In this paper, the refined plate theory (RPT), Hamilton’s principle, and isogeometric analysis (IGA) are applied to investigate the static bending, free vibration and buckling behaviors of functionally graded graphene-platelet-reinforced piezoelectric (FG-GRP) plates resting on a Winkler elastic foundation. The graphene platelets (GPLs) are distributed in polyvinylidene fluoride (PVDF) as a power function along the plate thickness direction to generate functionally gradient materials (FGMs). The modified Halpin–Tsai parallel model predicts the effective Young’s modulus of each graphene-reinforced piezoelectric composite plate layer, and the rule of the mixture can be used to calculate the effective Poisson’s ratio, mass density, and piezoelectric properties. Under different graphene distribution patterns and boundary conditions, the effects of a plate’s geometric dimensions, GPLs’ physical properties, GPLs’ geometric properties and the elastic coefficient of the Winkler elastic foundation on deflections, frequencies and bucking loads of the FG-GRP plates are investigated in depth. The convergence and computational efficiency of the present IGA are confirmed versus other studies. Furthermore, the results illustrate that a small amount of GPL reinforcements can improve the FG-GRP plates’ mechanical properties, i.e., GPLs can improve the system’s vibration and stability characteristics. The more GPL reinforcements spread into the surface layers, the more effective it is at enhancing the system’s stiffness. Functionally gradient materials (FGMs), first developed in 1987, are composite materials with two or more distinct phases. FGMs provide designers with a range of options to distribute strength and stiffness in an appropriate manner ,3,4. NovOn the other hand, piezoelectric ceramic, one kind of smart material, has excellent electro-mechanical coupling behaviors. Piezoelectric sensors can convert mechanical energy to electrical energy, making them beneficial in civil engineering, automotive and aerospace . With th1-continuity of the displacement fields, which presents challenges to the traditional finite element analysis (FEA) framework [1-continuity of displacement fields required by RPT. In recent years, researchers have frequently used IGA to analytically calculate the mechanical properties of functionally graded composites. On the basis of IGA and TSDT, Kiani et al. [Many scholars have proposed theoretical models that combine shear deformation theory  with varramework . Furtherramework  originalramework ,44, T-spi et al. ,46 invesi et al.  utilizedi et al.  combinedi et al.  investigTo the best of the authors’ knowledge, no literature is available for the analysis of functionally graded graphene-platelet-reinforced piezoelectric structures based on isogeometric analysis. As a result, the purpose of this work is to investigate the static bending, free vibration and buckling behaviors of functionally graded graphene-platelet-reinforced piezoelectric plates embedded on a Winkler elastic foundation using isogeometric analysis and refined plate theory. The object of this paper is to development isogeometric analysis of graphene-reinforced functionally gradient piezoelectric plates resting on Winkler elastic foundations. This paper is organized as follows. In a, width b, and thickness h on Winkler elastic foundation is established. The FG-GRP plate is supposed to be made of a multi-layer polymer composite reinforced by graphene platelets, where the GPL reinforcements are functionally graded along the thickness direction with a power law distribution. Furthermore, the thickness of each independent layer may be described as As illustrated in In this research, three graphene distribution patterns are generated by smoothly varying the graphene volume fractions along the thickness direction, as shown in The total graphene volume fraction is expressed as k-th layer of the FG-GRP plate can be written as follows:The volume fraction in the The U type:The X type:The O type:k-th layer asG and M symbolize graphene platelet and matrix material, and As demonstrated by Layek et al. , GPL reik-th layer may be predicted byFurthermore, the effective material properties, such as Poisson’s ratio, density, piezoelectric constant, and dielectric constant for the The displacement fields The in-plane strain and transverse shear strains corresponding to the displacement fields are shown ask-th layer constitutive relationship is represented asAccording to the generalized Hooke’s law, the For the FG-GRP plate, the constitutive equation is expressed asAccording to Equations (9)–(13), the FG-GRP plate’s mid-plane internal force The internal force The Galerkin weak form of the governing equations is calculated using the Hamilton principle .(18)δ∫tn and p denote the ith knot, the number of basic functions, and the polynomial order, respectively.The main elements of the B-spline curve are a set of control points According to the Cox–de Boor recursive formula , the B-sIt should be noted that the ratio 0/0 in the preceding Equation (20) is given as zero.The B-spline basis function is mostly made up of specified spline basis function orders and related knot vectors, and its expression is expressed as follows:The B-spline function can be a particular case of the NURBS function when weights of control points are constant. The bi-variate NURBS basis functions are written asThe NURBS spline surfaces are defined by supplying knot vectors and control points in two parameter directions, and the derivative of IP.By adopting the NURBS basis functions, the approximate mechanical displacement field Taking Equation (25) into Equation (9) yieldsith sublayer,After approximating the potential field, the system can be discretized into several sublayer elements along the thickness direction . The appHere, assuming that each individual piezoelectric layer has the same potential at the same height, we may obtain the electric field of each sublayer unit by substituting Equation (28) into Equation (13).U is the applied voltage to the upper and lower surfaces.The governing equation of motion of the FG-GRP plate can be found by inserting Equations (12), (26) and (30) into Equation (18):The element stiffness matrix for buckling analysis can be represented as:The edges of the FG-GRP plate are subjected to a uniaxial load and biaxial loads, as shown in To evaluate the impact of the Winkler elastic foundation, the additional matrix Eliminating the potential and assembling elements, the governing equations of FG-GRP are represented as:The governing equations for static analysis, free vibration and buckling behaviors are obtained as followsIn this section, static analysis, free vibration and buckling behaviors of FG-GRP plates on Winkler elastic foundation are investigated by isogeometric analysis. Unless otherwise specified, an FG-GRP plate with geometric size multiple . Furthermultiple  are:EgplThe following dimensionless formula is used in this paper unless otherwise specified:Firstly, the convergence of the IGA technique is examined by adopting Firstly, the FG-GRP plates are modelled with 7 × 7, 11 × 11 and 19 × 19 control points as shown in o et al. . It can N, more GPL reinforcements are spread on both sides of the plate to enhance the stiffness of the system. While for the other one, the O type plays opposite roles on the stiffness and dimensionless central deflections. Simultaneously, with increasing the number of layers N, the percentage deflection changes corresponding to the X and O types gradually converge when The effective material properties for the composite are determined by the length and thickness of the graphene reinforcements but have nothing to do with the width in Halpin Tsai’s parallel model . AssuminThe impact of the Winkler elastic coefficients In what follows, the influence of detailed parameters on free vibration analysis for an FG-GRP plate with As shown in The effect of the Winkler elastic coefficient on the dimensionless vibration frequencies of the FG-GRP plate is shown in To explore the impact of detailed parameters on the buckling behaviors, the uniaxial or biaxial in-plane forces must be applied to the piezoelectric plates.x and y directions is loaded from four directions, limiting the load it can carry. Next, the normalized critical buckling load The impact of the length-to-width ratio Isogeometric analysis integrated with the refined plate theory is utilized in this paper to analyze the static bending, free vibration and buckling behaviors of functionally graded graphene-platelet-reinforced piezoelectric plates on Winkler elastic foundations. When Hamilton’s principle is combined with isogeometric analysis, the isogeometric finite element governing equations of the functionally graded graphene-platelet-reinforced piezoelectric plate are obtained on the basis of the refined plate theory. Comparisons with other studies validate the accuracy and convergence of the present isogeometric analysis. Furthermore, the influences of a plate’s geometrical parameters, the elastic coefficient, and GPLs’ physical and geometric properties on the percentage change of central deflections, frequencies and critical buckling loads of a functionally graded graphene-platelet-reinforced piezoelectric plate are thoroughly investigated under different boundary conditions and graphene distribution patterns.The results of this paper indicate that adding a small amount of GPL not only decreases the central deflections, but also increases the vibration frequencies and critical buckling loads of functionally graded graphene-platelet-reinforced piezoelectric plates. Additionally, the X type represents the optimum distribution form, i.e., the higher the graphene volume fractions spread into the surface layer, the more effective it is to enhance the stiffness of the system. Additionally, increasing the graphene length-to-thickness ratio can significantly enhance system stiffness, that is, the longer and thinner the GPLs are, the more obvious the reinforcement is. In terms of a plate’s geometrical parameters, the effect of a functionally graded graphene-platelet-reinforced piezoelectric plate’s aspect ratio on central deflections, vibration frequencies and critical buckling loads should be handled differently depending on the graphene distribution pattern. For the X type, increasing the aspect ratio or plate surface area can improve system stiffness. In terms of the impacts of boundary conditions on the system, the stiffness of the functionally graded graphene-platelet-reinforced piezoelectric plate under the CCCC boundary condition is the highest one, followed by CCSS, CSSS, and SSSS. Furthermore, the dimensionless critical buckling load subjected to the uniaxial force is approximately twice as large as that subjected to the biaxial force. Effectively increasing the elastic coefficient of the Winkler elastic foundation can obtain a remarkable reinforcement effect on the plate stiffness.


