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Placing non-magnetic microparticles in a magnetic colloid makes it possible to control them by means of a magnetic field, which allows the creation of tunable composite materials. The choice of microparticles with appropriate properties can enable the creation of materials with tunable absorption of electromagnetic microwaves, which may be of interest in device engineering and radar detection. An experimental and theoretical study of the interaction of super high frequency electromagnetic waves with magnetic colloids containing microparticles of conductive filler (aluminum) under the additional influence of a constant magnetic field has been carried out in this work. The studies were performed using a cell based on a coaxial cable in the frequency range of 5–18 GHz. It was found that the formation of chain structures of aluminum particles in the magnetic field leads to a significant increase in the absorption coefficient of electromagnetic energy. The character of the frequency dependence and the absolute values of the absorption and reflection coefficients depend on the volume concentration of the conductive filler in a complex way. To interpret the obtained results, numerical modeling of the investigated system in the effective medium approximation by the finite element method has been carried out. The anisotropic distribution of electromagnetic energy losses in the transmission line is demonstrated. [ABSTRACT FROM AUTHOR]

The 3D shape‐changing hydrogels are highly pursued for numerous applications. However, up to now, the construction of complex 3D shape‐changing hydrogels remains a challenge. The reported design strategies are mainly applied to fabricate 2D ones by introducing anisotropic microstructures into hydrogel sheets/membranes. Herein, we present a convenient photolithography strategy for constructing complex 3D shape‐changing hydrogels by simultaneously modulating anisotropic microstructures and internal stress fields of gel sheets. When the precursor solution containing ultraviolet (UV) absorber is irradiated by single‐side UV light, the attenuated polymerization rate can cause the generation of asymmetric internal stress field in the resulting hydrogel sheet. In the meantime, the directional diffusion of unpolymerized monomers allows for the formation of vertical gradient structure within hydrogel. Therefore, by applying different photomasks to modulate the local gradient structures and internal stress fields of the gel sheets, they can spontaneously transform into various complex 3D shape‐changing hydrogels in the air. Response to the external stimuli, these 3D shape‐changing hydrogels (e.g., fighter plane, birdie, and multi‐storey origami lattices) can deform in a novel 3D1‐to‐3D2‐to‐3D3 mode. This new design strategy contributes to the development of complex biomedical implants and soft robotics. [ABSTRACT FROM AUTHOR]

Human hair keratin (HHK) has been successfully explored as raw materials for three‐dimensional scaffolds for soft tissue regeneration due to its excellent biocompatibility and bioactivity. However, none of the reported HHK based scaffolds is able to replicate the strain‐stiffening capacity of living tissues when responding to large deformations. In the present study, strain‐stiffening property was achieved in scaffolds fabricated from HHK via a synergistic effect of well‐defined, aligned microstructure and chemical crosslinking. Directed ice‐templating method was used to fabricate HHK‐based scaffolds with highly aligned (anisotropic) microstructure while oxidized dopamine (ODA) was used to crosslink covalently to HHKs. The resultant HHK‐ODA scaffolds exhibited strain‐stiffening behavior characterized by the increased gradient of the stress–strain curve after the yield point. Both ultimate tensile strength and the elongation at break were enhanced significantly (~700 kPa, ~170%) in comparison to that of HHK scaffolds lacking of aligned microstructure or ODA crosslinking. In vitro cell culture studies indicated that HHK‐ODA scaffolds successfully supported human dermal fibroblasts (HDFs) adhesion, spreading and proliferation. Moreover, anisotropic HHK‐ODA scaffolds guided cell growth in alignment with the defined microstructure as shown by the highly organized cytoskeletal networks and nuclei distribution. The findings suggest that HHK‐ODA scaffolds, with strain‐stiffening properties, biocompatibility and bioactivity, have the potential to be applied as biomimetic matrices for soft tissue regeneration. [ABSTRACT FROM AUTHOR]

[Display omitted] • Tubular carbon nanofibers/graphene aerogel (TGA) cross-linked by D 400 is constructed. • TGA can withstand 50 compression/release cycles and 80% compressive strain. • The conduction loss gradually dominates the dielectric loss when being compressed. • An ultra-broad EAB of 11.5 GHz is obtained under a compression strain range of 0–60%. • TGA delivers the thermal insulation performance comparable to commercial PS and PU foams and good water stability. The compressive strain-dependent microwave dissipation behavior gives aerogel the great possibility of achieving the broad-band absorption. However, there are few investigations that focus on the close association between the compression strain and microwave attenuation performance, and it still remains a vast challenge to construct the elastic microwave absorbers with the good mechanical durability. Herein, by attaching the intertwined tubular carbon nanofibers (TCNFs) to graphene skeleton, lightweight elastic TCNFs/graphene aerogel (TGA) with the anisotropic architecture was formed via chemical cross-linking, freeze-drying and subsequent reduction. When the compression strain is 60% along the vertical direction, the hybrid aerogel is endowed with the satisfactory impedance matching and enhanced conduction loss, originating from the dense cellular configuration. Thus, it harvests the most prominent microwave consumption of a minimum reflection loss (RL min) value of −46.1 dB and an effective absorption bandwidth (EAB) value of 7.1 GHz. By tuning the compressive strain, an ultrabroad EAB of 11.5 GHz is realized. Besides, the other favorable properties including fatigue resistance, heat insulating and water stability are also acquired. These intriguing features make the hybrid aerogel stand out among numerous absorbers. This study is instructive to develop multifunctional microwave absorbing materials for matching well with the practical environment. [ABSTRACT FROM AUTHOR]

In order to examine the micro-mechanism behind the thixotropic behavior of semi-solid alloys, microstructural effects on the compression deformation of semi-solid 7075 aluminum alloy prepared by recrystallization and partial melting (RAP) method were investigated. The fibrous and deformed microstructure of as-extruded 7075 aluminum alloy can transform into elongated and globular grains via reheating to semi-solid states, and exhibiting dominated {100}<001> recrystallization texture and preferred crystal growth in extrusion direction. The anisotropic microstructure of semi-solid alloys depends on the remelting temperatures to a great degree. Correspondingly, the initial peak stress of compression stress-strain curves also demonstrated as anisotropic behavior. It was analyzed that the crystallographic texture caused orientation dependent Young's modulus and a corresponding elastic response, and the disagglometation of the saturated solid skeleton led to an increase of viscoplastic stress, which relates to the amount of bonds between solid grains. [ABSTRACT FROM AUTHOR]