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Flexoelectricity arises in materials under strain gradients, which can be particularly significant for situations in which the existence of other electromechanical properties is absent or generating large flexoelectric properties is achievable. This effect has also been observed in some biological materials, whose understanding can hugely help to further enhance our understanding of vital biological processes like mechanotransduction, as well as the development of applications in regenerative medicine and drug delivery. While the field of flexoelectricity as a relevant topic in biological materials is relatively new and still developing, the current study aims to review available results on flexoelectric effects in biological materials such as cells and cell membranes, hearing mechanisms, and bone, and their potential applications in biomedical research. Therefore, we first provide a brief background on two main electromechanical couplings (piezoelectricity and flexoelectricity) and further, how flexoelectricity has been experimentally and theoretically identified. We then review flexoelectricity in different biological materials as the main aim of the current study. Within that, we provide additional emphasis on the influence of this effect on bone and bone remodeling. In particular, the study outlines current limitations and provides potential directions for future work, emphasizing the crucial role in the development of next-generation electromechanical devices and optimizing their function in the area of biomedical research.

Electrospun nanofibers exhibiting piezoelectricity are a specific class of smart materials which could provide electric stimulation to cells in a noninvasive way and contribute to tissue regeneration. During cell-material interaction, the materials display electromechanical behavior by transforming cell adhesion force into surface charge. In the process, how the cell adhesion states and the electromechanical properties of scaffolds determine the actual piezoelectric potential implemented on a cell is still unclear. Herein, we fabricated piezoelectric poly(vinylidene fluoride) (PVDF) nanofiber scaffolds with different topographies, and investigated their influences on cell morphology and cell adhesion-mediated electromechanical stimulation of mesenchymal stem cell (MSC). Our results demonstrated that MSC seeded on aligned piezoelectric nanofibers exhibited elongated morphology combined with higher intracellular calcium activity than those adhered on random nanofibers with rounded shape. The underlying mechanism was further quantitatively analyzed using a three-dimensional (3D) finite element method with respect to cell adhesion states and architecture parameters of nanofiber scaffolds. The results suggested that cell morphology and cell adhesion force influenced the piezoelectric output through modulating the location and magnification of force implemented on the scaffolds. In addition, the change of alignment, pore size and diameter of the nanofiber network could alter the mechanical property of the scaffolds, and then bias the actual piezoelectric output experienced by a cell. These findings provide new insights for probing the mechanism of cell self-stimulation on piezoelectric scaffolds, and pave the way for rational design of piezoelectric scaffolds for cell regulation and tissue regeneration.

Graphene (including its derivatives)-reinforced polymer composites (GRPCs) have been drawing tremendous attention from academic and industrial communities for developing smart materials and structures. Such interest stems from the excellent combination of the mechanical and electrical properties of these composites while keeping the beneficial intrinsic attributes of the polymers, including flexibility, easy processability, low cost and good biological and chemical compatibility. The electromechanical performances of these GRPCs are of great importance for the design and optimization of engineering structures and components. Extensive work has been devoted to this topic. This paper reviews the recent studies on the electromechanical behaviors of GRPCs. First the methods and techniques to manufacture graphene and GRPCs are introduced, in which the pros and cons of each method are discussed. Then the experimental examination and theoretical modeling on the electromechanical behaviors of the nanocomposites are presented and discussed.

