Bulk Modulus Research Articles

Compressive Behaviors of High-Strength Geopolymeric Concretes: The Role of Recycled Fine Aggregate

In this study, natural fine aggregates (NFAs) in high-strength fly ash (FA)/ground granulated blast furnace slag (GGBFS)-based geopolymer concretes were both partially and completely replaced by RFAs to prepare geopolymer recycled fine aggregate concrete (GRFC). Herein, the impacts of RFA content (0%, 25%, 50%, 75%, and 100%) on the fresh and hardened performance and microstructural characteristics of a GRFC were investigated. The results indicated that with increasing RFA substitution ratio, the setting time of the GRFC decreases. In addition, the compressive strength and elastic modulus decrease. However, owing to the enhanced adhesion of the geopolymer matrix and recycled aggregate, RFA has a relatively small impact on the compressive strength, with a maximum strength loss of 9.7% at a replacement level of 75%. When the RFA content is less than 75%, the internal structure of the concrete remains relatively compact. The incorporation of RFA in concrete has been found to adversely affect its compressive strength and elastic modulus, while simultaneously increasing its brittleness. The increase in dosage of RFA leads to a reduction in the compressive strength and elastic modulus of concrete, while partial failure occurs when the GRFC constitutes 100% of the RFA. The existing stress–strain model for conventional concrete is recalibrated for the GRFC. Observed by SEM, with increasing RFA, the damage is mainly concentrated at the interface associated with the attached cement. Although the recalibrated model predicts the stress–strain responses of the GRFC reasonably well, an acceptable range of deviation is present when predicting the residual stress due to the relatively high strength and brittle behavior of the GRFC during compression. Through this research, the applicability of RFA is expanded, making it feasible to apply large quantities of this material.

Pressure and temperature dependent ab-initio quasi-harmonic thermoelastic properties of tungsten

We present the ab-initio temperature and pressure dependent thermoelastic properties of body-centered cubic tungsten. The temperature dependent quasi-harmonic elastic constants (ECs) are computed at several reference volumes including both the phonon and the electronic excitations contribution to the free energy and interpolated at different temperatures and pressures. Good agreement with the experimental ECs on a single crystal at ambient pressure is found. The pressure and temperature dependence of the shear sound velocity measured on polycrystalline tungsten by Qi et al is also in agreement with theory. Some discrepancies are found instead for the compressional velocity at high temperature and this is attributed to the temperature derivative of the bulk modulus, higher in theory than in experiment. These conclusions are reached both by PBE and by PBEsol functionals. The two give elastic properties with a similar pressure and temperature dependence although the latter is closer to experiment at 0 K.

Comprehensive Analysis of Mechanical, Economic, and Environmental Characteristics of Hybrid PE/PP Fiber-Reinforced Engineered Geopolymer Composites

Engineered Geopolymer Composites (EGCs), known for their excellent tensile properties and lower carbon emissions, have gained widespread attention in the field of fiber-reinforced concrete. However, the high cost of high-performance synthetic fibers, a crucial component of EGCs, limits their practical engineering applications. In this study, by using low-cost PP fibers hybridized with PE fibers and adjusting the fly ash/ground granulated blast furnace slag (FA/GGBS) ratio, cost-effective, high-performing hybrid PE/PP-reinforced engineered geopolymer composites (H-EGCs) were developed. This study conducted axial compressive and tensile tests on H-EGCs with different FA/GGBS ratios (7:3, 6:4, and 5:5) and PP fiber replacement ratios (0%, 25%, 50%, 75%, and 100%), investigated the influence of FA/GGBS and PP fiber replacement ratio on static mechanical behavior, and evaluated the economic and environmental benefits based on mechanical performance indicators. The result indicated that the compressive strength of H-EGCs can reach 120 MPa when the FA/GGBS ratio is 5:5; however, an increase in FA/GGBS and PP fiber replacement ratio leads to a loss in compressive strength and elastic modulus. The incorporation of PP fibers in moderate amounts enhances ultimate tensile strain by reducing crack control ability, and the maximum tensile deformation capacity (7.82–9.66%) was obtained for H-EGCs with a PP fiber replacement ratio of 50%. The optimal economic and environmental benefits of H-EGCs are observed when the FA/GGBS ratio is 5:5 and the PP fiber replacement ratio is set at 50%.

