Flow Cytometry Analysis of Cytotoxicity In Vitro and Long‐Term Toxicity of HA‐40 wt% BaTiO3 Nanoparticles In Vivo

The development of new implantable biomaterials requires bone‐mimicking physical properties together with desired biocompatible property. In continuation to our earlier published research to establish compositional dependent multifunctional bone‐like properties and cytocompatibility response of hydroxyapatite (HA)‐BaTiO₃ composites, the toxicological property evaluation, both in vitro and in vivo, were conducted on HA‐40 wt% BaTiO₃ and reported in this work. In particular, this work reports in vitro cytotoxicity of mouse myoblast cells as well as in vivo long‐term tissue and nanoparticles interaction of intra‐articularly injected HA‐40 wt% BaTiO₃ and BaTiO₃ up to the concentration of 25 mg/mL in physiological saline over 12 weeks in mouse model. The careful analysis of flow cytometry results could not reveal any statistically significant difference in terms of early/late apoptotic cells or necrotic cells over 8 d in culture. Extensive histological analysis could not record any signature of cellular level toxicity or pronounced inflammatory response in vital organs as well as at knee joints of Balb/c mice after 12 weeks. Taken together, this study establishes nontoxic nature of HA‐40 wt% BaTiO₃ and therefore, HA‐40 wt% BaTiO₃ can be used safely for various biomedical applications.     

Reactive Hydrothermal Liquid‐Phase Densification (rHLPD) of Ceramics – A Study of the BaTiO3[TiO2] Composite System

A densification process called reactive hydrothermal liquid‐phase densification (rHLPD), based on principles of hydrothermal reaction, infiltration, reactive crystallization, and liquid‐phase sintering, is presented. rHLPD can be used to form monolithic ceramic components at low temperatures. The densification of barium titanate–titania composite monoliths was studied to demonstrate proof of concept for this densification model. Permeable, green titania (anatase) compacts were infiltrated with aqueous barium hydroxide solutions and reacted under hydrothermal conditions in the temperature range 90°C–240°C. The effects of reaction time and temperature on the conversion of titania (anatase) into barium titanate were studied. Utilizing a 72 h reaction at 240°C between l.0 M Ba(OH)₂, an anatase (TiO₂) powder compact, and a corresponding Ba/Ti ratio of 1.5, it was possible to crystallize a composite 95 wt% (88 mol%) BaTiO₃ and 5 wt% (12 mol%) TiO₂. The composite had a relative density of ~90% with a compressive strength of 172 ± 21 MPa and a flexural strength of 49 ± 4 MPa.     

BaTiO3 nanocubes-Gelatin composites for piezoelectric harvesting: Modeling and experimental study

Flexible composites containing BaTiO₃ nanoparticles into Gelatin bio-polymer matrix were designed and investigated. Following the idea that the electric field concentration in corners/edges at the interfaces between dissimilar materials give rise to enhanced effective permittivity in composites, cuboid-like BaTiO₃ nanoparticles have been employed as nanofillers into Gelatin matrix by using an inexpensive solution-based processing method. As predicted by finite element method simulations developed for cubic-like inclusions into a homogeneous polymer matrix, the experimental permittivity of xBT-(1-x)Gelatin composites increases when increasing the high-permittivity filler addition. For the composition x = 40 wt% (corresponding to 12 vol% BaTiO₃ addition), permittivity reaches ε_r ～15.7 with respect to ε_r ～9.8 of pure Gelatine (measured at 10⁵ Hz), while the average piezoelectric coefficient d₃₃ as determined by piezoelectric force microscopy shows a remarkable increase up to 21 pm/V in composites with x = 40 wt%, in comparison to ～7 pm/V in pure Gelatin. By using the experimentally determined material constants, the simulated piezoelectric voltage output vs. time has shown a similar increase (about a doubling of its amplitude) of the harvesting signal in the composite with x = 40 wt% BT, with respect to one of the polymer matrix, thus demonstrating the beneficial role of embedding BT nanoparticles into the biopolymer for increasing the mechanical harvesting response.     