Clay is a widely used material with unique properties that vary depending on water content and applied pressure. In this study, the electromechanical behavior of clay samples from Afyonkarahisar, Turkey, is investigated by examining the relationship between electrical resistivity, water content, and mechanical loading under uniaxial pressure. The samples with a water content of 10%, 20%, and 30% were tested using a uniaxial loading machine in accordance with ASTM D 2216 and the Turkish standard TS 1900-1. The analysis included measurements of stress, deformation, and electrical conductivity of the soil. A comparative assessment of samples with varying water content revealed that at low moisture levels (10%), the specific electrical resistivity initially decreases due to soil compaction and reduced porosity. However, as stress increases further, resistivity rises significantly as microcracks begin to develop, disrupting conductive pathways. In contrast, at higher water contents (20% and 30%), resistivity consistently decreases with increasing stress, while conductivity increases markedly. This indicates that at elevated saturation levels, the presence of water facilitates charge carrier mobility through ionic conduction, resulting in lower resistivity and higher conductivity. Comparisons with previous studies on clays such as bentonite and kaolinite reveal similar qualitative trends, although differences in the rate of resistivity change suggest a distinct mineralogical influence in Afyonkarahisar clay. This study contributes to a deeper understanding of the geotechnical behavior of this regional clay and supports more accurate performance predictions in engineering and construction applications.

Graphene–copper (Gr–Cu) composite conductors have demonstrated Gr‐enhanced electrical and thermal properties. However, the conductors’ coupled mechanical and electrical responses remain unexplored despite the importance of their mechanical flexibility and robustness. Here, the electromechanical behavior of a recently developed microscale Gr‐Cu composite, called axially continuous graphene–copper (ACGC) wire, has been investigated by developing and utilizing a customized tensile testing method. Experimental studies have shown that 80 μm‐diameter ACGC (hereafter ACGC80) wires exhibit 3.681% and 3.173% higher compared to as‐received and annealed Cu wires, respectively. More importantly, the Gr‐enhanced electrical performance of the ACGC80 has been observed even after significant plastic deformation under uniaxial tension. To be specific, the conductivity of ACGC80 is 3.139%, 3.144%, and 3.088% higher than that of annealed copper wire at 3, 6, and 9% strain, respectively. Analysis indicates that ACGC80 deforms by forming highly localized plastic deformation zones along its length. This result suggests that graphene in ACGC80 serves as an effective electron pathway even after applying a large strain because the pronounced damage to graphene is limited to only a small fraction of ACGC80. The ACGC80 conductor has great potential to advance emerging applications in flexible interconnects, wearable electronics, and high‐power transmission for microchips. This study investigates the electromechanical behavior of 80 μm‐diameter axially continuous graphene–copper (ACGC80) wires by developing a customized tensile testing method. Experimental studies have shown that ACGC80 wires exhibit higher electrical conductivity compared to as‐received and annealed Cu wires, and more importantly, the Gr‐enhanced electrical performance of the ACGC80 has been observed even after significant plastic deformation under uniaxial tension.

This paper investigates the electromechanical behavior of functionally graded piezoelectric composite beams containing axially functionally graded (AFG) beam and piezoelectric actuators subjected to electrical load. The mechanical properties of the AFG beam are assumed to be graded along the axial direction. Employing the electromechanical coupling theory and load simulation method, the expression for the simulation load of the piezoelectric actuators is obtained. Based on Euler-Bernoulli beam theory and the obtained simulation load, the differential governing equation of the piezoelectric composite beams subjected to electrical load is derived. The integration-by-parts approach is utilized to solve the differential governing equation, and the expression for the deflection of the piezoelectric composite beams is obtained. The accuracy of the proposed method is validated by the finite element method. The bending response of the functionally graded piezoelectric composite beams is investigated through the proposed method. In the numerical examples, the effects of electrical load, actuator thickness, AFG beam thickness and AFG beam length on the electromechanical behavior of the functionally graded piezoelectric composite beams are studied.