Development of Biphasic Injectable Hydrogels for Meniscus Scaffold from Photocrosslinked Glycidyl Methacrylate-Modified Poly(Vinyl Alcohol)/Glycidyl Methacrylate-Modified Silk Fibroin

The development of a hydrogel material with a modified chemical structure of poly(vinyl alcohol) (PVA) and silk fibroin (SF) using glycidyl methacrylate (GMA) (denoted as PVA-g-GMA and SF-g-GMA) is an innovative approach in the field of biomaterials and meniscus tissue engineering in this study. The PVA-g-GMA/SF-g-GMA hydrogel was fabricated using different ratios of PVA-g-GMA to SF-g-GMA: 100/0, 75/25, 50/50, 25/75, and 0/100 (w/w of dry substances), using lithium phenyl (2,4,6-trimethylbenzoyl)phosphinate (LAP) as a free radical photoinitiator, for 10 min at a low ultraviolet (UV) intensity (365 nm, 6 mW/cm2). The mechanical properties, morphology, pore size, and biodegradability of the PVA-g-GMA/SF-g-GMA hydrogel were investigated. Finally, for clinical application, human chondrocyte cell lines (HCPCs) were mixed into PVA-g-GMA/SF-g-GMA solutions and fabricated into hydrogel to study the viability of live and dead cells and gene expression. The results indicate that as the SF-g-GMA content increased, the compressive modulus of the PVA-g-GMA/SF-g-GMA hydrogel dropped from approximately 173 to 11 kPa. The degradation rates of PVA-g-GMA/SF-g-GMA 100/0, 75/25, and 50/50 reached up to 15.61%, 17.23%, and 18.93% in 4 months, respectively. In all PVA-g-GMA/SF-g-GMA conditions on day 7, chondrocyte cell vitality exceeded 80%. The PVA-g-GMA/SF-g-GMA 75:25 and 50:50 hydrogels hold promise as a biomimetic biphasic injectable hydrogel for encapsulated augmentation, offering advantages in terms of rapid photocurability, tunable mechanical properties, favorable biological responses, and controlled degradation.

Real and In-Silico Microgels Show Comparable Bulk Moduli Below and Above the Volume Phase Transition.

The compressibility of soft colloids influences their phase behavior and flow properties, especially in concentrated suspensions. Particle compressibility, which is proportional to the reciprocal of the bulk modulus K, is a key parameter for soft polymer-based particles that can be compressed in crowded environments. Here, microgels with different degrees of crosslinking, i.e.softness, are investigated below and above their volume phase transition temperature VPTT. By combining molecular dynamics simulations with small-angle neutron scattering with contrast variation, a change in the particle bulk moduli of two orders of magnitude is observed. The degree of crosslinking has a significant impact on the bulk modulus of the swollen microgel, while above the VPTT the values of K are almost independent of the crosslinking density. The excellent agreement between experimental results and simulations also highlight that the model microgels posses both the internal architecture and the elastic properties of real polymeric networks. This paves the way to a systematic use of simulations to investigate the behavior of dense microgelsuspensions. This article is protected by copyright. All rights reserved.

Reinforcing ethyl cellulose aerogels with poly(lactic acid) for enhanced bone regeneration

Abstract  Developing double porous biodegradable and biocompatible scaffolds that can incorporate and release drugs in a controlled manner holds immense potential in regenerative medicine. This study presents a synthesis method for preparing a macro-mesoporous scaffold, where poly(lactic acid) adds to the macroporous region and mechanical properties, and ethyl cellulose adds to the surface area (182 m2/g). High surface area enables the incorporation of model drug indomethacin with an entrapment efficiency of 17.0% and its later controlled release profile. The resulting scaffold has desirable mechanical properties in the range of a natural trabecular bone with a compressive modulus of 22.4 MPa. The material is stable in the simulated body fluids for 120 days before the slow degradation starts. In vitro studies demonstrate the material's ability to support bone cell adhesion, proliferation, and differentiation, promoting osteogenic activity. Overall, the unique combination of poly(lactic acid) and ethyl cellulose produces advanced materials with tailored macro and mesopore properties, remarkable mechanical properties, optimal degradation rate, and drug delivery potential, making it a promising candidate for bone scaffolds in regenerative medicine and tissue engineering.

PCL/β-TCP composite scaffolds with advanced geometries promote hMSCs osteogenic differentiation.

