Nanocomposite Disk Research Articles

Hydrothermal and Mechanosynthesis of Mixed‐Cation Double Perovskite Scintillators for Radiation Detection

AbstractThis article details work performed on the synthesis and characterization of an inorganic mixed‐cation double halide perovskite, Cs2Ag.6Na.4In.85Bi.15Cl6 (CANIBIC). Single crystals have been created via a hydrothermal reaction, milled into a powder, and pressed into pellets, while nanocrystals have been directly synthesized via mechanosynthesis. A computational model is constructed to predict the X‐ray diffraction pattern of CANIBIC; this model aligns very well with the X‐ray diffraction pattern measured for CANIBIC crystal powder. This model can therefore be developed in the future as a tool to predict lattice parameters and crystal structures of other novel double‐halide perovskites. Photoluminescence spectra obtained from each format show broad emission centered at 630 nm, as is typical for self‐trapped exciton emission; self‐trapped exciton emission is also confirmed by investigating photoluminescence intensity as a function of laser power. Nanocomposites are produced via the loading of nanocrystals of CANIBIC into PMMA. Although nanocomposite disks consisting of a small proportion of CANIBIC nanocrystals in PMMA have a smaller mass attenuation coefficient than a pressed pellet of CANIBIC, these disks have comparatively bright radioluminescence due to their optical transparency. These nanocomposite disks are therefore a particularly useful format for the practical use of the CANIBIC scintillator.

Dispersion and Homogeneity of MgO and Ag Nanoparticles Mixed with Polymethylmethacrylate.

This study aims to examine the impact of the direct and indirect mixing techniques on the dispersion and homogeneity of magnesium oxide (MgO) and silver (Ag) nanoparticles (NPs) mixed with polymethylmethacrylate (PMMA). NPs were mixed with PMMA powder directly (non-ethanol-assisted) and indirectly (ethanol-assisted) with the aid of ethanol as solvent. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscope (SEM) were used to evaluate the dispersion and homogeneity of MgO and Ag NPs within the PMMA-NPs nanocomposite matrix. Prepared discs of PMMA-MgO and PMMA-Ag nanocomposite were analyzed for dispersion and agglomeration by Stereo microscope. XRD showed that the average crystallite size of NPs within PMMA-NP nanocomposite powder was smaller in the case of ethanol-assisted mixing compared to non-ethanol-assisted mixing. Furthermore, EDX and SEM revealed good dispersion and homogeneity of both NPs on PMMA particles with ethanol-assisted mixing compared to the non-ethanol-assisted one. Again, the PMMA-MgO and PMMA-Ag nanocomposite discs were found to have better dispersion and no agglomeration with ethanol-assisted mixing when compared to the non-ethanol-assisted mixing technique. Ethanol-assisted mixing of MgO and Ag NPs with PMMA powder obtained better dispersion, better homogeneity, and no agglomeration of NPs within the PMMA-NP matrix.

Application of Chebyshev-based GDQ and Newmark methods to viscothermoelasticity responses of FG composite annular systems

This study explores the thermo-viscoelasticity response of annular disks made of a functionally graded graphene platelet reinforced composite (FG-GPLRC). Random orientation is considered for GPL nanofillers. A power-law model with a controller index is also used to determine the GPL volume fraction distribution along the radial direction. The effective thermomechanical properties of the nanocomposite medium are calculated through the one-point and two-point correlation homogenization processes. The Kelvin-Voigt technique is employed to design the viscosity nature of the system. Coupled thermoelasticity is considered to attain the governing formulation because the considered disk is subjected to a sudden high temperature. Furthermore, by incorporating generalized thermoelasticity based on the Lord-Shulman concept, the physical structure of the problem is altered. The transient governing equations are solved based on a hybrid approach. The spatial dependency is solved using a Chebyshev-based generalized differential quadrature (GDQ) method, while the time dependency is calculated using an average acceleration-based Newmark technique. After confirming the described formulation and method with previous research, different parametric samples are given to explain more about the behavior of viscoelastic nanocomposite disks that are heated quickly and rotated at a constant rate.

