Optimal trajectory smoothing for direct energy deposition additive manufacturing processes

In free form additive manufacturing processes (e.g., metal blown powder, glass filament, ceramic paste extrusion), part quality depends on both the rate at which the part is built and where material is deposited. This creates a natural conflict between these two criteria at locations where the curvature of the programmed path is small, such as corners, because at these locations it is not possible to precisely follow the path without changing acceleration and, hence, varying the part build rate due to the variation in path velocity. In some additive manufacturing processes it is not possible to easily vary the material feed rate to maintain a constant part build rate when path velocity varies; thus, uneven material deposition occurs. In this work an optimal trajectory smoothing methodology is created that formulates the path following problem as an optimal dynamic system boundary value problem. The methodology naturally allows a trade-off between path following error and velocity error and is experimentally applied in a blown powder direct metal deposition additive manufacturing process. The results show that path and velocity errors increase as the corner angle decreases and the velocity entering the corner increases; however, they can be decreased by increasing the corner's leg length. Further, as the weight on velocity error increases, the velocity error, excess deposited material, and total print time decrease asymptotically while path error increases asymptotically.     

Localization of Au Nanoclusters on Layered Double Hydroxides Nanosheets: Confinement‐Induced Emission Enhancement and Temperature‐Responsive Luminescence

Gold nanoclusters (Au NCs) stand for a new type of fluorescent nanomaterials with outstanding optical properties due to their discrete electronic energy and direct electron transition. However, relative low quantum yield (QY) of Au NCs in aqueous or solid state has limited their photofunctional applications. To improve the fluorescent performances of Au NCs and find an effective approach for the fabrication of Au NCs‐based films, in this work, Au NCs are localized onto 2D layered double hydroxides (LDHs) nanosheets via a layer‐by‐layer assembly process; the as‐fabricated (Au NCs/LDH)_n ultrathin films (UTFs) show an ordered and dense immobilization of Au NCs. The localization and confinement effects imposed by LDH nanosheets induce significantly increased emissive Au(I) units as confirmed by X‐ray photoelectron spectroscopy and periodic density functional theoretical simulation, which further results in promoted QY (from 2.69% to 14.11%) and prolonged fluorescence lifetime (from 1.84 µs to 14.67 µs). Moreover, the ordered (Au NCs/LDH)_n UTFs exhibit well‐defined temperature‐dependent photoluminescence (PL) and electrochemiluminescence (ECL) responses. Therefore, this work supplies a facile strategy to achieve the immobilization of Au NCs and obtain Au NCs‐based thin films with high luminescent properties, which have potential applications in PL and ECL temperature sensors.     

Metals by Micro‐Scale Additive Manufacturing: Comparison of Microstructure and Mechanical Properties

Many emerging applications in microscale engineering rely on the fabrication of 3D architectures in inorganic materials. Small‐scale additive manufacturing (AM) aspires to provide flexible and facile access to these geometries. Yet, the synthesis of device‐grade inorganic materials is still a key challenge toward the implementation of AM in microfabrication. Here, a comprehensive overview of the microstructural and mechanical properties of metals fabricated by most state‐of‐the‐art AM methods that offer a spatial resolution ≤10 μm is presented. Standardized sets of samples are studied by cross‐sectional electron microscopy, nanoindentation, and microcompression. It is shown that current microscale AM techniques synthesize metals with a wide range of microstructures and elastic and plastic properties, including materials of dense and crystalline microstructure with excellent mechanical properties that compare well to those of thin‐film nanocrystalline materials. The large variation in materials' performance can be related to the individual microstructure, which in turn is coupled to the various physico‐chemical principles exploited by the different printing methods. The study provides practical guidelines for users of small‐scale additive methods and establishes a baseline for the future optimization of the properties of printed metallic objects—a significant step toward the potential establishment of AM techniques in microfabrication.     

Additive Manufacturing of Material Scaffolds for Bone Regeneration: Toward Application in the Clinics

Additive manufacturing (AM) allows the fabrication of customized bone scaffolds in terms of shape, pore size, material type, and mechanical properties. Combined with the possibility to obtain a precise 3D image of the bone defects using computed tomography or magnetic resonance imaging, it is now possible to manufacture implants for patient-specific bone regeneration. This paper reviews the state-of-the-art of the different materials and AM techniques used for the fabrication of 3D-printed scaffolds in the field of bone tissue engineering. Their advantages and drawbacks are highlighted. For materials, specific criteria, are extracted from a literature study: biomimetism to native bone, mechanical properties, biodegradability, ability to be imaged (implantation and follow-up period), histological performances, and sterilization process. AM techniques can be classified in three major categories: extrusion-based, powder-based, and vat photopolymerization. Their price, ease of use, and space requirement are analyzed. Different combinations of materials/AM techniques appear to be the most relevant depending on the targeted clinical applications (implantation site, presence of mechanical constraints, temporary or permanent implant). Finally, some barriers impeding the translation to human clinics are identified, notably the sterilization process.     