Critical-sized mandibular bone defects, arising from e.g. resections after tumor surgeries, are currently treated with autogenous bone grafts. This treatment is considered very invasive and is associated with limitations such as morbidity, and graft resorption. Tissue engineering approaches propose to use 3D scaffolds that combine structural features, biomaterial properties, cells and biomolecules to create biomimetic constructs. However, mimicking the complex anatomy and composition of the mandible poses a challenge in scaffold design. In our study, we evaluated the dual effect of complex pore geometry and material composition on the osteogenic potential of 3D printed scaffolds. The scaffolds were made of polycaprolactone (PCL) alone (TCP0), or with a high concentration of β-tricalcium phosphate (β-TCP) up to 40% w/w (TCP40), with two complex pore geometries, namely a star- (S) and a diamond-like (D) shape. SEM and micro-CT images confirmed high fidelity during the printing process. The D-scaffolds displayed higher compressive moduli than the corresponding S-scaffolds. TCP40 scaffolds in simulated body fluid showed deposition of minerals on the surface after 28 days. Subsequently, we assessed the differentiation of seeded bone marrow-derived human mesenchymal stromal cells (hMSCs) over 28 days. The early expression of RUNX2 in the cell nuclei confirmed the commitment towards an osteogenic phenotype. Moreover, ALP activity and collagen deposition displayed an increasing trend in the D-scaffolds. Collagen type I was mainly present in the deposited ECM, confirming deposition of bone matrix. Lastly, Alizarin Red staining showed successful mineralization on all the TCP40 samples, with higher values for the S-shaped scaffolds. Taken together, our study demonstrated that the complex pore architectures of scaffolds comprised TCP40 stimulated osteogenic differentiation and mineralization of hMSCs in vitro. Future research will aim to validate these findings in vivo.

Composite Thickness and Stiffness Analysis of the Nasal Septum.

Background: The nasal septum supports the structure of the nose and is frequently manipulated during septorhinoplasty. Objective: To compare measurements of thickness and compressive Young's modulus (YM) between different regions of nasal septa from human anatomic specimens. Study Design: Case series. Methods: Cartilaginous septa from human anatomic specimens were dissected. Septum thickness was measured at 24 points with regular intervals using a digital caliper. Compressive YM was determined at 14 regions using a force gauge. Two-tailed student's t-tests were used to compare the average thickness and YM between different regions. Results: Septa from 40 human anatomic specimens were included, with age ranging from 50 to 89. Fifty percent of specimens were female. The mean (standard deviation) thickness of the septum was 1.75 (0.76) mm. The mean YM was 2.38 (1.29) MPa. The septum was thickest near the maxillary crest (3.09 [1.17] mm) and the keystone area (2.52 [0.91] mm) and thinnest near the anterior septal angle (1.29 [0.58] mm). The septum was most stiff posteriorly (2.90 [1.32] MPa) and least stiff anteriorly (1.80 [1.15] MPa). Conclusion: The nasal septum is thickest posteriorly, inferiorly, and along its bony edges. The septum is stiffest posteriorly, ventrally, and along its bony edges.

Quantitative Insight into the Compressive Strain Rate Sensitivity of Polylactic Acid, Acrylonitrile Butadiene Styrene, Polyamide 12, and Polypropylene in Material Extrusion Additive Manufacturing

AbstractHerein, a research and engineering gap, i.e., the quantitative determination of the effects of the compressive loading rate on the engineering response of the most popular polymers in Material Extrusion (MEX) Additive Manufacturing (AM) is successfully filled out. PLA (Polylactic Acid), ABS (Acrylonitrile Butadiene Styrene), PP (Polypropylene), and PA12 (Polyamide 12) raw powders were evaluated and melt-extruded to produce fully documented filaments for 3D printing. Compressive specimens after the ASTM-D695 standard were then fabricated with MEX AM. The compressive tests were carried out in pure quasi-static conditions of the test standard (1.3 mm/min) and in accelerated loading rates of 50, 100, 150, and 200 mm/min respectively per polymer. The experimental and evaluation course proved differences in engineering responses among different polymers, in terms of compressive strength, elasticity modulus, toughness, and strain rate sensitivity index. A common finding was that the increase in the strain rate increased the mechanical response of the polymeric parts. The increase in the compressive strength reached 25% between the lowest and the highest strain rates the parts were tested for most polymers. Remarkable variations of deformation and fracture modes were also observed and documented. The current research yielded results with valuable predictive capacity for modeling and engineering modeling, which hold engineering and industrial merit.

