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Natural tissues, like ligaments and tendons, display not just robust mechanical performance but also complex anisotropic structures extending beyond one-directional arrangements. However, fabricating hydrogel actuators with biomimetic three-dimensional anisotropy remains challenging. Herein, a simple strategy involving curving-stretching induced alignment is proposed to prepare anisotropic Fe 3+ -cross-linked poly(acrylic acid)-poly(acrylamide) hydrogel actuators. These hydrogels exhibit exceptional mechanical properties, boasting a fracture stress of 7.1 MPa and a superior modulus of 33.2 MPa when prestretched to 200% strain, which are 2.3 times and 4.9 times higher than their unstretched counterparts. The stretched anisotropic hydrogel gripper, stronger than its unstretched counterpart, can lift heavy objects while also achieving rapid responsiveness to stimuli. This work introduces a novel and effective method for fabricating anisotropic hydrogels, highlighting their broad applicability in fields such as soft robotics, biomedical devices, and beyond.

This work showcases a novel strategy for the synthesis of shape-dependent alloy nanostructures with the incorporation of solid substrates, leading to remarkable enhancements in the electrocatalytic performance. Herein, an aqueous medium approach has been used to synthesize an octahedral Pd X Cu Y alloy of different Pd:Cu ratios to better comprehend their electrocatalytic potential. With the aim to outperform high activity and efficient stability, zirconium oxide (ZrO 2 ), graphene oxide nanosheets (GONs), and hexagonal boron nitride nanosheets (hBNNs) solid substrates are occupied to decorate the optimized Pd 3 Cu 7 catalyst with a minimum 5 wt % metal loading. When compared to the counterparts and different ratios, the Pd 3 Cu 7 @hBNNs catalyst exhibited an optimal activity for hydrogen evolution reaction (HER). The lower overpotential and Tafel values observed are 64 and 51 mV/dec for Pd 3 Cu 7 @hBNNs followed by Pd 3 Cu 7 @ZrO 2 , which showed a 171 mV overpotential and a 98 mV/dec Tafel value, respectively. Meanwhile, the Pd 3 Cu 7 @GONs were found to have a 202 mV overpotential and a 110 mV/dec Tafel value. The density functional theory, which achieves a lower free energy (Δ G H* ) value for Pd 3 Cu 7 @hBNNs than the other catalysts for HER, further supports its excellent performance in achieving the Volmer-Heyrovsky mechanism path. Moreover, the superior HER activity and sturdier resilience after 8 h of stability may be due to the synergy between the metal atoms, monodisperse decoration, and the coordination effect of the support material.

Two-dimensional (2D) layered materials with low crystal symmetries have exhibited unique anisotropic physical properties. Here, we report systematic studies on the photoresponse of field effect transistors (FETs) fabricated using quasi-one-dimensional ZrS 3 nanoflakes. The as-fabricated phototransistors exhibit a broadband photocurrent response from ultraviolet to visible regions, where the responsivity and detectivity can be enhanced via additional gate voltages. Furthermore, benefiting from the strong in-plane anisotropy of ZrS 3 , we observe a gate-voltage and illumination wavelength-dependent polarized photocurrent response, while its sub-millisecond-time response speed is also polarization-dependent. Our results demonstrate the flexible tunability of photodetectors based on anisotropic layered semiconductors, which substantially broadens the application of low symmetry layered materials in polarization-sensitive optoelectronic devices.

Owing to their anisotropic and hierarchical structure, tendons exhibit an outstanding mechanical performance despite the low polymer concentration and softness of the constituent materials. Here, we propose a tendon-mimicking, strong, and tough hydrogel with a multiscale hierarchical and anisotropic structure. An isotropic, precursor double-network hydrogel is transformed into an anisotropic hydrogel by stretching, solvent exchange, and subsequent fixation via ionic crosslinking. Solvent exchange induces densification of the stretched polymer network, enhancement of linear alignment of polymer chains, and microphase separation, leading to anisotropic toughening of the hydrogel. The resulting anisotropic hydrogels show high strength and toughness, which vary over a wide range (1.2-3.3 MPa of strength and 4.9-8.8 MJ/m 3 of toughness, respectively), controlled by the degree of pre-stretching. Furthermore, a hierarchical architecture is constructed by braiding the anisotropic hydrogel strands into a rope, resulting in an improved mechanical performance (4.7 MPa of strength in a four-strand hydrogel rope) compared to separated unbraided strands of a hydrogel (2.3 MPa of strength). The higher hierarchical hydrogel cable, prepared by braiding four hydrogel ropes, can withstand a heavy load even up to 13 kg. These results represent that a hierarchical assembly of anisotropic hydrogels exhibits high mechanical performance and a hierarchically anisotropic structure, which are reminiscent of tendons.

