Novel hybrid magnetoactive composite scaffolds based on poly(3-hydroxybutyrate) (PHB), gelatin, and magnetite (Fe
O
) were fabricated by electrospinning. The morphology, structure, phase composition, ...and magnetic properties of composite scaffolds were studied. Fabrication procedures of PHB/gelatin and PHB/gelatin/Fe
O
scaffolds resulted in the formation of both core-shell and ribbon-shaped structure of the fibers. In case of hybrid PHB/gelatin/Fe
O
scaffolds submicron-sized Fe
O
particles were observed in the surface layers of the fibers. The X-ray photoelectron spectroscopy results allowed the presence of gelatin on the fiber surface (N/C ratio-0.11) to be revealed. Incubation of the composite scaffolds in saline for 3 h decreased the amount of gelatin on the surface by more than ~75%. The differential scanning calorimetry results obtained for pure PHB scaffolds revealed a characteristic melting peak at 177.5 °C. The presence of gelatin in PHB/gelatin and PHB/gelatin/Fe
O
scaffolds resulted in the decrease in melting temperature to 168-169 °C in comparison with pure PHB scaffolds due to the core-shell structure of the fibers. Hybrid scaffolds also demonstrated a decrease in crystallinity from 52.3% (PHB) to 16.9% (PHB/gelatin) and 9.2% (PHB/gelatin/Fe
O
). All the prepared scaffolds were non-toxic and saturation magnetization of the composite scaffolds with magnetite was 3.27 ± 0.22 emu/g, which makes them prospective candidates for usage in biomedical applications.
Pure BiFeO3 (BFO) and doped Bi0.9La0.1FeO3 (BLFO) thin films were prepared on Pt/TiO2/SiO2/Si substrates by a modified sol–gel technique using a separate hydrolysis procedure. The effects of final ...crystallization temperature and La doping on the phase structure, film morphology, and nanoscale piezoelectric properties were investigated. La doping and higher crystallization temperature lead to an increase in the grain size and preferred (102) texture of the films. Simultaneously, a decrease in the average effective piezoelectric coefficient (about 2 times in La-doped films) and an increase in the area of surface non-polar phase (up to 60%) are observed. Phase separation on the films’ surface is attributed to either a second phase or to a non-polar perovskite phase at the surface. As compared with undoped BFO, La-doping leads to an increase in the average grain size and self-polarization that is important for future piezoelectric applications. It is shown that piezoelectric activity is directly related to the films’ microstructructure, thus emphasizing the role of annealing conditions and La-doping that is frequently used to decrease the leakage current in BFO-based materials.
With the recent thriving of low-power electronic microdevices and sensors, the development of components capable of scavenging environmental energy has become imperative. In this article, we studied ...bidomain congruent LiNbO 3 (LN) single crystals combined with magnetic materials for dual, mechanical, and magnetic energy harvesting applications. A simple magneto-mechano-electric composite cantilever, with a trilayered long-bar bidomain LN/spring-steel/metglas structure and a large tip proof permanent magnet, was fabricated. Its vibration and magnetic energy harvesting capabilities were tested while trying to optimize its resonant characteristics, load impedance, and tip proof mass. The vibration measurements yielded a peak open-circuit voltage of 2.42 kV/g, a short-circuit current of <inline-formula> <tex-math notation="LaTeX">60.1~\mu \text{A} </tex-math></inline-formula>/g, and an average power of up to 35.6 mW/g 2 , corresponding to a power density of 6.9 mW/(cm<inline-formula> <tex-math notation="LaTeX">^{{3}}\cdot \text {g}^{{2}} </tex-math></inline-formula>), at a low resonance frequency of 29.22 Hz and with an optimal load of 40 <inline-formula> <tex-math notation="LaTeX">\text{M}\Omega </tex-math></inline-formula>. The magnetic response revealed a resonant peak open-circuit voltage of 90.9 V/Oe and an average power of up to <inline-formula> <tex-math notation="LaTeX">49.9~\mu \text{W} </tex-math></inline-formula>/Oe 2 , corresponding to a relatively large magnetoelectric coefficient of 1.82 kV/(cm<inline-formula> <tex-math notation="LaTeX">\cdot </tex-math></inline-formula>Oe) and a power density of <inline-formula> <tex-math notation="LaTeX">9.7~\mu \text{W} </tex-math></inline-formula>/(cm<inline-formula> <tex-math notation="LaTeX">^{{3}}\cdot \text {Oe}^{{2}} </tex-math></inline-formula>). We thus developed a system that is, in principle, able to scavenge electrical power simultaneously from low-level ambient mechanical and magnetic sources to feed low-power electronic devices.
