Ultrahigh Electrostrictive Effect in Lead-Free Ferroelectric Ceramics Via Texture Engineering.

The electrostrictive effect, which induces strain in ferroelectric ceramics, offers distinct advantages over its piezoelectric counterpart for high-precision actuator applications, including anhysteretic behavior even at high frequencies, rapid reaction times, and no requirement for poling. Historically, commercially available electrostrictive materials have been lead oxide-based. However, global restrictions on the use of lead in electronic components necessitate the exploration of lead-free electrostrictive ceramics with a high strain performance. Although various engineering strategies for producing materials with high strain have been proposed, they typically come at the expense of increased strain hysteresis. Here, we describe the extraordinary electrostrictive response of (Ba0.95Ca0.05)(Ti0.88Sn0.12)O3 (BCTS) ceramics with ultrahigh electrostrictive strain and negligible hysteresis achieved through texture engineering leveraging the anisotropic intrinsic lattice contribution. The BCTS ceramics exhibit a high unipolar strain of 0.175%, a substantial electrostrictive coefficient Q33 of 0.0715 m4 C-2, and an ultralow hysteresis of less than 0.8%. Notably, the Q33 value is three times greater than that of high-performance lead-based Pb(Mg1/3Nb2/3)O3 electrostrictive ceramics. Multiscale structural analyses demonstrate that the electrostrictive effect dominates the BCTS strain response. This research introduces a novel approach to texture engineering to enhance the electrostrictive effect, offering a promising paradigm for future advancements in this field.

Enhanced Electromechanical Performance in Lead-free (Na,K)NbO3-Based Piezoceramics via the Synergistic Design of Texture Engineering and Sm-Modification.

Next-generation electromechanical conversion devices have a significant demand for high-performance lead-free piezoelectric materials to meet environmentally friendly requirements. However, the low electromechanical properties of lead-free piezoceramics limit their application in high-end transducer applications. In this work, a 0.96K0.48Na0.52Nb0.96Sb0.04O3-0.04(Bi0.5-xSmx)Na0.5ZrO3 (abbreviated as T-NKN-xSm) ceramic was designed through phase regulation and texture engineering, which is expected to solve this difficulty. Through our research, we successfully demonstrated the enhanced electromechanical performance of lead-free textured ceramics with a highly oriented [001]c orientation. Notably, the T-NKN-xSm textured ceramics doped with 0.05 mol % Sm exhibited the optimal electromechanical performance: piezoelectric coefficient d33 ≈ 710 pC N-1, longitudinal electromechanical coupling k33 ≈ 0.88, planar electromechanical coupling kp ≈ 0.80, and Curie temperature Tc ≈ 244 °C. Finally, we conducted a detailed investigation into the phase and domain structures of the T-NKN-Sm ceramics, providing valuable insights for achieving high electromechanical properties in NKN-based ceramics. This research serves as a crucial reference for the development of advanced electromechanical devices by facilitating the utilization of lead-free piezoelectric materials with superior performance and environmental benefits.

Antibody- and aptamer-free SERS substrate for ultrasensitive and anti-interference detection of SARS-CoV-2 spike protein in untreated saliva.

Sensitive and anti-interference detection of targeted signal(s) in body fluids is one of the paramount tasks in biosensing. Overcoming the complication and high cost of antibody/aptamer-modification, surface-enhanced Raman spectroscopy (SERS) based on antibody/aptamer-free (AAF) substrates has shown great promise, yet with rather limited detection sensitivity. Herein, we report ultrasensitive and anti-interference detection of SARS-CoV-2 spike protein in untreated saliva by an AAF SERS substrate, applying the evanescent field induced by the high-order waveguide modes of well-defined nanorods for SERS for the first time. A detection limit of 3.6 × 10-17 M and 1.6 × 10-16 M are obtained in phosphate buffered saline and untreated saliva, respectively; the detection limits are three orders of magnitude improved than the best records from AAF substrates. This work unlocks an exciting path to design AAF SERS substrates for ultrasensitive biosensing, not limited to detection of viral antigens.

Optimize multilayer matching layer design for tone-burst underwater acoustic transducers.