Hydrogel strain sensors have attracted tremendous attention in medical monitoring, flexible wearable devices, and human-machine interfaces. However, traditional hydrogels exhibit isotropic sensing performance based on their isotropic structure. Therefore, it is challenging to fabricate a hydrogel with an anisotropic structure similar to human tissues for achieving anisotropic sensing characteristics. Herein, we proposed a simple and effective method for preparing anisotropic poly(vinyl alcohol) (PVA) conductive hydrogels, which demonstrated anisotropic mechanical properties and anisotropic ion conductivity. The anisotropic hydrogel was successfully constructed through first thermal stretching and then directional freezing. The mechanical strength of hydrogels along the parallel stretching direction (stress of 1596 kPa and toughness of 3.69 MJ/m 3 ) was higher than that of the hydrogels along the vertical stretching direction (stress of 883.1 kPa and toughness of 1.96 MJ/m 3 ). Moreover, the hydrogel showed anisotropic conductivity on the advantage of the different ion channels. The prepared hydrogel sensor exhibited anisotropic sensing for multidirectional stress in the strain range from 0.5 to 100%. The gauge factors (GF) parallel to the stretching direction were greater than the GF vertical to the stretching direction. The anisotropic hydrogel sensors are expected to have broad application prospects in flexible wearable devices and medical monitoring.

The multifunctional combined nanoplatform has a wide application prospect in the synergistic treatment of cancer. Nevertheless, the traditional treatment of phototherapy is limited by the catalytic nanomaterial itself, so the effect is not satisfactory. Here, the arris of the anisotropic truncated octahedral Au (TOh Au) was coated with noble metal Pt to form a spatial separation structure, which enhanced the local surface plasmonic resonance and thus boosted the photocatalytic effect. In this system, the highly efficient photocatalysis provides a strong guarantee for oncotherapy. On the one hand, the structure of arris deposition adequately improves the efficiency of photothermal conversion, which substantially improves the effectiveness of photothermal therapy. On the other hand, in situ oxygen production of Pt ameliorates tumor hypoxia, and through the O 2 self-production and sales mode, the growth and development of tumor were inhibited. Meanwhile, under the enhanced photocatalysis, more O 2 were produced, which greatly evolved the treatment effect of photodynamic therapy. In the end, the addition of hyaluronic acid can specifically target osteosarcoma cells while improving the retention time and biocompatibility of the material in the body. Thus, the nanocomposite shows superexcellent synergistic enhancement of photothermal conversion efficiency and photodynamic capability in vitro and in vivo , which provides a potential possibility for osteosarcoma cure.

Magnetoactive elastomers (MAEs), one kind of typical novel magnetoactive driver applied in the soft robotic area, have become one of the research hotspots as they can provide biologically friendly driving methods with safe, preprogrammed, and easy-to-implement properties. In this study, novel MAEs embedding soft magnetic iron microparticles with radial chains, which can be molded in one piece, achieve 3D deformation, and co-work between multiple MAEs under single homogeneous stimuli, are proposed. Then, two kinds of novel magnetoactive drivers are established based on the proposed MAEs, which can achieve the synchronous pumping behavior of heart and the extension behavior of muscle under applied homogeneous magnetic fields. The experimental data show that (1) for the pumping behavior, the maximum instantaneous flow rate and total pumping volume can reach 200.1 and 52.3 mL/min, respectively, under 120 BPM applied harmonic magnetic field with 0-300 mT amplitude; (2) the muscle extension behavior can achieve a strain of 0.925 without a loading mass and carry a load of 40 times its own weight with a pronounced dynamic movement. It should be emphasized that the behavior of the proposed magnetoactive drivers can be excited by remote homogeneous magnetic fields, and it has great application potential in biomimetic or bioinspired soft driving systems.

