Stiffness Self‐Tuned Shape Memory Hydrogels for Embolization of Aneurysms

An aneurysm is a life‐threatening vascular disease. Embolization with shape memory (SM) hydrogel coils is promising for the treatment of the intractable aneurysms. However, single temperature‐triggered SM is softened in a catheter, and delivery of multiple coils is required, which may clog the catheter and complicate operation procedure. Here, a radiopaque temperature/pH dual responsive shape memory hydrogel with self‐tuned stiffness is fabricated by copolymerizing acrylonitrile (AN, dipole–dipole interaction monomer), N‐acryloyl 2‐glycine (ACG, pH‐sensitive H‐bonding monomer), and polyethylene glycol diacrylate. Under slightly acidic conditions without eliciting cytotoxicity, additional supramolecular PACG hydrogen bonds combined with cyano dipole–dipole pairings contribute to the body temperature‐triggered SM effect with an unprecedented high 430 MPa (10 °C) and 16 MPa (37 °C) Young's modulus. A carotid aneurysm is created in a dog to test the embolization of this SM hydrogel. At 37 °C, the hydrogel's high stiffness ensures its smooth delivery through a catheter. After being transported into the aneurysm sac, secondary swelling occurs concurrent with appropriate decrease of stiffness upon contacting neutral blood, thus enhancing the packing density and reducing recanalization rate and delivery times. This stiffness adaptive SM hydrogel holds its great potential as permanent embolic agents for treating a variety of aneurysms.     

Radiopaque Highly Stiff and Tough Shape Memory Hydrogel Microcoils for Permanent Embolization of Arteries

Transcatheter arterial embolization of aneurysm with metal microcoils is notoriously prone to recanalization arising from the low filling ratio due to their extreme rigidity. Smart hydrogel microcoils with tunable modulus may essentially significantly improve the therapeutic efficacy. Here, a radiopaque highly stiff body‐temperature‐triggered shape memory (SM) hydrogel is fabricated for the first time by introducing reversible hydrophobic dipole pairing microdomains in the flexibly crosslinked network, followed by BaSO₄ precipitation. This radiopacification does not affect their mechanical performances as well as the SM effect. It is demonstrated that the mechanical properties of SM hydrogels are comparable to those of rubbers and can be modulated by adjusting temperature ranging from 20 to 40 °C. Benefiting from the thermoresponsive mechanical properties, the stiff radiopaque hydrogel strip can easily pass through a catheter under the protection of cool saline for delivery into pig's renal artery, and spontaneously and rapidly transformed into a microcoil upon contacting blood. Real‐time angiogram reveals that continuous delivery of several hydrogel microcoils can efficiently occlude the blood supply. The kidneys are atrophied considerably over three month postoperative follow‐up, and no recanalization occurs throughout the experimental time. These novel hydrogel microcoils are promising to be developed as novel permanent embolic agents for treating aneurysm.     

Freestanding Single Crystalline Fe–Pd Ferromagnetic Shape Memory Membranes – Role of Mechanical and Magnetic Constraints Across the Martensite Transition

Substrate‐attached and freestanding single crystalline Fe₇₀Pd₃₀ ferromagnetic shape memory alloy membranes, which were synthesized by molecular beam epitaxy on MgO (001) and later released from their substrates, are characterized with respect to their structural, thermal and magnetic properties. Residing in the two‐phase region of austenite and the correct martensite phase with face centered tetragonal (fct) structure at room temperature, they reveal martensite transition with little hysteresis at 326 K and 320 K, respectively. Comparing substrate‐attached with freestanding films, which show fundamentally different magnetic fingerprints, it is proposed that domain structure is capable of posing a bias on the austenite → fct‐martensite phase transition by favoring martensite variants with their easy axis aligned along the field – just as the substrate constitutes a mechanical constraint on the transition. If confirmed, this would suggest thermo‐magnetic actuation as an alternative where only moderate magnetic fields are feasible, but moderate temperature changes are possible.     

Hydration‐Induced Shape and Strength Recovery of the Feather

As necessary appendages to the bird wing for flight, feathers have evolved to address the requirements of aerial locomotion. One of the recently discovered, fascinating aspects of this is their ability to recover shape and strength with hydration. This feature significantly enhances the effectiveness of a bird's flying capability as it allows for the natural restoration of feathers damaged by predators or other external forces. Herein, this capability is analyzed and it is demonstrated that the feather shaft can regain approximately 80% of its strength in the calamus, and 70% in the rachis when subject to a hydration step after being bent to failure. The matrix of the nano‐composite structure within the feather shaft is thought to swell and soften when hydrated, reorienting the stiffer buckled fibers back to their original position. Upon drying, the strength is recovered. Experimental results are found to support this hypothesis, and a finite element calculation of hydration‐induced recovery demonstrates the effect. Smart, self‐healing composites based on approaches learned from the feather have the potential to allow for the creation of a new class of resilient materials.     