In this study, a theoretical model has been constructed to address the optimization of matching layers for tone burst excitation underwater acoustic transducers and to investigate the functional mechanism change of matching layers. Single, double, and triple matching layers are attached to piezoelectric composite plates, and tone burst signals with a different number of burst-cycles are applied. Acoustic pressure function (Sp) and acoustic pressure transient response (PTR) are compared among these transducers. The results demonstrated that when the cycle number M ≤ 2, more matching layers lead to shorter ringdown with similar PTR amplitude. Since the objective is for better axial resolution, three matching layers have noticeable advantage, whereas for the case of M > 5, far detection distance is the main objective, and more matching layers caused the decrease in PTR amplitude. Besides, matching layers become part of the resonance structure; they do not serve as a transmission medium anymore. Therefore, the transducer with single matching is optimal for the long tone burst excitation. For the case of 2-5 cycle excitation, one may use double matching layers, which has a balance between the transmitting voltage response amplitude and bandwidth. With the increase in M, the role of matching layers changes from a bridging transmission medium to amplifying vibration velocity and introducing additional vibration modes to broaden the bandwidth.

Phase-field simulation on the interaction of oxygen vacancies with charged and neutral domain walls in hexagonal YMnO3.

A three-dimensional model of the interaction between the charged or neutral domain walls and oxygen vacancies in the hexagonal manganite YMnO3was proposed, and simulated using Landau-Ginzburg-Devonshire (LGD) theory, dynamic diffusion equation and Maxwell's equation. The calculation proves that stiffness anisotropic factors can adjust the domain wall state and ultimately affect the distribution of oxygen vacancies. The head-to-head domain wall corresponds to low oxygen vacancy density, and the tail-to-tail domain wall corresponds to high oxygen vacancy density. The electrostatic field generated by the bound charge is the key factor leading to the change of oxygen vacancy distribution. Finally,e-index lawNd=aeb*dP/dzcan fit the relationship between the oxygen vacancy concentration and the polarization gradient alongzdirection. Our theory provides a new way to modulate the distribution of oxygen vacancies through domain wall morphology in hexagonal YMnO3.

Enhancing the Temperature Stability of 0.42PNN-0.21PZ-0.37PT Ceramics through Texture Engineering.

Although the MPB composition 0.42PNN-0.21PZ-0.37PT ceramic has high piezoelectric properties, its temperature stability at room temperature is rather poor due to the low phase-transition temperature. By texture engineering using BaTiO3 (BT) as the template, the temperature stability of this material can be greatly improved. In the temperature range from room temperature up to 140 °C, the high effective piezoelectric strain constant d33* of 0.42PNN-0.21PZ-0.37PT-3BT only changed by 4.9% from 1278 to 1215 pm/V, while the d33* of the nontextured counterpart changed by 46.7% from the room temperature value of 920 pm/V with the maximum deviation to 1350 pm/V at 80 °C. In addition, the textured ceramic has higher piezoelectric properties, lower dielectric loss, and slightly higher coercive field. The room-temperature figure-of-merit d33 × g33 for PNN-PZT-2BT is increased by as much as 42% compared with the nontextured counterpart. Our results demonstrated that texture engineering is an effective way to improve the temperature stability of the MPB composition piezoceramics.

Lead-Free Ultrasonic Phased Array Transducer for Human Heart Imaging.

Substantial advancement has been made in recent years on lead-free piezoelectric materials, but up to date, it is still a challenge to make a true medical imaging ultrasonic array transducer with center frequency <3 MHz. There are two major obstacles: the difficulty of fabricating large enough uniform lead-free piezoelectric materials with high piezoelectric coefficient, and the severe electrical impedance mismatch of an array element to the imaging system due to the relatively low dielectric constant of lead-free materials compared to lead-based piezoelectric materials. We resolved these two issues by employing texture engineering and stacking piezoelectric-layer design, which allowed us to fabricate an 80 element phased array transducer with the center frequency of 2.9 MHz and a bandwidth >80% for human heart imaging. The high-quality lead-free (Ba0.95Ca0.05)(Ti0.94Zr0.06)O3 textured ceramic plate has the size of 23×22×0.8 mm3 with the piezoelectric constant d33 = 570 pC/N. Phantom imaging and internal clinical human heart imaging demonstrated that this lead-free phased array can produce comparable imaging quality to that of a commercial PZT-5H ceramic-based phased array transducer, which demonstrated the practicality of using lead-free materials to replace PZT ceramics in phased array transducers for medical imaging applications.

