4D Printing based piezoelectric composite for medical applications

Additive manufacturing (AM), otherwise known as three‐dimensional (3D) printing, is driving major innovations in many areas, such as engineering, manufacturing, art, education, and medicine. Although a considerable amount of progress has been made in this field, additional research work is required to overcome various remaining challenges. Recently, one of the actively researched areas lies in the AM of smart materials and structures. Electroactive materials incorporated in 3D printing have given birth to 4D printing, where 3D printed structures can perform as actuating and/or sensing systems, making it possible to deliver electrical signals under external mechanical stimuli and vice versa. In this paper, we present a lightweight, low cost piezoelectric material based on the dispersion of inorganic ferroelectric submicron particles in a polymer matrix. We report on how the proposed material is compatible with the AM process. Finally, we discuss its potential applications for healthcare, especially in smart implants prostheses. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 109–115     

Analysis of temperature effect in dielectric response of electrostrictive polymers for pseudo-pyroelectric operations

Thanks to their flexibility and easy processability, electroactive polymers have gained a lot of attention over the last decades. More specifically, dielectric electrostrictive polymers have been demonstrated to provide interesting ways for mechanical actuation and energy harvesting or for electrocaloric applications. This Letter aims at presenting an additional application potential of such materials, showing their ability in terms of converting thermal energy into electrical energy. More particularly, it is shown that such materials, once polarized through the application of a bias electric field, allow a polarization variation with the temperature, yielding the so-called pseudo-pyroelectric effect. Theoretical analysis, supported by experiments, therefore demonstrates that such a material can exhibit pseudo-pyroelectric activity that can be tuned with the applied electric field.     

Influence of Plasticizers on the Electromechanical Behavior of a P(VDF‐TrFE‐CTFE) Terpolymer: Toward a High Performance of Electrostrictive Blends

This work aims at providing a complete analysis of the effect of plasticizers on the electrostrictive terpolymer performance. To achieve this, several plasticizing agents such as 2‐ethylhexyl phtalate (DEHP), diisononyl phtalate (DINP), and palamoll 652 have been incorporated in the polymer matrix. Experimental results demonstrate that the proposed novel materials exhibited excellent electromechanical enhancement in terms of transverse strain and mechanical energy density under a moderate electric field, which is definitively critical in recent microscale actuation. Another objective of this article was to explore material characteristics as a function of the DINP content, and it was found that the plasticizer weigh fraction was the key parameter determining performance of the modified fluorinate terpolymer blends. Accordingly, it was revealed that high performance flexible actuators can be achieved merely by employing a simple and cheap plasticizer, thus making it possible to overcome the current technological barrier of conventional electroactive polymers that suffer from the high applied electric field usually required to reach sufficient strain. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 355–369     

Physical structure of P(VDF-TrFE)/barium titanate submicron composites

Dynamic Dielectric Spectroscopy and Thermo Stimulated Current were used to investigate of the dielectric relaxation of hybrid Poly(vinylidene-fluoride-trifluoroethylene)/barium titanate 700 nm composites with 0–3 connectivity. The results obtained by this method allow us to describe the physical structure of these composites in the glassy state at a nanometric scale. The decrease of the activation enthalpies and activation entropies involved in the dynamics of the α relaxation is attributed to: the decrease of Cooperative Rearranging Region sizes and an increase of intra/inter macromolecular interactions in the amorphous phase with the volume fraction.     

Molecular mobility in piezoelectric hybrid nanocomposites with 0–3 connectivity: Volume fraction influence

Thermo Stimulated Current and Dynamic Dielectric Spectroscopy studies were carried out on hybrid ferroelectric Polyamide 11/Barium Titanate to investigate dielectric relaxation modes. The correlated results obtained by both methods allow us to describe precisely the molecular mobility of this 0–3 nanocomposite; in this work we will focus on the influence of the 700 nm nanoparticles volume fraction. The dielectric spectroscopy shows that the molecular mobility associated with the liquid dynamic is not influenced by the volume fraction. The evolution of low frequency relaxation, observed by depolarization currents techniques, have been attributed to the decrease of Cooperative Rearranging Region size and the increase of intra/inter macromolecular interactions in the soft amorphous phase.     

Molecular mobility in piezoelectric hybrid nanocomposites with 0-3 connectivity: Particles size influence

Polyamide 11/barium titanate nanocomposites have been studied by a combination of dynamic dielectric spectroscopy, thermo stimulated current and differential scanning calorimetry. The correlation between results obtained by dielectric and calorimetric methods allows us to describe the evolution of the physical structure of the hybrid nanocomposites. The molecular mobility of 0-3 connectivity nanocomposites has been explored. The influence of the nanoparticles size is specifically studied. The smaller sized fillers produce a shift of the relaxation modes observed above the glass transition temperature of polyamide 11 towards lower frequency. The increase of the organic/inorganic interface induces an increase of the ratio rigid amorphous phase/soft amorphous phase. The interfaces favour local ordering stabilized by hydrogen bonds at a nanometric scale.     