Synergistic effects on gamma-ray shielding by novel light-weight nanocomposite materials of bentonite containing nano Bi2O3 additive

In recent years, nanocomposites have gained prominence as potential materials in the γ-radiation shielding and protection areas compared to other conventional materials. In view of this, the present study is devoted to fabricate new nanocomposites, based on raw bentonite clay (RB), as a natural, abundant and low-cost matrix. This was then intercalated with bismuth oxide nanoparticles (Bi2O3 NPs), as a non-toxic nano-additive for the formation of RB/(Bi2O3)x nanocomposites using Bi2O3(x) NPs + raw bentonite clay(1- x), where x = 0, 0.1, 0.2, 0.3 and 0.4 fractional weight. Conventional pressing method at 200 bar was used to prepare nanocomposite disks with different compositions. Fourier-transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) confirmed the successful preparation of various assembled nanocomposites. Moreover, the as-prepared nanocomposites as well as the Bi2O3 NPs were examined using scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The SEM images confirmed that the Bi2O3 NPs were successfully incorporated into the bentonite clay layers and its average particle size was in the range 20.74–25.61 nm. Bulk density, effective porosity (%), and heaviness (H) were also determined by different nanofiller loading percentages. Measurements of the γ-ray shielding performance were studied and determined at various γ-ray photon energies emitted from various standard point sources of γ-rays (133Ba,137Cs and 60Co) using NaI(Tl) scintillation detector. Thus, some shielding parameters such as mass attenuation coefficients (μm), effective atomic number (Zeff) and effective electron density (Nel) were measured at 356.01, 662.66, 1173.23 keV, and 1332.50 keV. It was confirmed that the γ-ray shielding properties were enhanced by increasing the loading percentage of Bi2O3 NPs. Therefore, the 40Bi nanocomposite specimen, containing 40.0 wt% Bi2O3 NPs, was characterized to exhibit the highest values of μm (0.1712 at 356.01 keV), Zeff (22.78 at 356.01 keV), and Nel (4.32 at 356.01 keV). It is evident that the addition of Bi2O3 NPs into RB clay leads to vast improvements in γ-ray shielding properties. Such materials would be good candidates for use in construction and civil engineering, as well as in the fabrication of building materials used in medical and nuclear establishments.

Hygro-thermal buckling analysis of polymer–CNT–fiber-laminated nanocomposite disk under uniform lateral pressure with the aid of GDQM

In this research, we study the thermal buckling performance of multi-scale hybrid laminated nanocomposite (MHLC) disk (MHLCD) subjected hygro-mechanical loading. The matrix material is reinforced with carbon nanotubes (CNTs) or carbon fibers (CF) at the nano- or macro-scale, respectively. The disk is modeled based on higher order shear deformation theory. We present a modified Halpin–Tsai model to predict the effective properties of the MHLCD. The minimum total potential energy principle is employed to establish the governing equations of the system, which is finally solved by the generalized differential quadrature method. To validate the approach, numerical results are compared with available results from the literature. Subsequently, a comprehensive parameter study is carried out to quantify the influence of different parameters such as stiffness of the substrate, patterns of temperature increase, moisture coefficient, stacking sequence of the CFs, weight fraction and distribution patterns of CNTs, outer radius to inner radius ratio and inner radius to thickness ratio on the response of the plate. Some new results related to critical buckling of an MHLCD are also presented, which can serve as benchmark solutions for future investigations.