Low-Concentration Gelatin Methacryloyl Hydrogel with Tunable 3D Extrusion Printability and Cytocompatibility: Exploring Quantitative Process Science and Biophysical Properties.

Three-dimensional (3D) bioprinting of hydrogels with a wide spectrum of compositions has been widely investigated. Despite such efforts, a comprehensive understanding of the correlation among the process science, buildability, and biophysical properties of the hydrogels for a targeted clinical application has not been developed in the scientific community. In particular, the quantitative analysis across the entire developmental path for 3D extrusion bioprinting of such scaffolds is not widely reported. In the present work, we addressed this gap by using widely investigated biomaterials, such as gelatin methacryloyl (GelMA), as a model system. Using extensive experiments and quantitative analysis, we analyzed how the individual components of methacrylated carboxymethyl cellulose (mCMC), needle-shaped nanohydroxyapatite (nHAp), and poly(ethylene glycol)diacrylate (PEGDA) with GelMA as baseline matrix of the multifunctional bioink can influence the biophysical properties, printability, and cellular functionality. The complex interplay among the biomaterial ink formulations, viscoelastic properties, and printability toward the large structure buildability (structurally stable cube scaffolds with 15 mm edge) has been explored. Intriguingly, the incorporation of PEGDA into the GelMA/mCMC matrix offered improved compressive modulus (∼40-fold), reduced swelling ratio (∼2-fold), and degradation rates (∼30-fold) compared to pristine GelMA. The correlation among microstructural pore architecture, biophysical properties, and cytocompatibility is also established for the biomaterial inks. These photopolymerizable bio(material)inks served as the platform for the growth and development of bone and cartilage matrix when human mesenchymal stem cells (hMSCs) are either seeded on two-dimensional (2D) substrates or encapsulated on 3D scaffolds. Taken together, this present study unequivocally establishes a significant step forward in the development of a broad spectrum of shape-fidelity compliant bioink for the 3D bioprinting of multifunctional scaffolds and emphasizes the need for invoking more quantitative analysis in establishing process-microstructure-property correlation.

Machine Learning-Based Prediction of Elastic Properties Using Reduced Datasets of Accurate Calculations Results

In this paper, the applicability of machine learning for predicting the elastic properties of binary and ternary bcc Ti and Zr disordered alloys with 34 different doping elements is explored. The original dataset contained 3 independent elastic constants, bulk moduli, shear moduli, and Young’s moduli of 1642 compositions calculated using the EMTO-CPA method and PAW-SQS calculation results for 62 compositions. The architecture of the system is made as a pipeline of a pair of predicting blocks. The first one took as the input a set of descriptors of the qualitative and quantitative compositions of alloys and approximated the EMTO-CPA data, and the second one took predictions of the first model and trained on the results of the PAW-SQS calculations. The main idea of such architecture is to achieve prediction accuracy at the PAW-SQS level, while reducing the resource intensity for obtaining the training set by a multiple of the ratio of the training subsets sizes corresponding to the two used calculation methods (EMTO-CPA/PAW-SQS). As a result, model building and testing methods accounting for the lack of accurate training data on the mechanical properties of alloys (PAW-SQS), balanced out by using predictions of inaccurate resource-effective first-principle calculations (EMTO-CPA), are demonstrated.

Tuning the mechanical characteristics of ZnO nanosheets via C, F, and P doping: A DFT approach

This study investigates the impact of doping with carbon (C), fluorine (F), and phosphorus (P) atoms on the structural and mechanical properties of 2 × 2 and 3 × 3 ZnO monolayers using Density Functional Theory (DFT) calculations. Our analysis reveals a notable decrease in both the elastic and bulk moduli of the monolayers upon doping, with the most significant reduction observed in the P-doped structure. For the pristine structure, the elastic modulus is measured at 78.84 N/m for the 2×2 monolayer and 79.46 N/m for the 3×3 monolayer, while the bulk modulus is 62.47 N/m and 63.94 N/m, respectively. Following P doping, the elastic modulus decreases by 56.02 % (34.67 N/m) in the 2 × 2 monolayer and 46.40 % (42.59 N/m) in the 3 × 3 monolayer. Similarly, the bulk modulus experiences substantial decreases of 53.09 % (29.30 N/m) in the 2 × 2 monolayer and 42.96 % (36.47 N/m) in the 3×3 monolayer upon P doping. Additionally, C and F doping result in reductions of 26.10 % and 11.04 % in the elastic modulus of the 2×2 monolayer and 26.27 % and 10.92 % in the 3×3 monolayer, respectively. The corresponding bulk modulus reductions are 14.51 % and 10.79 % in the 2×2 monolayer and 20.12 % and 11.15 % in the 3×3 monolayer, respectively. These findings underscore the considerable influence of various dopants on the mechanical characteristics of ZnO nanosheets, with P doping inducing the most significant reductions in both elastic and bulk moduli, suggesting its efficacy in tuning the mechanical properties of ZnO nanosheets for diverse applications.