Structural and piezoelectric properties of <001> textured PZT‐PZNN piezoelectric ceramics

Rhombohedral 0.69Pb(Zr_0.47Ti_0.53)‐0.31Pb(Zn_0.6Ni_0.4)NbO₃ (PZT‐PZNN) ceramics were textured using 10.0 vol. % BaTiO₃ (BT) platelets along the <001> direction at 950°C with a high Lotgering factor of 95.3%. BT platelets did not react with the PZT‐PZNN ceramics, and the textured PZT‐PZNN ceramic had a tetragonal structure. The PZT‐PZNN ceramics exhibited a strain of 0.174% with a piezoelectric strain constant (d*₃₃) of 580 pC/N at 3.0 kV/mm. The textured PZT‐PZNN ceramic showed an increased strain of 0.276% and d*₃₃ of 920 pC/N at 3.0 kV/mm, which can be explained by the domain rotation. However, the d₃₃ values of the textured specimens are smaller than those of the untextured specimens because of the small remanent polarization and relative dielectric constant of BT platelets. The textured PZT‐PZNN ceramic synthesized in this work can be used for piezoelectric multilayer actuators because of its large strain and low sintering temperature.     

Enhanced resistivity and strain stability of BiFeO3–BaTiO3 ceramics by hot-press sintering in oxygen atmosphere

Even though BiFeO₃–BaTiO₃ (BF–BT) with high Curie temperature and excellent piezoelectric properties is very suitable for high-temperature applications, its rapid reduction in resistivity with temperature limits its further application. So far, there is no effective method to improve the resistivity of BF–BT at a high-temperature state. In this work, hot-press sintering combined with an oxygen atmosphere was used to prepare (1 − x)BF–xBT (x = 0.2–0.33) ceramics for the first time, which reduced the sintering temperature from 1000 to 920°C. The controllable grain size can be achieved by adjusting the sintering temperature and the applied pressure. The X-ray photoelectron spectroscopy results confirmed that using hot-press sintering effectively avoided the generation of heterovalent Fe ions, and the resistivity of BF–BT ceramics at the high-temperature stage was improved by two orders of magnitude. It was found that hot-press sintering can cause the oriented growth of the sample along the (1 1 0) direction, and further refined X-ray diffraction was used to accurately analyze the changes in the lattice structure. The hot-press sintered samples obtained larger polarization strength, especially the electro-induced strain showed excellent temperature stability in the wide temperature range of 30–170°C. Hot-pressing sintering combined with an oxygen atmosphere is more suitable for preparing high insulation and electrical breakdown resistance ceramics.     

Microstructure and electrical properties of Er-doped 0.67 Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 ceramics with BaTiO3 templates

In this study, [001]-oriented Er-doped 0.67 Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (0.67PMN-0.33 PT) textured ceramics with different BaTiO₃ (BT) template concentrations were explored. The samples were prepared by tape-casting. Er³⁺ was added to modify the electrical properties of the polycrystalline ceramics, and the BT template was used to improve the texture of polycrystalline ceramics. The 0.67PMN-0.33 PT textured ceramics contained coexisting rhombohedral and tetragonal phases. The ceramics became increasingly textured as the sintering temperature increased up to 1250 °C. The piezoelectric coefficient of 0.67PMN-0.33 PT with 5 wt% BT was 634 pC/N, which is 1.2 times than that of randomly oriented 0.67PMN-0.33 PT. The strain of the ceramic with 5 wt% BT increased by 12.5% relative to a random control specimen. Analysis of the electrical properties and microstructure suggested that the enhancement of the piezoelectric coefficient and strain may be caused by the addition of Er³⁺ and the BT template. First, the directional growth of grains along the template affected the change-of-phase distribution of the system and formed a more adaptive phase. Second, Er³⁺ was substitutionally doped on the A-site of the perovskite to form local heterostructures. Finally, the relaxation components of the templates and Er³⁺ changed in the solid solution with the matrix. The solid solution of the BT templates and Er-doped-matrix powder changed the relaxation degree, which affected the interactions at the polar nanoregions and increased the piezoelectric coefficient of the ceramics.     