In addition, this pressure sensor has excellent durability (>2000 cycles) and shorter response times (490 ms), which has broad research prospects in human health detection and motion detection.With the improvement of science and technology, flexible sensors have become a hot research topic. Flexible sensors have broad application in human health detection and motion detection and other fields. In this paper, the silk fibroin/graphene nanofiber membranes were prepared by double needle electrospinning. In addition, the high sensitivity of the three-dimensional composite hierarchy was obtained by superimposing a monolayer silk fibroin/graphene nanofiber membrane, which was prepared via double needle electrospinning. In addition, the three-dimensional hierarchy was encapsulated by polydimethylsiloxane to prepare a pressure sensor. The sensitivity of the pressure sensor can achieve 7.7 Pa The sensor is very crucial as a man–machine interaction interface . The phy−1) and a wide operating range (0–20 kPa). The strain sensor showed excellent sensitivity (strain coefficients 22.6–83.7) and 27% large working strain.Graphene (Gr), a two-dimensional carbon material which consists of a single layer of SP  carbon aSilk is a natural protein fiber, which possesses unique combined merits such as programmable biodegradability, good biocompatibility, and large-scale sustainable production. Compared with other biocompatible and biodegradable biomaterials, such as polycaprolactone (PCL), polylactic acid (PLA), poly(lactic-co-glycolic acid) (PLGA), etc., silk is a natural protein and is easy to obtain at a low cost. However, for natural biomaterials, silk has good regenerative properties and can be processed into various forms of materials . Thus, sElectrospinning is a common technique for preparing nano-sized fibers. Electrospinning is possibly not as new as forcespinning (FS) or the centrifugal spinning method for the fabrication of nanofibers. However, the electrospinning technology is more mature and reliable. Furthermore, the prepared nanofibers are more uniform. In addition, the fiber orientation is adjustable . Thus, i3CH2OH  was obtained from Chuandong Chemical Co. Ltd., Chongqing, China. Polyvinylpyrrolidone  was obtained from Aladdin Chemical Co. Ltd., Shanghai, China.Silk fibroin extracted from silkworm cocoons provided by the Southwest University. 1,1,1,3,3,3-Hexafluoro-2-propanol  was obtained from Aladdin Chemical Co. Ltd., Shanghai, China. Graphene , was obtained from Aochuang technology Co. Ltd., Shenzhen, China. CH2CO3 (0.05 wt%) for 30 min each time. Then, they were washed with deionized water to remove the sericin before drying. Silk fibroin fibers were dissolved in CaCl2/EtOH/H2O solution . After 5 days of dialysis, the SF solution was centrifuged at 8000 r/min for 10 min. Then, the desired SF solids were obtained by freeze-drying SF solution at −40 °C. The preparation process is shown in The cocoons were cut into pieces and boiled twice in NaThe weight of 3.2 g silk fibroin was dissolved in 20 mL of HFIP. Electrospinning solution A was obtained. The optimal dispersion ratio of graphene and PVP is 1:3 (As shown in Twenty milliliters of solution A (SF/HFIP) and 20 mL of solution B (Gr/PVP/ethanol) were put into two syringes for electrospinning at the same time. The distance between the syringe needle and the roller was 15 cm, and the syringe was propelled at a speed of 2.0 mL/h. Voltage parameters have positive voltage of 20 KV and negative voltage of 2 KV, respectively. The preparation process is shown in The production process of SF/Gr sensor was divided into three steps. The first step was to extract silk fibroin from a silkworm cocoon. Then, electrospinning solution was prepared. Graphene was poured into anhydrous ethanol. The PVP was added as a dispersant and sonication for 2 h to make graphene disperse evenly in anhydrous ethanol. Secondly, SF/Gr nanofiber membrane was prepared by electrostatic spinning. Finally, SF/Gr nanofiber membrane was encapsulated by PDMS to obtain an SF/Gr flexible pressure sensor.The surface morphology of SF/Gr nanofiber membranes was analyzed by SEM . The porosity and diameter distribution of nanofibers were analyzed using the software ImageJ  by SEM images. In addition, the water contact angle of nanofiber membranes was characterized by an Optical Contact Angle Tester . The thermostability was performed on TG 209F3 Thermogravimetric Analyzer from NETZSCH , amide II (1600–1500 cm−1), and amide III (1350–1200 cm−1), respectively. As can be seen from −1, 1517 cm−1, and 1240 cm−1. There are three characteristic peaks of PVP, which should appear in the vicinity of 1290 cm−1, 1660 cm−1 and 1463 cm−1, respectively. They are attributed to the stretching vibration of CN, C=O, and CH2 bond, respectively. As can be seen from −1. The other two characteristic peaks may not appear because silk fibroin protein has the same groups in the same position. This may lead to the fusion of the peaks. It can be seen that the addition of graphene and PVP has almost no effect on the structure of silk fibroin. Graphene has almost no activity in the infrared spectrum. It can be judged that PVP and graphene are physically bound to silk fiber.Four membranes were tested by the infrared spectrometer . Silk fiThe mechanical properties of the four nanofiber membranes are shown in S) is calculated as S = (Δ0I/I)/ΔP. I0 is the initial current of the sensor under no pressure. ΔI is the relative change of current when the sensor is subjected to pressure. ΔP is applied pressure. As shown in −1. Therefore, the SF/Gr sensor named Gr10 mg-3 was selected for follow-up research.The sensing performance of pressure sensors can be evaluated by response time, sensitivity, stability, etc. The sensitivity test system consists of two parts. The first part is the pressure applying system, which is supplied by a universal stretcher machine. The second part is an electrical signal monitoring system, which consists of an electrochemistry workstation and computer. When the SF/Gr sensor is subjected to pressure, the transmitted electrical signal changes with the change of resistance due to the deformation of the three-dimensional network structure inside the sensor. The sensitivity  of the sensor circuit consists of the volume resistance (vR) of the graphene sheet, the resistance of silk fiber and PVP fiber (GPR), and the contact resistance between the graphene sheets (CR). Copper foil is a conductive metal, and its resistance can be ignored. The calculation formula is as follows:The SF/Gr pressure sensor model is shown in the figure below. The total resistance . Therefore, it can be approximated that the change of the total resistance is caused by contact resistance of graphene. The sensor circuit can be modeled (S = (I − I0/I0)/ΔP. With the increase of graphene concentration, the graphene sheets dispersed more densely in the fiber network and the more graphene was contacted under pressure. In addition, the resistance value was decreased. The I was increased, while I0 was close to 0. Therefore, the sensitivity showed an increasing trend. The sensitivity variation trend of Gr10 mg-1, Gr15 mg-1, and Gr20 mg-1 could prove this conclusion  composite membranes were prepared by electrospinning. The morphology, porosity, water contact angle, and diameter distribution of SF/Gr nanofiber membranes were characterized. The results suggested that SF/Gr nanofiber membranes possess good mechanical properties to make into 3D flexible sensors. Thus, the graphene/silk fibroin nanofiber membrane was packaged by PDMS into a pressure sensor. The prepared SF/Gr pressure sensor has a sensitivity of 7.7 Pa


Polypropylene (PP), as a general thermoplastic polymer, is broadly used in different fields. However, the high flammability, melt dripping and poor mechanical properties of PP are a constraint to the expansion of its applications. In this paper, PP composites containing a combination of a phenethyl-bridged DOPO derivative (PN-DOPO) and organic montmorillonite (OMMT) were prepared via melt blending. The synergistic effects of PN-DOPO and OMMT on the flame retardancy, thermal stability and mechanical properties of PP composites were investigated systematically. The results showed that 20 wt% addition of PN-DOPO with OMMT improved the flame retardancy of PP composites. In particular, the introduction of 17 wt% PN-DOPO and 3 wt% OMMT increased the LOI values of the PP matrix from 17.2% to 23.6%, and the sample reached the V-0 level and reduced the heat release rate and total heat release. TGA indicated that OMMT could improve the thermal stability of the PP/PN-DOPO blends and promote the char residues of PP systems. Rheological behaviour showed a higher storage modulus, loss modulus and complex viscosity of PP/PN-DOPO/OMMT composites, suggesting a more effective network structure. In addition, the tensile strength, flexural properties and impact strength of the PP/PN-DOPO/OMMT composites actually increased for a good dispersion effect. Combined with the char layer analysis, the introduction of OMMT promoted more continuous and compact structural layers containing an aluminium–silicon barrier and phosphorus-containing carbonaceous char in the condensed phase. OMMT can improve the flame retardancy, thermal stability and mechanical properties of PP, and, thus, PN-DOPO/OMMT blends can serve as an efficient synergistic system for flame-retarded PP composites. Polypropylene (PP), a general thermoplastic, is used in automotives, buildings, transportation and electronic devices owing to its excellent electrical insulation properties, corrosion resistance, comprehensive mechanical properties and easy processability ,2,3. HowIn order to improve