Regulatory effect of vascular endothelial growth factor on blood spinal cord barrier in presyrinx state of experimental syringomyelia

BACKGROUND： Vascular endothelial growth factor （VEGF） is able to regulate blood spinal cord barrier function as well as influence neovascularization and cause edema. OBJECTIVE： Through establishment of a rabbit model of syringomyelia, to explore the correlation between VEGF protein and mRNA expressions and function of blood spinal cord barrier and edema degree of spinal cord in presyrinx state. DESIGN, TIME AND SETTING： Randomized controlled animal study was performed in the Tumor Institute of the Fourth Hospital, Hebei Medical University from January to June 2007. MATERIALS： Atotal of 0.6 mL Kaolin solution （250 g/L, 37℃） was injected into the cisterna magna of 40 rabbits in the kaolin group to establish syringomyelia models. Goat anti-rabbit VEGF monoclonal antibody was provided by DIACLONE Company, USA; RT-PCR related reagents were provided by Huamei Bioengineering Co., Ltd., Beijing. METHODS： Sixty Chinese white rabbits were divided randomly into two groups： Kaolin group （n = 40） and control group （n = 20）. Physiological saline （0.6 mL at 37℃） was injected in rabbits of control group. On days 1,3, 7, 14 and 21 after kaolin injection, cervical cords samples were harvested after sacrifice of animal. MAIN OUTCOME MEASURES： VEGF protein and mRNA expressions were detected by immunohistochemistry and RT-PCR on days 1, 3, 7, 14, and 21 after kaolin injection. A quantitative analysis of blood spinal cord barrier function was performed by Evans blue technique. Water content of the spinal cord was measured by dry-wet weight technique. The correlation between the expression of VEGF protein and mRNA and the function of blood spinal cord barrier in the upper cervical cord of the presyrinx state was analyzed by linear correlation analysis. RESULTS： The water content and Evans blue content increased in the kaolin group on days 1 and 3 postoperatively compared with the control group （F = 7.387, 61.35, P 〈 0.05, 0.01）, and reached a peak on day 7 （F = 135.94, 528.35, P 〈 0.01）. They declined slowly to day 21 postoperatively, but both contents were still higher than the control group （F = 11.51, 58.63, P 〈 0.01）. VEGF protein expression increased on day 1, and stronger positive expression was seen on days 3, 7 and 14. It decreased on day 21. VEGF protein expression was higher than the control group at each time point （F = 137.4-468.5, P 〈 0.01 ）. VEGF mRNA expression showed the same pattern in the cervical cord at different time points. By statistical analysis, the expression of VEGF protein and mRNA had a significantly positive correlation with the structural and functional changes of the blood spinal cord barrier in the presyrinx state （r = 0.604-0.979, P 〈 0.05）. CONCLUSION： In the presyrinx state of syringomyelia, the expressions of VEGF protein and mRNA can influence the structure and function of the blood spinal cord barrier and play an important role in the formation and development of spinal cord edema and syringomyelia.

Improved piezoelectric and luminescent properties in Sm-modified Bi_(0.5)Na_(0.5)TiO_(3)-BaTiO_(3) multifunctional ceramics

The 0.93(Na_(0.5)Bi_(0.5))_(1–x)Sm_(x)TiO_(3)-0.07BaTiO_(3) multifunctional ceramics were prepared by solid-phase reaction method.The phase structure,microstructure,electrical and photoluminescent properties were systematically studied.With increasing x,the ceramics undergoes the phase transition from rhombohedral to tetragonal with some rhombohedral distortion,along with a reduced grain size and increased relative density.On the other hand,the Sm3+doping enhances the electric-field driven reversible phase transition and domain size,and reduces the domain walls,thereby contributing to improved piezoelectricity and decreased depolarization temperature(T_(d))from 91℃ to 40℃.Excellent piezoelectric properties of d_(33)=213 pC/N and kp=29.9% are achieved in the x=0.010 ceramic.Under excitation(407 nm),the Sm^(3+)-doped ceramic exhibits bright reddish-orange fluorescence at 564,599,646 nm and 710 nm.A polarization-induced enhancement of photoluminescence is obtained in BNBT-_(x)Sm ceramics with an improved relative intensity of emission band at 646 nm.These results indicate that Sm^(3+)-doped BNBT ceramics show great potential in electro-optic integration and coupling device applications.