Sonodynamic Effects of a Novel Ether-Group Modified Porphyrin Derivative Combined With Pulsed Low-Intensity Ultrasound on PC-9 Cells.

Sonodynamic therapy (SDT) is a developing modality for cancer treatment based on the synergistic effect of ultrasound and chemical compounds which are known as sonosensitizers. The development of more efficient sonosensitizers has become an urgent issue in this field. In this study, a novel porphyrin derivative (BBTPP) mediated SDT was evaluated on PC-9 cells. Pulsed low-intensity ultrasound (PLIU) was used for its little thermal and mechanical damage. The accumulation of drugs in cells was evaluated through porphyrin fluorescence, and the cytotoxicity of BBTPP was evaluated using a cell counting kit-8 assay. The sonodynamic effect was investigated by Hoechst 33342/PI and Annexin V-FITC/PI double staining, which showed an apoptotic rate of 18.87% in the BBTPP-SDT group, as compared with 1.71%, 1.4%, 1.57%, 3.61%, 11.18% in the control, BBTPP, hematoporphyrin monomethyl ether (HMME), ultrasound, and HMME-SDT groups, respectively. The sono-toxic effect of BBTPP was significantly superior to HMME. Our results showed that BBTPP-SDT resulted in much higher intracellular reactive oxygen species (ROS) and lipid peroxidation levels which were evaluated by 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) and Liperfluo assay, respectively. The expressions of Bax, Bcl-2, caspase-9, caspase-8, and cleaved caspase-3 proteins were evaluated to investigate the apoptotic mechanism of BBTPP-SDT. The results of this study showed that the combination of BBTPP and PLIU induced the generation of ROS, resulting in lipid peroxidation, and activated both the extrinsic and intrinsic apoptotic pathways of PC-9 cells. Our results also suggested that the ether group introduced in the side chain of porphyrin could enhance the sono-toxicity of porphyrin-based sensitizers under the sonication of PLIU. These results supported the possibility of BBTPP as a promising sonosensitizer, and an appropriate side chain could enhance the sono-sensitivity of porphyrins.

Involvement of hydrogen peroxide in sonodynamical effect with sinoporphyrin sodium in hypoxic situation.

Sonodynamic therapy (SDT) represents a noninvasive therapeutic method via the activation of certain chemical sensitizers using low-intensity ultrasound to generate various reactive oxygen species (ROS). In this work, we conducted systematic experiments to evaluate the production of hydrogen peroxide (H2O2) in sinoporphyrin sodium (DVDMS) mediated SDT (DVDMS-SDT). We found that the fluorescence intensities of H2O2-specific probe BES-H2O2 and Amplex Red increased significantly exposure to DVDMS-SDT while decreased with the introduction of catalase (H2O2 scavenger), indicating the production of H2O2. And the fluorescence intensity of H2O2 susceptible probes were positively correlated with DVDMS concentration, ultrasound intensity and irradiation time. Under the same molarity concentration, DVDMS has advantages over proto-porphyrin IX (PpIX) and hemoporrin monomethyl ether (HMME) in H2O2 production, indicating that the yield of H2O2 depends on the properties of sensitizer. More importantly, DVDMS-SDT is involved in the process of H2O2 even in the oxygen-free condition, showing its greater superiority for the treatment of tumor under hypoxia environment.

Self-heating phenomenon of piezoelectric elements excited by a tone-burst electric field.

Tone-burst excitation is often used for ultrasonic transducers of specific operation modes or for overcoming transducer overheating problems associated with continuous wave (CW) excitation. In this study, a theoretical model for the self-heating phenomenon of a piezoelectric disc element is established to estimate the temperature rise induced by a tone-burst electric field. An analytical solution for the temperature rise of the piezoelectric element is obtained by using Laplace transform method. Numerical simulations and experimental measurements are performed to investigate the influence of different excitation parameters on the temperature rise. By comparing the experimental results with the simulation results, the temperature-rise difference between tone-burst and CW excitations is quantified, and the validity of the theoretical model is verified. Furthermore, a multiparameter estimation method is proposed for the heat convection coefficient and dielectric properties under high-field operating conditions. These results are useful in both optimization of heat dissipation performance and characterization of high-power ultrasonic transducers.

Energy Integration Method for Calculating keff and its Application in Design Optimization of Disk Resonators via Convex Edge.