Influence of sintering temperature on energy storage properties of BaTiO3–(Sr1−1.5xBix) TiO3 ceramics

The effect of sintering temperature on microstructure, dielectric properties and energy storage properties of BaTiO₃–(Sr_1?1.5xBi_x)TiO₃ (x = 0.09) (BT–SBT) ceramics was investigated. The sintering temperature has pronounced influence on the grain size, shrinkage, and dielectric properties of the BT–SBT ceramics. With increasing sintering temperature, the dielectric constant increases largely. However, the increasing tendency of the dielectric breakdown strength (BDS) is less noticeable but become more evident with the consideration of Weibull modulus. For the BT-SBT ceramics, the unreleased energy density decreases and the electric field stability of the energy storage efficiency enhances with the increase of sintering temperature.     

3D printing of porous scaffolds BaTiO3 piezoelectric ceramics and regulation of their mechanical and electrical properties

A series of porous scaffolds of piezoelectric ceramic barium titanate (BaTiO₃) were successfully fabricated by Digital Light Processing (DLP) 3D printing technology in this work. To obtain a high-precision and high-purity sample, the debinding sintering profile was explored and the optimal parameters were determined as 1425 °C for 2h. With the increase of scaffolds porosity from 10% to 90%, the compressive strength and piezoelectric coefficient (d₃₃) decreased gradually. The empirical formulas about the mechanical and piezoelectric properties were obtained by adjusting BaTiO₃ ceramics with different porosity. In addition, the distribution of potential and stress under 100 MPa pressure were studied by the finite element method (FEM).     

Structural and Magnetoelectric Behavior of Lanthanum Manganite‐Based Multiferroic Heterostructures

The effect of fabrication method on the structure of (100 ? x) wt% BaTiO₃ + x wt% La_0.7Ba_0.3MnO₃ (BT + BLM) and (100 ? x) wt% Na, Bi, Sr‐doped PZT + x wt% La_0.65Pb_0.35MnO₃ (PZTNB‐1 + PLM) magnetoelectric ceramics was studied. Profound interdiffusion of two interacting phases occurs in nearly all cases. The BT + BLM and PZTNB‐1 + PLM ceramics exhibit low piezoelectric parameters even with small manganite contents (10–20 wt%). The increased content of the magnetostrictive phase complicates the polarization process due to the high conductivity of La_0.7Ba_0.3MnO₃ and La_0.65Pb_0.35MnO₃. Doping of BaTiO₃ and PZTNB‐1 with small additions of manganite components affects piezoelectric properties, thereby lowering efficiency of the resulting material.     

Low‐temperature sintering and enhanced piezoelectric properties of random and textured PIN–PMN–PT ceramics with Li2CO3

Low‐temperature sintered random and textured 36PIN–30PMN–34PT piezoelectric ceramics were successfully synthesized at a temperature as low as 950°C using Li₂CO₃ as sintering aids. The effects of Li₂CO₃ addition on microstructure, dielectric, ferroelectric, and piezoelectric properties in 36PIN–30PMN–34PT ternary system were systematically investigated. The results showed that the grain size of the specimens increased with the addition of sintering aids. The optimum properties for the random samples were obtained at 0.5 wt% Li₂CO₃ addition, with piezoelectric constant d₃₃ of 450 pC/N, planar electromechanical coupling coefficient k_p of 49%, peak permittivity ε_max of 25 612, remanent polarization P_r of 36.3 μC/cm². Moreover, the low‐temperature‐sintered textured samples at 0.5 wt% Li₂CO₃ addition exhibited a higher piezoelectric constant d₃₃ of 560 pC/N. These results indicated that the low‐temperature‐sintered 36PIN–30PMN–34PT piezoelectric ceramics were very promising candidates for the multilayer piezoelectric applications.     

