Piezoelectric flexible sensors are emerging as key components in medical applications, offering unique electromechanical properties for various diagnostic and therapeutic purposes. In this study, ceramic-filled silicone composites were developed as high-performance piezoelectric materials suitable for soft biomedical sensing applications. To enhance their electromechanical response, a multi-parametric design strategy was adopted, combining three approaches: the use of bimodal particle size distribution and the dielectrophoretic alignment of these particles within the matrix, supported by an optimized poling process. Results revealed that composites with an oriented particle distribution, consisting of 25 % of micro-sized particles and 75 % of nano-sized particles exhibited significant improvements in piezoelectric coefficient (d33) compared to composites with randomly distributed particles. Additionally, the piezoelectric transverse coefficient (d31) was significantly improved under in situ poling conditions, particularly in nano-rich and hybrid systems. These findings underline the potential of combining particle alignment, size hybridization, and poling optimization in enhancing the performance of piezoelectric composites for innovative medical sensor applications.

ABSTRACT This paper reports on the establishment of an effective and reliable characterization method for evaluating the electrostrictive behavior of materials subjected to high‐frequency electric fields (kilohertz range). The material studied is the relaxor ferroelectric polymer P(VDF–TrFE–CFE), which is considered a promising candidate for high‐speed actuation in adaptive optics systems. To assess the electrostrictive response of P(VDF–TrFE–CFE) under such conditions, the proposed approach relies on Maxwell's formulation of electrostrictive strain . The permittivity and mechanical modulus were first experimentally characterized in the kilohertz (kHz) range before being implemented in a numerical model developed in COMSOL based on Maxwell's equations. The comparison between experimental measurements and numerical predictions enabled the assessment of the electrostrictive behavior of P(VDF–TrFE–CFE) under high‐frequency electric excitation. The proposed methodology provides a robust framework for evaluating the stability of electromechanical properties in relaxor ferroelectric polymers operating in the kilohertz range. This foundational approach is essential for advancing the development of next‐generation actuator materials and will facilitate progress toward rapid‐response adaptive optical systems.

Understanding how polymer blending and processing routes influence the piezoelectric performance of PVDF is crucial for designing high-performance flexible sensors and energy harvesters. In this study, the effect of incorporating polylactic acid (PLA) and varying the processing method on the β-phase content, crystallinity, and piezoelectric response (d₃₃) of PVDF-based materials is investigated. Melt-processed PVDF/PLA blends (5

The use of plasticized P(VDF-TrFE-CFE), a relaxor ferroelectric polymer, has shown major improvements over the past few years. Dedicated to telescopes active optics actuators for the Live-Mirror project, the analysis of the plasticizer (here, DNOP) interaction with various polymer matrixes for high permittivity and softness is investigated here. Contrary to CTFE-based terpolymers, a large proportion of TrFE leads to plasticized films of low Young's modulus (< 50MPa). Moreover, the amount of termonomer not only leads to a low crystalline fraction but also increases the number of amorphous - crystalline interfaces where it can accumulate and get trapped. Therefore, the obtention of large S-33 of 2.5% at 30V/mu m (here 6 mu m), measured by interferometry, vows great displacements for 4D-printed multilayer actuators.

This work presents a comprehensive study on the synthesis and application of Al2O3 fibers derived from an ammonium aluminum carbonate hydroxide (AACH) precursor. Through a hydrothermal route, the influence of critical synthesis parameters, including aluminum nitrate and urea concentrations, reaction temperature and time, and stirring conditions, on fiber morphology and aspect ratio was systematically investigated. The as-synthesized AACH fibers were subsequently converted into thermodynamically stable α-alumina fibers via controlled annealing. These high-aspect ratio alumina fibers were incorporated into polydimethylsiloxane (PDMS) to produce electrically insulating, thermally conductive composites. The thermal performance of fiber-filled composites was benchmarked against that of particle-filled counterparts, with the former exhibiting significantly enhanced thermal conductivity. Furthermore, the dielectrophoretic alignment of alumina fibers led to an additional increase in thermal conductivity, underlining the importance of high-aspect ratio fillers. This study uniquely combines the controlled synthesis of alumina fibers with their incorporation and alignment in a polymer matrix, presenting a novel and effective approach for engineering anisotropic, thermally conductive, and electrically insulating composite materials. Dielectrophoretic alignment of α-Al2O3 fibers synthesized through optimized hydrothermal conditions and incorporated into PDMS composites deliver over 95 % higher thermal conductivity than spherical fillers.

