Inspired by shape-morphing organisms in nature, researchers have developed various hydrogels with stimuli-responsive swelling, shrinking, bending, folding, origami, rolling, twisting, or locomotion. These smart hydrogels are usually created by patterning or 4D printing. The shape morphing of hydrogels allows the fabrication of helixing, twisting, and rolling microstructures, all of which are hard to reproduce directly by ordinary techniques. More importantly, under external stimuli (e.g., solvent, humidity, temperature, light, pH, and electric/magnetic fields), many hydrogels exhibit recoverable shape morphing and thus find promising applications in grippers, sensors, valves, soft robotics, etc. Since shape morphing determines the functions of hydrogels in a great number of cases, herein, recent advances of stimuli-responsive hydrogels are summarized, with their types, shape-morphing mechanisms, fabrication methods, shape-morphing modes, and extensive applications covered. The conclusion and perspectives are also presented to guide the design and fabrication of functional hydrogels.

Liquid crystal elastomers (LCEs) are renowned for their large, reversible, and anisotropic shape change in response to various external stimuli due to their lightly cross‐linked polymer networks with an oriented mesogen direction, thus showing great potential for applications in robotics, bio‐medics, electronics, optics, and energy. To fully take advantage of the anisotropic stimuli‐responsive behaviors of LCEs, it is preferable to achieve a locally controlled mesogen alignment into monodomain orientations. In recent years, the application of 4D printing to LCEs opens new doors for simultaneously programming the mesogen alignment and the 3D geometry, offering more opportunities and higher feasibility for the fabrication of 4D‐printed LCE objects with desirable stimuli‐responsive properties. Here, the state‐of‐the‐art advances in 4D printing of LCEs are reviewed, with emphasis on both the mechanisms and potential applications. First, the fundamental properties of LCEs and the working principles of the representative 4D printing techniques are briefly introduced. Then, the fabrication of LCEs by 4D printing techniques and the advantages over conventional manufacturing methods are demonstrated. Finally, perspectives on the current challenges and potential development trends toward the 4D printing of LCEs are discussed, which may shed light on future research directions in this new field.

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Metal‐organic frameworks (MOFs) are crystalline materials with permanent pores constructed by self‐assembly of organic ligands and metal clusters through coordination bonds. Due to their diversity and tunability, MOFs have been used as precursors to be converted into other types of functional materials by pyrolytic recrystallization. Laser‐induced synthesis has been proven to be a powerful pyrolytic processing technique with fast and accurate laser irradiation, low loss, high efficiency, selectivity and programmability, which endow MOF derivatives with new features. Laser‐induced MOF derivatives exhibit high versatility in multidisciplinary research fields. In this review, we first briefly introduce the basic principles of laser smelting and the types of materials for laser preparation of MOF derivatives. Subsequently, we focus on the peculiarity of the engineering of structural defects and their applications in catalysis, environmental protection, and energy fields. Finally, we highlight the challenges and opportunities at the current stage with the aim of elucidating the future direction of the rapidly growing field of laser‐induced synthesis of MOF derivatives.This article is protected by copyright. All rights reserved

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Mullite has an orthorhombic crystal structure, with various advantages, such as high mechanical strength, and stable chemical and physical properties. Especially, mullite whiskers have been widely acknowledged to be potential candidates as reinforcing elements in the fabrication of ceramic-matrix composites. Various strategies have been developed to synthesize mullite whiskers, such as catalytic methods, liquid-phase reaction, molten salt reaction, solid-state reaction and high-energy ball milling process. In different synthesis methods, the underlying mechanisms governing the anisotropic grain growth of mullite grains vary. This paper aims to offer an overview on the progress in fabrication of mullite whiskers with different methods, and the perspectives on these special materials are briefly discussed.

Abstract. The initial cooling temperature has important effect on the bending change and section size of rolled heavy rail, when rolled heavy rail is on the cooling bed for natural cooling. In the paper, the heat-stress couple method is adopted to carry on numerical simulation to cooling process of 60kg/m U75V heavy rail, and we has obtained the bending change value and section size of rolled heavy rail in different initial cooling temperature. The study is of great reference value on the design of cooling bed which is for hundred-meter high speed heavy rail and the formulation of cooling technological parameters.