Modeling of hysteretic behavior in ferroelectric polymers

Controlling the polarization state of ferroelectric materials, and more particularly piezoelectric polymers, is critical to ensure good operation of actuators or sensors using such energy conversion mechanisms. More specifically, the modeling and prediction of the hysteretic behavior of such materials is a critical aspect for the fabrication of robust and accurate devices. The purpose of this article is to present a model based on mathematical functions describing hysteretic behavior as a sum of elementary polarizations arising from combined avalanche and saturation physical effects. Predicted responses show good agreement with experimental measurements, and extension of the model for taking into account electric field‐induced crystallization during operations is presented. Finally, the proposed model is simple to implement and does no require heavy computational and memory requirements, as it relies on pure mathematical functions and only requires unidimensional distribution of elementary polarizations. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 499–508     

Enhanced electrostriction based on plasticized relaxor ferroelectric P(VDF‐TrFE‐CFE/CTFE) blends

The purpose of this work aims at enhancing the electrostrictive strain response and the mechanical energy density under moderate electric field, which is essential for actuator applications. For achieving this, plasticized effects as well as the influence of chlorofluoroethylene and chlorotrifluoroethylene defects on the electromechanical behavior of the copolymer matrix poly(vinylidene fluoride‐trifluoroethylene) (P(VDF‐TrFE)) are investigated. Experimental results showed that the plasticized terpolymer‐based CFE presented better electrical and mechanical performances than the CTFE one. Furthermore, such interesting properties exhibited superior advantages when CFE was combined with (DEHP) plasticizer, resulting in excellent electrostrictive strain response as well as mechanical energy density. Another aspect of this work reports on the influence of the composition, especially the CTFE content, on the electromechanical properties of the neat and plasticized P(VDF‐TrFE‐CTFE). This enables the determination of the desired terpolymer compositions for given applications, which are based on different criteria, such as crystallinity, elastic modulus, dielectric permittivity, and so forth. All the results demonstrated a possibility to realize high performance electroactive polymer actuators while achieving significant improved strain response and energy density under relatively low electric field. Such an investigation allows overcoming the current technological barrier of conventional electroactive polymers that suffer from the high applied electric field usually required to reach sufficient strain. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1368–1379     

Development of anisotropic ferromagnetic composites for low-frequency induction heating technology in medical applications

Modern medical applications such as varicose treatment, hyperthermia, or even endovenous thermal ablation require to bring heat flux locally through the human body. The challenge behind such techniques resides in converting electrical power into heat flux and transfer it directly to the targeted area without contaminating and damaging the surrounding tissues. Low-frequency induction heating (LFIH) of catheters made out of biocompatible magnetic composites is an elegant solution. By inserting the catheter through the varicose to be treated and by exciting it through LFIH, it seems possible to reach a temperature high enough to properly heal the damaged area while preserving the surrounding healthy ones. Although recent published results seem promising, an optimized procedure is still required to achieve further improvements. Many directions lying on the active material formulation have been largely explored in the past (variations of particle content, nature, size, and shape). In this work, we propose an alternative solution, which involves the processing of ferromagnetic composites under a constant homogeneous magnetic field, leading to the strong anisotropic behavior due to particles alignment. Remarkably, experimental results demonstrate that by exciting such anisotropic composites along the alignment direction enhances the LFIH effect by more than 30%. Moreover, improvements can also be noticed in the perpendicular direction, meaning that the structured distribution is enough to increase the ferromagnetic properties. Furthermore, the resulting composite is highly flexible, making it easier to be integrated in several medical devices (e.g. endovenous thermal catheter, electromagnetic tracking system, and so on).     

Influence of the crystallization on the molecular mobility and ionic DC conductivity behaviors of relaxor ferroelectric P(VDF‐TrFE‐CTFE) terpolymers

The dynamics of semicrystalline poly(vinylidene fluoride‐trifluoroethylene‐chlorotrifluoroethylene) (P(VDF‐TrFE‐CTFE)) terpolymers were fully investigated as a function of temperature and frequency, by means of broadband dielectric spectroscopy. Four types of relaxation regimes were observed over the full dielectric spectroscopy, namely (second) relaxation in the sub‐glass state, (segmental dynamics) in the rubbery state, the Curie transition and space charge carrier motion at high temperatures. Constrained segmental dynamics were observed in the terpolymer containing the highest crystalline fraction for which a narrow relaxation time distribution was found. These results indicate a decreasing average size of the cooperative rearranging region over the crystalline fraction. A decrease of the strength index values also implied a more fragile behavior for terpolymers with a higher degree of crystallinity. An exceptional increase in dielectric strength was found as the crystallinity increased. This behavior could be explained by an enhanced interphase (constrained amorphous phase). The Curie transition showed an accelerating relaxation rate for a more fragile terpolymer. Moreover, a motion of the space charge carrier ions was observed in the higher temperature range. Finally, there was evidence that the segmental dynamics in the amorphous phase was responsible for the motion of the space charge carrier ions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1645–1657