This work presents a comprehensive study on the synthesis and application of Al2O3 fibers derived from an ammonium aluminum carbonate hydroxide (AACH) precursor. Through a hydrothermal route, the influence of critical synthesis parameters, including aluminum nitrate and urea concentrations, reaction temperature and time, and stirring conditions, on fiber morphology and aspect ratio was systematically investigated. The as-synthesized AACH fibers were subsequently converted into thermodynamically stable alpha-alumina fibers via controlled annealing. These high-aspect ratio alumina fibers were incorporated into polydimethylsiloxane (PDMS) to produce electrically insulating, thermally conductive composites. The thermal performance of fiber-filled composites was benchmarked against that of particle-filled counterparts, with the former exhibiting significantly enhanced thermal conductivity. Furthermore, the dielectrophoretic alignment of alumina fibers led to an additional increase in thermal conductivity, underlining the importance of high-aspect ratio fillers. This study uniquely combines the controlled synthesis of alumina fibers with their incorporation and alignment in a polymer matrix, presenting a novel and effective approach for engineering anisotropic, thermally conductive, and electrically insulating composite materials. Dielectrophoretic alignment of alpha-Al2O3 fibers synthesized through optimized hydrothermal conditions and incorporated into PDMS composites deliver over 95 % higher thermal conductivity than spherical fillers.

This study offers a detailed exploration of the dielectrophoretic structuring of filler size hybrid thermally conductive composites, emphasizing the impact of filler size hybridization on the thermal and mechanical properties of PDMS-Al2O3 composites. By comparing the performance of monodisperse and hybrid composites, we highlight the advantages of size hybridization in optimizing composite properties. The results indicate significant improvements in thermal conductivity and mechanical stiffness due to enhanced filler packing density and more efficient structuring. Our investigation into various compositions and size ratios reveals optimal thermal properties at specific hybridization levels, suggesting key parameters for superior composite performance. These results demonstrate the advantage of combining size hybridization with dielectrophoretic structuring to design advanced composites for thermal management, while emphasizing the need for future studies to tackle environmental concerns and investigate alternative polymer matrices.

The introduction of plasticizers in P(VDF-TrFE-CFE), a relaxor ferroelectric polymer, has shown major improvements over the past few years. The drastic gains in softness and dielectric permittivity at low frequency are undeniably relevant for actuation, but the interactions involved in such mechanism remain unclear. A parametric study of the terpolymer composition on its interaction with di-n-octyl phthalate (DNOP) is investigated here. In combination with a room-temperature Curie-like transition obtained for VDF/(VDF+TrFE) ratio below two-thirds, a large proportion of TrFE, contrary to CTFE-based terpolymers, leads to plasticized films of Young's moduli below 50 MPa. It was disclosed by FTIR that the amount of termonomer triggers the retention of DNOP, here theorized by electrostatic interactions, in accordance with the saturation of the mechanical properties for low-CFE content terpolymers. For the first time, this study unveils a close synergy between chemical affinity and physical properties of plasticized terpolymers. As a result, an extremely soft, crack-free terpolymer film (Y = 17.6 MPa) was successfully synthesized with 20 wt.% of DNOP. Although its electrical breakdown strength is undoubtedly affected, a combination of high molecular weight and purity unlocks great potential for substantial, low-powered displacements of 4D-printed multilayer actuators.

This research introduces a novel technology for creating lightweight, deformable optical mirrors with unique “live” capabilities. We developed dynamic hybrid electroactive polymer (EAP)‐based force actuators integrated with the optical surface through advanced additive manufacturing techniques. By refining 3D printer software and hardware controls, we achieved better accuracy and reliability in fabricating complex geometries. Additionally, doping and multilayer structuring enhanced the electromechanical performance of the material. Our study examines how the thickness of the EAP actuator and electrode size affect optical glass displacement. We found that optimal performance occurs with EAP layers thinner than 300 µm, and larger electrodes delay saturation in deformation behaviors. Improved electromechanical response was observed with the organic plasticizer diisononyl phthalate (DINP). Our model, validated by COMSOL Multiphysics simulations, aligned well with experimental data. These findings represent a significant advancement in EAP‐based actuators and their ability to correct optical surfaces precisely. They revolutionize the use of electroactive materials and open up exciting possibilities for future applications in active and adaptive optics, as well as precision control systems.