Hierarchical Nanocomposites Derived from Nanocarbons and Layered Double Hydroxides ‐ Properties,Synthesis, and Applications

The combination of one‐dimensional and two‐dimensional building blocks leads to the formation of hierarchical composites that can take full advantages of each kind of material, which is an effective way for the preparation of multifunctional materials with extraordinary properties. Among various building blocks, nanocarbons (e.g., carbon nanotubes and graphene) and layered double hydroxides (LDHs) are two of the most powerful materials that have been widely used in human life. This Feature Article presents a state‐of‐the‐art review of hierarchical nanocomposites derived from nanocarbons and LDHs. The properties of nanocarbons, LDHs, as well as the combined nanocomposites, are described first. Then, efficient and effective fabrication methods for the hierarchical nanocomposites, including the reassembly of nanocarbons and LDHs, formation of LDHs on nanocarbons, and formation of nanocarbons on LDHs, are presented. The as‐obtained nanocomposites derived form nanocarbons and LDHs exhibited excellent performance as multifunctional materials for their promising applications in energy storage, nanocomposites, catalysis, environmental protection, and drug delivery. The fabrication of LDH/carbon nanocomposites provides a novel method for the development of novel multifunctional nanocomposites based on the existing nanomaterials. However, knowledge of their assembly mechanism, robust and precise route for LDH/nanocarbon hybrid with well designed structure, and the relationship between structure, properties, and applications are still inadequate. A multidisciplinary approach from the scope of materials, physics, chemistry, engineering, and other application areas, is highly required for the development of this advanced functional composite materials.     

Additive Manufacturable Materials for Electrochemical Biosensor Electrodes

With the impending Industrial Revolution 4.0, the information produced by sensors will be central in many applications. This includes the healthcare sector, where affordable healthcare and precision medicine are highly sought after. Electrochemical sensors have the potential to produce affordable, high sensitivity and specificity, intuitive, and rapid point-of-care diagnostics. Underpinning these achievements is the choice of material and the fabrication thereof. In this review, the different types of materials used in electrochemical biosensors are reported, with a focus on synthetic conductive materials. The review demonstrates that there is an abundance of materials to select from, and compositing different types of materials further widens their applicability in biosensors. In addition, the fabrication of such materials using the state-of-the-art of fabrication technology, additive manufacturing (AM), is also detailed. The need for compositing is evident in AM, as the feedstock for certain AM technologies is inherently nonconductive. Both material choice and fabrication technologies limitations are also discussed to highlight opportunities for growth. The review highlights how recent technological advancements have the potential to drive the healthcare industry toward achieving its primary goals.     

PbSe Nanocrystals Produced by Facile Liquid Phase Exfoliation for Efficient UV–Vis Photodetectors

Lead selenide (PbSe)-based nanomaterials have been extensively investigated as building blocks for next-generation optoelectronic devices owing to their unique properties. In this work, PbSe nanocrystals (NCs) have been successfully fabricated by a facile liquid phase exfoliation approach and directly applied as active materials for photo-electrochemical (PEC)-type photodetectors (PDs). Taking advantage of broadband absorption and fast carrier dynamics, the PbSe NCs-based PDs exhibit excellent photo-current density (11.88 μA cm⁻²), photo-responsivity (12.37 mA W⁻¹), response/recovery time (0.12/0.13 s), and long-term cycling stability. The working mechanism of PbSe NCs-based PDs is explored by density functional theory calculations based on their structural and electronic properties under various conditions. It is anticipated that this contribution paves the way to readily fabricate low-dimensional PbSe NCs and extend their practical applications in PEC-type PDs.     

