Wrinkled 2D Materials: A Versatile Platform for Low‐Threshold Stretchable Random Lasers

A stretchable, flexible, and bendable random laser system capable of lasing in a wide range of spectrum will have many potential applications in next‐ generation technologies, such as visible‐spectrum communication, superbright solid‐state lighting, biomedical studies, fluorescence, etc. However, producing an appropriate cavity for such a wide spectral range remains a challenge owing to the rigidity of the resonator for the generation of coherent loops. 2D materials with wrinkled structures exhibit superior advantages of high stretchability and a suitable matrix for photon trapping in between the hill and valley geometries compared to their flat counterparts. Here, the intriguing functionalities of wrinkled reduced graphene oxide, single‐layer graphene, and few‐layer hexagonal boron nitride, respectively, are utilized to design highly stretchable and wearable random laser devices with ultralow threshold. Using methyl‐ammonium lead bromide perovskite nanocrystals (PNC) to illustrate the working principle, the lasing threshold is found to be ≈10 µJ cm^?2, about two times less than the lowest value ever reported. In addition to PNC, it is demonstrated that the output lasing wavelength can be tuned using different active materials such as semiconductor quantum dots. Thus, this study is very useful for the future development of high‐performance wearable optoelectronic devices.     

Engineered Fibrillar Fibronectin Networks as Three‐Dimensional Tissue Scaffolds

Extracellular matrix (ECM) proteins, and most prominently, fibronectin (Fn), are routinely used in the form of adsorbed pre‐coatings in an attempt to create a cell‐supporting environment in both two‐ and three‐dimensional cell culture systems. However, these protein coatings are typically deposited in a form which is structurally and functionally distinct from the ECM‐constituting fibrillar protein networks naturally deposited by cells. Here, the cell‐free and scalable synthesis of freely suspended and mechanically robust three‐dimensional (3D) networks of fibrillar fibronectin (fFn) supported by tessellated polymer scaffolds is reported. Hydrodynamically induced Fn fibrillogenesis at the three‐phase contact line between air, an Fn solution, and a tessellated scaffold microstructure yields extended protein networks. Importantly, engineered fFn networks promote cell invasion and proliferation, enable in vitro expansion of primary cancer cells, and induce an epithelial‐to‐mesenchymal transition in cancer cells. Engineered fFn networks support the formation of multicellular cancer structures cells from plural effusions of cancer patients. With further work, engineered fFn networks can have a transformative impact on fundamental cell studies, precision medicine, pharmaceutical testing, and pre‐clinical diagnostics.     

Multifunctional POSS‐Based Nano‐Photo‐Initiator for Overcoming the Oxygen Inhibition of Photo‐Polymerization and for Creating Self‐Wrinkled Patterns

Oxygen inhibition remains a challenge in photo‐curing technology despite the expenditure of considerable effort in developing a convenient, efficient, and low‐cost prevention method. Here, a novel strategy to prevent oxygen inhibition is presented; it is based on the self‐assembly of multifunctional nano‐photo‐initiators (F₂‐POSS‐(SH)₄‐TX/EDB) at the interface of air and the liquid monomer. These nano‐photo‐initiators consist of a thiol‐containing polyhedral oligomeric silsesquioxane (POSS) skeleton onto which fluorocarbon chains and thioxanthone and dimethylaminobenzoate (TX/EDB) photo‐initiator moieties are grafted. Real‐time Fourier‐transform infrared spectroscopy (FT‐IR) is used to investigate the photo‐polymerization of various acrylate monomers that are initiated by F₂‐POSS‐(SH)₄‐TX/EDB and its model analogues in air and in N₂. FT‐IR results show that F₂‐POSS‐(SH)₄‐TX/EDB decreases the effects of oxygen inhibition. X‐ray photo‐electron spectroscopy and atomic force microscopy reveal that the self‐assembly of F₂‐POSS‐(SH)₄‐TX/EDB at the air/(liquid monomer) interface forms a cross‐linked top layer via thiol–ene polymerization; this layer acts as a physical barrier against the diffusion of oxygen from the surface into the bulk layer. A mismatch in the shrinkage between the top and bulk layers arise as a result of the different types of photo‐cross‐linking reactions. Subsequently, the surface develops a wrinkled pattern with a low surface energy. This strategy exhibits considerable potential for preventing oxygen inhibition, and the wrinkled pattern may prove very useful in photo‐curing technology.     