the fire resistance of the PP matrix, phosphorus-, silicon- or nitrogen-based flame retardants are usually added into the matrix. The intumescent flame retardants (IFR) composed of charring agents, a gas source and acid sources have attracted interest because of their anti-dripping, low toxicity, low smoke and eco-friendly characteristics ,7. NeverAmong the commercial halogen-free FRs, phosphorus-based compounds possess unique advantages, such as a high chemical resistance, the nonproduction of toxicants and no transfer. Recently, 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) and its derivatives have attracted much attention because of their excellent flame-retardant efficiency, high reaction activity and low addition ,15. DOPOOMMT can form a barrier on the surface of a polymer during combustion and can improve the physical and mechanical properties of the polymer matrix at low concentrations. Furthermore, the thermal stability of flame-retarded composites increases with the increasing OMMT amount ,27,28. WBased on our previous reports, a novel phenethyl-bridged DOPO derivative (PN-DOPO) was prepared. The effects of PN-DOPO on the flame-retardant and thermal properties of the polymeric matrix, such as polyamide, epoxy resins and polylactide, were examined ,33,34,35In this study, PP/PN-DOPO/OMMT composites were prepared through melt mixing. The synergistic flame-retarded effect, thermal stability and rheological behaviour of PN-DOPO combined with OMMT on PP was evaluated. The composition structure and morphology of char residues were investigated systematically. Furthermore, the possible synergistic effect of PN-DOPO and OMMT on the flammability and mechanical properties of flame-retarded PP were also discussed.Polypropylene resin (F401) was purchased from Yangzi Petroleum Chemical Company  with a melt flow index of 2.5 g/min . The FR, phenethyl-bridged DOPO derivatives  at 190 °C with a screw speed of 50 rpm for 6 min. The UL-94 vertical combustion test was performed according to ASTM D3801 with a sample size of 130.0 × 13.0 × 3.2 mm. The LOI values were obtained using the LOI instrument according to ASTM D2863-06. The sample dimensions were 130.0 × 6.5 × 3.2 mm. Microscale combustion calorimeter (MCC) tests were conducted using an MCC-2 instrument . The powder samples (approximately 5–7 mg) were heated from 40 °C to 650 °C at a heating rate of 1 °C/s in an aluminium crucible. The heating atmosphere is a mixture of nitrogen flowing at 80 mL/min and oxygen flowing at 20 mL/min.The thermal stability of the samples was analysed via thermogravimetric analysis (TGA)  under nitrogen atmosphere at a flow rate of 60 mL/min. Each sample (approximately 6–10 mg) was heated from 30 °C to 700 °C at 10 °C/min heating rate.The morphology of the char residues after UL-94 tests was obtained via SEM  at an acceleration voltage of 10 kV.Energy dispersive spectrometry (EDS)  was performed to characterise the chemical composition of the residues. EDS analyses were recorded on SEM equipped with an EDS accessory under high vacuum conditions at a voltage of 30 kV.−8 mbar. The C, O, P, Si and Al on the char residue of the samples were investigated.X-ray photoelectron spectroscopy (XPS)  was performed using an Al Kα source at a base pressure of 1.0 × 10The rheological behaviour of samples was analysed using a Rheometric Analyzer  using parallel plates with diameters of 35 mm. Dynamic frequency sweep tests were measured at 190 °C using 1% strain in an angular frequency range of 0.1–100 rad/s.The mechanical properties of flame-retarded PP composites were measured using a CMT6104 universal testing machine . The tensile tests were measured according to ASTM D-638 using an extensometer. The flexural tests were performed according to ASTM D-790. For each sample, the results were an average of five specimens, and the range of standard deviations was within 5%. A notched Izod impact test was experimented using a pendulum impact tester  according to ASTM D-256.1 and t2 in the UL-94 test decreased gradually with increasing PN-DOPO content. Dripping was no longer observed when the PN-DOPO content was 15 wt%, and a UL-94 V-1 rating was attained. For PP/20 wt% PN-DOPO, the LOI value increased to 23.1% and attained a UL-94 test V-0 rating. The improvement in the flame retardancy of PP/PN-DOPO composites was apparent in the UL94 and LOI flammability test. This behaviour is mainly attributable to the principal gas phase activity of the DOPO derivatives [The UL-94 test and LOI measurement are widely used to evaluate the flame retardancy of polymers. ivatives .OMMT was incorporated into the PP/PN-DOPO composites to improve the flame-retardancy efficiency further and decrease the need for high loadings (20 wt%). The loading of PN-DOPO/PMMT compounds was maintained at 20 wt% in the PP samples. When 1 wt% and 3 wt% OMMT replaced the same content of PN-DOPO, respectively, the V-0 rating was reached, and the variation in LOI values was not evident. With increases in the OMMT amount, the UL-94 rating of V-1 was achieved for both PP-7 and PP-8. Moreover, the LOI values were slightly increased to 24.0% and 23.8%, respectively, which were higher than that of PP-3. However, for only 7 wt% OMMT content, the LOI value of PP-9 was 20.3%, and no rating was reached.As shown in pHRR), could be obtained from MCC tests [The MCC test is an effective method to investigate the combustion properties of polymers. The combustion behaviour of PP composites was analysed using MCC tests. Some important parameters, such as the specific HRR, total heat release (THR) and temperature of peak HRR  originated mainly from the P–O and P=O bonds. From the spectrum of PP/7%OMMT, the C1s spectra featured two bands with binding energies of 284.6 and 285.7 eV. For O1s spectra, the 532.3 eV peak can be attributed to the –O– bond. The 533.6 eV binding energy was ascribed to the C=O groups in carbonyl compounds. A single peak at 102.8 eV in the Si2p spectrum was assigned to the Si–O bond in clay platelets. The Si–O–Si structure generally acts as an enhanced framework for char formation and provides a synergistic effect on flame-retarded composites [XPS can be used to examine the chemical structure of char residues. The composition of residues was also characterised by XPS. ectively ,50. The mposites .1s spectra have three bands with binding energies of 284.7, 285.7 and 288.1 eV. The 284.7 and 285.7 eV peaks were assigned to the C–H or C–C groups and C–O group, respectively. Furthermore, the binding energies of 288.1 eV can be attributed to the C=O or carbonyl groups [From the spectrum of PP/17%PN-DOPO/3%OMMT, the Cl groups . Hence, Overall, XPS confirmed that the hybrid of phosphorus-, silicon- and aluminium-containing compounds could promote a more continuous and compact char layer. The char layer can effectively decelerate the mass and heat transfer between the solid and gas phases. In this case, the PP/PN-DOPO/OMMT composite exhibited a synergistic flame-retardant effect on char formation.The influence of the melt flow characteristics on the combustion behaviour of flame-retarded composites’ nanoclay-containing and phosphorus-containing FRs was investigated ,52. The Similar trends are observed in the complex viscosity of PP and flame-retarded PP composites . The visBased on the above results, the possible synergistic flame-retardant effect between OMMT and PN-DOPO can be discussed as follows. For pure PP, it burnt out without leaving any char residue, accompanied with vigorous dripping during combustion. For PP/PN-DOPO blends, the char residue of the sample with broken holes and many voids in the cavity structure was observed owing to gas phase quenching at the initial stage of combustion ,31. WithThe mechanical properties were investigated to evaluate the effects of OMMT/PN-DOPO compounds on PP. The mechanical properties of composites depend on the compatibility of the fillers within the matrix. This OMMT layer and flame retardant played a reinforcing role in PP composites. Additionally, the tensile strength and flexural property of composites were improved  with theIn conclusion, when OMMT and PN-DOPO were applied to flame-retarded PP, the composites imparted a presented significant synergistic flame-retardant effect on the combustion behaviour, melt viscosity, thermal stability and char formation. In addition, they also enhanced the mechanical properties, such as tensile strength, flexural properties and impact strength, compared with the PP/PN-DOPO system.Different ratios of PN-DOPO combined with OMMT were blended into PP to improve the flame retardancy of the samples. The effects of PN-DOPO/OMMT compounds on the flame retardancy, thermal stability and mechanical properties of the composites and the char morphology of the samples after burning were investigated systematically. When adding 17%PN-DOPO and 3%OMMT, the LOI value for PP/PN-DOPO/ OMMT composites increased to 23.6%, and the UL-94 test reached the V-0 level. The pHRR and THR values of the sample were reduced by 27.5% and 13.0%, respectively, compared with those of PP. TGA showed that the combination of PN-DOPO and OMMT could improve the thermal stability and the content of residues of the PP systems. PN-DOPO/OMMT blends could promote a more continuous and compact structural layer with a high yield of the aluminium–silicate barrier and phosphorus-containing carbonaceous compounds. Furthermore, the PP/PN-DOPO/OMMT composites showed higher tensile strength, flexural properties and impact strength than those of the GFPA6T/PN-DOPO mixtures. In summary, OMMT can be a highly effective and promising synergistic agent to improve the flame retardancy and mechanical properties of flame-retarded PP composites.