激光增材制造成形合金钢件质量特征及其检测评价技术现状(特邀)

无损检测技术是合金钢构件激光增材制造的重要技术支撑,是保证激光增材制造产品质量和在役安全性的关键技术,是贯穿产品全寿命安全保证的重要技术组成。金属激光增材制造合金钢件成形、组织和力学性能不同于传统技术制造构件性能,使得无损检测技术面临诸多挑战。综述了激光增材制造合金钢成形质量特性,包括成形缺陷和力学性能;基于无损检测技术,论述了无损检测技术在激光增材制造合金钢件质量评价中的应用,重点论述了无损检测技术在激光增材制造构件缺陷和力学性能中的应用现状;提出了基于超声和微磁检测技术评价材料力学性能的原理、标定方法和微磁传感器设计方案;最后总结了无损检测评价技术在激光增材制造合金钢件检测评价应用中面临的挑战和发展趋势。     

3D金属打印天线技术研究综述

近年来, 随着通信用户量的迅速增加和通信设备市场的快速发展, 数据速率高于10 Gbit/s的高速通信系统要求多种功能集成在天线上, 天线的制造要求趋于高精度、低成本和微型化. 3D打印或增材制造(additive manufacturing, AM)是一种直接从数字模型到零件制造的新兴产业技术, 可在短时间内生产出高精度和复杂的天线零件, 该技术已经成为了当前天线设计的研究热点.制造天线的AM技术主要有粉床熔合、材料挤压和材料喷射.文章首先简要介绍3D金属打印技术的基本原理、操作流程和分类, 接着重点分析几种3D金属打印天线技术的研究成果, 然后浅析3D金属打印天线技术的发展趋势, 最后对3D金属打印天线技术做了总结.     

Effective bandwidth of general Markovian traffic sources andadmission control of high speed networks

A prime instrument for controlling congestion in a high-speed network is admission control, which limits calls and guarantees a grade of service determined by delay and loss probability in the multiplexer. It is shown that for general Markovian traffic sources it is possible to assign a notional effective bandwidth to each source that is an explicitly identified, simply computed quantity with provably correct properties in the natural asymptotic regime of small loss probabilities. It is the maximal real eigenvalue of a matrix that is directly obtained from the source characteristics and the admission criterion, and for several sources it is simply additive. Both fluid and point process models are considered. Numerical results show that the acceptance set for heterogeneous classes of sources is closely approximated and conservatively bounded by the set obtained from the effective bandwidth approximation. The bandwidth-reducing properties of the leaky bucket regulator are exhibited numerically     

Electrospinning Preparation and Drug‐Delivery Properties of an Up‐conversion Luminescent Porous NaYF4:Yb3+, Er3+@Silica Fiber Nanocomposite

Up‐conversion (UC) luminescent porous silica fibers decorated with NaYF₄:Yb³⁺, Er³⁺ nanocrystals (NCs) (denoted as NaYF₄:Yb³⁺, Er³⁺@silica fiber) are prepared by the electrospinning process using cationic surfactant P123 as a template. Monodisperse and hydrophobic oleic acid capped β‐NaYF₄: Yb³⁺, Er³⁺ NCs are prepared by thermal decomposition methodology. Then, these NCs are transferred into aqueous solution by employing cetyltrimethylammonium bromide (CTAB) as secondary surfactant. The water‐dispersible β‐NaYF₄:Yb³⁺, Er³⁺ NCs are dispersed into precursor electrospinning solution containing P123 and tetraethyl orthosilicate (TEOS), followed by preparation of precursor fibers via electrospinning. Finally, porous α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber nanocomposites are obtained after annealing the precursor fibers containing β‐NaYF₄:Yb³⁺, Er³⁺ at 550 °C. The as‐prepared α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber possesses porous structure and UC luminescence properties simultaneously. Furthermore, the obtained nanocomposites can be used as a drug delivery host carrier and drug storage/release properties are investigated, using ibuprofen (IBU) as a model drug. The results indicate that the IBU–loaded α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber nanocomposites show UC emission of Er³⁺ under 980 nm NIR laser excitation and a controlled release property for IBU. Meanwhile, the UC emission intensity of IBU–α‐NaYF₄:Yb³⁺, Er³⁺@silica fiber system varies with the released amount of IBU.     

实时混粉梯度材料SLM成型系统构建与实验

为了在成型过程中,方便地在零件上按需获得梯度材料成分,采用了集成同步送粉碰撞混合、锥形聚集混合、气流混合等多重混粉动作的实时混粉方法,研制成梯度材料激光选区熔化增材制造系统,并展开了梯度材料成型实验验证,结合试样照片、显微图像及能谱仪检测,分析了成型效果。结果表明,系统可自由按需在水平及垂直方向添加成分渐变材料,可方便获得具有复杂外形结构的梯度材料零件;成型件梯度材料区域微区成分分析显示,各微区内元素平均质量分数离散程度小,成型过程中每层平均混粉时间10s~15s时,各微区主要元素变异系数不超0.59,达到了较好的混合均匀性。该研究为自由制造梯度材料零件提供了新途径。     

