Microstructural Design Research Articles

Self‐Supported Ni/Ni(OH)2 Electrodes for High‐Performance Alkaline and AEM Water Electrolysis

AbstractA novel tape‐cast Ni/Ni(OH)2 electrode is developed for water electrolysis applications. Through precise control of sintering temperature and in situ formation of Ni(OH)2 nanosheets, the electrode achieves an optimized hierarchical porous structure with interconnected channels, facilitating efficient gas bubble transport and release. The electrode exhibits remarkable hydrogen evolution reaction activity with overpotentials of 40 and 124 mV at 10 and 100 mA cm−2, respectively, comparable to noble metal catalysts. The unique microstructure enables rapid bubble detachment and enhanced mass transport, leading to a high current density of 0.91 A cm−2 at 1.8 V in alkaline water electrolysis. The inherent Ni/Ni(OH)2 composition demonstrates excellent stability over 1500 h of continuous operation and maintains consistent performance under intermittent conditions, making it particularly suitable for renewable energy integration. For anion exchange membrane water electrolysis, the electrode's smooth surface morphology prevents membrane damage while maintaining efficient mass transport, delivering 0.4 A cm−2 at 1.8 V. This study demonstrates that rational design of electrode microstructure through tape‐casting offers a promising pathway toward high‐performance, durable, and cost‐effective water electrolyzers.

Array-Patterned Micro-Structures in Spectacle Lenses Designed for Myopia Control via Image Blur

Using micro-structure components in spectacle lenses has enabled myopia progression control in children and teenagers. However, the optical design of these spectacle lenses has never been discussed, leading to a lack of correct understanding of the underlying optical treatment principles. In this work, array-patterned hexagonal lenslets with two powers of opposite signs were proposed to construct a lenslet array-integrated (LARI) spectacle lens developed for an ongoing, randomized, controlled clinical trial and to support the optical approach to myopia control leveraging retinal image blur. We found that the phase modulation induced by the micro-structures of the lenslet array contributes to the increase in RMS wavefront aberrations, leading to image blur, further inspiring the novel array-patterned micro-structure design with high-order phase elements (HOPEs). The optical performance of both LARI and HOPE spectacle lenses was investigated by simulation and experiment.

Ultrasensitive Flexible Strain Sensor Based on the Synergistic Integration of Wrinkle and Microcrack Architectures for Wearable Applications

Wearable strain sensors have significant applications in important domains such as electronic skin, personalized health monitoring, and human–computer interaction. A prevailing objective in numerous research initiatives is to achieve a balance between high sensitivity and stretchability. A strain sensor that integrates a stretchable wrinkled structure with a highly sensitive microcrack sensor to address this is developed. This sensor employs wrinkled microstructures, constructed by thermally depositing a gold film onto a flexible substrate. Due to its unique microstructural design, the sensor demonstrates a maximum strain of 75% and a gauge factor reaching 6657. Additionally, the sensor exhibits outstanding mechanical stability, maintaining consistent performance through 1000 stretching–releasing cycles. The application of this wrinkle structure strain sensor in human motion tracking, physiological signal monitoring, and speech recognition is validated. These findings underscore its practical value in wearable technology and offer novel insights for the advancement of next‐generation wearable electronic devices.

Reclaimed Asphalt Pavement in Concrete Pavements: Properties, Microstructure, and Design

Reclaimed asphalt pavement (RAP), when used as aggregate in concrete, is known to reduce the bulk concrete strength and modulus but not dramatically impact shrinkage, durability, or fracture properties, especially at lower replacement levels. This article presents an overview of RAP aggregates in concrete as it pertains to its effect on properties, microstructure, and pavement design. The mechanisms resulting in decreased strength and modulus for concrete containing RAP have been linked to: (1) the larger, more porous interfacial transition zone (ITZ) and (2) the dominance of an asphalt cohesion failure instead of an asphalt-cement adhesion failure. Despite these reductions in mechanical properties, multiple field studies have indicated that concrete with RAP can perform comparably to conventional concrete pavements, particularly when 10-15% RAP is used. The flexural capacity of concrete slabs with 22% RAP has shown similar behavior to virgin aggregate concrete given the similarities in fracture properties. Fatigue and accelerated pavement testing of rollercompacted concrete with high RAP contents (50-100%) have indicated a reduced fatigue life relative to plain concrete, requiring a slightly thicker design. Based on the literature, RAP aggregate replacement levels less than 25% can be used in concrete pavements without a significant change to the structural design.