Graphene is one of the most promising two-dimensional nanomaterials with broad applications in many fields. However, the variations and fluctuations in the material and geometrical properties are challenging issues that require more concern. In order to quantify uncertainty and analyze the impacts of uncertainty, a stochastic finite element model (SFEM) is proposed to propagate uncertainty for carbon atomic interactions under resonant vibration. Compared with the conventional truss or beam finite element models, both carbon atoms and carbon covalent bonds are considered by introducing plane elements. In addition, the determined values of the material and geometrical parameters are expanded into the related interval ranges with uniform probability density distributions. Based on the SFEM, the uncertainty propagation is performed by the Monte Carlo stochastic sampling process, and the resonant frequencies of graphene are provided by finite element computation. Furthermore, the correlation coefficients of characteristic parameters are computed based on the database of SFEM. The vibration modes of graphene with the extreme geometrical values are also provided and analyzed. According to the computed results, the minimum and maximum values of the first resonant frequency are 0.2131 and 16.894 THz, respectively, and the variance is 2.5899 THz. The proposed SFEM is an effective method to propagate uncertainty and analyze the impacts of uncertainty in the carbon atomic interactions of graphene. The work in this paper provides an important supplement to the atomic interaction modeling in nanomaterials. Graphene is a two-dimensional nanomaterial with promising potential in a wide range of applications. The quantitative analysis methods for the extraordinary properties of graphene mainly include both the experimental and numerical aspects . CompareThe finite element method has long-term development in terms of nonlinear problem solutions, parallel computing, dynamic motion modeling, etc. . The higIn this paper, the stochastic finite element model (SFEM) is proposed for resonant frequency computation and uncertainty propagation. Both the carbon atoms and the carbon covalent bonds are taken into consideration. The method descriptions, including geometrical configuration, material parameters, and computational method, are presented in According to the experimental measurements and observations, the periodic honeycomb lattice of graphene is presented in The assumptions and characteristics of the advanced finite plane element model of graphene are as follows.(a)The finite plane element model projects the precise three-dimensional structure in (b)The finite plane element model is an advanced method with a similar computational competence to the truss and beam finite element model of graphene, as shown in (c)L, 1R, and 2R are the length of the carbon covalent bonds, the radius of the carbon atoms, and twice the width of the carbon covalent bonds, respectively;The related geometrical parameters in the finite plane element model presented in (d)Since the carbon atoms and carbon covalent bonds in graphene are described as different geometrical components, the corresponding material parameters can be assigned to them;(e)The carbon atoms and carbon covalent bonds, as presented in L, 1R, and 2R are equal to 0.27 nm, 0.05 nm, and 0.032 nm, respectively. The typical examples are provided according to the changes in related geometrical parameters. For example, when L is as short as 0.1 nm, the period characteristic hexagon in graphene is presented in L is extruded to 0.4 nm, the period characteristic hexagon in graphene is presented in 2R also evidently impacts the configuration of the period hexagon cell in graphene and then influences the entire intrinsic lattice description. In 2R equals 0.01 nm and 0.04 nm, respectively. Therefore, the proposed geometrical configuration of the finite plane element is flexible to represent different shapes and combinations.In the initial geometrical model of graphene, the values of In addition to the related geometrical parameters in the finite plane element model of graphene, the material parameters are listed in E1 and P1 are presented in R1 and L are presented in The Monte Carlo stochastic simulation propagates the uncertainty of the parameters in the specific value intervals according to the uniform distribution. As presented in The plane element used in the finite element model of graphene is a two-dimensional 8-node quadrilateral element, as shown in u represents the displacement. The fundamental equations are derived from the element formulations and based on the principle of virtual work [ijσ is the Cauchy stress component, V and s are the volumes of the deformed body and the surface of the deformed body on which tractions are prescribed, respectively.The shape functions of the two-dimensional 8-node quadrilateral element in the finite plane element model are expressed as,ual work ,(2)∫vσiW can be indicated by:The internal virtual work Element formulations are obtained by differentiating this virtual work expression. In derivation, only linear differential terms are kept, and all higher-order terms are ignored, so that finally a linear set of equations can be obtained. In addition, the material constitutive law is used to create the relationship between stress increment and strain increment.Therefore, the Cauchy stress rate is:iv is the velocity and ix is the coordinates.According to the constitutive law, the stress change due to straining can be expressed as:The Cauchy stress rate can be written as:The hydrostatic pressure The competitive merits of the finite element model used for the numerical investigation of graphene are the economics of computational cost and feasibility of computation of a massive number of atoms. The resonant frequency computation by the finite plane element model based on Monte Carlo stochastic simulation is programmed in the following flowchart.As shown in Based on the Monte Carlo simulation, the stochastic sampling is performed within the specific interval ranges of the geometrical and material parameters, and the statistical results are presented in Compared with the reported results, the mean values of the resonant frequency of the first vibration mode are evidently larger than the expected value. However, it is worth noting that the minimum resonant frequency of the first vibration mode is as small as 0.2131 THz. In addition, the maximum resonant frequency of the first vibration mode is extended to 16.894 THz. Therefore, the results in the reported references ,21,22,23In order to describe the results more exactly, the probability density distributions of the resonant frequency of the stochastic samples are also presented in the histograms with the fitting curves, as shown in 1R, 2R, and L are the more critical factors to impact the resonant frequency of graphene. In other words, the length and the width of the carbon covalent bonds are essential in the finite plane element model of graphene. This consequence reaches good agreements with the assumption of the reported beam or truss finite element model of graphene [The correlation coefficients of geometrical and material parameters in the finite plane element model of graphene are computed by the Pearson and Spearman methods, as presented in graphene ,11,23. In addition, the widths of the carbon covalent bonds have positive correlation coefficients, while the lengths of the carbon covalent bonds present negative values. For the negative correlation coefficients, the Young’s modulus of carbon atoms in 1R, 2R, and L in 1E and 2E in 1V, 2V, 1P, and 2P present evident variations in Furthermore, the Young’s modulus of carbon covalent bonds has more evident impacts on resonant frequency than that of carbon atoms in In addition to the resonant frequency of graphene, the vibration modes are also computed by the finite plane element model of graphene. According to the above results, the length and width of the carbon covalent bonds are the more important factors influencing the resonant frequency of graphene. The extreme values of the geometrical parameters are introduced in the finite plane element model of graphene to compare the vibration modes. The differences in the vibration modes of the first four resonant vibration modes are presented and compared, as presented in Furthermore, the resonant vibration modes in The proposed stochastic finite plane element model of graphene is an effective alternative to the currently available approaches with competitive competencies in terms of computational performances and result consistency. In short, the following key points can be concluded based on the results.(1)The commonly shared nodes in carbon atoms and carbon covalent bonds in the two-dimensional 8-node quadrilateral element keep the geometrical connection and mechanical compatibility well.(2)The interval ranges of resonant frequencies computed by the finite plane element model completely include the results in the reported literature.(3)The correlation coefficients computed by the Pearson and Spearman methods have substantial agreements with small discrepancies in the geometrical and material parameters.(4)The length and the width of the carbon covalent bonds in the finite plane element model of graphene are the essential factors that impact the resonant frequencies.(5)The proposed finite element model not only has merits in terms of computational expense and feasibility in the massive stochastic sampling process but also is flexible in presenting the precise vibration modes of graphene with consideration of both carbon atoms and covalent bonds.