Analysis of the electromechanical-size-dependent bending of piezoelectric composite structural components with flexoelectricity has been considered by many researchers because of the developments of nanotechnology and the applicability of piezoelectric composite nanobeam structures in Micro/Nano-Electro-Mechanical Systems (MEMS/NEMS). Therefore, the work investigates the size-dependent electromechanical bending of piezoelectrically layered perforated nanobeams resting on elastic foundations including the flexoelectric effect. Within the framework of the modified nonlocal strain gradient elasticity theory, both the microstructure and nonlocality effects are captured. The governing equilibrium equations including piezoelectric and flexoelectric effects are derived using Hamilton’s principle. Closed forms for the non-classical electromechanical bending profiles are derived. The accuracy of the proposed methodology is verified by comparing the obtained results with the available corresponding results in the literature within a 0.3% maximum deviation. Parametric studies are conducted to explore effects of perforation parameters, elastic foundation parameters, geometric dimensions, nonclassical parameters, flexoelectric parameters, as well as the piezoelectric parameters on the bending behavior of piezoelectrically layered perforated nanobeams. The obtained results demonstrate that incorporation of the nondimensional elastic foundation parameters, Kp = 2 and Kw = 20, results in a reduction in the relative percentage reduction in the maximum nondimensional mechanical transverse deflection due to increasing the perforation filling ratio from 0.2 to 1 from 199.86% to 91.83% for a point load and 89.39% for a uniformly distributed load. On the other hand, with Kp = 5 and Kw = 50, the relative percentage difference of the electromechanical bending deflection due to increasing the piezoelectric coefficient, e311, reaches about 8.7% for a point load and 8.5% for a uniformly distributed load at a beam aspect ratio of 50. Thus, the electromechanical as well as mechanical behaviors could be improved by controlling these parameters. The proposed methodology and the obtained results are supportive in many industrial and engineering applications, i.e., MEMS/NEMS.

During a manufacturing process, when a straight carbon nanotube is placed on a substrate, e.g., production of transistors, its two ends are often misaligned. In this study, we investigate the effects of multiwall carbon nanotubes’ (MWCNTs) outer diameter and chirality on the change in conductance due to misalignment of the two ends. The length of the studied MWCNTs was 120 nm, while the diameters ranged between 4 and 7 nm. A mixed finite element-tight-binding approach was carefully designed to realize reduction in computational time by orders of magnitude in calculating the deformation-induced changes in the electrical transport properties of the nanotubes. Numerical results suggest that armchair MWCNTs of small diameter should work better if used as conductors, while zigzag MWCNTs of large diameter are more suitable for building sensors. Graphical Abstract

With increasing wind power penetrations, WTGs shoulder a higher responsibility. Traditional WTG control and modelling is generally designed assuming that the external grid is strong enough. However, in the case of weak grid in which power variations between synchronous generators (SG) and DFIG are more intense, more appropriate DFIG model needs to be built for electromechanical transient stability analysis of power system. Phase-locked loop (PLL) is typically employed in modern megawatt WTGs and tracks the WT's terminal voltage phase change, so as to provide reference frame for active/reactive power control. Thus power output of DFIG as well as other power source in the system subjects to PLL's dynamic responses. This work establishes a DFIG-based WT's electromechanical transient model considering the dynamic influence of PLL, and analyses its dynamic response which influences WTG electromechanical transient behaviour and system stability.

Stress and damage estimation is essential to ensure the safety and performance of concrete structures. The capsule-like smart aggregate (CSA) technique has demonstrated its potential for detecting early-stage internal damage. In this study, a 2 dimensional convolutional neural network (2D CNN) model that learned the EMI responses of a CSA sensor to integrally estimate stress and damage in concrete structures is proposed. Firstly, the overall scheme of this study is described. The CSA-based EMI damage technique method is theoretically presented by describing the behaviors of a CSA sensor embedded in a concrete structure under compressive loadings. The 2D CNN model is designed to learn and extract damage-sensitive features from a CSA’s EMI responses to estimate stress and identify damage levels in a concrete structure. Secondly, a compression experiment on a CSA-embedded concrete cylinder is carried out, and the stress–damage EMI responses of a cylinder are recorded under different applied stress levels. Finally, the feasibility of the developed model is further investigated under the effect of noises and untrained data cases. The obtained results indicate that the developed 2D CNN model can simultaneously estimate stress and damage status in the concrete structure.