Enhanced piezoelectric properties in BF-BT based lead-free ferroelectric ceramics for high-temperature devices

Due to the high Curie temperature (T_C), BiFeO₃–BaTiO₃ (BF-BT) ceramics have been broadly investigated in high-temperature piezoelectric devices. The piezoelectric constant is one of the most significant factors in determining the sensitivity and reliability of piezoelectric functional components. However, the poor piezoelectric constant (d₃₃) of BF-BT ceramic has prevented the practical application of the material. In this work, we innovatively introduce the 0.93Bi_0.5Na_0.5TiO₃-0.07BaTiO₃ (0.93NBT-0.07BT) component to 0.7BF-0.3BT ceramic, to build a morphotropic phase boundary (MPB) for enhancing d₃₃. The XRD analysis shows that the (0.7BF-0.3BT)-x(0.93NBT-0.07BT) ceramics are still in the MPB region with R–PC phases coexistence, and exhibits a homogeneous solid solution. Moreover, the introduction of 0.93NBT-0.07BT ceramic suppresses the generation of defects and facilitates grain growth, thus enhancing piezoelectric property. In consequence, an optimum piezoelectricity d₃₃ = 213 pC/N along with T_c～450 °C was obtained in (0.7BF-0.3BT)-0.01(0.93NBT-0.07BT). This research provides a new idea for the application of BF-BT ceramics in high-temperature piezoelectric devices.     

Effect of washing of barium titanate powders synthesized by hydrothermal method on their sinterability and piezoelectric properties

BaTiO₃ (BT) powders were synthesized by the hydrothermal method for fabricating lead-free barium titanate piezoelectric ceramics. The obtained powders were washed by distilled water and 0.01N acetic acid solutions separately, and utilized to obtain piezoelectric ceramics by traditional sintering. BT ceramics with the highest piezoelectric properties (d₃₃ value is over 190 pC/N) was obtained from the BT powder synthesized at 250 °C and washed by acetic acid solution. The influence of washing method and sintering temperature on the piezoelectric properties of BT ceramics were studied. The reasons were investigated by comparing the properties of BT powders and their compacts sintered at different temperature.     

Relaxor Ferroelectric BaTiO3–Bi(Mg2/3Nb1/3)O3 Ceramics for Energy Storage Application

Perovskite solid solution ceramics of (1 ? x)BaTiO₃–xBi(Mg_2/3Nb_1/3)O₃ (BT–BMN) (x = 0.05–0.2) were synthesized by solid‐state reaction technique. The results show that the BMN addition could lower the sintering temperature of BT‐based ceramics. X‐ray diffraction results reveal a pure perovskite structure for all studied samples. Dielectric measurements exhibit a relaxor‐like characteristic for the BT–BMN ceramics, where broadened phase transition peaks change to a temperature‐stable permittivity plateau (from ?50°C to 300°C) with increasing the BMN content (x = 0.2), and slim polarization–electric field hysteresis loops were observed in samples with x ≥ 0.1. The dielectric breakdown strength and electrical resistivity of BT–BMN ceramics show their maxima of 287.7 kV/cm and 1.53 × 10¹³ Ω cm at x = 0.15, and an energy density of about 1.13 J/cm³ is achieved in the sample of x = 0.1.     

