solutions to maintain their structure, and this in turn gives rise to surface charging that suppresses the material deposition. Here we report that the Stöber method, widely used for producing silica (silicon dioxide) nanostructures, can be adjusted to overcome this difficulty: when synthesis conditions are such that mineral precursor molecules do not deposit directly but first form clusters, DNA-silica hybrid materials that faithfully replicate the complex geometric information of a wide range of different DNA origami scaffolds are readily obtained. We illustrate this approach using frame-like, curved and porous DNA nanostructures, with one-, two- and three-dimensional complex hierarchical architectures that range in size from 10 to 1,000 nanometres. We also show that after coating with an amorphous silica layer, the thickness of which can be tuned by adjusting the growth time, hybrid structures can be up to ten times tougher than the DNA template while maintaining flexibility. These findings establish our approach as a general method for creating biomimetic silica nanostructures.

Sodium-ion batteries (SIBs) are still confronted with several major challenges, including low energy and power densities, short-term cycle life, and poor low-temperature performance, which severely hinder their practical applications. Here, a high-voltage cathode composed of Na V (PO ) O F nano-tetraprisms (NVPF-NTP) is proposed to enhance the energy density of SIBs. The prepared NVPF-NTP exhibits two high working plateaux at about 4.01 and 3.60 V versus the Na /Na with a specific capacity of 127.8 mA h g . The energy density of NVPF-NTP reaches up to 486 W h kg , which is higher than the majority of other cathode materials previously reported for SIBs. Moreover, due to the low strain (≈2.56% volumetric variation) and superior Na transport kinetics in Na intercalation/extraction processes, as demonstrated by in situ X-ray diffraction, galvanostatic intermittent titration technique, and cyclic voltammetry at varied scan rates, the NVPF-NTP shows long-term cycle life, superior low-temperature performance, and outstanding high-rate capabilities. The comparison of Ragone plots further discloses that NVPF-NTP presents the best power performance among the state-of-the-art cathode materials for SIBs. More importantly, when coupled with an Sb-based anode, the fabricated sodium-ion full-cells also exhibit excellent rate and cycling performances, thus providing a preview of their practical application.