Here, it is shown that epitaxial graphene films grown on SiC can increase the hardness of SiC up to 100% at low loads (up to 900 µN), and up to 30% at high loads (10 mN). By using a Berkovich diamond indenter and nanoindentation experiments, it is demonstrated that the 30% increase in hardness is present even for indentations depths of 175 nm, almost three hundred times larger than the graphene film thickness. The experiments also show that the yield point of SiC increases up to 77% when the SiC surface is coated with epitaxial graphene. These improved mechanical properties are explained with the formation of diamene under the indenter's pressure.Silicon carbide (SiC) is one of the hardest known materials. Its exceptional mechanical properties combined with its high thermal conductivity make it a very attractive material for a variety of technological applications. Recently, it is discovered that two‐layer epitaxial graphene films on SiC can undergo a pressure activated phase transition into a sp 2) ‐diamene (sp3) phase transition. The hardness of graphene coated SiC increases by 30% compared to bare SiC, even for indentation depths 300 times larger than the graphene coating thickness.This work shows that the yield point of SiC can be increased by 77% by coating SiC with epitaxial graphene. This enhancement is due to a pressure‐induced graphene (sp However, experiments on graphene grown by chemical vapor deposition (CVD) on a copper substrate showed no increase in hardness of the graphene coated copper substrate. Regarding the stiffness of substrates coated with graphene, no increase has been detected for exfoliated graphene on SiO2 substrates, while a 5% increase has been measured for copper coated with CVD compared to bare copper. For a copper substrate coated with graphene, a mild increase in bearing capacity has been shown during the initial elastic regime at low loads.Graphene has shown great potential for mechanical applications due to its exceptional mechanical properties.4, 52 to sp3 hybridization. This phase transition dramatically changes the elastic properties of the graphene/SiC system under pressure. In particular, purely elastic ångström indentation (Å‐indentation) measurements indicated a surface stiffness comparable to diamond, while no investigations on the plastic behavior have been performed.Very recently it has been reported that two‐layer epitaxial graphene grown on silicon carbide (SiC) can undergo a room temperature, pressure activated phase transition from sppressure.11 In  due to its extreme hardness, strength, and high thermal conductivity. Considering the technological interest in the exceptional mechanical properties of SiC, second only to diamond, here, we investigate how the hardness of a SiC substrate can be further improved when SiC is coated with an atomically thin and thermally conductive epitaxial graphene film. In particular, we conduct Berkovich hardness indentation tests on monolayer (1L) epitaxial graphene films grown on the Si‐face of SiC(0001), where a typical buffer carbon layer (BfL) sits in between graphene and SiC  substrates are investigated by indentation experiments using a Hysitron TI 950 Triboindenter with a diamond Berkovich indenter, applying loads in the range between 300 µN and 10 mN  direction using a Berkovich indenter. In Figure  induced by the pressure activated sp2 to sp3 phase transition in the two graphitic layers under the indenter. This 2D diamond‐like structure on SiC increases the resistance of SiC to yield compared to bare SiC, resulting in higher hardness. On the other hand, previous theoretical work predicts no graphene‐diamene phase transition at room temperature for >3 L. Indeed, we find that when SiC is coated with 10 L of epitaxial graphene, the hardness decreases of ≈88% compared to bare SiC. This is also in agreement with previous studies that did not show any improvement in the hardness of copper when coated with only one layer of CVD graphene. The increased hardness of the 1L/Bfl/SiC(0001) system is consistent with a coating harder than the SiC substrate. The hardness of the graphene/SiC composite structure decreases with increasing loads, reaching a plateau value of ≈40 GPa at 10 mN loads, a value which is 30% larger than the hardness of bare SiC at the same load and closer to the hardness of diamond, i.e., 60–150 GPa. Furthermore, compared to bare SiC, the hardness of 1L/Bfl/SiC(0001) and 2L/H‐SiC(0001) at lower loads, e.g. 500 µN, displays an incredible increase of up to 100%, compared to bare SiC, reaching values of 60 GPa , and 63% for the AFM nanoindentation experiment (10 nm).Furthermore, we investigate the presence of residual indentations at low loads (300–700 µN) on the surface of bare SiC(0001) and graphene coated SiC to determine the onset of plastic deformation. Interestingly, we observe residual indentations on the surface of bare SiC for all loads, while no residual indentations are present on the surface of 1L/Bfl/SiC at loads 300 and 400 µN  probe to apply a local load and simultaneously measure the electronic current flowing through the AFM tip‐sample contact, see 33 diamene structure, we have investigated the hardness of single crystal SiC coated with epitaxial graphene films. We find that when SiC is coated with 10L of epitaxial graphene, the hardness decreases of ≈88% compared to bare SiC. However, when SiC is coated with a 1 L epitaxial graphene plus a graphene‐like buffer layer, or two graphene layers (in this case the SiC surface is passivated with hydrogen), we observe a dramatic increase in hardness. Precisely, we observe that coating SiC with 1L graphene plus buffer layer can increase the hardness of up to 100% at low loads (between 500 and 900 µN) compared to bare SiC, increasing from 30 to 60 GPa, a value approaching the hardness of diamond. This increase in hardness falls off at high loads, reaching a plateau value of 30% at 10 mN. The experiments also show that the yield point and onset of plastic deformations in SiC increases up to 77% when the SiC surface is coated with epitaxial graphene. These findings shed light on the formation of diamene under the indenter's pressure. In particular, we show that the atomically thin diamene layer can improve hardness of SiC even at high loads, corresponding to indentations of ≈175 nm, i.e., almost 300 times larger than the graphene film thickness. This work opens new possibilities for designing ultra‐hard and ultra‐light thermally conductive coatings for SiC to improve its mechanical performances for applications such as body armors, high‐impact protective coatings, and for use in aeronautics, aerospace, and automobile industry.In conclusion, motivated by the recent discovery of a room temperature pressure activated phase transition of epitaxial graphene into a sp4 The first carbon layer on the Si‐face of SiC is called the buffer layer and this layer is partially covalently bonded to the SiC surface (≈30% sp3 bonded carbon atoms). The layers on top of the buffer layer have carbon atoms in sp2 configuration. Therefore, when we refer to single layer graphene, it is a structure comprised of a graphene layer and buffer layer. The quasi‐free standing bilayer graphene is prepared from single layer epitaxial graphene sample by intercalation in hydrogen atmosphere at an approximate pressure of 1000 mbar with hydrogen flow at 3.0 slph. Hydrogen atoms saturate Si—C bonds between SiC surface and buffer layer, which create Si—H bonds and turn sp3 bonded carbon atoms into sp2 configuration. More details about the growth procedure can be found in Reference. Schemes of the structures are presented in Figure Large area epitaxial graphene films are grown on the Si face of 6H silicon carbide (0001) substrates (II–VI Inc) by the thermal decomposition method.14 TheRtip, is ≈150 nm at room temperature and in humid atmosphere. The Berkovich tip indents the sample surface at a constant rate until the set maximum load is achieved, then is held for 5 s. The loading time for this process is 62 s. Finally, the tip is unloaded linearly in time within 5 s  byHere  We therefore use the following equation to describe the projected areaAt large contact depths the ideal tip area function, mentioned in Equation 29 We 0C kept at 24.56, describing the ideal Berkovich diamond indenter.The parameters in Equation S is defined as S = dP/dh, which can be obtained from the unloading part of a load‐displacement curve as shown in Figures Er isβ is a correction factor =1.034 for a Berkovich tip. The reduced elastic modulus is given byEi= 1140 GPa and νi= 0.07 are the known elastic modulus and Poisson's ratio of the indenter, and E and ν are the same parameters of the sample.Contact stiffness −1) in ambient conditions. The normal forces between 0 and 200 µN are used to indent a sample's surface. The investigated area is scanned before and after indentation experiment with the same tip in a tapping mode, to distinguish if the residual indentation was created or not.The AFM nanoindentation experiments are performed on a Bruker Multimode 8 AFM using a diamond AFM probe  in ambient conditions. The current dependency on normal load is measured at forces between 0 and 250 nN.The conductive AFM measurements are performed with a Bruker Multimode 8 AFM using a sharp conductive diamond probe (Adama innovation, tip radius ≈10 nm, normal spring constant 74 N mThe authors declare no conflict of interest.Supporting InformationClick here for additional data file.