Abstract 2: Heat Generating Nanocomposite To Reduce Infection

Purpose: To evaluate the combination of mild hyperthermia plus antibiotics for reducing Stapylococcus aureus biofilms associated with silicone materials. Methods: The additive effect of non-ablative hyperthermia with antibiotics was explored in a mouse model. Small disks of silicone with [4,4-bis(2-ethylhexyl)cyclopenta[2,1-b;3,4-b’]dithiophene-2,6-diyl-alt-2,1,3-benzoselenadiazole-4,7-diyl] (PCPDTBSe) nanoparticles were inoculated with Xen29 S. aureus biofilms. These disks were implanted in the flanks of hairless, immunocompetent Crl:SKH1-hrBR mice, with each mouse receiving with 1 silicone disk on the left flank and 1 nanocomposite disk on the right flank. After 24 hours, the mice were imaged using IVIS to evaluate the infection using the bioluminescent signature from the Xen 29. Mice were treated with either 200µL 2mg/mL Gentamicin orIP Saline, with or without laser (3W, CW, 800nm, 25s) applied directly over the flank 1 hour afterinjection. Mice were imaged using IVIS 24 hours after treatment. The disks and surrounding infected tissue were extracted and homogenized. The homogenate was diluted and plated in triplicate to calculate the CFU /g per disk. The change in IVIS luminescence before and after treatment was compared. A total of 14 mice were implanted and treated. 2 mice received treatment of IP Gentamicin only, 4 mice received IP saline and laser therapy, and 8 mice received IP Gentamicin and laser therapy. Results: Only mice treated with Gentamicin and laser therapy demonstrated a decrease in luminescence on IVIS after treatment, representing a decrease in bacterial burden. These mice also demonstrated the greatest percent decrease (-65.8%) of CFU/g on the nanocomposite disk relative to the silicone disk. This was also the only treatment group which saw a significant decrease in bacterial burden on the nanocomposite disk relative to the silicone disk. Conclusion: Mice treated with the combined Gentamicin and laser therapy had the largest percent reduction in biofilm burden on the BSe-Si disk relative to the Si disk. This supports the hypothesis that joint heat and antibiotic therapy can be effective at reducing biofilms in vivo. Ultimately, this technology may have clinical utility towards treating biofilms on indwelling medical devices, mitigating a major burden of disease.

On the nonlinear dynamics of a multi-scale hybrid nanocomposite disk

This is the first research on the nonlinear frequency analysis of a multi-scale hybrid nanocomposite (MHC) disk (MHCD) resting on an elastic foundation subjected to nonlinear temperature gradient and mechanical loading is investigated. The matrix material is reinforced with carbon nanotubes (CNTs) or carbon fibers (CF) at the nano- or macroscale, respectively. We present a modified Halpin–Tsai model to predict the effective properties of the MHCD. The displacement–strain of nonlinear vibration of multi-scale laminated disk via third-order shear deformation theory (TSDT) and using Von Karman nonlinear shell theory is obtained. Hamilton’s principle is employed to establish the governing equations of motion, which is finally solved by generalized differential quadrature method (GDQM) and perturbation method (PM). Finally, the results show that FG patterns, different orientation angle of the fiber, the VF and WCNT parameters, axial load, nonlinear temperature gradient, and applied temperature of the top surface play an essential impact on the linear and nonlinear dynamic responses of the MHCD. The more significant outcome of this research is that the effects of the VF, WCNT, $$\theta$$, and β parameters on the nonlinear frequency of the MHCD can be considered at the higher value of the large deflection parameter and the effect of negative axial load on the dynamic responses of the structure is more intensive. As an applicable result show that the best functionally graded (FG) pattern for serving the highest nonlinear dynamic response of an MHC reinforced annular plate is FG-A.

Inorganic Porous Bulk Discs as a Matrix for Thin-Layer Chromatography and Translucent Hard Composite Materials.