Optoelectronic and mechanical properties of gallium arsenide alloys: Based on density functional theory

First principles calculations based on density functional theory (DFT) were performed to investigate the structural, electronic, optical and mechanical properties of pristine GaAs compound and its alloy; Ga0.75Al0.25As, Ga0.75In0.25As, Ga0.75Sn0.25As, Ga0.75Ti0.25As. WIEN2K and Quantum expresso (QE) codes were adopted for calculations using generalized gradient approximation (GGA) in Perdew-Burke Erzenhoff (PBE) as exchange correlation function for both codes. Full potential linear augmented plane wave (FPLAPW) with the local orbital method was adopted as implement in WIEN2K code. In QE code, norm-conserving pseudopotentials were employed on a plane-wave expansion of the wave functions. Structural and electronic properties were elaborated since their result gives information about the optical and mechanical performance. Electronic band structure and optical parameters were performed using WIEN2K code. Underestimation of band gap observed from DFT calculations were corrected by using Modified Becke and Johnson (mBJ). Mechanical components were determined using QE with thermo_pw package. Lattice constant, volume, bulk modulus and other physical parameters were calculated for structural properties. Discrepancy in these parameters as observed in crystal structure is associated to difference in ionic radius of host and substituted atom. The results of band structure and density of states were calculated for electronic properties. All the studied compounds were semiconductors in nature except Ga0.75Sn0.25As which displayed metallic character. Optical parameters including extinction coefficient, absorption coefficient, refractive index, optical conductivity, optical reflectivity and energy loss function have been computed from the dielectric function at energy range of 0 to 25 eV using the Kramers-Kronig transformations. Calculated elastic function were used to compute the mechanical properties such as anisotropic, brittle characteristics, stiffness and many others. All the results were compared with available theoretical and experimental records.

Development and modeling of an ultra-robust TPU-MWCNT foam with high flexibility and compressibility

Abstract Developing a cost-effective industrially scalable manufacturing method that can improve the mechanical properties of nanocomposite foams with higher flexibility, compressibility, and, at the same time, mechanically robustness is of significant interest. In this study, porous thermoplastic polyurethane (TPU)/multiwalled carbon nanotube (MWCNT) was fabricated with the chemical blowing agent (CBA) by a combination of compounding-compression molding methods. The effects of CBA and MWCNT contents on the foam morphology, porosity, foam cell size, Young’s modulus, and compressibility of fabricated samples were investigated. Through conducting cyclic compressive tests, it was observed that nanocomposite foams exhibited consistent mechanical responses across multiple compressive cycles and demonstrated notable characteristics, including high compressibility (up to 76.4% compressive strain) and high elastic modulus (up to 8.8 ± 2.6 MPa). Moreover, theoretical approaches were employed to predict the elastic modulus of solid and foam TPU/MWCNT. For solid MWCNT/TPU, a specific micromechanical model based on different modifications of the Halpin-Tsai (HT) approach was used, which showed a good agreement with experimental data at different MWCNT contents. Furthermore, the constant parameters of Gibson and Ashby’s method were found to successfully predict the elastic modulus of foam TPU/MWCNT at different MWCNT and CBA percentages.

Enhancing Concrete Mechanical Properties through Basalt Fibers and Calcium Sulfate Whiskers: Optimizing Compressive Strength, Elasticity, and Pore Structure.