Recent Advances in Structural Design of Carbon/Magnetic Composites and their Electromagnetic Wave Absorption Applications.

Electromagnetic pollution protection and military stealth technologies underscore the urgent need to develop efficient electromagnetic wave-absorbing materials (EWAMs). Traditional EWAMs suffer from single absorption loss mechanisms, poor impedance matching, and weak reflection loss. To date, combining dielectric loss with magnetic loss in EWAMs have proven to be an effective approach to enhancing electromagnetic absorption performance. The structural design of composites plays a pivotal role in improving impedance matching and enhancing the attenuation of electromagnetic waves. It is widely regarded as one of the principal methods for fine-tuning electromagnetic parameters and response mechanisms. Among these, composites of carbon and magnetic materials have become a research hotspot due to their magnetoelectric synergistic effects and versatile microstructure design. Herein, the principles of electromagnetic wave absorption in terms of both the loss mechanism and impedance matching are outlined. The research progress on core-shell, skeleton, and hollow structure of carbon/magnetic composite EWAMs are summarized. The synthesis methods, absorption properties, and attenuation mechanisms of composites with these structures are described in detail. Finally, the limitations of carbon/magnetic composites in electromagnetic wave absorption are discussed, possible solutions are proposed, and future development directions for carbon/magnetic composite EWAMs are envisioned.

Machine Learning-Driven Scattering Efficiency Prediction in Passive Daytime Radiative Cooling

Passive daytime radiative cooling (PDRC) has emerged as a promising, electricity-free cooling approach that reflects sunlight while radiating heat through the atmospheric transparent window. However, the design and optimization of PDRC materials remain challenging, requiring significant time and resources for experimental and numerical modeling efforts. In this work, we developed a machine learning (ML)-driven approach to predict scattering efficiency in the wavelength of 0.3–2.5 μm, with the aim of eventually optimizing the microstructural design of PDRC materials. By employing ML models such as linear regression, neural networks, and random forests, we aimed to predict and optimize the scattering efficiency across different pore sizes and mixed-pore-size configurations. As a result, the random forest model demonstrated superior prediction performance with minimal error, effectively capturing complex, non-linear interactions between material features. We also leveraged data transformation techniques such as one-hot encoding for generative predictions in mixed-pore-size configurations. The presented ML-driven platform serves as a valuable open resource for PDRC researchers, facilitating the rapid and cost-effective optimization of PDRC materials and accelerating the development of sustainable cooling technologies.

Impact of thermal crosstalk on dependent failure rates of multilayer ceramic capacitors undergoing lifetime testing

Several research studies have investigated the degradation of BaTiO3-based dielectric capacitor materials, focusing on the impact of composition, defect chemistry, and microstructural design to limit the electromigration of oxygen vacancies under electric fields at finite temperatures. Electromigration can be a dominant mechanism that controls failure rates in the individual multilayer ceramic capacitor (MLCC) components in testing the reliability of failures with highly accelerated lifetime testing (HALT) to determine the mean time to failure of MLCCs surface mounted onto printed circuit boards (PCBs). Conventional assumptions often consider these failures as independent, with no interaction between components on the PCB. However, this study employs a Physics of Failure (PoF) approach to closely examine transient degradation and its impact on MLCC reliability, emphasizing thermal crosstalk and its influence on dependent and independent failure rates. Finite element analysis thermal modeling and infrared thermography were used to assess the impact of circuit layout and component spacing on heat dissipation and thermal crosstalk under various electrical stress conditions. The study distinguishes between dependent and independent failures under a HALT, quantified through a β′ factor reflecting common cause failures due to thermal crosstalk. Through a series of experimental and statistical analyses, the β′ factor is evaluated with respect to temperature, voltage, and component spacing. These insights highlight the importance of understanding the nature of the data in reliability testing of MLCCs and optimizing the layout design of high-density circuits to mitigate dependent failures, improving overall reliability and informing better design and packaging strategies.