Improving high-field strain and temperature stability on KNN-based ceramics sintered in reducing atmosphere via defect engineering

High-field strain and its temperature stability of(1-x)K_(0.48)Na_(0.52)Nb_(0.96)Ta_(0.04)O_(3)-xBaZrO_(3)+8%MnO+3%ZrO_(2)(in mole,KNNT-xBZ+8Mn)ceramics sintered in reducing atmosphere are improved simultaneously via defect design in A and B site.There is a conducting type transition from n-type to p-type at x=0.07.The BaZrO_(3) dopant not only induces the increase of defects(Zr′_(Nb),Ba_(Na),Ba_(K))concentration,but also results in the increase of defect(Mn″_(Nb))concentration,because more Mn ions as+2 oxidation state in ceramics is triggered by BaZrO3 doping modifcation.Defect dipoles(Mn″_(Nb)-V_(o),Zr′_(Nb)-V_(o),Ba_(Na)-V′_(Na),Ba_(Na)-V′_(Na))in poled and aged ceramics enhance the reversibility of the non-180°domains switching,which increases the high-field strain of KNNT-xBZ+8Mn ceramics.The reversibility of non-180°domain switching can be preserved to high temperature due to stable defect dipoles(Ba_(Na)-V′_(Na),Ba_(K)-V′_(K))in A-site.The KNNT-xBZ+8Mn ceramics at x=0.07 show the largest high-field strain coefficient(543 pm/V@20 kV/cm)and the highest temperature stability(125℃).The KNNT-xBZ+8Mn ceramic is a lead-free material with great potential to be applied in the fabrication of multilayer ceramic actuators with Ni inner electrodes in the future.

Enhanced piezoelectric properties and thermal stability of Bi_(0.5)Na_(0.5)TiO_(3)modified BiFeO_(3)-BaTiO_(3)ceramics with morphotropic phase boundary

Morphotropic phase boundary(MPB)plays a key role in tuning piezoelectric responses of ferroelectric ceramics.Here,Bi_(0.5)Na_(0.5)TiO_(3)modified BiFeO_(3)-BaTiO_(3)ternary solid solutions of 0.7BiFeO_(3)-(0.3-x)BaTiO_(3)-xBi_(0.5)Na_(0.5)TiO_(3)(referred to as BF-BT-xBNT,0.00≤x≤0.04)were prepared for lead-free piezo-electrics.All the ceramics exhibit an MPB with coexisting rhombohedral(R)and tetragonal(T)phases,and the R/T phase ratio decreases upon increasing x.The increment of BNT promotes the grain growth,lowers the leakage current and Curie temperature(TC),and gradually drives the ferroelectric to relaxor transition.Because of the MPB with appropriate R/T phase ratio,increased grain size and density,and decreased leakage current,the well-balanced performance between d_(33)=206 pC/N and TC=488℃is obtained in x=0.01 case.In addition,the further enhanced in-situ d_(33)=286e347 pC/N is obtained in BF-BT-xBNT ceramics along with the improved depolarization temperature T_(d)from 280 to 312℃,showing a potential application for lead-free piezoceramics at high temperature.

Progress and perspective of high strain NBT-based lead-free piezoceramics and multilayer actuators

In this review,the evolution of high strain Na_(0.5)Bi_(0.5)TiO_(3)-based lead-free piezoceramics and their multilayer actuators has been explored.First,in terms of Na_(0.5)Bi_(0.5)TiO_(3)-based ceramic materials,the origin of high strain,the typical chemical modification methods of obtaining large strain and extrinsic factors affecting the large strain are discussed.Then it briefly summarizes the problems existing in Na_(0.5)Bi_(0.5)TiO_(3)-based ceramics for multilayer actuator applications.Strategies to optimize strain performance by means of microstructure control and phase structure design are also discussed.Thereafter,in terms of multilayer actuator,we describe its characteristics,applications and preparation process systematically,as well as the recent development of Na_(0.5)Bi_(0.5)TiO_(3)-based multilayer actuator.At last,perspectives on directions of following work and promising fields for the applications of the materials and their devices are presented.

Microstructures and microwave dielectric properties of (Ba1-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 solid solutions

(Bal-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 (x=0.02,0.04,0.06,0.08,0.1) solid solutions were prepared by the conventional solid-state reaction process.It was found that (Ba1-xSrx)4(Sm0.4Nd0.6)28/3 Ti18O54 ceramics are fully composed of BaSm2Ti4O12 and BaNd2TisO14 phases for all the compositions.The increasing x value (0.02 ≤ x ≤ 0.1) in (Ba1-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 ceramics can not only obtain high Q ×f value but also effectively enhance the permittivity (εr).The (Ba1-xSrx)4(Sm0.4Nd0.6)28/3Ti18O54 ceramic with x=0.08,sintered at 1440 ℃ for 4 h,shows excellent microwave dielectric properties of permittivity (εr) ≈ 93.19,quality factor (Q × f) ≈ 9770.14 GHz (at 3.415 GHz),and almost near-zero temperature coefficient of resonant frequency (rf)≈ +4.56 ppm/℃.