Zirconia- and hafnia-based thin films have attracted tremendous attention in the past decade because of their unexpected ferroelectric behavior at the nanoscale, which enables the downscaling of ...ferroelectric devices. The present work reports an unprecedented ferroelectric rhombohedral phase of ZrO2 that can be achieved in thin films grown directly on (111)-Nb:SrTiO3 substrates by ion-beam sputtering. Structural and ferroelectric characterizations reveal (111)-oriented ZrO2 films under epitaxial compressive strain exhibiting switchable ferroelectric polarization of about 20.2 μC/cm2 with a coercive field of 1.5 MV/cm. Moreover, the time-dependent polarization reversal characteristics of Nb:SrTiO3/ZrO2/Au film capacitors exhibit typical bell-shaped curve features associated with the ferroelectric domain reversal and agree well with the nucleation limited switching (NLS) model. The polarization-electric field hysteresis loops point to an activation field comparable to the coercive field. Interestingly, the studied films show ferroelectric behavior per se, without the need to apply the wake-up cycle found in the orthorhombic phase of ZrO2. Overall, the rhombohedral ferroelectric ZrO2 films present technological advantages over the previously studied zirconia- and hafnia-based thin films and may be attractive for nanoscale ferroelectric devices.
The results of comprehensive research on the thermal behavior and molecular and crystalline structures of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV) films ...of different thicknesses, their molecular weights (Mw) and 3-hydroxyvalerate (3-HV) contents are reported. Increasing film thickness from 30 to 100 µm resulted in an isotropic crystal orientation, reducing the crystallite size of the orthorhombic α-phase in the b direction from 22 to 17 nm and increasing the degree of crystallinity of the PHB films without affecting their thermal behavior. Furthermore, despite resulting in the same degree of crystallinity and roughness, an ~8-fold decrease in PHB Mw from 803 kDa to 102 kDa resulted in a decreased number of piezoactive domains. The addition of 5.9% 3-HV resulted in anisotropy in the PHB crystalline structure and increased D(020) from 19 nm to 24 nm. Additionally, a further increase in the 3-HV content to 17.5% in the PHB-HV films led to a decrease in the melting temperature and a decrease in the degree of crystallinity from 57% to 23%, which resulted in the absence of local piezoresponse. Notably, the decrease in the Mw of PHB-HV (~17%) from 1177 kDa to 756 kDa resulted in an increase in the degree of crystallinity from 23% to 32%. Moreover, the PHB-HV films became smoother with increasing 3-HV content.The results of comprehensive research on the thermal behavior, molecular and crystalline structures of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHB-HV) films of different thicknesses, their molecular weights (Mw) and 3-hydroxyvalerate (3-HV) contents are reported. The film thickness affects the PHB film crystalline structure and crystallinity. A decrease in Mw leads to a smaller number of piezoactive domains in PHB films. The addition of HV significantly reduces the crystallinity and piezoresponse of PHB films. A decrease in Mw results in the increased crystallinity of PHB-HV films.
Nanotubes of self-assembled dipeptides exemplified by diphenylalanine (FF) demonstrate a wide range of useful functional properties, such as high Young's moduli, strong photoluminescence, remarkable ...piezoelectricity and pyroelectricity, optical waveguiding, etc., and became the object of intensive research due to their ability to combine electronic and biological functions in the same material. Two types of nanoconfined water molecules (bound water directly interacting with the peptide backbone and free water located inside nanochannels) are known to play a key role in the self-assembly of FF. Bound water provides its structural integrity, whereas movable free water influences its functional response. However, the intrinsic mechanism of water motion in FF nanotubes remained elusive. In this work, we study the sorption properties of FF nanotubes directly considering them as a microporous material and analyze the free water self-diffusion at different temperatures. We found a change in the regime of free water diffusion, which is attributed to water cluster size in the nanochannels. Small clusters of less than five molecules per unit cell exhibit ballistic diffusion, whereas, for larger clusters, Fickian diffusion occurs. External conditions of around 40% relative humidity at 30 °C enable the formation of such large clusters, for which the diffusion coefficient reaches 1.3 × 10
m
s
with an activation energy of 20 kJ mol
, which increases to attain 3 × 10
m
s
at 65 °C. The observed peculiarities of water self-diffusion along the narrow FF nanochannels endow this class of materials with a new functionality. Possible applications of FF nanotubes in nanofluidic devices are discussed.