Recent Advances in the Performance and Mechanisms of High-Entropy Alloys Under Low- and High-Temperature Conditions

High-entropy alloys, since their development, have demonstrated great potential for applications in extreme temperatures. This article reviews recent progress in their mechanical performance, microstructural evolution, and deformation mechanisms at low and high temperatures. Under low-temperature conditions, the focus is on alloys with face-centered cubic, body-centered cubic, and multi-phase structures. Special attention is given to their strength, toughness, strain-hardening capacity, and plastic-toughening mechanisms in cold environments. The key roles of lattice distortion, nanoscale twin formation, and deformation-induced martensitic transformation in enhancing low-temperature performance are highlighted. Dynamic mechanical behavior, microstructural evolution, and deformation characteristics at various strain rates under cold conditions are also summarized. Research progress on transition metal-based and refractory high-entropy alloys is reviewed for high-temperature environments, emphasizing their thermal stability, oxidation resistance, and frictional properties. The discussion reveals the importance of precipitation strengthening and multi-phase microstructure design in improving high-temperature strength and elasticity. Advanced fabrication methods, including additive manufacturing and high-pressure torsion, are examined to optimize microstructures and improve service performance. Finally, this review suggests that future research should focus on understanding low-temperature toughening mechanisms and enhancing high-temperature creep resistance. Further work on cost-effective alloy design, dynamic mechanical behavior exploration, and innovative fabrication methods will be essential. These efforts will help meet engineering demands in extreme environments.

In Situ Assembly of 3-(Tetrazol-5-yl)triazole Complexes with Ammonium Perchlorate for High-Performance Energetic Composites.

Advanced energetic composites possess promising properties and wide-ranging applications in explosives and propellants. Nonetheless, most metal-based energetic composites present significant challenges due to surface oxidation and low-pressure output. This study introduces a facile in situ method to develop energetic composites Cutztr@AP through the intermolecular assembly of nitrogen-rich energetic coordination polymers and high-energy oxidant ammonium perchlorate (AP). Morphological analysis reveals the unique structure of Cutztr@AP, where Cutztr is distributed throughout the interior and surface of the AP particles. The nonisothermal thermodynamic analysis reveals a heat release of 2378.2 J g-1 for Cutztr@AP2, outperforming the Cutztr/AP2 achieved through ultrasonic mixing (2000 J g-1). Notably, Cutztr@AP2 exhibits promising combustion and pressure output performances, including a significantly shorter duration, a larger flame area, and higher pressure values. This novel and facile preparation technique and microstructure design approach holds significant promise for high-performance propellants, gas generators, and other related applications.

Advanced phenomenological models guided heat treating processes for LPBF Ti-6Al-4V alloy

Ti-6Al-4V (Ti64) alloy produced by laser powder bed fusion (LPBF) technique consists of an α′-martensite phase, which is usually brittle. Hence, heat treatments are required to promote the α՛→α+β and/or α→β transformations for microstructural optimization to achieve balances between strength and ductility. To guide the selection of heat treatment parameters for the design of LPBF Ti64 microstructures exhibiting optimized strength and ductility, this work explores the suitability of a Johnson-Mehl-Avrami-Kolmogorov (JMAK) and Lifshitz-Slyozov-Wagner (LSW) models. The work showed that the JMAK model can effectively model the heat treatment processes to predict volume fraction of constituent phases in LPBF Ti64. The transformation kinetics was predicted by an extended non-isothermal JMAK model based on differential scanning calorimetry (DSC) experimental data recorded during continuous heating. Moreover, hardness, as a mechanical property index, was measured for a set of specimens. The hardness initially decreased, then remained constant, and finally slightly increased with the increase in β phase fraction and underlying evolution of microstructure. When the β phase fraction was small < 3%, hardness decreased with the continuous coarsening of α lath during heat treatment process. The measured hardness and α lath width for the specimens followed the Hall-Petch relationship. Moreover, the α lath width and heat treatment time at a given temperature were found to undergo the LSW model. Hardness became independent on the β phase fraction of 3-8%, owing to the competition between α lath coarsening and solution strengthening. The hardness slightly increased when the β phase fraction was greater than 8%, because solid solution strengthening of the α phase played a dominant role over the coarsening of α lath width. The experimentally verified JMAK and LSW models are therefore discussed as effective tools to guide the selection of heat treatment parameters for designing the microstructure and hardness/strength of LPBF Ti64 alloy.