Anisotropic superhydrophobic surfaces that have many superior properties, such as directional self-cleaning, droplet transport, heat transfer, and so on, are widely used in various fields. Different from symmetric surfaces, a water droplet often shows directional spreading, moving, and bouncing on asymmetric surfaces. To investigate the mechanisms and achieve controllability of droplet motions on asymmetric surfaces, a series of surfaces with inclined micro-conical arrays are fabricated by integrating the methods of soft lithography, hot-pressing, and crystal growth. We found that the droplet would spread along the reverse direction of micro-cone's orientation but bounce and detach off the surface and move toward the direction of micro-cone's orientation. To understand these interesting performances, a mathematical model is established from the perspective of force balance, and a series of numerical simulations are performed. Additionally, the relationship between the droplet motions and the micro-structural parameters, including the inclined angle, line space, and height, are studied. This work may provide useful insights into droplet controlling, anisotropic surface designing, and its applications.

A strategy is developed to enhance the barrier protection of polyethylene oxide (PEO)-metal-organic framework (MOF) composite films against chemical warfare agent simulants. To achieve enhanced protection, an impermeable high-aspect-ratio filler in the form of Laponite RD (LRD) clay platelets was incorporated into a composite PEO film containing MOF UiO-66-NH 2 . The inclusion of the platelets aids in mitigating permeation of inert hydrocarbons (octane) and toxic chemicals (2-chloroethyl ethyl sulfide, 2-CEES) of dimensions/chemistry similar to prominent vesicant threats while still maintaining high water vapor transport rates (WVTR). By utilizing small-angle neutron scattering, small-angle X-ray scattering, and wide-angle X-ray scattering, the LRD platelet alignment of the films was determined, and the structure of the films was correlated with performance as a barrier material. Performance of the membranes against toxic chemical threats was assessed using permeation testing of octane and 2-CEES, a common simulant for the vesicant mustard gas, and breathability of the membranes was assessed using WVTR measurements. To assess their robustness, chemical exposure ( in situ diffuse reflectance infrared Fourier transform spectroscopy) and mechanical (tensile strength) measurements were also performed. It was demonstrated that the barrier performance of the film upon inclusion of the LRD platelets exceeds that of other MOF-polymer composites found in the literature and that this approach establishes a new path for improving permselective materials for chemical protection applications.

Perovskite structures of organic and inorganic halides are peculiar structures with many interesting properties. Using their photoelectric effect, the structures have been used in photocells, photoelectric sensors, and light-emitting diodes. In conventional perovskite film crystallization, which is a one-step method, the MAPbI 3 crystals form disordered needlelike crystals at room temperature. Such needlelike crystal films have rough surfaces and low coverage to the substrate, resulting in insignificant photoelectric effects. With the assistance of an electric field and three-dimensional (3D) printing, the direction of the perovskite needlelike crystal can be arranged to make it orderly. In this way, the photoelectric sensor of the ordered MAPbI 3 perovskite needlelike crystal film can be prepared. This sensor has high sensitivity, high stability, and high response speed. Moreover, it has anisotropy and higher photoelectric sensitivity in the direction perpendicular to the needle crystal. Most interestingly, the sensors respond differently to polarized light in different directions, and this effect can be used to detect the direction and degree of polarization of polarized light.

Assembling Ti 3 C 2 T x MXene nanosheets into three-dimensional (3D) architecture with controllable alignment is of great importance for electromagnetic wave absorption (EMA) application. However, it is a great challenge to realize it due to the weak van der Waals interconnection between MXene nanosheets. Herein, we propose to introduce gelatin molecules as a "chemical glue" to fabricate the 3D Mxene@gelatin (M@G) nanocomposite aerogel using a unidirectional freeze casting method. The Ti 3 C 2 T x MXene nanosheets are well aligned in the M@G nanocomposite aerogel, yielding much enhanced yet anisotropic mechanical properties. Due to the unidirectional aligned microstructure, the M@G nanocomposite aerogel shows significantly anisotropic EMA properties. M@G-45 shows a -59.5 dB minimum reflection loss (RL min ) at 14.04 GHz together with a 6.24 GHz effective absorption bandwidth in the parallel direction (relative to the direction of unidirectional freeze casting). However, in the vertical direction of the same M@G aerogel, RL min is shifted to a much lower frequency (4.08 GHz) and the effective absorption bandwidth decreases to 0.86 GHz. The anisotropic electromagnetic energy dissipation mechanism was deeply investigated, and the impendence match plays a critical role for electromagnetic wave penetration. Our lightweight M@G nanocomposite aerogel with controllable MXene alignment is very promising in EMA application.