Intracellular Fate of Hydrophobic Nanocrystal Self‐Assemblies in Tumor Cells

Control of interactions between nanomaterials and cells remains a biomedical challenge. A strategy is proposed to modulate the intralysosomal distribution of nanoparticles through the design of 3D suprastructures built by hydrophilic nanocrystals (NCs) coated with alkyl chains. The intracellular fate of two water‐dispersible architectures of self‐assembled hydrophobic magnetic NCs: hollow deformable shells (colloidosomes) or solid fcc particles (supraballs) is compared. These two self‐assemblies display increased cellular uptake by tumor cells compared to dispersions of the water‐soluble NC building blocks. Moreover, the self‐assembly structures increase the NCs density in lysosomes and close to the lysosome membrane. Importantly, the structural organization of NCs in colloidosomes and supraballs are maintained in lysosomes up to 8 days after internalization, whereas initially dispersed hydrophilic NCs are randomly aggregated. Supraballs and colloidosomes are differently sensed by cells due to their different architectures and mechanical properties. Flexible and soft colloidosomes deform and spread along the biological membranes. In contrast, the more rigid supraballs remain spherical. By subjecting the internalized suprastructures to a magnetic field, they both align and form long chains. Overall, it is highlighted that the mechanical and topological properties of the self‐assemblies direct their intracellular fate allowing the control intralysosomal density, ordering, and localization of NCs.     

Inkjet printed System-in-Package design and manufacturing

Additive manufacturing technology using inkjet offers several improvements to electronics manufacturing compared to current non-additive masking technologies. Manufacturing processes can be made more efficient, straightforward and flexible compared to subtractive masking processes, several time-consuming and expensive steps can be omitted. Due to the additive process, material loss is minimal, because material is never removed as with etching processes. The amounts of used material and waste are smaller, which is advantageous in both productivity and environmental means. Furthermore, the additive inkjet manufacturing process is flexible allowing fast prototyping, easy design changes and personalization of products. Additive inkjet processing offers new possibilities to electronics integration, by enabling direct writing on various surfaces, and component interconnection without a specific substrate. The design and manufacturing of inkjet printed modules differs notably from the traditional way to manufacture electronics. In this study a multilayer inkjet interconnection process to integrate functional systems was demonstrated, and the issues regarding the design and manufacturing were considered.     

Emerging and Future Possible Strategies for Enhancing 1D Inorganic Nanomaterials‐Based Electrical Sensors towards Explosives Vapors Detection

Due to the necessity for maintaining homeland security and antiterrorism, a greatly growing demand exists for sensors that can detect explosives vapors. One‐dimensional inorganic nanomaterials represent one kind of the most promising materials for sensor fabrication due to the large surface‐to‐volume ratios, quantum confinement, high reaction activities, excellent electrical, optical, and chemical properties, unique anisotropic morphologies, and abundant structure tuning capabilities. All of these properties make the 1D inorganic nanomaterials ideal nanoscale building blocks in explosives vapors sensing applications. However, due to the big challenges, such as manufacturing technique with high cost and energy consumption, the difficulty of the assembling and patterning of 1D inorganic nanomaterials into functional devices, the weak repeatability for surface modification which hinder the development of sensors with high sensitivity, selectivity, low power consumption, simple structure, fast response and recovery procedures, high reliability and biocompatibility, more advanced strategies are needed for enhancing 1D‐inorganic‐nanomaterials‐based electrical sensors towards explosives vapors detection. In this article, a comprehensive review of the recent progresses on emerging and future possible strategies for enhancing 1D‐inorganic‐nanomaterials‐based electrical sensors towards explosives vapors detection is provided.     

Emerging Plasmonic Assemblies Triggered by DNA for Biomedical Applications

Plasmonic gold nanocrystal represents plasmonic metal nanomaterials, and has a variety of unique and beneficial properties, such as optical signal enhancement, catalytic activity, and photothermal properties tuned by local temperature, which are useful in physical, chemical, and biological applications. In addition, the inherent properties of predictable programmability, sequence specificity, and structural plasticity provide DNA nanostructures with precise controllability, spatial addressability, and targeting recognition, serving as ideal ligands to link or position building blocks during the self-assembly process. Self-assembly is a common technique for the organization of prefabricated and discrete nanoparticle blocks for the construction of extremely sophisticated nanocomposites. To this end, the integration of DNA nanotechnology with Au nanomaterials, followed by assembly of DNA-functionalized Au nanomaterials can form novel functional Au nanomaterials that are difficult to obtain through conventional methods. Here, recent progress in DNA-assembled Au nanostructures of various shapes is summarized, and their functions are discussed. The fabrication strategies that employ DNA for the self-assembly of Au nanostructures, including dimers, tetramers, satellites, nanochains, and other nanostructures with more complex geometric configurations are first described. Then, the characteristic optical properties and applications of biosensing, bioimaging, drug delivery, and therapy are discussed. Finally, the remaining challenges and prospects are elucidated.     