The in vivo experiment further demonstrated the distribution of targeted NPs in tumor tissues, with changes in NIRF and MR signals observed. Our study indicated that SPIO-aPD-L1-Cy5.5 NPs can be used to monitor PD-L1 expression in breast cancer as NIRF/MR contrast agents.Chemotherapy has remained the mainstay of treatment of triple-negative breast cancer; however, it is significantly limited by the associated side effects. PD-1/PD-L1 immune checkpoint inhibition therapy (ICI) has been a breakthrough for this patient population in recent years. PD-L1 expression is crucial in immunotherapy since it is a major predictor of PD-1/PD-L1 antibody response, emphasizing the significance of monitoring PD-L1 expression. Nonetheless, it is hard to assess the expression of PD-L1 before surgery, which has highlighted the urgency for a precise and noninvasive approach. Herein, we prepared a dual-mode imaging nanoparticle probe to detect PD-L1. The particle size, zeta potential, biocompatibility, and imaging ability of NPs were characterized. The synthesized NPs showed slight cytotoxicity and good T2 relaxivity. The targeted NPs accumulated more in 4T1 cells than nontargeted NPs  Triple-negative breast cancer (TNBC) is a subtype of breast cancer negative for PR/HR/Her-2 receptors, accounting for 10–20% of breast cancers. It has been established that TNBC exhibits a highly aggressive phenotype accounting for its poor prognosis . PD-1/PDαvβ3 [Molecular imaging enables noninvasive monitoring of changes in potential molecular targets of tumor cells. In recent years, contrast agents have been developed to detect tumors and improve treatment efficacy, involving recognizing specific receptors on the surface of tumor cells, such as αvβ3 , 10 and αvβ3 , 12, whiαvβ3 , 14. In αvβ3 , 16. Intαvβ3 , 18 and αvβ3 , 20.3+ as the signal unit, SPIO has some upsides. (1) The signal intensity of SPIO is higher than Gd chelate contrast agents at the same concentration. (2) SPIO absorption by the body is accompanied by efficient biodegradation and iron homeostasis mechanisms for treating the free irons [Superparamagnetic iron oxide (SPIO) nanoparticles are among the highest-ranked nanoparticles in medicine due to their unique physicochemical property (superparamagnetism) as well as their established biocompatibility and stability in aqueous solutions , 22. Moree irons , and thaee irons . Therefo3O4 and NHS-Cy5.5 to form stable amide linkages. Take 20 mg solution of PEG-COOH-coated Fe3O4 , replace the buffer with 0.02 M MES solution, and adjust the pH to 5.5. Then, 2 mg PD-L1 antibody (clone 10F.9G2) or IgG antibody (for the control group) was added, and the mixture was incubated at 26°C for 30 min in a shaker. Subsequently, 4 mg EDC was added to the mixture and incubated overnight in a shaker at 26°C. The solution was removed, and a magnetic separation column was used to remove the free antibody and rinse out the stagnant magnetic beads. 1 ml of the solution was treated at a time, and the obtained colorless solution was then measured. NHS-Cy5.5 was dissolved in anhydrous DMF and diluted to a 20 mg/mL solution. The magnetic beads were taken after coupling the PD-L1 antibody, and the volume was made to 10 mL. The NHS-Cy5.5 solution was added to the mixture and incubated at 26°C for 5 h in a shaker. The free Cy5.5 was removed using a 100 K ultrafiltration tube  until a clear colorless solution was observed. The volume of the product was made to 20 mL at a concentration of 1 mg/ml.Free amino groups of antibody IgG and anti-PD-L1 can react with the active group of PEG-COOH-coated FeThe nanostructure of the nanoparticles was determined by a transmission electron microscope . The zeta potential and size of the nanoparticles were studied by dynamic light scattering using a Zetasizer Nano ZS . The emission and excitation spectra were recorded by a fluorescence spectrometer .3 cells/well density and cultured overnight. The adherent cells were then incubated with 100 μL of the corresponding medium containing SPIO-aPD-L1-Cy5.5 of various Fe concentrations  for 24 h. Subsequently, the cells were washed three times with PBS, and then, 90 μL of fresh medium and 10 μL of CCK8 reagent were added. The 96-well plates were then incubated at a constant temperature for 2 h. In addition, a blank group (only add the 90 μL of fresh medium and 10 μL of CCK8 reagent) was set up. A microplate reader was used to record the absorbance at a wavelength of 450 nm. The cell viability was calculated using the following formula:Ae is the absorbance of the experimental well, Ac is the absorbance of the control well, and Ab is the absorbance of the blank well. The experiment was repeated three times.The CCK-8 method was used to examine the cytotoxicity of the molecular probe on 4T1 cells. The 4T1 cells were seeded in a 96-well plate at a 5 × 105 cells/mL overnight. Then, the cells were incubated with SPIO-aPD-L1-Cy5.5 NPs  at pH 7.4 for 4 h, and SPIO-IgG-Cy5.5 NPs were used as controls. To further validate the active targeting of the nanoparticles, a blocking group was made, which was designed to add antibody PD-L1  before adding SPIO-aPD-L1-Cy5.5. After the incubation, the cells were then washed three times in PBS, and DAPI was used to stain the nuclei for 10 minutes. Fluorescence images were acquired by confocal laser scanning microscopy .To evaluate the cellular uptake of the nanoparticles, 4T1 cells were seeded onto 35 mm glass-bottom culture dishes  at a density of 1 × 106 cells in 200 μL.All experiments followed animal ethics of the guiding opinions on the treatment of laboratory animals issued. All female Balb/c nude mice (aged 4 weeks) were obtained from the Experimental Animal Center of Guangxi Medical University. 4T1 cells were injected subcutaneously in the right flank at a concentration of 2 × 10MRI exams of SPIO-aPD-L1-Cy5.5 NPs were processed by a 3.0TMR  with a mouse coil . SPIO-aPD-L1-Cy5.5 NPs range 0–0.714 mg/ml Fe concentrations were dissolved in pure water, added to 1.5 ml EP tubes, and then scanned. T2-weighted MRI was performed for each tube using a fast spin-echo (FSE) sequence .in vivo MRI and NIRF, the nude mice were divided into two groups (consisting of 3 mice), including the experimental and control groups. All mice were scanned twice, before injection and 6 h after injection of 0.1 ml NPs into the tail vein, and the dose of Fe was 2 mg/kg. The fluorescent images were photographed by a fluorescence imaging system  . During imaging, mice were exposed to a 2% isoflurane and oxygen gas mixture and maintained under anesthesia. Relative signal intensity (RSI) was defined as the ratio of tumor to muscle signal and used to assess NPs targeting ability.For μm sectioning. Also, sections were stained with Prussian blue to visualize the accumulation of NPs.After the imaging, the mice were euthanized, and the tumor was collected. All tissues were fixed with 10% formalin. Subsequently, tumor specimens of the two groups were removed and paraffin-embedded for 4-3 , and the concentrations of Fe were determined using ICP-MS. The amount of Fe was shown as mg/kg tissue.This part uses Du's  method. in vivo toxicity of the NPs by observing the presence of damage within the sections by H&E staining. Blank Balb/c nude mice (aged 4 weeks) were divided into 2 groups (n = 3), and SPIO-aPD-L1-Cy5.5 and SPIO-IgG-Cy5.5 were injected. After 24 h, mice were sacrificed, and their hearts, livers, spleens, lungs, and kidneys were harvested. The obtained sections were stained with H&E staining, which helps us see if there is tissue damage.We monitored the x ± s). Independent samples t-test was performed using SPSS 23.0 software to compare RSI and Fe concentration between the SPIO-aPD-L1-Cy5.5 group and SPIO-IgG-Cy5.5 group. The statistical significance of the difference was expressed as p < 0.05.Each group of data was obtained by repeating three times and expressed as mean ± standard deviation  (We estimated the ely 50%) . AccordiA confocal laser scanning microscope (CLSM) was used to view the cellular uptake of the SPIO-aPD-L1-Cy5.5.4T1 cells treated with SPIO-aPD-L1-Cy5.5 displayed noticeable red fluorescence enhancement in the membrane. And blocking group demonstrated significantly reduced fluorescence signal. As a control, cells treated with SPIO-IgG-Cy5.5 showed significantly lower red fluorescence signals. And the results of the blocking and control groups indicated that the PD-L1 targeting strategy effectively enhanced the uptake of SPIO-aPD-L1-Cy5.5 by 4T1 cells .−1 mM−1. These results suggested that SPIO-aPD-L1-Cy5.5 could be applied as a sensitive MRI T2 contrast agent to visualize the in vivo drug delivery process.We used T2-weighted MR imaging to determine the T2-weighted relaxivity  for the MRI potential of SPIO-aPD-L1-Cy5.5. From in vivo contrast by intravenous injection of SPIO-aPD-L1-Cy5.5 NPs in 4T1-bearing mice. The T2 signals at the tumor sites were darker 6h after injection. In addition, we analyzed the relative signal intensity (RSI) between the two groups (preinjection and postinjection). The results suggested that the preinjection and postinjection RSI in the targeted group was 2.18 and 1.62, respectively, and the difference was statistically significant (p < 0.05). Besides, few iron nanoparticles were deposited in the tumor tissue in the targeted group . The Fe levels in the tumor tissue in the SPIO-aPD-L1-Cy5.5 group were significantly higher than in the SPIO-IgG-Cy5.5 group (p < 0.05).The distribution of Fe in tissues was validated by ICP-MS. The liver and spleen had the greatest accumulation of Fe ; howeverIn 4T1-bearing nude mice that received SPIO-aPD-L1-Cy5.5, NIRF signals were detected in the whole body. Besides, strong NIRF signals were observed in the tumor region in the targeted group at 6 h , in contin vivo.Moreover, H&E staining of SPIO-aPD-L1-Cy5.5 NPs showed normal pathological morphology and no histopathological damage response in tissue sections of all organs, compared with the nontargeted group . The cytIt has been established that PD-L1 is upregulated in TNBC, and its expression is negatively associated with poor patient prognosis and correlates with ICI treatment response rate. Therefore, an accurate means of monitoring PD-L1 expression at the tumor site can prevent PD-1/PD-L1 responders from discontinuing immunotherapy due to erroneous PD-L1 results , 29. How∗ value. In the present study, the NPs SPIO-aPD-L1-Cy5.5 synthesized was found to have a T2 relaxation rate of 199.48 s−1 mM−1; importantly, this complex exhibited excellent MR imaging properties in vivo.MRI is a well-established method in breast imaging, with various clinical applications, including the noninvasive differentiation between benign and malignant breast lesions, treatment effect evaluation, and the evaluation of high-risk patients. Commonly used contrast agents are broadly divided into T1-positive and T2-negative contrast agents. SPIO is widely acknowledged as a superparamagnetic material that provides a rapid reduction in the intensity of the T2 signal. Liu et al.  employedThe surface chemistry and size of SPIO nanoparticles can influence their biodistribution pattern and circulation time in the body. The biodistribution patterns of SPIO nanoparticles have been mostly characterized in the liver and spleen , 31. Stu∗ value at the tumor site, especially the targeted nanoparticles. The nanoparticles prepared by our group reached the tumor site via its enhanced permeation and retention (EPR) effects [The nanoprobe prepared by our group exhibited a relatively uniform and appropriate size. Furthermore, we demonstrated the biocompatibility and molecular imaging of NPs. The study showed that both targeted and nontargeted nanoparticles could effectively reduce the T2 effects , 37. The effects . Active  effects , 40. TheIn the present study, the T2-negative contrast agent SPIO exhibited more sensitive signal changes than the Gd agent while avoiding the nephrotoxicity associated with the latter. Moreover, the synthesized NPs allow effective, noninvasive, and real-time detection of the expression of PD-L1 in the tumor tissue. However, the relationship between the PD-L1 expression and changes in the MR signals was not quantified, warranting further studies.in vivo and H&E staining. This work provides the basis for future studies on molecular imaging of PD-L1 in cancer patients.In conclusion, our group designed a dual-modality PD-L1-targeted nanoparticle probe, which exhibited slight cytotoxicity and could specifically bind to the cell surface. Furthermore, we validated its biocompatibility and targeted ability by NIRF/MR imaging