To study the effects of basalt fibers (BFs), calcium sulfate whiskers (CSWs), and modified calcium sulfate whiskers (MCSWs) on the compressive strength and dynamic modulus of elasticity of concrete, this paper utilizes Mercury Intrusion Porosimetry (MIP) to measure the microstructure of concrete and calculate the fractal dimension of pore surface area. The results indicate that both CSWs and BFs can increase the compressive strength of concrete. CSWs can enhance the dynamic modulus of elasticity of concrete, while the effect of BFs on the dynamic modulus of elasticity is not significant. The improvement in compressive strength and dynamic modulus of elasticity provided by MCSWs is significantly greater than that provided by CSWs. Both CSWs and BFs can effectively improve the pore structure of concrete and have a significant impact on the surface fractal dimension. CSWs inhibit the formation of ink-bottle pores, while BFs increase the number of ink-bottle pores. Due to the ink-bottle pore effect, the fractal dimension of the capillary pore surface is generally greater than three, lacking fractal characteristics. The compressive strength and dynamic modulus of elasticity of concrete have a good correlation with the fractal dimensions of large pores and transition pores.

Influence of the Nature of Cement on the Physical and Mechanical Properties of Soil Concretes from Sandy Clay and Laterite

Soil concrete is a material produced by mixing the soil at the site with a hydraulic binder. This paper aims to study the influence of the nature of binder on the physical and mechanical properties of soil concrete. For the mixtures, three types of soil were chosen and studied: sandy clay with a granular class of 0/5 (SA5), laterite with a granular class of 0/5 (LA5), and laterite with a granular class of 0/10 (LA10). Three different cements were used: CEM I 52.5, CEM II 42.5, and CEM III 32.5, with cement contents of 150 and 250 kg/m3. The soil concretes were designed for a constant spread of 32–33 cm measured on a mini-slump. The results showed that LA5-based soil concrete has a higher water content of about 8.8% more than SA5 and LA10-based soil concretes. For all the mixtures, the lowest porosity values were obtained with CEM III 32.5, followed by CEM I 52.5, and finally CEM II 42.5. For the three types of cement and the same soil granular size, the compressive strength, static, and dynamic modulus of SA5-based soil concretes are higher than LA5. It was noted that the mechanical properties of soil concretes made with CEM III 32.5 are higher than those made with CEM I 52.5 and CEM II 42.5. Regardless of the type of cement used, the mechanical properties obtained on LA10-based soil concrete are higher than those on LA5-based soil concrete.

Glutenin-chitosan 3D porous scaffolds with tunable stiffness and systematized microstructure for cultured meat model

A glutenin (G)-chitosan (CS) complex (G-CS) was cross-linked by water annealing with aim to prepare structured 3D porous cultured meat scaffolds (CMS) here. The CMS has pore diameters ranging from 18 to 67 μm and compressive moduli from 16.09 to 60.35 kPa, along with the mixing ratio of G/CS. SEM showed the porous organized structure of CMS. FTIR and CD showed the increscent content of α-helix and β-sheet of G and strengthened hydrogen-bondings among G-CS molecules, which strengthened the stiffness of G-CS. Raman spectra exhibited an increase of G concentration resulted in higher crosslinking of disulfide-bonds in G-CS, which aggrandized the bridging effect of G-CS and maintained its three-dimensional network. Cell viability assay and immuno-fluorescence staining showed that G-CS effectively facilitated the growth and myogenic differentiation of porcine skeletal muscle satellite cells (PSCs). CLSM displayed that cells first occupied the angular space of hexagon and then ring-growth circle of PSCs were orderly formed on G-CS. The texture and color of CMS which loaded proliferated PSCs were fresh-meat like. These results showed that physical cross-linked G-CS scaffolds are the biocompatible and stable adaptable extracellular matrix with appropriate architectural cues and natural micro-environment for structured CM models.

Comprehensive Investigation of the Temperature-Dependent Electromechanical Behaviors of Carbon Nanotube/Polymer Composites.