Core/Shell Metal Halide Perovskite Nanocrystals for Optoelectronic Applications

Core/shell structured metal halide perovskite nanocrystals (NCs) are emerging as a type of material with remarkable optical and electronic properties. Research into this field has been developing and expanding rapidly in recent years, with significant advances in the studies of the shell growth mechanism and in understanding of properties of these materials. Significant enhancement of both the stability and the optical performance of core/shell perovskite NCs are of particular importance for their applications in optoelectronic technologies. In this review, the recent advances in core/shell structured perovskite NCs are summarized. The band structures and configurations of core/shell perovskite NCs are elaborated, the shell classification and shell engineering approaches, such as perovskites and their derivative shells, semiconductor shell, oxide shell, polymer shell, etc. are reviewed, and the shell growth mechanisms are discussed. The prospective of these NCs in lighting and displays, solar cells, photodetectors, and other devices is discussed in the light of current knowledge, remaining challenges, and future opportunities.     

Dielectric Properties of Sustainable Nanocomposites Based on Zein Protein and Lignin for Biodegradable Insulators

Two types of lignin, alkali lignin and lignosulfonic acid sodium salt, are blended into thermoplastic zein through melt mixing in order to develop biodegradable insulator materials for multifunctional applications in electronics. The effects of lignin type and content on the dielectric properties of the resulting bio‐nanocomposites are investigated. The results indicate that, by modifying the structural arrangement of the zein with the use of lignin, it is possible to obtain bio‐nanocomposites characterized by tunable dielectric properties. The bio‐nanocomposites containing low amounts of lignin derivatives exhibit extensive protein structural changes together with a modification of the dielectric properties compared to the pristine thermoplastic zein. Changes in the dielectric properties of these systems are also observed to change over time, indicating a loss of plasticizer, as is evident by a decrease in the glass‐transition temperature. At high frequencies, the resulting values of the dielectric permittivity and of the loss tangent demonstrate that the bio‐nanocomposite can be used as biodegradable dielectric material for transient (temporary) electronics.     

Tuning Magnetic Property and Autophagic Response for Self‐Assembled Ni–Co Alloy Nanocrystals

Induction of autophagy is a common response of cells upon exposure to nanomaterials and represents both a safety concern and an application niche for engineered nanomaterials. Herein, it is reported that the magnetic property and the autophagy‐inducing activity for Ni–Co alloy nanocrystal (NC) assemblies can be differentially “tuned” through altering the material composition. A series of Ni–Co alloy NC assemblies, composed of nanoparticles (NPs) with a size of about 30 nm, can be quickly synthesized under microwave irradiation in aqueous solution. A controllable self‐assembling effect is observed due to the strong magnetic moment of NPs and external magnetic field. Interestingly, the saturation magnetization (Ms) shows a ‘roller coaster’ effect with varying component molar ratio, while the autophagy‐inducing activity and toxicity of these alloy NCs presents an elevated tendency with the increase of nickel component. The autophagic response partly contributes to the observed cellular toxicity of the NC assemblies, as inhibition of autophagy partially but significantly reduces toxicity. Therefore, through tuning the composition of the alloy, optimal Ni–Co NCs satisfying the needs of different applications such as diagnostic imaging (maximum magnetization and low autophagic response) or magnetically‐directed cancer cell killing (maximum autophagic response and sufficient magnetization) may be designed and developed.     

An easily prepared Ag8GeS6 nanocrystal and its role on the performance enhancement of polymer solar cells

Novel Ag₈GeS₆ nanocrystal materials (AGS NCs) have recently earned affectionate attention due to its bulk band-gap of 1.4 eV, which makes it ideal as a broad-spectrum absorber material for both semiconductor photocatalyst and photovoltaic devices. In this paper, we investigated the role of AGS NCs as molecular dopant on solution-processed polymer solar cells (PSCs). Argyrodite AGS NCs was prepared via a colloidal synthesis process using simple inorganic compounds as precursors. Incorporating AGS NCs into PSCs leads to not only improved light absorption of active layer but also increased phase separation of donor and acceptor. Moreover, the doping effect of AGS NCs was also confirmed by nanoscale morphology and photocurrent generation mechanism analysis, revealing that AGS NCs could serve as both exciton dissociation centers and charge transfer medium. This study shows that employment of AGS NCs is a facile way to improve the electrical and optical properties of organic photovoltaic devices.