M = 9.09, SD = 0.80). The measures were based on the subjective appraisals of the sessions made by the participating children, including quantitative and qualitative assessments of the degree of satisfaction of the participants. The results showed that there were similar levels of satisfaction with the sessions that did or did not use serious games as a complement to the program. However, only satisfaction with the sessions that used serious games (and not satisfaction with the sessions that did not use them) contributed significantly to explaining both the enjoyment of the activities and the interest in the subjects. Satisfaction with serious games was significantly and positively associated with fun, easiness, ability to understand the session, and ability to cope with emotions. Qualitative analysis showed three main themes, namely: positive aspects, negative aspects, and opportunities for improvement of the program. Overall, these results indicate that children’s satisfaction with the ‘Me and Us of Emotions’ program is related to serious games, suggesting the relevance of using this complementary tool more often when intervening with younger generations.The use of serious games may be an appealing and complementary way to motivate curriculum-based social and emotional learning (SEL); still, investigation into this potential usefulness is scarce. This study aims to address the usefulness of serious games within the program ‘Me and Us of Emotions’. Specifically, we analyzed the differences in children’s satisfaction in sessions that did or did not use serious games as a complement to the intervention, explored the contribution of using serious games to the global satisfaction with the program, and explored children’s qualitative feedback regarding the sessions. The participants were 232 children (122 boys and 110 girls) aged between 8 and 12 years old ( The empirical literature has consistently established the importance of universal and preventive approaches to promoting social and emotional skills in children within school contexts ,2,3,4. PSEL also encourages prosociality and compassionate motives ,12. AccoThe majority of SEL programs have been traditionally taught within the curriculum ,4. In reOne way to measure the usefulness of serious games relies on assessing participant engagement, for example, the extent to which participants are sufficiently attracted to and involved in the program , which cDespite the relevance of knowing about participants’ engagement with the interventions to better interpret the outcomes and continuously improve the interventions, it is a rare practice in the SEL literature ,33. It bM = 9.09, SD = 0.80) of whom 52.6% (n = 122) were boys and 47.4% (n = 110) were girls. There were gender differences for age, t(230) = 2.74, p = 0.007, Cohen’s d = 0.360, with boys being significantly older than girls . Regarding school year, 44.8% (n = 104) were in the 3rd grade and 55.2% (n = 128) were in the 4th grade. Boys and girls were evenly distributed by school year, X2(1) = 0.952, p = 0.329.Participants were 232 children aged 8–12 years old  or a control group (CG). In the present study, only the data from the EG was used; participants in this group received the ‘Me and the Us of Emotions’ program.The Me and the Us of Emotions program  compriseSatisfaction with the program was assessed weekly after each session by each participating child. Children answered the question “How much did you like this session?” using a 5-point Likert response scale ranging from “I didn’t like it at all” to “I liked it a lot”. The total satisfaction scores by type of session were computed by summing answers provided to this item across sessions 2, 7, 8, 9, and 10  and across sessions 1, 3, 4, 5, and 6 .After sessions 9 and 10, both using serious games, participating children answered 4 questions: fun with serious games (“How often did you have fun playing this game?”); easiness (“How easy was it to understand how to play?”); usefulness in relation to understanding the session (“Did the game help you to understand the session?”); and usefulness in relation to understanding how to cope with emotion . All these questions were rated on a 5-point scale ranging from 1 “None” to 5 “Much”.This questionnaire included five items and was completed at the end of the program. The first item was “You think that the sessions were…” rated on a 5-point scale ranging from “Not good at all” to “Very good”. The other four items were “How would you rate the sessions?”; “Did you like the activities conducted during the session?”; “What is your interest in the subjects we talked about?”; “Did you like the music?”; and “Did you like the games?”, which were rated on a 5-point Likert scale ranging from “None” to “Very much”. In addition, four open-ended questions were included to be analyzed thematically .t-tests [t-test was also used to compare the satisfaction between the sessions that did and did not use serious games. Pearson product–moment correlations were performed to explore the relationships between the variables in the study [Statistical analyses were conducted using PASW Software . Descriptive statistics were computed to explore the demographic variables and gender differences were tested using independent sample t-tests . Additiohe study ,40. Multn = 59, M = 4.77, SD = 0.48 vs. M = 4.72, SD = 0.46, respectively), t(58) = 1.062, p = 0.292.The results showed no differences in satisfaction between the sessions that did and did not use serious games  = 1.132, p = 0.330, liking the music, F  = 0.498, p = 0.611, and liking the games, F  = 0.970, p = 0.385.No significant effects of satisfaction with the sessions that did and did not use serious games were found in enjoying the sessions, F  = 19.416, p < 0.001, accounting for 39.7% of that enjoyment. Only satisfaction with the sessions that used serious games was a significant predictor. The same predictive model was significant for the interest in the subjects being covered in the session, F  = 15.325, p < 0.001, with satisfaction with the sessions that did and did not use serious games accounting for 33.8% of the variance of that interest. Again, only satisfaction with the sessions that used serious games emerged as a significant predictor , easiness , ability to understand the session , and ability to cope with emotions .Satisfaction with the use of serious games (in sessions 9 and 10) was significantly and positively associated with fun  positive aspects, (b) negative aspects, and (c) opportunities for improvement to the program. In each major theme, participants’ responses were grouped into several sub-themes that best reflected participants’ verbalizations .Regarding the theme “positive aspects”, three sub-themes emerged, namely, learning emotion regulation strategies, experiencing positive emotions , and gaining knowledge about emotions . The theme “negative aspects” included a reduced opportunity for playing serious games and experiencing difficult emotions. Finally, the “opportunities for improvement” were the following: providing for less noise during the sessions and better behavior on the part of the participating children, addressing more emotions, using more serious games, and increasing the duration of the sessions.The value of universal social–emotional learning-based programs for children in school contexts is well-known ,3,4,7 buThe results showed that children reported similar levels of satisfaction with the sessions that did and did not use serious games as a complement to the program and that those diverse sessions did not differently impact on the enjoyment of the sessions, liking the music, and the liking games. The acceptability and the efficacy of traditional SEL programs have been previously proven ,6 as hasAlternatively, only satisfaction with the sessions that used serious games contributed to explaining both the enjoyment with the activities and the interest in the subjects; satisfaction with the sessions that did not use those games was not a significant contributor to that enjoyment and interest. So, although the children were similarly satisfied with all the sessions, using serious games helped them enjoy the activities more and be more interested in the sessions’ themes. Complementing sessions with serious games seemed to provide an appealing, interactive, and motivating environment, which aligns with previous literature that demonstrated that this complementary use of serious games could be a way of enhancing engagement and motivation in children .In the current study, the two final sessions that used serious games were assessed by children regarding their fun, easiness, usefulness to understand the session, and usefulness in managing the emotion. The results suggest that children who were more satisfied with serious games tended to experience more fun and more easiness and found the games more useful for understanding the session and managing emotions. Although the limitations linked to the correlational nature of these findings, they provide some indication that when serious games are included in face-to-face social–emotional skills-based programs, they can facilitate children’s acquisition of knowledge and skills, which is consistent with the results from the few existent studies ,27. AlsoThe qualitative study also highlighted the importance of serious games as a complementary tool to the programs. The “negative aspects” highlighted by children were the reduced opportunity for playing serious games and experiencing difficult emotions. In addition, the “opportunities for improvement” included suggestions not only for ameliorating climate and behavioral manifestations during the sessions , but also for increasing the session duration, targeting more emotions, and using more serious games. It seems that both individual and program factors were highlighted by children both as positive and negative aspects and, consequently, as aspects that could be further improved. Similarly, participant