Correlation between Crystallization Kinetics and Electroactive Polymer Phase Nucleation in Ferrite/Poly(vinylidene fluoride) Magnetoelectric Nanocomposites

Piezoelectric Stimulation Induces Osteogenesis in Mesenchymal Stem Cells Cultured on Electroactive Two-Dimensional Substrates

Physical cues have been shown to be effective in inducing osteogenic differentiation of mesenchymal stem cells (MSCs). Here, we propose piezoelectric stimulation as a potential osteogenic cue mimicking the electroactive properties of bone's extracellular matrix. When combined with a magnetostrictive component, piezoelectric polymers can be used for MSC stimulation by applying an external magnetic field. The deformation of the magnetostrictive component produces a deformation in the polymer matrix, generating a change in the surface charge that induces an electric field that can be transmitted to the cells. Cell adhesion, cytoskeleton changes, and metabolomics are the first evidence of MSC osteoblastogenesis and can be used to study initial MSC response to this kind of stimulation. In the current study, poly(vinylidene) fluoride (PVDF) piezoelectric films with and without cobalt ferrite oxide (CFO) crystallized from the melt in the presence of the ionic liquid 1-butyl-3-methyl-imidazolium chloride ([Bmim][Cl]) were produced. [Bmim][Cl] allowed the production of the β-phase, the most electroactive phase, even without CFO. After ionic liquid removal, PVDF and PVDF-CFO films presented high percentages of the β-phase and similar crystalline content. Incorporating CFO nanoparticles was effective, allowing the electromechanical stimulation of MSCs by applying a magnetic field with a bioreactor. Before stimulation, the initial response of MSCs was characterized in static conditions, showing that the produced films were biocompatible and noncytotoxic, allowing MSC adhesion and proliferation in the short term. Stimulation experiments revealed that MSCs electromechanically stimulated for 3 days in PVDF-CFO supports showed longer focal adhesions and decreased vimentin cytoskeletal density, both signals of early osteogenic differentiation. Furthermore, they rearranged their energy metabolism toward an osteogenic phenotype after 7 days of culture under the same stimulation. The results prove that MSCs respond to electromechanical stimulation by osteogenic differentiation.

High-performance piezoelectric composites via β phase programming

Polymer-ceramic piezoelectric composites, combining high piezoelectricity and mechanical flexibility, have attracted increasing interest in both academia and industry. However, their piezoelectric activity is largely limited by intrinsically low crystallinity and weak spontaneous polarization. Here, we propose a Ti₃C₂T_x MXene anchoring method to manipulate the intermolecular interactions within the all-trans conformation of a polymer matrix. Employing phase-field simulation and molecular dynamics calculations, we show that OH surface terminations on the Ti₃C₂T_x nanosheets offer hydrogen bonding with the fluoropolymer matrix, leading to dipole alignment and enhanced net spontaneous polarization of the polymer-ceramic composites. We then translated this interfacial bonding strategy into electrospinning to boost the piezoelectric response of samarium doped Pb (Mg_1/3Nb_2/3)O₃-PbTiO₃/polyvinylidene fluoride composite nanofibers by 160% via Ti₃C₂T_x nanosheets inclusion. With excellent piezoelectric and mechanical attributes, the as-electrospun piezoelectric nanofibers can be easily integrated into the conventional shoe insoles to form a foot sensor network for all-around gait patterns monitoring, walking habits identification and Metatarsalgi prognosis. This work utilizes the interfacial coupling mechanism of intermolecular anchoring as a strategy to develop high-performance piezoelectric composites for wearable electronics.