Nickel@Nickel Oxide Core–Shell Electrode with Significantly Boosted Reactivity for Ultrahigh‐Energy and Stable Aqueous Ni–Zn Battery

The main bottlenecks of aqueous rechargeable Ni–Zn batteries are their relatively low energy density and poor cycling stability, mainly arising from the low capacity and inferior reversibility of the current Ni‐based cathodes. Additionally, the complicated and difficult‐to‐scale preparation procedures of these cathodes are not promising for large‐scale energy storage. Here, a facile and cost‐effective ultrasonic‐assisted strategy is developed to efficiently activate commercial Ni foam as a robust cathode for a high‐energy and stable aqueous rechargeable Ni–Zn battery. 3D Ni@NiO core–shell electrode with remarkably boosted reactivity and an area of 300 cm² is readily obtained by this ultrasonic‐assisted activation method (denoted as SANF). Benefiting from the in situ formation of electrochemically active NiO and porous 3D structure with a large surface area, the as‐fabricated SANF//Zn battery presents ultrahigh capacity (0.422 mA h cm^?2) and excellent cycling durability (92.5% after 1800 cycles). Moreover, this aqueous rechargeable SANF//Zn battery achieves an impressive energy density of 15.1 mW h cm^?3 (0.754 mW h cm^?2) and a peak power density of 1392 mW cm^?3, outperforming most reported aqueous rechargeable energy‐storage devices. These findings may provide valuable insights into designing large‐scale and high‐performance 3D electrodes for aqueous rechargeable batteries.     

Exploiting Microphase‐Separated Morphologies of Side‐Chain Liquid Crystalline Polymer Networks for Triple Shape Memory Properties

We report a new strategy to achieve triple shape memory properties by using side‐chain liquid crystalline (SCLC) type random terpolymer networks (XL‐ TP‐n), where n is the length of flexible methylene spacer (n = 5, 10, and 15) to link backbone and mesogen. A lower glass transition temperature (T_g = T_low) and a higher liquid crystalline clearing temperature (T_cl = T_high) of XL‐TP‐n serve as molecular switches to trigger a shape memory effect (SME). Two different triple shape creation procedures (TSCPs), thermomechanical treatments to obtain temporary shapes prior to the proceeding recovery step, are used to investigate the triple shape memory behavior of XL‐TP‐n. The discrete T_g and T_cl as well as unique microphase‐separated morphologies (backbone‐rich and mesogen‐rich domains) within smectic layers of XL‐TP‐n enables triple shape memory properties. Motional decoupling between backbone‐rich and mesogen‐rich domains is also critical to determine the resulting macroscopic shape memory properties. Our strategy for obtaining triple shape memory properties will pave the way for exploiting a broad range of SCLC polymers to develop a new class of actively moving polymers.     

Unusual Aspects of Supramolecular Networks: Plasticity to Elasticity,Ultrasoft Shape Memory,and Dynamic Mechanical Properties

Supramolecular bonds have been widely used for designing polymers because of their reversible nature. In contrast, utilization of their dynamic equilibrium nature to access materials of unusual mechanical properties has been poorly explored. Taking full advantage of this latter attribute requires the design of polymer networks with high contents of supramolecular bonds. In this work, polymer networks with high contents of self‐complementary hydrogen bonds (ureidopyrimidinone) are synthesized using thiol–acrylate click addition. The excellent tunability of the network allows a range of intriguing mechanical properties to be achieved including the transition from plasticity to elasticity, ultrasoft shape memory polymer, strong strain rate dependence, and high mechanical damping. Materials with such versatile dynamic behaviors may open up a range of new applications.     

Coupling of Micromagnetic and Structural Properties Across the Martensite and Curie Temperatures in Miniaturized Ni‐Mn‐Ga Ferromagnetic Shape Memory Alloys

Micromagnetic structure evolution in Ni‐Mn‐Ga ferromagnetic shape memory thin films is investigated by means of temperature dependent magnetic force microscopy (TD‐MFM). The center of interest is the magnetic properties of epitaxial Ni‐Mn‐Ga thin films on MgO substrates across thermally induced phase transitions. Experimental results are discussed within the framework of competing magnetic interactions arising in stressed thin ferromagnetic films. Measurements on 14M martensite specimens are supplemented by three‐dimensional micromagnetic simulations. Corresponding calculated MFM micrographs are compared to experimental data. The influence of twin variant dimension and orientation on micromagnetic domain formation and wall structure is depicted from a theoretical point of view. A micromagnetic model system of partial flux closure is proposed and calculated analytically to estimate a stress induced magneto crystalline anisotropy constant in austenite Ni‐Mn‐Ga.     

