Low-field giant magneto-ionic response in polymer-based nanocomposites

Piezoelectric biomaterials with embedded ionic liquids for improved orthopedic interfaces through osseointegration and antibacterial dual characteristics

Orthopedic implant failures, primarily attributed to aseptic loosening and implant site infections, pose significant challenges to patient recovery and lead to revision surgeries. Combining piezoelectric materials with ionic liquids as interfaces for orthopedic implants presents an innovative approach to addressing both issues simultaneously. In this study, films of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) incorporated with 1-ethyl-3-methylimidazolium hydrogen sulfate ([Emim][HSO4]) ionic liquid were developed. These films exhibited strong antibacterial properties, effectively reducing biofilm formation, thereby addressing implant-related infections. Furthermore, stem cell-based differentiation assays exposed the potential of the composite materials to induce osteogenesis. Interestingly, our findings also revealed the upregulation of calcium channel expression as a result of electromechanical stimulation, pointing to a mechanistic basis for the observed biological effects. This work highlights the potential of piezoelectric materials with ionic liquids to improve the longevity and biocompatibility of orthopedic implants. Offering dual-functionality for infection prevention and bone integration, these advancements hold significant potential for advancing orthopedic implant technologies and improving patient outcomes.

Multifunctional Magnetoelectric Sensing and Bending Actuator Response of Polymer-Based Hybrid Materials with Magnetic Ionic Liquids

With the evolution of the digital society, the demand for miniaturized multifunctional devices has been increasing, particularly for sensors and actuators. These technological translators allow successful interaction between the physical and digital worlds. In particular, the development of smart materials with magnetoelectric (ME) properties, capable of wirelessly generating electrical signals in response to external magnetic fields, represents a suitable approach for the development of magnetic field sensors and actuators due to their ME coupling, flexibility, robustness and easy fabrication, compatible with additive manufacturing technologies. This work demonstrates the suitability of magnetoelectric (ME) responsive materials based on the magnetic ionic liquid (MIL) 1-butyl-3-methylimidazolium tetrachloroferrate ([Bmim][FeCl4]) and the polymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE) for magnetic sensing and actuation device development. The developed sensor works in the AC magnetic field and has frequency-dependent sensitivity. The materials show voltage responses in the mV range, suitable for the development of magnetic field sensors with a highest sensitivity (s) of 76 mV·Oe-1. The high ME response (maximum ME voltage coefficient of 15 V·cm-1·Oe-1) and magnetic bending actuation (2.1 mm) capability are explained by the magnetoionic (MI) interaction and the morphology of the composites.

Electrospun Magnetic Ionic Liquid Based Electroactive Materials for Tissue Engineering Applications

Functional electrospun fibers incorporating ionic liquids (ILs) present a novel approach in the development of active microenviroments due to their ability to respond to external magnetic fields without the addition of magnetic particles. In this context, this work reports on the development of magnetically responsive magneto-ionic fibers based on the electroactive polymer poly(vinylidene fluoride) and the magnetic IL (MIL), bis(1-butyl-3-methylimidazolium) tetrathiocyanatocobaltate ([Bmim]₂[(SCN)₄Co]). The PVDF/MIL electrospun fibers were prepared incorporating 5, 10 and 15 wt.% of the MIL, showing that the inclusion of the MIL increases the polar β-phase content of the polymer from 79% to 94% and decreases the crystallinity of the fibers from 47% to 36%. Furthermore, the thermal stability of the fibers decreases with the incorporation of the MIL. The magnetization of the PVDF/MIL composite fibers is proportional to the MIL content and decreases with temperature. Finally, cytotoxicity assays show a decrease in cell viability with increasing the MIL content.

Characterization of Thermal, Ionic Conductivity and Electrochemical Properties of Some p-Tosylate Anions-Based Protic Ionic Compounds

In the present work, six protic ionic liquid (PIL) compounds based on p-toluene sulfonic acid [PTSA] anion along with different cations viz. tetraethylenepentammonium [TEPA], triethylammonium [TEA], pyridinium [Py], N-methylpiperidinium [Pip], 1-methylimidazolium [Im], and N-methylpyrrolidinium [Pyrr] were synthesized using the standard neutralization reaction method. The structural characterization of these compounds was achieved using FTIR, 1H and 13C NMR spectroscopies. Thermal behavior was studied using differential scanning calorimetry to determine the melting point (Tm) and crystallization (Tc) temperatures. Thermogravimetric analysis was carried out to determine the thermal stability and degradation temperatures (Tdec) and to ascertain the hygroscopic or hydrophobic nature of the synthesized compounds. Structural effects on the outcome of various properties were witnessed and discussed in detail. Electrochemical impedance spectroscopy was utilized to study the electrical transport properties of the PILs at different temperatures. Cyclic voltammetry was performed to analyze the electrochemical stability of these PILs. Low values of activation energy indicating easy proton transportation along with good electrochemical stability make the PILs a potential candidate for use in the preparation of polymer electrolytes membranes for fuel cell applications.