Enhanced voltage response in TiO2nanoparticle-embedded piezoelectric nanogenerator

Poly (vinylidene fluoride) (PVDF) and its copolymers have piqued a substantial amount of research interest for its use in modern flexible electronics. The piezoelectricβ-phase of the polymers can be augmented with the addition of suitable fillers that promoteβ-phase nucleation. In this work, we report an improved output voltage response of poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) with the incorporation of 10 wt.% Titanium (IV) oxide nanoparticles into the polymer matrix. The nano-filler was dispersed in the polymer matrix to form nanocomposite films via the solution casting technique. X-ray Diffraction and Scanning Electron Microscopy measurements were performed to verify the structure and morphology of the films. Fourier Transform Infrared Spectroscopy revealed enhancement in theβ-phase nucleation from ∼15% to ∼36% with the addition of 10 wt.% titania nanoparticles. Thermogravimetric analysis and Differential Scanning Calorimetry results show improved thermal stability of the nanocomposite film, up to 345 °C, as compared to pristine PVDF-HFP. We also demonstrate a facile method for the fabrication of a piezoelectric nanogenerator withβ-PVDF-HFP/TiO₂nanocomposite as an active layer. The outputs from the fabricated nanogenerator reached up to 8.89 V through human finger tapping motions, paving way for its potential use in the field of sensors, actuators, and self-sustaining flexible devices.

Enhanced cellular osteogenic differentiation on CoFe2O4/P(VDF-TrFE) nanocomposite coatings under static magnetic field

Cellular responses can be regulated and manipulated through combining stimuli-responsive biomaterial with external stimulus. In this present, the magneto-responsive CoFe₂O₄/P(VDF-TrFE) nanocomposite coatings were designed to understand cell behaviors of preosteoblasts, as well as get insight into the underlying mechanism of osteogenic differentiation under static magnetic field (SMF). CoFe₂O₄/P(VDF-TrFE) nanocomposite coatings with differential magnetic property (low, medium and high magnetization) were prepared by incorporation of different mass fraction of CoFe₂O₄ nanoparticles (6%, 13 %, 20 %) into P(VDF-TrFE) matrix. Cell experiments indicated that all nanocomposite coatings with the assistance of SMF could promote the cell attachment, proliferation and osteogenic differentiation of MC3T3-E1 cells. Among different nanocomposite coatings, low magnetization coating (6%) showed a higher ALP activity and gene expression of Runx2, Col-I, OCN. Molecular biology assays demonstrated that the combination of nanocomposite coatings and SMF could significantly up-regulate the expression level of α2β1 integrin and p-ERK. Whereas, the addition of inhibitor U0126 down-regulated sharply the expression level of p-ERK, which indicated that cellular osteogenic differentiation of MC3T3-E1 cells was governed through α2β1 integrin-mediated MEK/ERK signaling pathways during CoFe₂O₄/P(VDF-TrFE) nanocomposite coatings were combined with SMF. This work provided a promising strategy to enhance cellular osteogenic differentiation through a remote-control manner, which exhibited great potential in the application of bone tissue repair and regeneration.

Bioinspired Three-Dimensional Magnetoactive Scaffolds for Bone Tissue Engineering

Bone tissue repair strategies are gaining increasing relevance due to the growing incidence of bone disorders worldwide. Biochemical stimulation is the most commonly used strategy for cell regeneration, while the application of physical cues, including magnetic, mechanical, or electrical fields, is a promising, however, scarcely investigated field. This work reports on novel magnetoactive three-dimensional (3D) porous scaffolds suitable for effective proliferation of osteoblasts in a biomimetic microenvironment. This physically active microenvironment is developed through the bone-mimicking structure of the scaffold combined with the physical stimuli provided by a magnetic custom-made bioreactor on a magnetoresponsive scaffold. Scaffolds are obtained through the development of nanocomposites comprised of a piezoelectric polymer, poly(vinylidene fluoride) (PVDF), and magnetostrictive particles of CoFe₂O₄, using a solvent casting method guided by the overlapping of nylon template structures with three different fiber diameter sizes (60, 80, and 120 μm), thus generating 3D scaffolds with different pore sizes. The magnetoactive composites show a structure very similar to trabecular bone with pore sizes that range from 5 to 20 μm, owing to the inherent process of crystallization of PVDF with the nanoparticles (NPs), interconnected with bigger pores, formed after removing the nylon templates. It is found that the materials crystallize in the electroactive β-phase of PVDF and promote the proliferation of preosteoblasts through the application of magnetic stimuli. This phenomenon is attributed to both local magnetomechanical and magnetoelectric response of the scaffolds, which induce a proper cellular mechano- and electro-transduction process.

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.