Magnesium-stabilized amorphous calcium carbonate (Mg-ACC), amorphous magnesium calcium silicate hydrate (MCSH), and hydroxyapatite (HAp) are prepared by a precipitation method. By cold-pressing these particles, it is possible to produce porous bulk discs with a narrow pore size distribution. These porous inorganic discs (Mg-ACC, MCSH, and HAp) are investigated as stationary phases to study the chromatographic behavior and adsorption ability of rhodamine B, methylene blue, and ribonuclease. The adsorption affinities of different biomolecules can be easily observed and evaluated through this method. Furthermore, by infiltrating fabricated opaque porous discs with benzyl ether, which has a similar refractive index as the used inorganic particles (Mg-ACC, MCSH, and HAp), their optical properties significantly change and the discs become translucent. Moreover, by infiltrating the MCSH discs with a light-curing polymer, translucent composites with good surface hardness are fabricated. By doping particles with ions such as Ni2+, Co2+, Fe3+, and Eu3+, the color and UV-visible spectrum of the bulk discs can be adjusted. Typically, by using iron-doped MCSH particles as the inorganic matrix, nanocomposites, which show a steep UV-absorption edge at 400 nm, are fabricated. Our work provides a simple and economical method to evaluate the affinity of biomolecules to inorganic materials and a novel way to fabricate translucent hard composite materials. The fabricated nanocomposite discs show a great UV shielding effect and superior surface hardness compared to polymethyl methacrylate and commercial sunglasses, suggesting their potential as new sunglass materials.

Microwave-assisted synthesis of platelet-like cobalt metal-organic framework, its transformation to porous layered cobalt-carbon nanocomposite discs and their utilization as anode materials in sodium-ion batteries

Abstract In this work a facile microwave-assisted synthesis of a platelet-like cobalt-based metal-organic framework (MOF) material is presented. This material was synthesized from cobalt(II) acetylacetonate and biphenyl-4,4′-dicarboxylic acid (Bpdc) in N,N’-dimethylformamide at 160°C. As-prepared Co-Bpdc MOF product with a platelet-like disc architecture was transformed by heat treatment in a nitrogen atmosphere at 800°C to porous cobalt-carbon nanocomposite discs. It is demonstrated that this synthetic strategy allows for obtaining magnetic microporous carbon layered discs with homogeneously incorporated metallic cobalt nanoparticles with a size of ca. 4 nm. The Co-C nanocomposite material was characterized by a variety of physico-chemical methods. It is shown that both Co-Bpdc MOF and Co-C nanocomposite were electrochemically active in sodium battery system as a material for the negative electrode. The high capacity retention over 80% and capacities over 200 mAh g–1 in the sodium-ion battery systems have been achieved.

Effect of slow-cooling protocol on biaxial flexural strengths of bilayered porcelain-ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) disks

ObjectiveThe present study investigated the biaxial flexural strengths of bilayered ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) disks with various layering porcelains veneered using a slow-cooling protocol. MethodsFive porcelain materials (VITA VM9, Cercon Ceram Kiss, and Vintage ZR with experimental coefficient of thermal expansions; CTEs of 8.45, 9.04, and 9.61ppm/°C) were veneered on Ce-TZP/A disks and slow-cooled after firing to fabricate bilayered specimens (core-to-porcelain thickness: 0.8mm/1.5mm). Biaxial flexural strengths of the specimens with the porcelain layer in tension were tested based on the piston-on-three-ball method (ISO 6872:2008). The data were statistically analyzed using Weibull distribution and Fisher’s exact test. ResultsTensile stresses were observed in the entire porcelain layer while compressive stress at the surface of the Ce-TZP/A layer shifted to tensile stress at the interface between the materials. The cases of small CTE mismatches between the materials showed high Weibull characteristic strengths at the internal and external surfaces of the specimens, except the VM9 group (CTE: 9.0–9.2ppm/°C). The maximum tensile stress was observed on the surface of the porcelain layer, where cracks originated and continuously propagated into the Ce-TZP layer. The Ce-TZP/A fractured into two pieces for large CTE mismatches between the materials, resulting in significantly lower flexural strengths than those fracturing into three pieces for small CTE mismatches. SignificanceFlexural strengths and fracture behaviors of bilayered porcelain-Ce-TZP/A disks were influenced by the CTE mismatches, and a small CTE mismatch between the materials was preferred when using a slow-cooling protocol.