Advanced Li-ion batteries with high energy and power densities are urgently required in many applications including automobiles. Aging of these batteries and irreversible capacity loss are still the ...factors preventing their further use, and novel methods of their study are prerequisite for the understanding of degradation at nanoscale. In this work, we use Kelvin Probe Force Microscopy (KPFM) to assess the distribution of surface potential in graphite anodes of commercial Li-batteries before and after aging at high C rates. In the aged sample, we observed an apparent core-shell-type potential distribution on large crack-free particles. We attribute this core–shell potential distribution to the remnant Li+ ions stacked in graphite particles causing irreversible capacity loss. The results corroborate the “radial” model used to explain the specific capacity fading mechanism at high C rate cycling in commercial batteries.
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•We observed a core–shell surface potential on graphite particles of an aged anode.•We observed a mosaic surface potential on graphite particles of an unaged anode.•Our results corroborate “radial” and “mosaic” models of Li distribution.
Fibrous peptide networks, such as the structural framework of self-assembled fluorenylmethyloxycarbonyl diphenylalanine (Fmoc–FF) nanofibrils, have mechanical properties that could successfully mimic ...natural tissues, making them promising materials for tissue engineering scaffolds. These nanomaterials have been determined to exhibit shear piezoelectricity using piezoresponse force microscopy, as previously reported for FF nanotubes. Structural analyses of Fmoc–FF nanofibrils suggest that the observed piezoelectric response may result from the noncentrosymmetric nature of an underlying β-sheet topology. The observed piezoelectricity of Fmoc–FF fibrous networks is advantageous for a range of biomedical applications where electrical or mechanical stimuli are required.
Nerve injuries pose a drastic threat to nerve mobility and sensitivity and lead to permanent dysfunction due to low regenerative capacity of mature neurons. The electrical stimuli that can be ...provided by electroactive materials are some of the most effective tools for the formation of soft tissues, including nerves. Electric output can provide a distinctly favorable bioelectrical microenvironment, which is especially relevant for the nervous system. Piezoelectric biomaterials have attracted attention in the field of neural tissue engineering owing to their biocompatibility and ability to generate piezoelectric surface charges. In this review, an outlook of the most recent achievements in the field of piezoelectric biomaterials is described with an emphasis on piezoelectric polymers for neural tissue engineering. First, general recommendations for the design of an optimal nerve scaffold are discussed. Then, specific mechanisms determining nerve regeneration via piezoelectric stimulation are considered. Activation of piezoelectric responses via natural body movements, ultrasound, and magnetic fillers is also examined. The use of magnetoelectric materials in combination with alternating magnetic fields is thought to be the most promising due to controllable reproducible cyclic deformations and deep tissue permeation by magnetic fields without tissue heating. In vitro and in vivo applications of nerve guidance scaffolds and conduits made of various piezopolymers are reviewed too. Finally, challenges and prospective research directions regarding piezoelectric biomaterials promoting nerve regeneration are discussed. Thus, the most relevant scientific findings and strategies in neural tissue engineering are described here, and this review may serve as a guideline both for researchers and clinicians.
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A concept of piezo-responsive hydrogen-bonded π-π-stacked organic frameworks made from Knoevenagel-condensed vanillin–barbiturate conjugates was proposed. Replacement of the substituent at the ether ...oxygen atom of the vanillin moiety from methyl (compound 3a) to ethyl (compound 3b) changed the appearance of the products from rigid rods to porous structures according to optical microscopy and scanning electron microscopy (SEM), and led to a decrease in the degree of crystallinity of corresponding powders according to X-ray diffractometry (XRD). Quantum chemical calculations of possible dimer models of vanillin–barbiturate conjugates using density functional theory (DFT) revealed that π-π stacking between aryl rings of the vanillin moiety stabilized the dimer to a greater extent than hydrogen bonding between carbonyl oxygen atoms and amide hydrogen atoms. According to piezoresponse force microscopy (PFM), there was a notable decrease in the vertical piezo-coefficient upon transition from rigid rods of compound 3a to irregular-shaped aggregates of compound 3b (average values of d33 coefficient corresponded to 2.74 ± 0.54 pm/V and 0.57 ± 0.11 pm/V), which is comparable to that of lithium niobate (d33 coefficient was 7 pm/V).
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