Modulating Surface Potential by Controlling the β Phase Content in Poly(vinylidene fluoridetrifluoroethylene) Membranes Enhances Bone Regeneration

Bioelectricity plays a vital role in living organisms. Although electrical stimulation is introduced in the field of bone regeneration, the concept of a dose-response relationship between surface potential and osteogenesis is not thoroughly studied. To optimize the osteogenic properties of different surface potentials, a flexible piezoelectric membrane, poly(vinylidene fluoridetrifluoroethylene) [P(VDF-TrFE)], is fabricated by annealing treatment to control its β phases. The surface potential and piezoelectric coefficients (d₃₃ ) of the membranes can be regulated by increasing β phase contents. Compared with d₃₃  = 20 pC N^-1 (surface potential = -78 mV) and unpolarized membranes, bone marrow mesenchymal stem cells (BM-MSCs) cultured on the d₃₃  = 10 pC N^-1 (surface potential = -53 mV) membranes have better osteogenic properties. In vivo, d₃₃  = 10 pC N^-1 membranes result in rapid bone regeneration and complete mature bone-structure formation. BM-MSCs on d₃₃  = 10 pC N^-1 membranes have the lowest reactive oxygen species level and the highest mitochondrial membrane electric potential, implying that these membranes provide the best electrical qunantity for BM-MSCs' proliferation and energy metabolism. This study establishes an effective method to control the surface potential of P(VDF-Trfe) membranes and highlights the importance of optimized electrical stimulation in bone regeneration.

Harnessing Cell Dynamic Responses on Magnetoelectric Nanocomposite Films to Promote Osteogenic Differentiation

The binding of cell integrins to proteins adsorbed on the material surface is a highly dynamic process critical for guiding cellular responses. However, temporal dynamic regulation of adsorbed proteins to meet the spatial conformation requirement of integrins for a certain cellular response remains a great challenge. Here, an active CoFe₂O₄/poly(vinylidene fluoride-trifluoroethylene) nanocomposite film, which was demonstrated to be an obvious surface potential variation (Δ V ≈ 93 mV) in response to the applied magnetic field intensity (0-3000 Oe), was designed to harness the dynamic binding of integrin-adsorbed proteins by in situ controlling of the conformation of adsorbed proteins. Experimental investigation and molecular dynamics simulation confirmed the surface potential-induced conformational change in the adsorbed proteins. Cells cultured on nanocomposite films indicated that cellular responses in different time periods (adhesion, proliferation, and differentiation) required distinct magnetic field intensity, and synthetically programming the preferred magnetic field intensity of each time period could further enhance the osteogenic differentiation through the FAK/ERK signaling pathway. This work therefore provides a distinct concept that dynamically controllable modulation of the material surface property fitting the binding requirement of different cell time periods would be more conducive to achieving the desired osteogenic differentiation.

Local probing of magnetoelectric properties of PVDF/Fe3O4 electrospun nanofibers by piezoresponse force microscopy

The coupling of magnetic and electric properties in polymer-based magnetoelectric composites offers new opportunities to develop contactless electrodes, effectively without electrical connections, for less-invasive integration into devices such as energy harvesters, sensors, wearable and implantable electrodes. Understanding the macroscale-to-nanoscale conversion of the properties is important, as nanostructured and nanoscale magnetoelectric structures are increasingly fabricated. However, whilst the magnetoelectric effect at the macroscale is well established both theoretically and experimentally, it remains unclear how this effect translates to the nanoscale, or vice versa. Here, PVDF/Fe₃O₄ polymer-based composite nanofibers are fabricated using electrospinning to investigate their piezoelectric and magnetoelectric properties at the single nanofiber level.