Objective: This biomechanical pre-clinical study aimed to assess the consequences on mechanical properties of long term cold storage (+2 to +8 degrees C) of arterial allografts. Methods: Femoropopliteal arterial segments were collected from multiorgan donors and stored at +2 to +8 degrees C for twelve months in saline solution with added antibiotics. Mechanical characterisation was carried out using two different tests, with the aim of defining the physiological modulus and the maximum stress and strain borne by the sample before rupture. These characterisations were carried out after zero, six, and twelve months of storage for each sample (T0, T6, and T12, respectively). For comparison, the same tests were performed on cryopreserved femoropopliteal segments after thawing. Results: Twelve refrigerated allografts (RAs), each divided into three segments, and 10 cryopreserved allografts (CAs) were characterised. The median (interquartile range [IQR]) Young's modulus was not statistically significantly different between the storage times for cold stored allografts: RAT0, 164 (150, 188) kPa; RAT6, 178 (141, 185) kPa; RAT12, 177 (149, 185) kPa. The median (IQR) Young's modulus of the CA group (153; 130, 170 kPa) showed no significant differences from the RA groups, irrespective of storage time. Furthermore, median (IQR) maximum stress and strain values were not significantly different between the different groups: for maximum stress: RAT0, 1.58 (1.08, 2.09) MPa; RAT6, 1.74 (1.55, 2.36) MPa; RAT12, 2.25 (1.87, 2.53) MPa; CA, 2.25 (1.77, 2.61) MPa; and for maximum strain: RAT0, 64% (50, 90); RAT6, 79% (63, 84); RAT12, 72% (65, Conclusion: Cold storage for up to twelve months appears to have no impact on the mechanical characteristics of human arterial allografts. Therefore, this preservation method, which would greatly simplify routine care, seems feasible. Other indicators are being studied to verify the safety of this preservation process before considering its use in vivo.

To treat cardiovascular diseases (i.e., a major cause of mortality after cancers), endovascular-technique-based guidewire has been employed for intra-arterial navigation. To date, most commercially available guidewires (e.g., Terumo, Abbott, Cordis, etc.) are non-steerable, which is poorly suited to the human arterial system with numerous bifurcations and angulations. To reach a target artery, surgeons frequently opt for several tools (guidewires with different size integrated into angulated catheters) that might provoke arterial complications such as perforation or dissection. Steerable guidewires would, therefore, be of high interest to reduce surgical morbidity and mortality for patients as well as to simplify procedure for surgeons, thereby saving time and health costs. Regarding these reasons, our research involves the development of a smart steerable guidewire using electroactive polymer (EAP) capable of bending when subjected to an input voltage. The actuation performance of the developed device is assessed through the curvature behavior (i.e., the displacement and the angle of the bending) of a cantilever beam structure, consisting of single- or multi-stack EAP printed on a substrate. Compared to the single-stack architecture, the multi-stack gives rise to a significant increase in curvature, even when subjected to a moderate control voltage. As suggested by the design framework, the intrinsic physical properties (dielectric, electrical, and mechanical) of the EAP layer, together with the nature and thickness of all materials (EAP and substrate), do have strong effect on the bending response of the device. The analyses propose a comprehensive guideline to optimize the actuator performance based on an adequate selection of the relevant materials and geometric parameters. An analytical model together with a finite element model (FEM) are investigated to validate the experimental tests. Finally, the design guideline leads to an innovative structure (composed of a 10-stack active layer screen-printed on a thin substrate) capable of generating a large range of bending angle (up to 190°) under an acceptable input level of 550 V, which perfectly matches the standard of medical tools used for cardiovascular surgery.