FRACTAL GEOMETRIES DESIGN FOR THREE-DIMENSIONAL PRINTING: ANALYSIS OF PERFORMANCE AND VIBRATION RESPONSE FOR PRODUCT DESIGN

Additive Manufacturing (AM) has enhanced the development of complex designs and geometries that are difficult or impossible to achieve with conventional manufacturing methods. Therefore, research focused on the analysis of the functional properties related to the behavior conferred by the filling material and the internal structure became especially relevant. In this sense, fractal geometry is one of the most established theories to characterize complex geometries based on repetitive self-similar patterns that allow complex shapes to be described and relate them to mechanical, rheological and morphological properties. The design of fractal microstructures promises the development of advanced materials with improved mechanical properties and multiple functions related to vibration absorption, weight reduction, among others. In relation to the compatibility of elastic materials with three-dimensional printing processes, the study of fractal geometries in terms of geometric design and its correlation with improved mechanical behavior is established as an objective. Several TPU-based fractal samples were designed and tested using compression processes to characterize the behavior of elastic fractal geometries as a function of fractal dimension. Specifically, Sierpinski pyramids-based specimens were designed to explore the influence of fractal dimensions and iterations on the elasticity of the samples. Additionally, a case study was carried out to by using Finite Element Method (FEA) in order to analyze the stress distribution and vibrational behavior based on fractal order. The results demonstrated a notable variation in compression behavior and vibrational behavior depending on the fractal order, highlighting the potential of fractal geometries to enhance mechanical performance in AM applications. Keywords: Fractal Geometries, Product Design, Three-Dimensional Printing, Performance, Thermoplastic Polyurethane.

In-vivo and ex-vivo evaluation of bio-inspired structures fabricated via PBF-LB for biomedical applications.

Titanium-based lattice structures have gained significant attention in biomedical engineering due to their potential to mimic bone-like behavior and improve implant performance. This study evaluates the performance of bio-inspired Ti64 TPMS Gyroyd and Stochastic lattice structures fabricated via Powder Bed Fusion-Laser Beam (PBF-LB), focusing on their in-vivo and ex-vivo mechanical and biological responses for biomedical applications. Utilizing an SLM 280 HL printer, samples exhibited notable geometric accuracy essential for mechanical integrity. The study highlights significant mechanical properties and geometric precision improvements achieved through chemical etching. Mechanical characterization revealed that the as-built Gyroid lattice had the highest elastic modulus (3.64GPa) and yield strength (200.65MPa), which improved post-etching (3.62GPa and 219.35MPa, respectively). The Stochastic lattice demonstrated lower yield strength values post-etching (169.81MPa). In-vivo analyses in horse models, both structures demonstrated excellent biocompatibility and osseointegration with no adverse inflammatory responses. Ex-vivo push-out tests showed that the chemically etched Gyroid structure achieved the highest resistance to push-out force (1645.407N) and most significant displacement (2.754mm), indicating superior energy absorption (4920.425mJ). These findings underscore the critical influence of microstructural design and surface treatments on implant functionality, offering novel insights into improving biomedical implant performance through lattice architecture and post-processing.

Role of twin thickness gradient and grain size gradient in work hardening of gradient nanotwinned metals

Abstract Gradient nanotwinned (GNT) structures exhibit superior strength and work hardening compared to homogeneous nanotwinned (HNT) structures. However, the relative effectiveness of twin thickness gradient (TTG) versus grain size gradient (GSG) on enhancing material properties remains unclear. In this study, the tensile behavior of various homogeneous, TTG, GSG, and dual gradient (DG) nanotwinned (NT) specimens was investigated using molecular dynamics simulations (MDs). The mechanisms of plastic deformation and the additional dislocation densities in different gradient structures were compared. The results indicate that both TTG and GSG structures facilitate dislocation slip within grains by stabilizing grain boundaries (GBs), dispersing shear bands, and promoting grain rotation. For the components in the DG structure, the extra dislocation density generated by the DG structure is approximately the average of the densities produced by the TTG and GSG structures individually. For the gradient structure as a whole, an appropriately designed DG can yield a higher extra dislocation density than a single gradient. This study contributes to the further enhancement of work hardening in NT metals through microstructural design.