Greener Solvent-Based Processing of Magnetoelectric Nanocomposites

Polymer-based magnetoelectric (ME) nanocomposites are an enabling material technology for a wide range of applications in the area of digitalization strategies. Due to its highest piezoelectric response among polymers, poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) is the piezoelectric matrix most used in polymer-based ME materials with over 80% of the total reports, with the resulting composites typically processed from solutions with N,N-dimethylformamide (DMF), a toxic solvent. Nevertheless, environmentally friendlier approaches and sustainable technologies are increasingly being required. This work demonstrates that P(VDF-TrFE)/Co₂Fe₂O₄ nanocomposites can be successfully prepared from solution using three different environmentally friendlier solvents: dimethyl sulfoxide (DMSO), N,N'-dimethylpropyleneurea (DMPU), and triethyl phosphate (TEP) with different dipole moments. It is shown that the prepared composite films, with a maximum ME voltage coefficient of 35 mV cm^-1 Oe^-1 and a maximum sensitivity of 2.2 mV T^-1, are suitable for applications, highlighting the path for a new generation of more sustainable ME sensors.

Magnetic materials: a journey from finding north to an exciting printed future

The potential implications/applications of printing technologies are being recognized worldwide across different disciplines and industries. Printed magnetoactive smart materials, whose physical properties can be changed by the application of external magnetic fields, are an exclusive class of smart materials that are highly valuable due to their magnetically activated smart and/or multifunctional response. Such smart behavior allows, among others, high speed and low-cost wireless activation, fast response, and high controllability with no relevant limitations in design, shape, or dimensions. Nevertheless, the printing of magnetoactive materials is still in its infancy, and the design apparatus, the material set, and the fabrication procedures are far from their optimum features. Thus, this review presents the main concepts that allow interconnecting printing technologies with magnetoactive materials by discussing the advantages and disadvantages of this joint field, trying to highlight the scientific obstacles that still limit a wider application of these materials nowadays. Additionally, it discusses how these limitations could be overcome, together with an outlook of the remaining challenges in the emerging digitalization, Internet of Things, and Industry 4.0 paradigms. Finally, as magnetoactive materials will play a leading role in energy generation and management, the magnetic-based Green Deal is also addressed.

Design of Ionic-Liquid-Based Hybrid Polymer Materials with a Magnetoactive and Electroactive Multifunctional Response

Multifunctional materials with sensor and actuator capabilities play an increasing role in modern technology. In this scope, hybrid materials with magnetic sensing and an electromechanical actuator response based on magnetic ionic liquids (MILs) and the polymer poly(vinylidene fluoride) (PVDF) have been developed. MILs comprising different cation alkyl chain lengths [C_nmim]⁺ and sharing the same anion [FeCl₄]^- were incorporated at 20 wt % into the PVDF matrix and the morphological, physical, chemical, and functional properties of the materials were evaluated. An increasing IL alkyl chain length leads to the formation of a porous structure, together with an increase in the electroactive PVDF β-phase content of the polymer and a decrease in the crystallinity degree and thermal stability. The magnetic susceptibility of the [C_nmim][FeCl₄]/PVDF films reveals a paramagnetic behavior. The multifunctional response is characterized by a magnetoionic response that decreases with increasing IL alkyl chain length, the highest magnetoionic coefficient (1.06 ± 0.015 V cm^-1 Oe^-1) being observed for [C₂mim][FeCl₄]/PVDF. The electromechanical actuator response is characterized by a highest displacement of 1.1 mm for the [C₄mim][FeCl₄]/PVDF film by applying a voltage of 4 V at a frequency of 100 mHz. Further, their solution processing makes these multiresponsive materials compatible with additive manufacturing technologies.

Magnetoelectrics: Three Centuries of Research Heading towards the 4.0 Industrial Revolution

Magnetoelectric (ME) materials composed of magnetostrictive and piezoelectric phases have been the subject of decades of research due to their versatility and unique capability to couple the magnetic and electric properties of the matter. While these materials are often studied from a fundamental point of view, the 4.0 revolution (automation of traditional manufacturing and industrial practices, using modern smart technology) and the Internet of Things (IoT) context allows the perfect conditions for this type of materials being effectively/finally implemented in a variety of advanced applications. This review starts in the era of Rontgen and Curie and ends up in the present day, highlighting challenges/directions for the time to come. The main materials, configurations, ME coefficients, and processing techniques are reported.