Natural polysaccharide crystals, such as cellulose and chitin microfibrils, are considered piezoelectric thanks to the low symmetry of their crystal structures. However, the polycrystalline nature of macroscopic samples hinders the investigation of the piezoelectric properties of these crystals. β-chitin microfibrils have a specific three-dimensional orientation in the housing tube of tubeworm Lamellibrachia satsuma where all the molecular chains possess the same chain polarity. Here, we exploited this unique tissue architecture for piezoelectric characterization at the macroscopic scale. Based on direct piezoelectric measurements with varying loading direction, amplitude, and frequency, we obtained a piezoelectric coefficient close to 1 pC/N unambiguously related to the tensile coefficient of the β-chitin crystal. This study evidences experimentally for the first time the tensile piezoelectricity of materials made of crystalline polysaccharides and ultimately contributes to the development of piezoelectric materials based on abundant polysaccharides.

Textile-based Joule heaters in combination with multifunctional materials, fabrication tactics, and optimized designs have changed the paradigm of futuristic intelligent clothing systems, particularly in the automobile field. In the design of heating systems integrated into a car seat, conductive coatings via 3D printing are expected to have further benefits over conventional rigid electrical elements such as a tailored shape and increased comfort, feasibility, stretchability, and compactness. In this regard, we report on a novel heating technique for car seat fabrics based on the use of smart conductive coatings. For easier processes and integration, an extrusion 3D printer is employed to achieve multilayered thin films coated on the surface of the fabric substrate. The developed heater device consists of two principal copper electrodes (so-called power buses) and three identical heating resistors made of carbon composites. Connections between the copper power bus and the carbon resistors are made by means of sub-divide the electrodes, which is critical for electrical–thermal coupling. Finite element models (FEM) are developed to predict the heating behavior of the tested substrates under different designs. It is pointed out that the most optimized design solves important drawbacks of the initial design in terms of temperature regularity and overheating. Full characterizations of the electrical and thermal properties, together with morphological analyses via SEM images, are conducted on different coated samples, making it possible to identify the relevant physical parameters of the materials as well as confirm the printing quality. It is discovered through a combination of FEM and experimental evaluations that the printed coating patterns have a crucial impact on the energy conversion and heating performance. Our first prototype, thanks to many design optimizations, entirely meets the specifications required by the automobile industry. Accordingly, multifunctional materials together with printing technology could offer an efficient heating method for the smart textile industry with significantly improved comfort for both the designer and user.

Despite technological advances, including heparin-coated prostheses, acute ischemia remains a serious and relatively common complication of bypass thrombosis. Piezoelectric composites are innovative materials and are used as sensors in many indications. Our objective was to develop a "smart" prosthesis that could detect a stenosis or thrombosis and alert the surgeon in real time.

This paper reports a novel monitoring technique of bearings' bidirectional load (axial and radial) based on a smart sensor coating, which is screen printed onto the surface of a cross-shaped steel substrate. To ensure the accuracy and stability of measurement as well as the durability of the printed coating, the developed prototype is built according to design rules commonly used in electronic circuits. The finite element model (FEM) is used to predict the mechanical property of the tested substrate under either unidirectional or bidirectional loads. Regarding the output voltage of the piezoelectric sensor, experimental results are revealed to be well-corelated to the numerical simulation. It is pointed out that the output signal generated from the sensor (electrode) could be particularly affected due to the capacitive parasite coming from the conductive tracks (CTs). Such a phenomenon might be reduced by printing them on the dielectric layer rather than on the piezocomposite layer. The study also investigates a highly anisotropic shape of electrodes (rectangular instead of circle), indicating that the orientation of such electrodes (axial or radial) does affect the output measurement. To sum up, the high performance of a sensor network coating depends not only on the ultimate characteristics of its own materials, but also on its structural design. Such an issue has been rarely reported on in the literature, but is nonetheless crucial to achieving reliable condition monitoring of bearings, especially for multidirectional loads-a key signature of early failure detection.