factors have been emphasized in other studies, such as attitudes toward learning and motivation, as well as program factors, such as length ,35.Some limitations of the present study should be considered. The first limitation is related to the sample size. Although the current sample is considered large, not all participants consistently reported their satisfaction after each session . In addition, the access to serious games was not equal for all children in the session due to time constraints. Although online access to serious games was possible through the ‘Me and the Us of Emotions’ program online platform, some children may not have had a sufficient internet connection at home. A further limitation was that the specific aspects concerning the fun, easiness, and usability of the serious games assessed in sessions 9 and 10 were not evaluated in the other sessions that used games; so, the findings may be specific to the games used in those sessions (and the cumulative effect of the intervention) and not to the use of serious games in general. Future studies should consider the same measurement methods over time. The control group was on a waiting list and not active, which limited the possible comparison of the complementary aspect of serious games between the groups. Future studies should also address the impact of serious games on participants’ emotional development. The current findings should be seen as a preliminary assessment of the potential usefulness of serious games as a complementary tool for social–emotional learning programs, and a larger study informed by these results is ongoing.Both political and educational audiences have come to realize that a child’s social and emotional well-being are important and can be fostered in school contexts through SEL programs. The present paper analyzed children’s perceptions of using serious games as a complement to the social–emotional activities of the ‘Me and the Us of Emotions’ program. Our quantitative and qualitative findings converge to suggest the usefulness of adding serious games as a complement to a social–-emotional skills-based program, as they contribute to enhancing children’s satisfaction. Given the importance of SEL programs and the benefits they have been found to provide ,4,7, it


Land use change has long-term effects on the structure of soil microbial communities, but the specific community assembly processes underlying these effects have not been identified. To investigate effects of historical land use on microbial community assembly, we sampled soils from several currently forested watersheds representing different historical land management regimes . We characterized bacterial and fungal communities using amplicon sequencing and used a null model approach to quantify the relative importance of selection, dispersal, and drift processes on bacterial and fungal community assembly. We found that bacterial communities were structured by both selection and neutral  processes, while fungal communities were structured primarily by neutral processes. For both bacterial and fungal communities, selection was more important in historically disturbed soils compared with adjacent undisturbed sites, while dispersal processes were more important in undisturbed soils. Variation partitioning identified the drivers of selection to be changes in vegetation communities and soil properties  that occur following forest disturbance. Overall, this study casts new light on the effects of historical land use on soil microbial communities by identifying specific environmental factors that drive changes in community assembly. Soil microbial communities play key roles in terrestrial ecosystems, facilitating essentially all ecosystem processes . HoweverIn addition to effects of present land use, currently unmanaged ecosystems with different historical management regimes may also host distinct microbial communities . For exaTo investigate microbial community assembly across historical land uses, we sampled soils from eight forested watersheds at the Coweeta Hydrologic Lab in North Carolina, USA. Four of the watersheds were disturbed ~4–8 decades previously by management activities including clear-cutting, cable-logging, conversion to pine monoculture, and pasture conversion Table . AdjacenBray) then distinguishes between specific neutral processes, where compositional turnover less than or greater than null expectations indicates homogenizing dispersal or dispersal limitation + drift, respectively. Turnover not differing from null indicates drift alone. We determined differences between bacterial and fungal βNTI distributions using a Kruskal–Wallis test and determined effects of historical disturbance on the proportions of specific processes using Z-tests. We investigated potential drivers of selection  by conducting variation partitioning on βNTI matrices, similar to the approach of Fillinger et al L. tulipies Table  suggestsDispersal processes were more important in structuring bacterial and fungal communities in reference soils than in disturbed soils Fig. . GreaterOverall, our results reveal clear legacies of historical land use on soil microbial community assembly; contrary to what has been shown for recently disturbed systems, microbial communities in historically disturbed sites can be more strongly shaped by selection than their undisturbed counterparts. However, it is possible that these patterns are specific to our soils within temperate forests of the eastern US, which should be assessed by future work. Regardless, the differences in community assembly we report are likely to influence ecosystem recovery following forest disturbance. For example, ecosystem processes associated with specific fungal taxa may recover slowly or not at all following forest disturbance, as these taxa will not be quickly recruited from undisturbed sites via dispersal Fig. . In geneSupplementary information


A very attractive advantage of graphene is that its Fermi level can be regulated by electrostatic bias doping. It is of great significance to investigate and control the spatial location of graphene emission for graphene thermal emitters, in addition to tuning the emission intensity and emission spectrum. Here, we present a detailed theoretical model to describe the graphene emission characteristics versus gate voltages. The experimentally observed movement of the emission spot and temperature distribution of graphene emitters are basically in agreement with those from the theoretical model. Our results provide a simple method to predict the behavior of graphene emitters that is beneficial for achieving the spatial dynamic regulation of graphene infrared emission arrays. As a high-profile two-dimensional material, graphene has attracted extensive interest in worldwide for its excellent electrical, thermal, and optical properties ,2,3,4. IIn recent years, graphene thermal emission due to Joule heating has attracted a great deal of attention, and many studies have focused on enhancing the emission intensity or tuning the emission spectrum of heated graphene ,9,10,11.In this work, we start with the charge conservation and tunability of carrier density and present a detailed theoretical model to calculate the distribution of the voltage, carrier density, locally generated heating power, and temperature along graphene. We find that this model can provide a clear and simple picture of the device behavior, in agreement with the results from simulations and experiments. For example, the calculated positions of minimized carrier density are consistent with those extracted from graphene infrared emission images. Under low gate voltages, maximum temperatures in the experiments are lower than those calculated by the temperature equation, but measured temperatures under high gate voltages are similar to those calculated by the equation. Moreover, the occurrence of another hot spot could be explained by simply introducing a locally trapped charges function into the carrier density equation. These results are helpful for realizing the controllable spatial emission of graphene emitters in the future.x is the direction along graphene (from drain to source), V(x) is the electrostatic potential, e is the electron charge, and w is the width of graphene. According to the charge conservation, the current is constant everywhere along graphene, so the carrier density depends on the electrostatic potential distribution, which could be written as [The theoretical model is based on the assumption that the carrier density of graphene is minimized when the Fermi level crosses the Dirac point, where the conduction band and valence band touch each other. For graphene thermal emitters on a itten as (2)V(x)=Here, we ignore the recombination length of electrons and holes in graphene, so carriers are either electrons or holes but cannot be both. Therefore, the point that separates electron and hole regions has the lowest charge density, resulting in the highest resistance. According to charge conservation in the steady state and Joule heating, the current is equal everywhere and heating is proportional to the resistance, so the hottest place would occur at the point separating electron and hole regions. Meanwhile, according to Equation , only insgn(x) is sign function, Combining Equations (1) and (2) with boundary conditions, we can obtain the electrostatic potential expression along graphene and the position expression with minimum carrier density.The expressions for current, local carrier density, and Fermi level can also be derived as follows:Because the infrared emission intensity is related to the local Joule heating of graphene, and considering the presence of the carrier density . In the simulation, different kinds of carrier density in graphene are taken into account with the following equations: ,15.(10)The hot spot location, maximum temperature, and current calculated from equations and simulations are compared in A graphene flake was mechanically exfoliated on a p-doped A constant drain voltage of 70 V was applied to the graphene thermal emitter, while recording the spatial locations of graphene infrared emission as a function of applied gate voltages by an infrared CCD. All measurements were performed in vacuum to avoid the oxidation of graphene, and the emission intensity at each gate voltage in Through correcting the infrared CCD with a blackbody 590 K–740 K), temperatures of hot spots in 0 K–740 Kubstrate ,17, as tInterestingly, we found that a stationary light spot appeared at a place about 20 graphene . In viewThe relationship between temperature and gate voltage is calculated using Equations (8), (9) and (11) and plotted in In summary, we theoretically and experimentally investigated the spatial location of thermal emission in gate-controlled long channel graphene devices. The observed movement of the emission spot and temperature distribution are consistent with those obtained by the theoretical model, confirming that controlling the gate voltage is an effective method to tune the emission location and emission intensity. In addition, the relationship between the carrier density and Fermi level could be deduced by the theoretical model, which is helpful to understand the internal mechanism of graphene emission.