High‐dimensional Bayesian optimization for metamaterial design

AbstractMetamaterial design, encompassing both microstructure topology selection and geometric parameter optimization, constitutes a high‐dimensional optimization problem, with computationally expensive and time‐consuming design evaluations. Bayesian optimization (BO) offers a promising approach for black‐box optimization involved in various material designs, and this work presents several advanced techniques to adapt BO to address the challenges associated with metamaterial design. First, variational autoencoders (VAEs) are employed for efficient dimensionality reduction, mapping complex, high‐dimensional metamaterial microstructures into a compact latent space. Second, mutual information maximization is incorporated into the VAE to enhance the quality of the learned latent space, ensuring that the most relevant features for optimization are retained. Third, trust region‐based Bayesian optimization (TuRBO) dynamically adjusts local search regions, ensuring stability and convergence in high‐dimensional spaces. The proposed techniques are well incorporated with conventional Gaussian processes (GP)‐based BO framework. We applied the proposed method for the design of electromagnetic metamaterial microstructures. Experimental results show that we achieve a significantly high probability of finding the ground‐truth topology types and their geometric parameters, leading to high accuracy in matching the design target. Moreover, our approach demonstrates significant time efficiency compared with traditional design methods.

A review on recent advances in polymeric microneedle loading cells: Design strategies, fabrication technologies, transdermal application and challenges.

Microneedle systems (MNs) loading living cells are a powerful platform to treat various previously incurable diseases in the era of precision medicine. Herein, an overview of recent advances in MN-based strategies for cell delivery is summarized, including material selection, design of morphological structures, and processing methods. We also systematically outlined the law of microstructural design relative to the structure-effective/function relationship in transdermal delivery or precision medicine and the design principles of cell microneedle (CMN). Furthermore, the representative works of precision treatments focusing on inflammatory skin diseases were tracked and discussed using CMN. Indeed, it highlights a practical path to solving the dilemma of cell therapy and raising the hope of precision medicine. However, there are still some challenges in developing CMN since they need multi-dimensional comprehensive properties, including mechanical properties, cell viability preservation, release, therapeutic effect, etc. The manuscript could provide insights into developing an innovative fit-to-purpose vehicle in cell therapy for interested researchers.

Analysis of the optimal heat treatment temperature for AlNiCo-based semi-hard magnetic materials based on temperature-dependent yield strength prediction model

To improve the starting characteristics of permanent magnet hysteresis motors, AlNiCo-based on semi-hard magnetic materials (ASMM) is proposed. The microstructural design is carried out by combining the advantages of soft magnetic composites (SMCs) and AlNiCo8 while choosing BaTiO3 with the negative thermal expansion property to eliminate the voids. The material composition as well as the range of heat treatment temperatures are determined by the phase transition kinetics. The temperature-dependent yield strength prediction model considering stress-equivalent magnetic fields is then developed. The model establishes the quantitative relationship between yield strength, ambient temperature, magnetostriction coefficient, elastic modulus, and Poisson's ratio. The comparisons between the model and experiments are made. It can be obtained that the yield strain is related to the microstructure and morphology, and the optimum heat treatment temperature is 680°C under the condition of ensuring the highest yield strength. This method can be used to optimize the parameters of the material preparation process and provide a reference for the optimized design of high-speed and ultra-high-speed motors.

High Corrosion Resistance of Aluminum Alloy Friction Stir Welding Joints via In Situ Rolling

Despite the extensive use of 7xxx aluminum alloys in aerospace, intergranular corrosion is yet to be appropriately addressed. In this work, in situ rolling friction stir welding (IRFSW) was proposed to improve the corrosion resistance of joints via microstructural design. A gradient-structured layer was successfully constructed on the surface of the joint, and the corrosion resistance was improved by in situ rolling. The intergranular corrosion depth of the IRFSW joint was reduced by 59.8% compared with conventional joints. The improved corrosion resistance was attributed to the redissolved precipitates, the disappearance of precipitate-free zones, and the discontinuous distribution of grain boundary precipitates. This study offers new insights for enhancing the corrosion resistance of aluminum alloy FSW joints.