Construction of an electric microenvironment in piezoelectric scaffolds fabricated by selective laser sintering

It is well established that the electric microenvironment plays a vital role in promoting bone regeneration and repair. In this work, a BaTiO₃ polymer scaffold was fabricated by selective laser sintering to overcome the challenges in manufacturing a 3D porous structure. More significantly, the orderly orientated dipoles of poled BaTiO₃ deflect when a force is applied to the scaffolds, which results in a large number of charges generated on the scaffolds. The results indicated that the poled scaffold with 20 wt% BaTiO₃ presented the highest electrical output performances under the same external force. The electric cues efficiently enhanced the cell viability, adhesion and proliferation under the action of ultrasound. Simultaneously, the tensile strength and modulus were significantly increased by 61.3% and 34.9%, respectively, which were attributed to the fact that crack propagation was prevented by BaTiO₃ nanoparticles. All of these positive results demonstrated that 3D piezoelectric scaffolds present great potential in bone regeneration.     

Remarkably High‐Temperature Stability of Bi(Fe1−xAlx)O3–BaTiO3 Solid Solution with Near‐Zero Temperature Coefficient of Piezoelectric Properties

The 0.72Bi(Fe_1?xAl_x)O₃–0.28BaTiO₃ (x = 0, 0.01, 0.03, 0.05, and 0.07, abbreviated as BFAx–BT) lead‐free high‐temperature ceramics were prepared by the conventional ceramic processing. Systematic investigation on the microstructures, crystalline structures, dielectric and piezoelectric properties, and high‐temperature stability of piezoelectric properties was carried out. The crystalline structures of BFAx–BT ceramics evolve from rhombohedral structure with x < 0.01 to the coexistence of rhombohedral structure and pseudocubic phases with x ≈ 0.01, finally to pseudocubic phases when x > 0.03. Remarkably high‐temperature stability with near‐zero temperature coefficient of piezoelectric properties (TCk_p), together with improved piezoelectric properties has been achieved for x = 0.01 BFAx–BT ceramics. The BFAx–BT(x = 0.01) ceramics simultaneously show the excellent piezoelectric properties of d₃₃ = 151 pC/N, k_p = 0.31 and super‐high‐temperature stability of T_d = 420°C, TCk_p = 1 × 10^?4. It is considered that the observed strong piezoelectricity and remarkably high‐temperature stability should be ascribed to the phase coexistence of rhombohedral and pseudocubic phases. The rhombohedral phases have a positive TCk_p value and the pseudocubic phases possess a negative TCk_p value. Thus, the TCk_p value of BFAx–BT ceramics can be tuned by composition of x.     

Giant electromechanical strain response in lead‐free SrTiO3‐doped (Bi0.5Na0.5TiO3–BaTiO3)–LiNbO3 piezoelectric ceramics

Lead‐free 0.985[(0.94?x)Bi_0.5Na_0.5TiO₃–0.06BaTiO₃–xSrTiO₃]–0.015LiNbO₃ [(BNT–BT–xST)–LN, x=0‐0.05] piezoelectric ceramics were prepared using a conventional solid‐state reaction method. It was found that the long‐range ferroelectric order in the unmodified (BNT–BT)–LN ceramic was disrupted and transformed into the ergodic relaxor phase with the ST substitution, which was well demonstrated by the dramatic decrease in remnant polarization (P_r), coercive field (E_c), negative strain (S_neg) and piezoelectric coefficient (d₃₃). However, the degradation of the ferroelectric and piezoelectric properties was accompanied by a significant increase in the usable strain response. The critical composition (BNT–BT–0.03ST)–LN exhibited a maximum unipolar strain of ~0.44% and corresponding normalized strain, S_max/E_max of ~880 pm/V under a moderate field of 50 kV/cm at room temperature. This giant strain was associated with the coexistence of the ferroelectric and ergodic relaxor phases, which should be mainly attributed to the reversible electric‐field‐induced transition between the ergodic relaxor and ferroelectric phases. Furthermore, the large field‐induced strain showed relatively good temperature stability; the S_max/E_max was as high as ~490 pm/V even at 120°C. These findings indicated that the (BNT–BT–xST)–LN system would be a suitable environmental‐friendly candidate for actuator applications.     