Biaxial flexural strength of the bilayered disk composed of ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) and veneering porcelain

ObjectiveHerein we investigated the flexural strengths of bilayered ceria-stabilized zirconia/alumina nanocomposite (Ce-TZP/A) disks using different veneering porcelains. MethodsCommercial (VITA VM9, Cercon Ceram Kiss, and IPS e.max Ceram) and experimental porcelains (Vintage ZR with coefficient of thermal expansions: CTEs of 8.45, 9.04, and 9.61ppm/°C) with various layer thicknesses (1.0, 1.5, and 2.0mm) were applied to Ce-TZP/A disks (0.8mm thickness, n=180). Biaxial flexural tests of the specimens with the porcelain layer in tension were evaluated based on the piston-on-three-ball method (ISO 6872: 2008). The calculated strengths were statistically analyzed using the two-parameter Weibull distribution with the maximum likelihood estimation. ResultsAlthough no significant differences were observed among the experimental porcelains, most specimens with the thinner layer of commercial porcelain showed higher Weibull characteristic strengths at the external surfaces than those with the thicker layer. Irrespective of the porcelain material, the thinner porcelain layer showed significantly higher strengths at the interface between the layers. Fracture origins were always observed at the bottom surface and continuously propagated into Ce-TZP/A substrates. The maximum tensile stress was located at the interface in specimens with the 1.0mm porcelain layer, except for IPS e.max Ceram. Porcelain delamination was dominant in the case of the higher CTE value and thicker layer thickness of the porcelain. SignificanceThe calculated biaxial flexural strengths and the stress distributions for bilayered Ce-TZP/A disks were dependent on the porcelain materials. Optimum behavior was observed for a combination of a small CTE mismatch between the materials and a low core-to-porcelain thickness ratio.

The use of adsorption method to preparation of polyaniline/ZnO nanocomposite varistor

ZnO nanosheets were synthesized using a cost effective and simple precipitation method. Polyaniline/zinc oxide nanocomposites in various weight ratios were produced by the synthesis of polyaniline as a conducting polymer followed by adsorption of polymer chains on the ZnO nanosheets. UV–Vis spectroscopy, X-ray diffraction patterns, and SEM technique were utilized to characterize the nanocomposite structure. The polyaniline/ZnO nanocomposites prepared in various weight percent of polyaniline and ZnO nanosheets were pressed as thin disks at a pressure of 60 MPa and their usage electrical varistors were studied. The current–voltage characteristics of thin polyaniline/ZnO nanocomposites disk varistors were investigated. The results demonstrated good varistor behavior of polyaniline/ZnO nanocomposite disks so that they can be used to protect the electrical circuits from over voltages in the range of 250–550 V. The efficiency of ZnO percent on the varistors properties of polyaniline/ZnO nanocomposites disks was experimented. According to the results, the nanocomposites sample containing 99.01 wt% of ZnO showed minimum breakdown voltage (250 V) and highest nonlinear coefficient (4.28) and also the lifetime of this sample is high. From the UV–Vis spectra recorded for polyaniline/ZnO nanocomposites samples with various ZnO percent, it was found that absorption and light absorption band gap decreased by reducing ZnO content in nanocomposites samples. The band gap in the best sample is 3 eV.

The effects of laser patterning 10CeTZP-Al2O3 nanocomposite disc surfaces: Osseous differentiation and cellular arrangement in vitro

Customized square grid arrangements of different groove depths (1.0, 1.5 and 3.0 µm) and separations (10 and 30 µm) were successfully laser patterned, using a nanosecond pulsed fibre laser, on the surface of 10 mol% ceria-stabilized zirconia and alumina (10CeTZP-Al2O3) nanocomposite discs (diameter: 10 mm; thickness: 1.5 mm). The patterned surfaces and the in vitro biological response of osteoblasts (SAOS-2) towards them were thoroughly analysed. In terms of composition, the laser treatment was found to cause superficial monoclinic-tetragonal zirconia phase transformation and alumina evaporation. In vitro, the most effective grid configuration for osseous differentiation was found to be 1.5 µm groove depth and 10 µm groove separation, and confocal microscopy revealed that the cells show a tendency to be sorted as groove depth increases. It is thought that custom-made patterns could be produced to guide cell attachment in vivo, which could favour implant integration and reduce healing time.

Effect of Surface Modification on Viability of L929 Cells on Zirconia Nanocomposite Substrat.