Chemical Approaches to Three‐Dimensional Semiconductor Photonic Crystals

We review recent efforts to make three‐dimensional semiconductor photonic crystals using self‐assembly techniques. These approaches, which utilize a synthetic opal as a template to shape the semiconductor material (see Figure), provide a simple and inexpensive alternative to lithographic methods. Since the resulting structures can, in principle, have a complete photonic bandgap – a property that would allow ultimate control over the flow of light – these materials may have serious implications for modern photonics.     

Three‐Dimensional Printing of Complex‐Shaped Alumina/Glass Composites

Alumina/glass composites were fabricated by three‐dimensional printing (3DP?) and pressureless infiltration of lanthanum‐alumino‐silicate glass into sintered porous alumina preforms. The preforms were printed using an alumina/dextrin powder blend as a precursor material. They were sintered at 1600 °C for 2 h prior to glass infiltration at 1100 °C for 2 h. The influence of layer thickness and sample orientation within the building chamber of the 3D‐printer on microstructure, porosity, and mechanical properties of the preforms and final composites was investigated. The increase of the layer thickness from 90 to 150 µm resulted in an increase of the total porosity from ～19 to ～39 vol% and thus, in a decrease of the mechanical properties of the sintered preforms. Bending strength and elastic modulus of sintered preforms were found to attain significantly higher values for samples orientated along the Y‐axis of the 3D‐printer compared to those orientated along the X‐ or the Z‐axis, respectively. Fabricated Al₂O₃/glass composites exhibit improved fracture toughness, bending strength, Young's modulus, and Vickers hardness up to 3.6 MPa m^1/2, 175 MPa, 228 GPa, and 12 GPa, respectively. Prototypes were fabricated on the basis of computer tomography data and computer aided design data to show geometric capability of the process.     

Two‐ and Three‐Dimensional Alignment and Patterning of Carbon Nanotubes

Alignment or patterning of carbon nanotubes (CNTs) is particularly important for fabricating functional devices such as field emitters, nanophotonics, nanoelectronics, and ultrahydrophobic materials. This work briefly reviews recent progress on the synthesis of two‐dimensional CNT patterns, and then particularly concentrates on describing the pillar‐shaped fabrication and very interesting patterns of three‐dimensionally aligned CNTs formed by pyrolysis of iron(II ) phthalocyanine. The possible formation mechanism of the structures is discussed. The Figure shows the pillar‐shaped alignment of three‐dimensional CNTs.     

Ideal Three‐Dimensional Electrode Structures for Electrochemical Energy Storage

Three‐dimensional electrodes offer great advantages, such as enhanced ion and electron transport, increased material loading per unit substrate area, and improved mechanical stability upon repeated charge–discharge. The origin of these advantages is discussed and the criteria for ideal 3D electrode structure are outlined. One of the common features of ideal 3D electrodes is the use of a 3D carbon‐ or metal‐based porous framework as the structural backbone and current collector. The synthesis methods of these 3D frameworks and their composites with redox‐active materials are summarized, including transition metal oxides and conducting polymers. The structural characteristics and electrochemical performances are also reviewed. Synthesis of composite 3D electrodes is divided into two types — template‐assisted and template‐free methods — depending on whether a pre‐made template is required. The advantages and drawbacks of both strategies are discussed.     