In situ synthesis of Ni(OH)2 nanobelt modified electroactive poly(vinylidene fluoride) thin films: remarkable improvement in dielectric properties

A facile and low cost synthesis of Ni(OH)2 nanobelt (NB) modified electroactive poly(vinylidene fluoride) (PVDF) thin films with excellent dielectric properties has been reported via in situ formation of Ni(OH)2 NBs in the PVDF matrix. The formation and morphology of the NBs are confirmed by UV-visible spectroscopy and field emission scanning electron microscopy respectively. A remarkable improvement in electroactive β phase nucleation (∼82%) and the dielectric constant (ε ∼ 3.1 × 10(6) at 20 Hz) has been observed in the nanocomposites (NCs). The interface between the NBs and the polymer matrix plays a crucial role in the enhancement of the electroactive β phase and the dielectric properties of thin films. Strong interaction via hydrogen bonds between Ni(OH)2 NBs and the PVDF matrix is the main reason for enhancement in β phase crystallization and improved dielectric properties. The NC thin films can be utilized for potential applications as high energy storage devices like supercapacitors, solid electrolyte batteries, self-charging power cells, piezoelectric nanogenerators, and thin film transistors and sensors.

Improving the thermal stability, electroactive β phase crystallization and dielectric constant of NiO nanoparticle/C–NiO nanocomposite embedded flexible poly(vinylidene fluoride) thin films

Increasing β phase nucleation and formation of microcapacitors in flexible high dielectric NiO NPs/C–NiO NCs modified PVDF films.

Enhanced electroactive and mechanical properties of poly(vinylidene fluoride) by controlling crystallization and interfacial interactions with low loading polydopamine coated BaTiO₃

Poly(vinylidene fluoride) (PVDF) is a semi-crystalline polymer and the polar β-phase of PVDF shows superb electroactive properties. In order to enhance the β-phase of PVDF, extreme low content of BaTiO3 nanoparticles (BT-NPs) coated with polydopamine (Pdop) were incorporated into PVDF matrix by solution casting. The β-phase of the resulting PVDF nanocomposites film was dramatically increased and the d33 value reached 34.3±0.4 pCN(-1). It is found that the Pdop layer could improve the dispersibility and stability of the BT NPs in solution and endow the BT NPs good dispersity in the PVDF matrix. Moreover, the interfacial interaction between PVDF chains and the surface of BT-Pdop nanoparticles (BT-Pdop NPs) were revealed, in which the CF2 groups on PVDF could interact with the electron-rich plane of aromatic ring of Pdop moiety. This interaction, led to the increase of the crystallization activation energy as derived from the DSC nonisothermal crystallization measurement. The α-β crystal transformation, organization of interfacial interactions as well as the prevention of agglomeration of BT-NPs confer the improvement of mechanical and thermal properties of PVDF, such as toughness, tensile strength, elongation at break, and thermal conductivity.

Development of magnetoelectric CoFe2O4 /poly(vinylidene fluoride) microspheres

Magnetoelectric microspheres based on piezoelectric poly(vinylidene fluoride) (PVDF) and magnetostrictive CoFe₂O₄ (CFO), a novel morphology for polymer-based ME materials, have been developed by an electrospray process.

Effects of dynamic vulcanization on the kinetics of isothermal crystallization in a miscible polymeric blend

Is it possible to determine the state of phase separation using the free energy of folding parameter?

Enhancement of dielectric permittivity and ferroelectricity of a modified cobalt nanoparticle and polyvinylidene fluoride based composite

A remarkable increase in the amount of polar β phase has been observed upon dispersion of cobalt nanoparticles in the PVDF matrix. A significant improvement in the dielectric constant of PVDF has been achieved.

Effect of in situ synthesized Fe2O3 and Co3O4 nanoparticles on electroactive β phase crystallization and dielectric properties of poly(vinylidene fluoride) thin films

A simple and low cost in situ process has been developed to synthesize Fe2O3-Co3O4 nanoparticles (NPs) loaded poly(vinylidene fluoride) (PVDF) thin films. The electroactive β phase nucleation mechanism and the dielectric properties of the films have been investigated by X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry and using an LCR meter. Results confirmed that the electroactive β phase crystallization in the PVDF matrix is due to the fast nucleating or catalytic effect of the in situ NPs. Homogenous dispersion of in situ Fe2O3-Co3O4 NPs in the polymer matrix leads to strong interfacial interaction between the NPs and the polymer resulting in enhanced β phase nucleation in PVDF and a large dielectric constant of the thin films. The observed variation in the electroactive β phase nucleation by NPs (Fe2O3-Co3O4) and the dielectric properties of the thin films have been explained on the basis of surface charge, size, geometrical shape and extent of agglomeration of the NPs in the polymer matrix.