Introduction: Zirconia bioceramic can be considered for metallic replacement in dental implant applications. A proper method of surface modification may promote better osseointegration. Methods: In study evaluated viability of fibroblast cell following surface treatment. Therefore, viability L929 cells were characterized using MTT assay and scanning electron microscopy. Results: The viability assessment determined significant differences A-Y-TZP20 without surface treatment as compared to laser surface treatment (B), laser surface treatment + hydroxyapatiteyttrium stabilized tetragonal zirconia nanocomposite coat (C) and control. This study demonstrated that L929 cells approximately proliferated and spread on A-Y-TZP20 nanocomposite disk in laser surface treatment(B), Laser surface treatment + hydroxiapatite-yttrium stabilized tetragonal zirconia nanocomposite coat (C) groups similar to control group. Conclusion: Laser surface treatment showed positive effect on the viability of L929 cells.

The evaluation of prepared microgroove pattern by femtosecond laser on alumina-zirconia nano-composite for endosseous dental implant application

Ceramic dental materials, especially alumina (20%vol)-yttrium stabilized tetragonal zirconia poly crystal (A-Y-TZP20), have been considered as alternatives to metals for endosseous dental implant application. For increasing the bone-to-implant contact as well as the speed of bone formation, a new surface modification can be effective. The aim of this study was to design microgroove patterns by femtosecond laser on A-Y-TZP20 nano-composite disks for endosseous dental implant application. The phase composition and the morphology of the A-Y-TZP20 nano-composite samples were characterized using X-ray diffraction and Scanning electron microscopy equipped with energy dispersive X-ray spectroscopy techniques. Statistical analysis was submitted to Kolmogorov-Smirnov test and Student's t test for independent variables, with a 5% significance level. EDAX analysis revealed a significant decrease in the relative content of contaminants like carbon (p < 0.05) in laser surface-treated group as compared to non surface-treated group. X-ray diffraction did not show any change in the crystalline structure induced by laser processing. It was concluded that the femtosecond laser is a clean and safe method for surface modification of A-Y-TZP20.

The Diametrically Loaded Cylinder for the Study of Nanostructured Aluminum–Graphene and Aluminum–Alumina Nanocomposites Using Digital Image Correlation

Non-contact methods for characterization of metal matrix composites have the potential to accelerate the development and study of advanced composite materials. In this study, diametrical compression of small disk specimens was used to understand the mechanical properties of metal matrix micro and nano composites. Analysis was performed using an inverse method that couples digital image correlation and the analytical closed form formulation. This technique was capable of extracting the tension and compression modulus values in the metal matrix nanocomposite disk specimens. Specimens of aluminum and aluminum reinforced with either Al2O3 nanoparticles or graphene nanoplatelets (GNP) were synthesized using a powder metallurgy approach that involved room temperature milling in ethanol, and low temperature drying followed by single action compaction. The elastic and failure properties of MMNC materials prepared using the procedure above are presented.

Shear compaction processing of SiC nanoparticles reinforced magnesium composites directly from magnesium chips

In this work, a novel synthesis technique, shear compaction processing (SCP), is developed to produce magnesium (Mg) based composite from Mg machining chips and nano-sized silicon carbide (SiC) particulates reinforcement. During the process, Mg machining chips are first loaded into the container and slightly compacted, and then SiC nanoparticles are added on top of the compacted Mg chips. A scroll-faced rotating tool with a designated diameter is plunged into the Mg chips at a selected spindle rotation speed and feed rate. Due to the huge amounts of heat generation, the softened materials are compressed and synthesized to form a nanocomposite disk eventually. The results show that the SCP process is a feasible solution for producing a void-free bulk nanocomposite material directly from Mg chips and SiC nanoparticles in a single step. The microstructural analysis with optical microscopy and scanning electron microscopy clearly shows the significant grain refinement in the produced nanocomposite disk. The reinforcement of nanoparticles is uniformly distributed in the mixed domain. Good interfacial bonding is captured between the matrix and SiC nanoparticles. The produced specimen has a higher hardness than the parent material, and also exhibits excellent wear resistance. The significant improvement is attributed to the resulting fine-grained microstructure and homogenous distribution of SiC nanoparticles throughout the matrix material of Mg, due to severe plastic deformation and mixing during the SCP process.