Three‐Dimensional Printing of Multifunctional Nanocomposites: Manufacturing Techniques and Applications

The integration of nanotechnology into three‐dimensional printing (3DP) offers huge potential and opportunities for the manufacturing of 3D engineered materials exhibiting optimized properties and multifunctionality. The literature relating to different 3DP techniques used to fabricate 3D structures at the macro‐ and microscale made of nanocomposite materials is reviewed here. The current state‐of‐the‐art fabrication methods, their main characteristics (e.g., resolutions, advantages, limitations), the process parameters, and materials requirements are discussed. A comprehensive review is carried out on the use of metal‐ and carbon‐based nanomaterials incorporated into polymers or hydrogels for the manufacturing of 3D structures, mostly at the microscale, using different 3D‐printing techniques. Several methods, including but not limited to micro‐stereolithography, extrusion‐based direct‐write technologies, inkjet‐printing techniques, and popular powder‐bed technology, are discussed. Various examples of 3D nanocomposite macro‐ and microstructures manufactured using different 3D‐printing technologies for a wide range of domains such as microelectromechanical systems (MEMS), lab‐on‐a‐chip, microfluidics, engineered materials and composites, microelectronics, tissue engineering, and biosystems are reviewed. Parallel advances on materials and techniques are still required in order to employ the full potential of 3D printing of multifunctional nanocomposites.     

Sculpting Asymmetric,Hollow‐Core,Three‐Dimensional Nanostructures Using Colloidal Particles

Colloidal elements have historically played a key role in “bottom‐up” self‐assembly processes for nanofabrication. However, these elementary components can also interact with light to generate complex intensity distributions and facilitate “top‐down” lithography. Here, a nanolithography technique is demonstrated based on oblique illuminations of colloidal particles to fabricate hollow‐core 3D nanostructures with complex symmetry. The light–particle interaction generates an angular light distribution as governed by Mie scattering, which can be compounded by multiple illuminations to sculpt novel 3D structures in the underlying photoresist. The fabricated geometry can be controlled by the particle parameters and illumination configurations, enabling the fabrication of a large variety of asymmetric hollow nanostructures. The proposed technique has high pattern versatility, is low cost and high throughput, and can find potential application in nanoneedles, nanonozzles, and materials with anisotropic properties.     

Three‐Dimensional Exploration and Mechano‐Biophysical Analysis of the Inner Structure of Living Cells

A novel mechanobiological method is presented to explore qualitatively and quantitatively the inside of living biological cells in three dimensions, paving the way to sense intracellular changes during dynamic cellular processes. For this purpose, holographic optical tweezers, which allow the versatile manipulation of nanoscopic and microscopic particles by means of tailored light fields, are combined with self‐interference digital holographic microscopy. This biophotonic holographic workstation enables non‐contact, minimally invasive, flexible, high‐precision optical manipulation and accurate 3D tracking of probe particles that are incorporated by phagocytosis in cells, while simultaneously quantitatively phase imaging the cell morphology. In a first model experiment, internalized polystyrene microspheres with 1 μm diameter are three‐dimensionally moved and tracked in order to quantify distances within the intracellular volume with submicrometer accuracy. Results from investigations on cell swelling provoked by osmotic stimulation demonstrate the homogeneous stretching of the cytoskeleton network, and thus that the proposed method provides a new way for the quantitative 3D analysis of the dynamic intracellular morphology.     

Co@Co3O4 Core–Shell Three‐Dimensional Nano‐Network for High‐Performance Electrochemical Energy Storage

An alternative routine is presented by constructing a novel architecture, conductive metal/transition oxide (Co@Co₃O₄) core–shell three‐dimensional nano‐network (3DN) by surface oxidating Co 3DN in situ, for high‐performance electrochemical capacitors. It is found that the Co@Co₃O₄ core–shell 3DN consists of petal‐like nanosheets with thickness of <10 nm interconnected forming a 3D porous nanostructure, which preserves the original morphology of Co 3DN well. X‐ray photoelectron spectroscopy by polishing the specimen layer by layer reveals that the Co@Co₃O₄ nano‐network is core–shell‐like structure. In the application of electrochemical capacitors, the electrodes exhibit a high specific capacitance of 1049 F g^?1 at scan rate of 2 mV/s with capacitance retention of ～52.05% (546 F g^?1 at scan rate of 100 mV) and relative high areal mass density of 850 F g^?1 at areal mass of 3.52 mg/cm². It is believed that the good electrochemical behaviors mainly originate from its extremely high specific surface area and underneath core‐Co “conductive network”. The high specific surface area enables more electroactive sites for efficient Faradaic redox reactions and thus enhances ion and electron diffusion. The underneath core‐Co “conductive network” enables an ultrafast electron transport.