Multifarious wearable electronics with flexible touch screens have been invented for extensive outdoor activities. One challenge associated with these wearable electronics is the development of materials with both high dielectric permittivity and anisotropic light transmission, which is responsible for high touch sensitivity and screen peep-proof protection, respectively. Herein, we demonstrated a scalable approach for assembling and aligning anisotropic cellulose in a polymer matrix through the thickness direction via the assistance of an electric field to address this challenge. The alignment of silver-coated fibrillated celluloses in the polymer matrix not only significantly increases dielectric permittivity but also effectively enhances optical anisotropy. The impact of alignment degree and filler content on the dielectric and optical properties of polymer composite films has been systematically studied. The kinetics and aligning mechanisms of silver-coated fibrillated celluloses are revealed by in situ optical microscope images while an electric field is applied. We believe that this study provides a facile strategy to enhance both dielectric permittivity and optical anisotropy of polymer composite films by the alignment of embedding nanoparticles via an AC electric field, which is essential for future flexible electronics and display technology.

Anisotropic composite films of polyaniline (PANI) with single-walled carbon nanotube (SWCNT) were prepared by in situ electropolymerization on highly oriented high-density polyethylene (HDPE) films. Polarized UV-vis and Raman spectra confirm the anisotropic arrangement of PANI molecular chains in the composite films. The conductivities of 16.6 ± 0.2 and 2.07 ± 0.2 S cm -1 have been obtained for doped PANI/0.8 wt % SWCNT measured along and perpendicular to the direction of the HDPE molecular chain, respectively. The response of PANI/0.8 wt % SWCNT films used as ammonia sensors is much higher along the chain direction of HDPE than that perpendicular to the chain direction of HDPE with an anisotropic ratio of 1.8 at 100 ppm ammonia. This is attributed to the well-ordered array of PANI/0.8 wt % SWCNT induced by the oriented HDPE films. Moreover, the high ammonia response for PANI/0.8 wt % SWCNT may be attributed to the charge-transfer effect between PANI and SWCNT.

Improved and more rapid healing of full-thickness skin wounds remains a major clinical need. Silk fibroin (SF) is a natural protein biomaterial that has been used in skin repair. However, there has been little effort aimed at improving skin healing through tuning the hierarchical microstructure of SF-based matrices and introducing multiple physical cues. Recently, enhanced vascularization was achieved with SF scaffolds with nanofibrous structures and tunable secondary conformation of the matrices. We hypothesized that anisotropic features in nanofibrous SF scaffolds would promote cell migration, neovascularization, and tissue regeneration in wounds. To address this hypothesis, SF nanofibers were aligned in an electric field to form anisotropic porous scaffolds after lyophilization. In vitro and in vivo studies indicated good cytocompatibility, and improved cell migration and vascularization than nanofibrous scaffolds without these anisotropic features. These improvements resulted in more rapid wound closure, tissue ingrowth, and the formation of new epidermis, as well as higher collagen deposition with a structure similar to the surrounding native tissue. The new epidermal layers and neovascularization were achieved by day 7, with wound healing complete by day 28. It was concluded that anisotropic SF scaffolds alone, without a need for growth factors and cells, promoted significant cell migration, vascularization, and skin regeneration and may have the potential to effectively treat dermal wounds.

Innovative sound absorbers, the design of which is based on carbon nanotubes and graphene derivatives, could be used to make more efficient sound absorbing materials because of their excellent intrinsic mechanical and chemical properties. However, controlling the directional alignments of low-dimensional carbon nanomaterials, such as restacking, alignment, and dispersion, has been a challenging problem when developing sound absorbing forms. Herein, we present the directionally antagonistic graphene oxide-polyurethane hybrid aerogel we developed as a sound absorber, the physical properties of which differ according to the alignment of the microscopic graphene oxide sheets. This porous graphene sound absorber has a microporous hierarchical cellular structure with adjustable stiffness and improved sound absorption performance, thereby overcoming the restrictions of both geometric and function-orientated functions. Furthermore, by controlling the inner cell size and aligned structure of graphene oxide layers in this study, we achieved remarkable improvement of the sound absorption performance at low frequency. This improvement is attributed to multiple scattering of incident and reflection waves on the aligned porous surfaces, and air-viscous resistance damping inside interconnected structures between the urethane foam and the graphene oxide network. Two anisotropic sound absorbers based on the directionally antagonistic graphene oxide-polyurethane hybrid aerogels were fabricated. They show remarkable differences owing to the opposite alignment of graphene oxide layers inside the polyurethane foam and are expected to be appropriate for the engineering design of sound absorbers in consideration of the wave direction.