Temperature‐Dependent Phase Transitions in the Lead‐Free Piezoceramics (1 – x – y)(Bi1/2Na1/2)TiO3–xBaTiO3–y(K0.5Na0.5)NbO3 Observed by in situ Transmission Electron Microscopy and Dielectric Measurements

Lead‐free piezoelectric (1 – x – y)(Bi_1/2Na_1/2)TiO₃–xBaTiO₃–y(K_0.5Na_0.5)NbO₃ (BNT–BT–KNN) ceramics were examined in situ under increasing temperature in the transmission electron microscope. Changing superstructure reflections indicate a transition from rhombohedral to tetragonal to cubic phase with broad coexistence regions. The additional evolution of the microstructure in combination with dielectric measurements leads to a model of two relaxor‐type phase evolutions with temperature.     

A novel Si3N4/BAS/BN composite synthesized by spark plasma sintering

Based on good thermomechanical and electromagnetic properties of silicon nitride (Si₃N₄), barium aluminosilicate (BaO–BaTiO₃–SiO₂ or BAS), and boron nitride (BN), a novel combination of Si₃N₄/BAS/BN composites was fabricated by spark plasma sintering (SPS) after traditional powder mixing process. The effect of different amounts of BN (3–9 wt%) on the mechanical properties of composite was studied. The phases were observed by X-ray diffraction, and the microstructures were identified by scanning electron microscopy (SEM). The optimal sample is the one containing 3 wt% of BN and is sintered under a final pressure of 50 MPa. This sample has a hardness of 9.03 GPa, a flexural strength of 418.75 MPa, an elastic modulus of 934.46 MPa, and a loss tangent of less than 0.002 in 38% of the X-band frequencies. The optimal sample thickness was determined via the Nicolson-Ross-Weir (NRW) technique considering the mechanical strength limits.     

The effects of BaTiO3 on the handleability and mechanical strength of the prepared piezoelectric calcium phosphate silicate for bone tissue engineering

Natural bone is a piezoelectric material that can generate electrical signals when subjected to an external force. Although many studies have attempted to develop piezoelectric biomaterials for bone regeneration, post-treatment steps, such as sintering, are always needed. In this study, we prepared an injectable and piezoelectric bone substitute based on nanosized BaTiO₃ (nBT)-added calcium phosphate silicate (CPS). The impacts of nBT on the CPS handleability and mechanical strength were characterized, and show that adding nBT could improve the CPS handleability but affect the CPS mechanical strength in a concentration-dependent manner (from 25.3 ± 1.0 MPa for 10BC to 13.5 ± 1.0 MPa for 40BC). In addition, our approach could fabricate a piezoelectric bone substitute with comparable piezoelectricity to the native bone without any post-treatment. The in vitro analyses demonstrated that nBT/CPS was biocompatible and could promote osteoblast differentiation. In conclusion, our results strongly indicate that the injectable formulation based on nBT/CPS can be a promising candidate in bone tissue engineering, and further research is needed to investigate the biomaterial's performance in bone defect animal models.     

Effects of Mg‐Doping and of Reinforcing Multiwalled Carbon Nanotubes Content on the Structure and Properties of Hydroxyapatite Nanocomposite Ceramics

Surfactant‐assisted hydrothermal synthesis of magnesium‐doped hydroxyapatite (Ca_10?xMg_x(PO₄)₆(OH)₂) with 0 ≤ x ≤ 1) was realized in aqueous solution at 90°C. β‐TCP phase was formed in the Mg_0.6‐HA sample after heat treatment at 1000°C. Magnesium was found to degrade the sintering ability of Mg_x‐HA ceramics. Flexural strength (σ_f) was found to decrease as a function of Mg‐doped HA. The using of carbon nanotubes as reinforcing agents mitigated the strength loss of Mg‐HA ceramics. The flexural strength of Mg_0.6‐HA was then increased by nearly 20% from approximately 33 to 39 MPa with an optimum addition of 3 wt% of multi‐walled nanotubes.