The performances of flexible piezoresistive sensors based on polymer nanocomposites are significantly affected by the environmental temperature; therefore, comprehensively investigating the temperature-dependent electromechanical response behaviors of conductive polymer nanocomposites is crucial for developing high-precision flexible piezoresistive sensors in a wide-temperature range. Herein, carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composites widely used for flexible piezoresistive sensors were prepared, and then the temperature-dependent electrical, mechanical, and electromechanical properties of the optimized CNT/PDMS composite in the temperature range from -150 to 150 °C were systematically investigated. At a low temperature of -150 °C, the CNT/PDMS composite becomes brittle with a compressive modulus of ∼1.2 MPa and loses its elasticity and reversible sensing capability. At a high temperature (above 90 °C), the CNT/PDMS composite softens, shows a fluid-like mechanical property, and loses its reversible sensing capability. In the temperature range from -60 to 90 °C, the CNT/PDMS composite exhibits good elasticity and reversible sensing behaviors and its modulus, resistivity, and sensing sensitivity decrease with an increasing temperature. At room temperature (30 °C), the CNT/PDMS composite exhibits better mechanical and piezoresistive stability than those at low and high temperatures. Given that environmental temperature changes have significant effects on the sensing performances of conductive polymer composites, the effect of ambient temperature changes must be considered when flexible piezoresistive sensors are designed and fabricated.

Atom pair bond approach: an efficient method for determining the lattice parameters of NiAs-type compounds and comparative analysis with computational databases

Comparison of EOS properties such as lattice parameters, bulk modulus, etc calculated by density functional theory (DFT) with experiments is used, in general, to assess the precision reachable in computations, when using different codes and potentials. DFT calculations using a large number of codes and potentials by different groups, have reported excellent precision (0.02 Å) in the lattice parameters of 71 elements. It is of interest to study the precision levels reachable in compounds of hexagonal NiAs type crystal structure, in which a wide range of electrical conductivity and magnetic order are found to occur. In this study, lattice parameters for 42 intermetallic compounds of the NiAs type structure are determined from internal radii using the Atom Pair Bond method. These values are compared with the lattice parameters reported from the high throughput DFT computational techniques such as AFLOW and Materials Project compilations. Precision in lattice parameters obtainable in the three methods is assessed in comparison with those reported from the experiments. Selection of a set of compounds of same crystal structure brings out the role of differences in the electronic structure of elements involved. In the APB method, lattice parameters are obtained by the best-fit equations defined by radii change in a large number of compounds with a particular structure, and do not involve several approximations, unlike in DFT. It is interesting to see that the simple APB approach could estimate lattice parameters with accuracies comparable to DFT methods.

An In Situ-Gelling Conductive Hydrogel for Potential Use in Neural Tissue Engineering.

Cerebral cavitation is usual following acute brain injuries, such as stroke and traumatic brain injuries, as well as after tumor resection. Minimally invasive implantation of an injectable scaffold in the cavity is a promising approach for potential regeneration of tissue loss. This study aimed at designing an in situ-gelling conductive hydrogel containing silk fibroin (SF), brain decellularized extracellular matrix (dECM), and carbon nanotubes (CNT) for potential use in brain tissue regeneration. Two percent w/v SF hydrogels with different concentrations of dECM (0.1%, 0.2%, or 0.3% w/v) and CNTs (0.05%, 0.1%, or 0.25% w/v) were fabricated and characterized. It was observed that with the addition of dECM, the porosity decreased, whereas swelling and electrical conductivity tended to increase. The addition of dECM also led to a faster resorption rate, but no significant change in compressive modulus. Addition of CNTs, on the other hand, led to a denser, stronger, and more regular porous structure, higher swelling ratio, faster gelation time, slower degradation rate, and a significant increase in electrical conductivity. dECM and CNTs combined together resulted in superior porosity, swelling, resorption rate, mechanical properties, and electrical conductivity compared with SF scaffolds containing only dECM or CNTs. Hydrogel samples containing 2% SF, 0.3% dECM, and 0.1% CNTs had a high porosity (58.9%), low swelling ratio (15.9%), high conductivity (2.35 × 10-4 S/m), and moderate degradation rate (37.3% after 21 days), appropriate for neural tissue engineering applications. Cell evaluation studies also showed that the hydrogel systems support the cell adhesion and growth, with no sign of significant cytotoxicity. Impact statement Tissue loss and formation of a fluid-filled cavity following stroke, traumatic brain injury, or brain tumor resection lead to sensorimotor and/or cognitive deficits. The lack of a healthy extracellular matrix in the cavity avoids the endogenous cell migration and axonal sprouting and may also worsen the secondary injuries to peri-lesional tissue. Due to the brain anatomy, simple implantation of tissue engineering scaffolds to the injured site is not possible in many cases. Therefore, the development of injectable scaffolds that support neural growth and differentiation is crucial for tissue repair or limiting the expansion of damage region.