Adhesion and Surface Interactions of a Self‐Healing Polymer with Multiple Hydrogen‐Bonding Groups

The surface properties and self‐adhesion mechanism of self‐healing poly(butyl acrylate) (PBA) copolymers containing comonomers with 2‐ureido‐4[1H]‐pyrimidinone quadruple hydrogen bonding groups (UPy) are investigated using a surface forces apparatus (SFA) coupled with a top‐view optical microscope. The surface energies of PBA–UPy4.0 and PBA–UPy7.2 (with mole percentages of UPy 4.0% and 7.2%, respectively) are estimated to be 45–56 mJ m^?2 under dry condition by contact angle measurements using a three probe liquid method and also by contact and adhesion mechanics tests, as compared to the reported literature value of 31–34 mJ m^?2 for PBA, an increase that is attributed to the strong UPy–UPy H‐bonding interactions. The adhesion strengths of PBA–UPy polymers depend on the UPy content, contact time, temperature and humidity level. Fractured PBA–UPy films can fully recover their self‐adhesion strength to 40, 81, and 100% in 10 s, 3 h, and 50 h, respectively, under almost zero external load. The fracture patterns (i.e., viscous fingers and highly “self‐organized” parallel stripe patterns) have implications for fabricating patterned surfaces in materials science and nanotechnology. These results provide new insights into the fundamental understanding of adhesive mechanisms of multiple hydrogen‐bonding polymers and development of novel self‐healing and stimuli‐responsive materials.     

Impact of Reactive Amphiphilic Copolymers on Mechanical Properties and Cell Responses of Fibrin‐Based Hydrogels

Mechanical properties of hydrogels can be modified by the variation of structure and concentration of reactive building blocks. One promising biological source for the synthesis of biocompatible hydrogels is fibrinogen. Fibrinogen is a glycoprotein in blood, which can be transformed enzymatically to fibrin playing an important role in wound healing and clot formation. In the present work, it is demonstrated that hybrid hydrogels with their improved mechanical properties, tunable internal structure, and enhanced resistance to degradation can be synthesized by a combination of fibrinogen and reactive amphiphilic copolymers. Water‐soluble amphiphilic copolymers with tunable molecular weight and controlled amounts of reactive epoxy side groups are used as reactive crosslinkers to reinforce fibrin hydrogels. In the present work, copolymers that can influence the mechanical properties of fibrin‐based hydrogels are used. The reactive copolymers increase the storage modulus of the hydrogels from 600 Pa to 30 kPa. The thickness of fibrin fibers is regulated by the copolymer concentration. It could be demonstrated that the fibrin‐based hydrogels are biocompatible and support cell proliferation. Their degradation rate is considerably slower than that of native fibrin gels. In conclusion, fibrin‐based hydrogels with tunable elasticity and fiber thickness useful to direct cell responses like proliferation and differentiation are produced.     

The Effect of H‐ and J‐Aggregation on the Photophysical and Photovoltaic Properties of Small Thiophene–Pyridine–DPP Molecules for Bulk‐Heterojunction Solar Cells

The performance of organic semiconductors in optoelectronic devices depends on the functional properties of the individual molecules and their mutual orientations when they are in the solid state. The effect of H‐ and J‐aggregation on the photophysical properties and photovoltaic behavior of four electronically identical but structurally different thiophene–pyridine–diketopyrrolopyrrole molecules is studied. By introducing and changing the position of two hexyl side chains on the two peripheral thiophene units of these molecules, their aggregation in thin films between H‐type and J‐type is effectively tuned, as evidenced from the characteristics of optical absorption, fluorescence, and excited state lifetime. The two derivatives that assemble into J‐type aggregates exhibit a significantly enhanced photovoltaic performance, up to an order of magnitude, compared to the two molecules that form H‐type aggregates. The reasons for this remarkably different behavior are discussed.     

Self-Healing,Photothermal-Responsive,and Shape Memory Polyurethanes for Enhanced Mechanical Properties of 3D/4D Printed Objects

Additive manufacturing is a promising technology that can directly fabricate structures with complex internal geometries, which is barely achieved by traditional manufacturing. However, the mechanical properties of fused deposition modeling (FDM)-printed objects are inferior to those of conventionally manufactured products. To improve the mechanical properties of the printed products, a series of novel thermoplastic polyurethanes with self-healing properties, intrinsic photothermal effects, and excellent printability are designed and synthesized by introducing dynamic oxime–carbamate bonds and hydrogen bonds into the polymer chains. On-demand introduction of near-infrared (NIR) irradiation, direct heating, and sunlight irradiation enhances interfacial bonding strength and thus improve the mechanical properties of the printed product. Additionally, mechanical anisotropy of the printed products can be sophistically manipulated by regulating the self-healing conditions. Support-free printing and healing of damaged printed products are also achieved owing to the self-healing properties of the material. Moreover, the as-prepared materials exhibit shape-memory properties NIR irradiation or direct heating effectively triggers shape-memory recovery and demonstrates their potential in 4D printing by printing a man-like robot. This study not only provides a facile strategy for obtaining high-performance printed products but also broadens the potential applications of FDM technology in intelligent devices.     