A Worm-like Soft Robot Based on Adhesion-Controlled Electrohydraulic Actuators.

Worms are organisms characterized by simple structures, low energy consumption, and stable movement. Inspired by these characteristics, worm-like soft robots demonstrate exceptional adaptability to unstructured environments, attracting considerable interest in the field of biomimetic engineering. The primary challenge currently involves improving the motion performance of worm-like robots from the perspectives of actuation and anchoring. In this study, a single segment worm-like soft robot driven by electrohydraulic actuators is proposed. The robot consists of a soft actuation module and two symmetrical anchoring modules. The actuation modules enable multi-degree-of-freedom motion of the robot using symmetric dual-electrode electrohydraulic actuators, while the anchoring modules provide active friction control through bistable electrohydraulic actuators. A hierarchical microstructure design is used for the biomimetic adhesive surface, enabling rapid, reversible, and stable attachment to and detachment from different surfaces, thereby improving the robot's surface anchoring performance. Experimental results show that the designed robot can perform peristaltic and bending motions similar to a worm. It achieves rapid bidirectional propulsion on both dry and wet surfaces, with a maximum speed of 10.36 mm/s (over 6 velocity/length ratio (min-1)).

Fast simulation of the influence of a refractive free-form microstructure on a wave field based on scalar diffraction theory

We present a novel fast simulation approach to simulate the influence of refractive freeform microstructures on a wave field. The FRISP (Finite Refractive Index Selective Propagation) method combines the Rayleigh-Sommerfeld diffraction integral with a thin element approximation and provides a comprehensive framework for understanding the optical properties of these microstructures. The main advantage of this method is its reduced complexity, which leads to a remarkable reduction in computation time by more than two orders of magnitude compared to finite-difference time-domain (FDTD) methods. This efficiency facilitates the iterative optimization of refractive microstructures and thus represents a practical tool to improve this type of microstructures. The verification of the FRISP method is realized by comparing the focal position and spot size of refractive microstructures. For this purpose, we compare FDTD, Mie theory and experimental data on microspheres with the predictions of FRISP. This comparison demonstrates the robustness and reliability of the approach, emphasizes its validity and demonstrates it as a valuable tool for the design and analysis of microstructures.

Facile Interfacial Reduction Suppresses Redox Chemical Expansion and Promotes the Polaronic to Ionic Transition in Mixed Conducting (Pr,Ce)O2-δ Nanoparticles.

Mixed ionic/electronic conductors (MIECs) are essential components of solid-state electrochemical devices, such as solid oxide fuel/electrolysis cells. For efficient performance, MIECs are typically nanostructured, to enhance the reaction kinetics. However, the effect of nanostructuring on MIEC chemo-mechanical coupling and transport properties, which also impact cell durability and efficiency, has not yet been well understood. In this work, Pr0.2Ce0.8O2-δ (PCO20) nanopowders were prepared by coprecipitation, then sintered in a modified dilatometer at three different temperatures (600, 725, and 850 °C) for microstructure evolution, resulting in three samples with different average particle sizes (23, 30, and 53 nm). The chemical strain and electronic/ionic conductivity were then measured simultaneously on stable nanostructures in four isotherms from 550 to 400 °C with steps in pO2 (1 to 10-4 atm O2). A microcrystalline bar was prepared and measured for comparison. Particle size reduction led to a monotonically decreasing isothermal redox chemical strain, confirmed by in situ high-temperature, controlled-atmosphere XRD measurements. The corresponding conductivity measurements provided defect chemical insight into the particle size-dependent chemical expansion behavior. The significant weakening of the pO2 dependence and decreased activation energy for electrical conduction with decreasing particle size indicated a decrease in the reduction enthalpy of PCO, shifting the transition from (Pr) polaronic to ionic behavior to higher pO2. STEM-EELS measurements confirmed the majority of Pr was reduced to 3+ in the nanoparticles, while Ce remained 4+. These results demonstrate suppression of deleterious chemical expansion and tailoring of the dominant charge carrier simply through controlling the particle size, providing insights for MIEC microstructural design.