Effects of thermal and electrical histories on structure and dielectric behaviors of(Li_(0.5)Nd_(0.5))^(2+)-modified(Bi_(0.5)Na_(0.5))TiO_(3)-BaTiO_(3) ceramics

The effect of thermal and electrical histories on structure and dielectric behaviors is studied using 0.95(Bi_(0.5)Na_(0.5))_(0.97)(Li_(0.5)Nd_(0.5))_(0.03)TiO_(3)-0.05BaTiO_(3)(abbreviated as BNTLN0.03-BT5)ceramic as a selected system.Subtle structure change caused by annealing treatment,and pronounced phase transition and domain switching by electrical poling,are observed to occur,respectively.The dielectric constant and its strong frequency dispersion in unpoled samples decrease evidently by electrical poling due to electric field-induced ordered domain.The high temperature Maxwell-Wagner relaxor behavior vanishes by annealing treatment due to the loss of electrical inhomogeneity with interface charging effects.Piezoelectric properties are improved evidently by annealing treatment at 900℃,implying a new appropriate method to improve piezoelectric properties.

Photocurrent density and electrical properties of Bi_(0.5)Na_(0.5)Ti0_(3)-BaNi_(0.5)Nb_(0.5)0_(3) ceramics

In this work,the (1-x)Bi_(0.5)Na_(0.5)TiO_(3)-xBaNi_(0.5)Nb_(0.5)O_(3)(BNT-BNN;0.00≤x≤ 0.20)ceramics were prepared via a high-temperature solid-state method.The crystalline structures,photovoltaic effect,and electrical properties of the ceramics were investigated.According to X-ray diffraction,the system shows a single perovskite structure.The samples show the normal ferroelectric loops.With the increase of BNN content,the remnant polarization(P_(r))and coercive field(E_(c))decrease gradually.The optical band gap of the samples narrows from 3.10 to 2.27 eV.The conductive species of grains and grain boundaries in the ceramics are ascribed to the double ionized oxygen vacancies.The open-circuit voltage(V_(∝))of ~15.7 V and short-circuit current(J_(sc))of ~1450 nA/cm^(2) are obtained in the 0.95BNT-0.05BNN ceramic under 1 sun illumination(AM1.5G,100 mW/cm^(2)).A larger V_(∝) of 23 V and a higher J_(sc) of 5500 nA/cm^(2) are achieved at the poling field of 60 kV/cm under the same light conditions.The study shows this system has great application prospects in the photovoltaic field.

Dielectric behaviors and relaxor characteristics in Bi_(0.5)Na_(0.5)TiO_(3)-BaTiO_(3) ceramics

Microstructure and dielectric behaviors of heating/cooling and bias-field were investigated in lead-free ceramics(1-x)Bi_(0.5)Na_(0.5)TiO_(3)-xBaTiO_(3)(BNT-xBT,x=0,0.02,0.04,0.06,0.08 and 0.10).The relaxor characters and the Vogel–Fulcher law of frequency-dependent dielectric properties were analyzed.Three dielectric anomalies with pronounced frequency dispersion at Td,a maximum dielectric with variable frequency-dispersion at Tm and a third Maxwell–Wagner-type relaxation over a wide temperature range in high-temperature region were observed.The significant dielectric thermal hysteresis,low barrier energy,high freezing temperature in heating process and the maximum dielectric tunability appeared in x=0.4 ceramic.

Enhanced energy storage properties of Bi0.5Li0.5TiO3 modified Sr0.1Bi0.45Na0.45TiO3 based ceramics

Lead-free (1-x)Sr0.1Bi0.45Na0.45TiO3-xBi0.5Li0.5TiO3 (x = 0-0.4) ceramics were successfully prepared by a solid-state reaction technique. The effects of amount of Bi0.5Li0.5TiO3 on structure and electrical properties were examined. The X-ray diffraction (XRD) analysis revealed that all the investigated specimens have a perovskite structure. An obvious change in microstructure with the increase of Bi0.5Li0.5TiO3 concentration was observed. This study demonstrated that relaxor could be stabilized in Sr0.1Bi0.45Na0.45TiO3 based ceramics by lowering the tolerance factor and electronegativity difference. Besides, a dielectric anomaly related to thermal evolution of crystallographic symmetry was emerged at the depolarization temperature. Upon incorporation of 26 mol% Bi0.5Li0.5TiO3, the specimens were able to withstand an electric field intensity of 106.9 kV/cm with an energy density of 0.88 J/cm(3) and an energy efficiency of 65%.

A new insight into structural complexity in ferroelectric ceramics

The structure of the ferroelectrics has been widely studied in order to pursuing the origin of high electromechanical responses. However, some experiments on structure of ferroelectrics have yielded different results. Here, we report that the controversial phase structure is due to the adaptive diffraction of nanodomains which hides the natural crystal structure, and the electric-field-induced phase transition is that the natural crystal structure reappears due to the coalescent nanodomains or ordering nanodomains by applying a high electric field. The temperature dependence of dielectric constant with different measurement frequencies and X-ray diffraction (XRD) patterns of unpoled, poled, and annealing after poled ceramics in Bi0.5Na0.5TiO3–BaTiO3 (BNT–BT) ceramics authenticate the statement. These results provide a new insight into the origin of structural complexity in ferroelectric ceramics, which is related to the key role of nanodomains.