Piezoelectric resonators have been extensively used as filters, actuator, and sensors. The effective electromechanical coupling coefficient ( [Formula: see text] is the most useful parameter to evaluate the electromechanical conversion efficiency of piezoelectric resonators. However, even for simple geometry piezoelectric resonators, such as disks, the coupling between different modes makes the resonant characteristics very complex. The coupling causes low electromechanical coupling efficiency of the intended mode. We propose a finite-element-based energy integration method to calculate [Formula: see text] of piezoelectric resonators. This method is more accurate than the conventional resonance-antiresonance method and provides a powerful tool for the design optimization of pure mode resonators. A special case studied here is the fundamental thickness extensional (TE) mode of PZT-8 disks in the aspect ratio range of 2-20. Our results showed that multimode coupling near this mode can be greatly suppressed by modifying the edge surface of the disk to a convex shape. Such an optimized design could enhance [Formula: see text] of the fundamental TE mode by as much as 10%-45% depending on the aspect ratio.

Plasmonic Enhanced Reactive Oxygen Species Activation on Low-Work-Function Tungsten Nitride for Direct Near-Infrared Driven Photocatalysis.

Realizing near-infrared (NIR) driven photocatalytic reaction is one of the promising strategies to promote the solar energy utilization and photocatalytic efficiencies. However, effective reactive oxygen species (ROS) activation under NIR irradiation remains to be great challenge for nearly all previously reported photocatalysts. Herein, the cubic-phase tungsten nitride (WN) with strong plasmonic NIR absorption and low-work function (≈3.59 eV) is proved to be able to mediate direct ROS activation by both of experimental observation and theoretical simulation. The cubic WN nanocubes (NCs) are synthesized via the hydrothermal-ammonia nitridation process and its NIR-driven photocatalytic properties, including photocatalytic degradation, hydroxylation, and de-esterification, are reported for the first time in this work. The 3D finite element simulation results demonstrate the size dependent and wavelength tuned plasmonic NIR absorption of the WN NCs. The NIR-driven photocatalytic mechanism of WN NCs is proposed based on density functional theory (DFT) calculated electronic structure and facet dependent O2 (or H2 O) molecular activation, radicals scavenging test, spin trapped electron paramagnetic resonance measurements, and ultraviolet photoelectronic spectrum (UPS). Overall, the results in this work pave a way for the application of low-work-function materials as highly reactive NIR photocatalyst.

Grain-Oriented Ferroelectric Ceramics with Single-Crystal-like Piezoelectric Properties and Low Texture Temperature.

High-performance piezoelectrics are pivotal to various electronic applications including multilayer actuators, sensors, and energy harvesters. Despite the presence of high Lotgering factor F001, two key limitations to today's relaxor-PbTiO3 textured ceramics are low piezoelectric properties relative to single crystals and high texture temperature. In this work, Pb(Yb1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PYN-PMN-PT) textured ceramics with F001 ∼ 99% were synthesized at only 975 °C through liquid-phase-assisted templated grain growth, where of particular significance is that single-crystal properties, i.e., very large electrostrain Smax/Emax ∼ 1830 pm V-1, giant piezoelectric figure of merit d33 × g33 ∼ 61.3 × 10-12 m2 N-1, high electromechanical coupling k33 ∼ 0.90, and Curie temperature Tc ∼ 205 °C, were simultaneously achieved. Especially, the Smax/Emax and d33 × g33 values correspond to ∼180% enhancement as compared to the regularly 1200 °C-textured ceramics with F001 ∼ 96%, representing the highest values ever reported on piezoceramics. Phase-field simulation revealed that grain misorientation has a stronger influence on piezoelectricity than texture fraction. The ultrahigh piezoelectric response achieved here is mainly attributed to effective control of grain orientation features and domain miniaturization. This work provides important guidelines for developing novel ceramics with significantly enhanced functional properties and low synthesis temperature in the future and can also greatly expand application fields of piezoceramics to high-performance, miniaturized electronic devices with multilayer structures.

Hematoporphyrin monomethyl ether mediated sonodynamic antimicrobial chemotherapy on porphyromonas gingivalis in vitro.