Biological naïve extracellular matrices (ECMs) exhibit anisotropic functions in their physical, chemical, and morphological properties. Representative examples include anisotropic skin layers or blood vessels simultaneously facing multiphasic environments. Here, anisotropically multifunctional structures called BiFACIAL ( biomimetic freestanding anisotropic catechol- interfaces with asymmetrically layered) films were developed simply by contacting two polysaccharide solutions of heparin-catechol (Hep-C) and chitosan-catechol (Chi-C). Such anisotropic characters were due to controlling catechol cross-linking by alkaline pH, resulting in a trimodular structure: a rigid yet porous Hep-C exterior, nonporous interfacial zone, and soft/highly porous Chi-C interior. The anisotropic features of each layer, including the porosity, rigidity, rheology, composition, and ionic strength, caused the BiFACIAL films to show spontaneously biased stimuli responses and differential behaviors against biological substances (e.g., blood plasma). The films could be created in situ in live animals and imitated the structural/functional aspects of the representative anisotropic tissues (e.g., skin and blood vessels), providing valuable ECM-like platforms for the creation of favorable environments or for tissue regeneration or disease treatment by effectively manipulating cellular behaviors.

Cellulose paper has been extensively used in microfluidic analytical devices because of its hydrophilic nature. However, cellulose is randomly packed in paper without any particular orientation or channels within the bulk of the material, necessitating a complicated design of hydrophilic microchannels to guide the liquid flow. Herein, we develop an anisotropic mesoporous microfluidic framework (named as white wood) with aligned cellulose nanofibers and inherent microchannels via a facile one-step delignification process from natural wood. The hydrophilic nature of the innate microchannels in white wood makes it ideal for application as a pump-free microfluidic chip, exhibiting a fast and anisotropic liquid and large solid particle (as demonstrated with carbon nanotubes) mass transport, with a high transport speed along the channel direction approximately five times faster than that perpendicular to the channel direction. The anisotropic mass transport is further exemplified in the fabrication of chitosan films with aligned microstructures and birefringence, formed by virtue of unidirectional capillary forces exerted by the microchannels. We envision that our anisotropic mesoporous framework can have great applications to pump-free microfluidics, and the simple preparation process will pave a new way for the development of microfluidic devices based on chemically modified wood.

Assembling particular building blocks into composites with diverse targeted structures has attracted considerable interest for understanding its new properties and expanding the potential applications. Anisotropic organization is considered as a frequently used targeted architecture and possesses many peculiar properties because of its unusual shapes. Here, we show that anisotropic graphene monoliths (AGMs), three-dimensional architectures of well-aligned graphene sheets obtained by a dip-coating method using cellulose acetate fibers as templates show thermal-insulating, fire-retardant, and anisotropic properties. They exhibit a feature of higher mechanical strength and thermal/electrical conductivities in the axial direction than in the radial direction. Elastic polymer resins are then introduced into the pores of the AGMs to form conductive and flexible composites. The composites, as AGMs, retain the unique anisotropic properties, revealing opposite resistance change under compressions in different directions. The outstanding anisotropic properties of AGMs make them possible to be applied in the fields of thermal insulation, integrated circuits, and electromechanical devices.

The past decade has witnessed increased research effort on multiphase magnetoelectric (ME) composites. In this scope, this paper presents the application of novel materials for the development of anisotropic magnetoelectric sensors based on δ-FeO(OH)/P(VDF-TrFE) composites. The composite is able to precisely determine the amplitude and direction of the magnetic field. A new ME effect is reported in this study, as it emerges from the magnetic rotation of the δ-FeO(OH) nanosheets inside the piezoelectric P(VDF-TrFE) polymer matrix. δ-FeO(OH)/P(VDF-TrFE) composites with 1, 5, 10, and 20 δ-FeO(OH) filler weight percentage in three δ-FeO(OH) alignment states (random, transversal, and longitudinal) have been developed. Results have shown that the modulus of the piezoelectric response (10-24 pC·N(-1)) is stable at least up to three months, the shape and magnetization maximum value (3 emu·g(-1)) is dependent on δ-FeO(OH) content, and the obtained ME voltage coefficient, with a maximum of ∼0.4 mV·cm(-1)·Oe(-1), is dependent on the incident magnetic field direction and intensity. In this way, the produced materials are suitable for innovative anisotropic sensor and actuator applications.