Understanding the Shape Memory Behavior of Self‐Bending Materials and Their Use as Sensors

By depositing layers composed of poly (N‐isopropylacrylamide)‐based microgels and the polyelectrolyte polydiallyldimethylammonium chloride on a flexible substrate, responsive materials that bend upon drying can be fabricated; the extent of the bending depends on atmospheric humidity. This study shows that the bending conformation/direction can be templated, and exhibits shape memory. Detailed examination of the bilayer system leads to an understanding of the phenomena leading to this behavior. By close examination of microscopy images and diffraction patterns, this study is able to determine that the dried polymer‐based layer is composed of both amorphous and crystalline phases; the amorphous phase can readily absorb water, which results in actuation, while the crystalline phases template the bending characteristics of the device. With an understanding of the bending behavior of the devices, this study is able to generate humidity sensors by interfacing them with stretchable strain sensors, which are also developed specifically for the bendable materials.     

Architecture of Conjugated Donor–Acceptor (D–A)‐Type Polymer Films with Cross‐Linked Structures

A series of new donor–acceptor (D–A)‐type semiconducting conjugated polymers (SCPs), which can form cross‐linked structural and supramolecular assembly films by hydrogen‐bonding, is successfully synthesized. The microstructures of supramolecular assembly films are further investigated by X‐ray diffraction (XRD), high‐ resolution transmission electron microscopy (HRTEM), and variable‐temperature Fourier transform infrared (FT‐IR) absorption spectra. As electronic transmission (ET) materials, the SCPs demonstrate superior properties by means of fabricating electron‐only devices with the configuration of ITO/ET (SCPs)/Ca/Al. According to space‐charge‐limited current (SCLC) measurements, fluorine‐containing SCPs exhibit much smaller threshold voltages and much higher electron mobilities than Alq₃. Meanwhile, a significant enhancement for their luminescence properties is verified by the photoluminescence (PL) and electroluminescent (EL) spectra of cross‐linked‐type SCPs, compared to non‐cross‐linked‐type SCPs. The fabricated polymer light‐emitting diodes (PLEDs) with the configuration of ITO/PEDOT:PSS/EML (SCPs)/BCP/LiF/Al are able to emit the color from green to red with moderately low turn‐on voltages. These results suggested that cross‐linked D–A‐type SCP can become a potential candidate as a kind of multifunctional materials applied in the field of optoelectronic devices.     

Identification of Quaternary Shape Memory Alloys with Near‐Zero Thermal Hysteresis and Unprecedented Functional Stability

Improving the functional stability of shape memory alloys (SMAs), which undergo a reversible martensitic transformation, is critical for their applications and remains a central research theme driving advances in shape memory technology. By using a thin‐film composition‐spread technique and high‐throughput characterization methods, the lattice parameters of quaternary Ti–Ni–Cu–Pd SMAs and the thermal hysteresis are tailored. Novel alloys with near‐zero thermal hysteresis, as predicted by the geometric non‐linear theory of martensite, are identified. The thin‐film results are successfully transferred to bulk materials and near‐zero thermal hysteresis is observed for the phase transformation in bulk alloys using the temperature‐dependent alternating current potential drop method. A universal behavior of hysteresis versus the middle eigenvalue of the transformation stretch matrix is observed for different alloy systems. Furthermore, significantly improved functional stability, investigated by thermal cycling using differential scanning calorimetry, is found for the quaternary bulk alloy Ti_50.2Ni_34.4Cu_12.3Pd_3.1.     

Reversible Formation of g‐C3N4 3D Hydrogels through Ionic Liquid Activation: Gelation Behavior and Room‐Temperature Gas‐Sensing Properties

Many unique properties arise when the 3D stacking of layered materials is disrupted, originating nanostructures. Stabilization, and further reorganization of these individual layers into complex 3D structures, can be essential to allow these properties to persist in macroscopic systems. It is demonstrated that a simple hydrothermal process, assisted by ionic liquids (ILs), can convert bulk g‐C₃N₄ into a stable hydrogel. The gelation occurs through delamination of the layered structure, driven by particular interactions between the IL and the carbon nitride sheets, forming an amphiphilic foam‐like network. This study employs spectroscopic and computational tools to unravel the gelation mechanism, and provides a rational approach toward the stabilization of 2D materials in hydrogels. The solution‐processable hydrogels can also be used as building blocks of complex devices. Chemiresistive gas sensors employing g‐C₃N₄ 3D hydrogels exhibit superior response at room temperature, enabling effective gas sensing under low power conditions.