Transparent Stretchable Dual-Network Ionogel with Temperature Tolerance for High-Performance Flexible Strain Sensors

A stretchable transparent double network ionogel composed of physically cross-linked poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)) and chemically cross-linked poly(methyl methacrylate-co-butylmethacrylate) (P(MMA-co-BMA)) elastomer networks within [EMIM][TFSI] ionic liquid was fabricated through a facile one-pot thermal polymerization. The dual-network (DN) ionogel presents good mechanical performance (failure tensile stress 2.31 MPa, strain 307%) with a high loading of ionic liquid (70 wt %) for achieving required ionic conductivity (>0.1 S/m at room temperature). The transparent chemical cross-linked P(MMA-co-BMA) elastomer network endows high transparency (>93%) and high stretchability to the DN ionogel. The DN ionogel maintains good toughness, elasticity, and transparency in a wide temperature range (-40 to 80 °C) for the application in a harsh environment. In addition, the sensitivity of the DN ionogel to the change of environment temperature and deformation was detected and described. The practical potential of the DN ionogel in flexible electronic devices is further revealed by fabricating DN ionogel strain sensors to detect the movement of different human limbs including the bending of the finger, wrist, and elbow as well as the slight throat jitter during the swallowing and vocalization, showing fast response, high sensitivity, and good repeatability.

Self-assembled full nanowire P(VDF-TrFE) films with both anisotropic and high bidirectional piezoelectricity

With the explosive growth of flexible electronics, the prototype piezoelectric polymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] has gained tremendous attention due to potential applications in flexible sensors, energy harvesters, and new smart devices. However, full realization of these applications is still challenging due to the lack of high quality films with strong piezoelectricity, which requires tailored molecular organization. Here we report unique 'full nanowire' P(VDF-TrFE) films with substantially enhanced bidirectional performance by a simple self-assembly via selective vapor annealing. Structural analysis showed that the solvent molecules significantly enhanced the copolymer chain mobility, giving highly ordered nanowires, whose quantity increased with time and finally formed a full flat-on lamellar nanowire array with backbones highly aligned along the film plane, leading to high lateral piezoelectricity as revealed by vector piezoresponse force microscopy and confirmed by electrical measurements. Surprisingly, the nanowire films also showed a much higher vertical piezoelectric coefficient (-35.2 pC N-1 directly measured by using a Berlincourt meter) than that of usually crystallized films owing to simultaneously enhanced molecular order and dipole switching ability. The scalability of the new method might boost industrial applications, and the findings may provide hints on new routes to nanostructured polymers with novel functionalities and deepen our understanding of the self-assembly of random copolymers.

Ionic-Liquid-Based Printable Materials for Thermochromic and Thermoresistive Applications

Smart materials exhibiting thermochromic and themoresistive properties based on the electroactive polymer poly(vinylidene fluoride) (PVDF) and the ionic liquid (IL) bis(1-butyl-3-methylimidazolium) tetrachloronickelate ([Bmim]₂[NiCl₄]) have been developed with different contents of [Bmim]₂[NiCl₄] (10, 20, and 40 wt %) within the polymer matrix. The morphology of the composites is studied, and the thermochromic and thermoresistive properties are evaluated. Independently of the IL content, the PVDF/[Bmim]₂[NiCl₄] composites present a porous morphology and thermochromic response, revealed by the color change of the composites from transparent to dark blue, attributed to the tetrahedral complex NiCl₄^2- formed after a dehydration process. Further, the electrical conductivity increases with increasing IL content and decreases with increasing temperature. It is also shown that the incorporation of the IL into the PVDF matrix leads to an increase in the electroactive β phase and a decrease in the degree of crystallinity and thermal stability with increasing [Bmim]₂[NiCl₄] content. The printability and applicability of the developed materials as sensors are also demonstrated.

Hydrophilic Poly(vinylidene Fluoride) Film with Enhanced Inner Channels for Both Water- and Ionic Liquid-Driven Ion-Exchange Polymer Metal Composite Actuators

This study presents a novel and facile strategy to fabricate a hydrophilic poly(vinylidene fluoride) (PVDF) electrolyte film with enhanced inner channels for a high-performance and cost-effective ion-exchange polymer metal composite (IPMC) actuator. The resultant PVDF composite film is composed of hierarchical micro/nanoscale structures: well-defined polymer grains with a diameter of ∼20 μm and much finer particles with a diameter of ∼390 nm, producing three-dimensional interconnected, hierarchical inner channels to facilitate ion migration of IPMC. Interestingly, the electrolyte matrix film has a high porosity of 15.8% and yields a high water uptake of 44.2% and an ionic liquid (IL, [EMIm]·[BF₄]) uptake of 38.1% to make both water-driven and IL-driven IPMC actuators because of the introduction of polar polyvinyl pyrrolidone. Compared to the conventional PVDF/IL-based IPMC, both water-driven and IL-driven PVDF-based IPMCs exhibit high ion migration rates, thus effectively improving the actuation frequency and producing remarkably higher levels of actuation force and displacement. Specifically, the force outputs are increased by 13.4 and 3.0 folds, and the displacement outputs are increased by 2.2 and 1.9 folds. Using an identical electrolyte matrix, water-driven IPMC exhibits stronger electromechanical performance, benefiting to make IPMC actuator with high levels of force and power outputs, whereas IL-driven IPMC exhibits a more stable electromechanical performance, benefiting to make long lifetime IPMC actuator in air. Thus, the resultant IPMCs are promising in the design of artificial muscles with tunable electromechanical performance for flexible actuators or displacement/vibration sensors at low cost.