Free vibration analysis of thick disks with variable thickness containing orthotropic-nonhomogeneous material using finite element method

Free vibration analysis of thick functionally graded nanocomposite annular and solid disks with variable thickness reinforced by single-walled carbon nanotubes (SWCNTs) is presented. Four types of distribution of uniaxial aligned SWCNTs are considered: uniform and three kinds of functionally graded (FG) distribution through radial direction of the disk. The effective material properties of the nanocomposite disk are estimated by a micro mechanical model. The axisymmetric conditions are assumed and employing the graded finite element method (GFEM), the equations are solved. The solution is considered for four different thickness profiles, namely constant, linear, concave and convex. The achieved results show that the type of distribution and volume fraction of CNTs and thickness profile have a great effect on normalized natural frequencies.

Tissue mechanics of piled critical size biomimetic and biominerizable nanocomposites: Formation of bioreactor-induced stem cell gradients under perfusion and compression

BackgroundPerfusion bioreactors are used to solve problems in critical size bone tissue engineering. Biominerizable and biocompatible nanocomposites are suitable scaffold materials for this purpose because they offer mineral components in organic carriers. Human adipose derived stem cells (ASCs) can potentially be used to increase bone healing. Materials and methodsElectrospun nanocomposite disks of poly-lactic-co-glycolic acid and amorphous calcium phosphate nanoparticles (PLGA/a-CaP) were seeded with ASCs and eight disks were stacked in a bioreactor running with normal culture. Under perfusion and uniaxial cyclic compression, load-displacement curves as a function of time were assessed. Stiffness and energy dissipation were recorded. Moreover, stem cell densities in the layers of the piled scaffold were determined as well as their morphologies and differentiation status. ResultsWhile the stiffness of the cell free constructs increased over time based on the transformation of the a-CaP nanoparticles into flake-like apatite, ASC-seeded constructs showed a constant stiffness. Stem cell density gradients had a linear increase from the bottom to the top of the pile (r2>0.95). Stem cells were getting more roundish at higher flow rates. Some osteogenesis was found upon osteopontin immunostaining, while no endothelial cell differentiation and no chondrogenesis was triggered. ConclusionsThe fabrication of a critical size bone graft is presented based on a biominerizable bone-biomimetic nanocomposite with preserved stiffness when seeded with ASCs. The cell densities of ASCs inside the piled construct varied with a linear gradient. Beginning osteogenesis was triggered by the dynamic culture conditions including perfusion and compression.

Nonlinear analysis of functionally graded nanocomposite rotating thick disks with variable thickness reinforced with carbon nanotubes

In this paper the nonlinear elasticity solution of functionally graded nanocomposite rotating thick disks with variable thickness reinforced with single-walled carbon nanotubes (SWCNTs) is presented. Four distribution types of uniaxial aligned SWCNTs are considered: uniform and three types of functionally graded (FG) distributions along radial direction of the disk. The effective material properties of the nanocomposite disk are estimated by a micro-mechanical model. The governing nonlinear equations are based on the axisymmetric theory of elasticity with the geometric nonlinearity in axisymmetric complete form. The nonlinear graded finite element method (NGFEM) based on Rayleigh–Ritz energy formulation with the Picard iterative scheme is employed to solve the nonlinear equations. The solution is considered for four different thickness profiles, namely constant, linear, concave and convex. The effects of different types of distributions and volume fractions of CNTs and various types of thickness profiles on the displacement and stresses of the rotating disks as well as comparison between linear and nonlinear responses are investigated. The achieved results show that the displacement and stress fields can be controlled by changing the type of distribution and volume fraction of CNTs as well as the thickness profile. Moreover, the difference between linear and nonlinear results are noticeable in high angular velocities; thus, for obtaining accurate results, the geometric nonlinearity must be considered.