This study aimed to evaluate the efficacy of hematoporphyrin monomethyl ether (HMME)-mediated sonodynamic antimicrobial chemotherapy (SACT) on Porphyromonas gingivalis (P. gingivalis). P. gingivalis (ATCC 33277) was used in the present study. The bacterial suspension was randomly divided into five groups: Group 1 was incubated for 2 h in the dark with HMME in various concentrations (10, 20, 30 and 40 µg/mL). Then exposed to 1 MHz ultrasound frequency with 3 W/cm2 ultrasound intensity for 10 min. Group 2 was incubated with 40 µg/mL HMME and then irradiated with 2, 4, 6, 8 and 10 min ultrasonic time. Group 3 received different HMME concentration (10, 20, 30 and 40 µg/mL) treatment alone with no ultrasound as the HMME control group. Group 4 received ultrasound treatment alone in different ultrasonic time (2, 4, 6, 8 and 10 min) with no HMME as the ultrasound control group. Group 5 received no treatment as the no treatment control group. After the SACT, the bactericidal effect was determined by the colony forming unit assay. The intracellular content of reactive oxygen species (ROS) was detected using the laser scanning confocal microscope based on DCFH-DA. 4.7 lg reduction in CFU, When P. gingivalis was treated with ultrasound (3 W/cm2 for 10 min) at 40 µg/mL HMME concentration (P < 0.01). The intracellular ROS in SDT group had a significant difference in comparison with the no treatment control group (P < 0.01). HMME mediated SACT can be a potential antibacterial therapy to significantly inhibit P. gingivalis growth.

Ultra-large electric field-induced strain in potassium sodium niobate crystals.

Electromechanical coupling in piezoelectric materials allows direct conversion of electrical energy into mechanical energy and vice versa. Here, we demonstrate lead-free (K x Na1-x )NbO3 single crystals with an ultrahigh large-signal piezoelectric coefficient d 33* of 9000 pm V-1, which is superior to the highest value reported in state-of-the-art lead-based single crystals (~2500 pm V-1). The enhanced electromechanical properties in our crystals are realized by an engineered compositional gradient in the as-grown crystal, allowing notable reversible non-180° domain wall motion. Moreover, our crystals exhibit temperature-insensitive strain performance within the temperature range of 25°C to 125°C. The enhanced temperature stability of the response also allows the materials to be used in a wider range of applications that exceed the temperature limits of current lead-based piezoelectric crystals.

Hematoporphyrin monomethyl ether-mediated sonodynamic therapy induces A-253 cell apoptosis.

It has been found that >90% of oral cancer patients suffer from squamous cell carcinoma (SCC). The 5-year survival rate of SCC is ~50%, despite the availability of different treatments. Sonodynamic therapy (SDT) has been developed as a novel therapy for cancer, resisting bacterial infection and inhibiting atherosclerotic plaque progression. The present study investigated the efficacy of hematoporphyrin monomethyl ether (HMME)-mediated SDT on the A-253 epidermoid cancer cell line. The cytotoxicity of HMME and the survival rate of cells following SDT were examined by the MTT assay. Apoptosis and necrosis of cells were detected using flow cytometry with Annexin V and propidium iodide (PI) staining, and fluorescence microscopy with Hoechst 33258 and PI staining. Intracellular reactive oxygen species (ROS) and Ca2+ levels were measured using a fluorescence microscope based on 2',7'-dichlorofluorescein diacetate and fluo-3/acetoxymethylester, respectively. Results of the MTT assay demonstrated that a lower concentration (<10 µg/ml) of HMME had no significant effect on the A-253 cells, but SDT combined with ultrasonic treatment for 1 min and 10 µg/ml HMME decreased the cell survival rate by 27%. Flow cytometry analysis revealed that A-253 cells in the SDT group had a higher rate of late apoptosis compared with the control group. Furthermore, fluorescence quantitation of apoptotic A-253 cells demonstrated that the percentages of apoptotic cells were increased in the ultrasound and SDT group compared with those in the control group. In the present study, the ROS level in the SDT group was elevated compared with that in the control group. The Ca2+ levels were increased to 181.2 and 268.7% in the ultrasound and SDT groups, respectively, relative to the control group. Taken together, the findings of the present study demonstrated that HMME-SDT significantly induces the apoptosis of A-253 cells together with intracellular ROS generation and Ca2+ overload. Thus, HMME-SDT may be a promising treatment option for patients with SCC.