This study focuses on the development of a piezoelectric device capable of generating feedback vibrations to the user who manipulates it. The objective here is to explore the possibility of developing a haptic system that can replace physical buttons on the tactile screen of in-car systems. The interaction between the user and the developed device allows completing the feedback loop, where the user’s action generates an input signal that is translated and outputted by the device, and then detected and interpreted by the user’s haptic sensors and brain. An FEM (finite element model) via ANSYS multiphysics software was implemented to optimize the haptic performance of the wafer structure consisting of a BaTiO3 multilayered piezocomposite coated on a PET transparent flexible substrate. Several parameters relating to the geometric and mechanical properties of the wafer, together with those of the electrodes, are demonstrated to have significant impact on the actuation ability of the haptic device. To achieve the desired vibration effect on the human skin, the haptic system must be able to drive displacement beyond the detection threshold (~2 µm) at a frequency range of 100–700 Hz. The most optimized actuation ability is obtained when the ratio of the dimension (radius and thickness) between the piezoelectric coating and the substrate layer is equal to ~0.6. Regarding the simulation results, it is revealed that the presence of the conductive electrodes provokes a decrease in the displacement by approximately 25–30%, as the wafer structure becomes stiffer. To ensure the minimum displacement generated by the haptic device above 2 µm, the piezoelectric coating is screen-printed by two stacked layers, electrically connected in parallel. This architecture is expected to boost the displacement amplitude under the same electric field (denoted E) subjected to the single-layered coating. Accordingly, multilayered design seems to be a good alternative to enhance the haptic performance while keeping moderate values of E so as to prevent any undesired electrical breakdown of the coating. Practical characterizations confirmed that E=20 V/μm is sufficient to generate feedback vibrations (under a maximum input load of 5 N) perceived by the fingertip. This result confirms the reliability of the proposed haptic device, despite discrepancies between the predicted theory and the real measurements. Lastly, a demonstrator comprising piezoelectric buttons together with electronic command and conditioning circuits are successfully developed, offering an efficient way to create multiple sensations for the user. On the basis of empirical data acquired from several trials conducted on 20 subjects, statistical analyses together with relevant numerical indicators were implemented to better assess the performance of the developed haptic device.

Intelligent textiles are predicted to see a surprising development in the future. The consequence of this revived interest has been the growth of automobile industry and the improvement of innovative methods for the incorporation of electrical and thermal features into textiles materials. In the present work, the development of a smart stretchable heating device integrated into a car-seat headrest has been identified as a target application. The need for smart conductive materials is becoming increasingly apparent, but they still represent a great challenge for the heating textile area, particularly in additive manufacturing. Polymer-based composites reinforced with copper and carbon powders, attractive as advanced coatings, seems to be good solutions to this issue. Such composites are now acquainted as ideal materials for electronic device engineering and fabrication, thanks to their excellent electrical and thermal conductivities while maintaining suitable mechanical compliance. For easier process and integration, an extrusion 3D printer is employed to achieve thin films coated on the surface of the textile substrate. The developed heater device consists of two principal copper electrodes (so-called power bus), and one heating resistor made of carbon composites designed in different configurations. Finite element models (FEM) are developed to predict the heating behavior of the tested fabric substrates under different pattern suggestions. Experimental measurements via a thermal camera are in consistent with the numerical solutions. It is pointed out that the design optimization based on an adequate tuning of the pattern's parameters allows to solve inevitable matters in terms of temperature regularity and overheating effect.

This paper reports on a novel technique of a bearing load monitoring based on the use of smart sensor coating. For easier process and integration, screen printing is carried out to achieve multilayered thin film deposited on an outer bearing or a simple flat steel substrate. The formulation of piezoelectric ink is relied on the development of a UV curable barium titanate/polyurethane acrylate (BaTiO3/PUA) composite. A new design is proposed to enhance the sensitivity of the smart coating, which consists of three stacked layers: piezocomposite layer, dielectric layer (if needed), and conductive layer including electrodes and conductive tracks (CT). On one hand, the dimensions of the coating electrodes are revealed to be critical to the sensing performance. On the other hand, the CT has small impact on the piezoelectric measurement. As a result, no dielectric treatment is required between the composite and the conductive layers, leading to simplified printing process. Full characterizations of dielectric and mechanical properties, together with direct sensing measurement through electromechanical coupling are investigated on the home-made structure. Analytical and finite element models are developed to predict the mechanical properties of the tested substrate as well as the sensor sensitivity under different applied loads. Experiments are conducted on a 4-point bending (4 PB) setup, allowing to validate the analytical and numerical solutions. Good agreement between the model-predicted sensor outputs and the empirical measurements are observed, confirming high reliability of the proposed approach. It is eventually pointed out that the piezoelectric smart coating has higher sensitivity and easier integration than classical piezoresistive technology. Indeed, the printed sensor is capable to provide a direct voltage signal instead of a traditional strain gage where signal conditioning is needed. Accordingly, piezoelectric sensing together with printing technology could offer an efficient method for on-line and in situ monitoring of bearing.