Porous Ultrathin NiSe Nanosheet Networks on Nickel Foam for High-Performance Hybrid Supercapacitors.

Transition metal selenides (TMSs) with excellent electrochemical activity and high intrinsic electrical conductivity have attracted considerable attention owing to their potential use in energy storage devices. However, the low energy densities of the reported TMSs, which originate from the small active surface area and poor electrolyte ion mobility, substantially restrict their application potential. In this work, porous ultrathin nickel selenide nanosheet networks (NiSe NNs) on nickel foam are fabricated by using a novel, facile method, that is, selenylation/pickling of the pre-formed manganese-doped α-Ni(OH)2 . Removal of Mn resulted in NNs with a highly porous structure. The 3D framework of the NNs and the inherent nature of the NiSe affords high ion mobility, abundant accessible activated sites, vigorous electrochemical activity, and low resistance. One of the highest specific capacities of TMSs ever reported, that is, 443 mA h g-1 (807 µAh cm-2 ) at 3.0 A g-1 , is achieved with the NNs as electrodes. The assembled NiSe NNs//porous carbon hybrid supercapacitor delivers a high energy density of 66.6 Wh kg-1 at a power density of 425 W kg-1 , with excellent cycling stability. This work provides a new strategy for the production of novel electrode materials that can be applied in high-performance hybrid supercapacitors, and a fresh pathway towards commercial applications of hybrid supercapacitors based on TMS electrodes.

Enhanced Piezoelectric Effect Derived from Grain Boundary in MoS2 Monolayers.

Recent discovery of piezoelectricity that existed in two-dimensional (2D) layered materials represents a key milestone for flexible electronics and miniaturized and wearable devices. However, so far the reported piezoelectricity in these 2D layered materials is too weak to be used for any practical applications. In this work, we discovered that grain boundaries (GBs) in monolayer MoS2 can significantly enhance its piezoelectric property. The output power of piezoelectric devices made of the butterfly-shaped monolayer MoS2 was improved about 50% by the GB-induced piezoelectric effect. The enhanced piezoelectricity is attributed to the additional piezoelectric effect induced by the existence of deformable GBs which can promote polarization and generates spontaneous polarization with different piezoelectric coefficients along various directions. We further made a flexible piezoelectric device based on the 2D MoS2 with the GBs and demonstrated its potential application in self-powered precision sensors for in situ detecting pressure changes in human blood for health monitoring.

Single-Crystal High-Frequency Intravascular Ultrasound Transducer With 40- µ m Axial Resolution.

Intravascular ultrasound (IVUS) is one of the most useful tools available today to assist intravascular stenting procedures. Having higher resolution is very important for helping doctors to evaluate the nature of atherosclerotic plaques. The current commercial IVUS systems have a spatial resolution of 70- [Formula: see text] in the axial direction and 200- [Formula: see text] in the lateral direction, which are insufficient for accurate diagnosis. We report here a three-matching-layer IVUS transducer design using a 0.72Pb(Mg1/3Nb2/3O3 - 0.28PbTiO3 single crystal, which can improve the axial resolution to [Formula: see text] without sacrificing the penetration depth. Wire phantom imaging and in vitro porcine coronary artery imaging show noticeably better axial resolution and similar penetration depth compared with a commercial IVUS transducer.

Defect dynamics in clusters of self-propelled rods in circular confinement.

Rod-shaped active micro/nano-particles, such as bacterial and bipolar metallic micro/nano-motors, demonstrate novel collective phenomena far from the equilibrium state compared to passive particles. We apply a simulation approach --dissipative particle dynamics (DPD)-- to explore the collectively ordered states of self-propelled rods (SPRs). The SPRs are confined in a finite circular zone and repel each other when two rods touch each other. It is found that for a long enough rods system, the global vortex patterns, dynamic pattern oscillation between hedgehog pattern and vortex pattern, and hedgehog patterns are observed successively with increasing active force Fa. For the vortex pattern, the total interaction energy between the rods U is linear with active force Fa, i.e., U ∼ Fa . While the relation U ∼ Fa2 is obtained for the hedgehog structure. It is observed that a new hedgehog pattern with one defect core is created by two ejections of polar cluster in opposite directions from the original hedgehog pattern, and then merges into one through the diffusion of the two aggregates, i.e., the creation and annihilation of topological charges.