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Materials, Volume 12, Issue 20 (October-2 2019)

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Open AccessArticle
Optically Transparent Metamaterial Absorber Using Inkjet Printing Technology
Materials 2019, 12(20), 3406; https://doi.org/10.3390/ma12203406 (registering DOI) - 17 Oct 2019
Abstract
An optically transparent metamaterial absorber that can be obtained using inkjet printing technology is proposed. In order to make the metamaterial absorber optically transparent, an inkjet printer was used to fabricate a thin conductive loop pattern. The loop pattern had a width of [...] Read more.
An optically transparent metamaterial absorber that can be obtained using inkjet printing technology is proposed. In order to make the metamaterial absorber optically transparent, an inkjet printer was used to fabricate a thin conductive loop pattern. The loop pattern had a width of 0.2 mm and was located on the top surface of the metamaterial absorber, and polyethylene terephthalate films were used for fabricating the substrate. An optically transparent conductive indium tin oxide film was introduced in the bottom ground plane. Therefore, the proposed metamaterial absorber was optically transparent. The metamaterial absorber was demonstrated by performing a full-wave electromagnetic simulation and measured in free space. In the simulation, the 90% absorption bandwidth ranged from 26.6 to 28.8 GHz, while the measured 90% absorption bandwidth was 26.8–28.2 GHz. Therefore, it is successfully demonstrated by electromagnetic simulation and measurement results. Full article
(This article belongs to the Special Issue Metamaterials and Devices)
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Open AccessCorrection
Correction: Effect of Hygrothermal Aging and Surface Treatment on the Dynamic Mechanical Behavior of Flax Fiber Reinforced Composites. Materials 2019, 12(15), 2376
Materials 2019, 12(20), 3405; https://doi.org/10.3390/ma12203405 (registering DOI) - 17 Oct 2019
Abstract
The Y-axis in both Figure 3 and Figure 4 of [...] Full article
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Open AccessArticle
Performance of Fly Ash Geopolymer Concrete Incorporating Bamboo Ash at Elevated Temperature
Materials 2019, 12(20), 3404; https://doi.org/10.3390/ma12203404 (registering DOI) - 17 Oct 2019
Abstract
This paper presents the experimental results on the behavior of fly ash geopolymer concrete incorporating bamboo ash on the desired temperature (200 °C to 800 °C). Different amounts of bamboo ash were investigated and fly ash geopolymer concrete was considered as the control [...] Read more.
This paper presents the experimental results on the behavior of fly ash geopolymer concrete incorporating bamboo ash on the desired temperature (200 °C to 800 °C). Different amounts of bamboo ash were investigated and fly ash geopolymer concrete was considered as the control sample. The geopolymer was synthesized with sodium hydroxide and sodium silicate solutions. Ultrasonic pulse velocity, weight loss, and residual compressive strength were determined, and all samples were tested with two different cooling approaches i.e., an air-cooling (AC) and water-cooling (WC) regime. Results from these tests show that with the addition of 5% bamboo ash in fly ash, geopolymer exhibited a 5 MPa (53%) and 5.65 MPa (66%) improvement in residual strength, as well as 940 m/s (76%) and 727 m/s (53%) greater ultrasonic pulse velocity in AC and WC, respectively, at 800 °C when compared with control samples. Thus, bamboo ash can be one of the alternatives to geopolymer concrete when it faces exposure to high temperatures. Full article
(This article belongs to the Special Issue Supplementary Cementitious Materials in Concrete)
Open AccessArticle
Meso-Scale Simulation of Concrete Uniaxial Behavior Based on Numerical Modeling of CT Images
Materials 2019, 12(20), 3403; https://doi.org/10.3390/ma12203403 (registering DOI) - 17 Oct 2019
Abstract
It is important to study the failure mechanism of concrete by observing the crack expansion and capturing key structures at the mesoscale. This manuscript proposed a method for efficiently identifying aggregate boundary information by X-ray computed tomography technology (CT) and a discrete element [...] Read more.
It is important to study the failure mechanism of concrete by observing the crack expansion and capturing key structures at the mesoscale. This manuscript proposed a method for efficiently identifying aggregate boundary information by X-ray computed tomography technology (CT) and a discrete element modeling method (DEM) for equivalent random polygon aggregates. This method overcomes the shortcomings of the Grain Based Model (GBM) which is impossible to establish a mesoscopic model with a large difference in grain radius. Through the above two methods, the CT slice images were processed in batches, and the numbers of edges, axial length, elongation of the aggregate were identified. The feasibility of the method was verified by the comparison between experimental and simulating results. Three mesoscopic models for different porosities were established. Based on aggregate statistics, this manuscript achieved the meso-model recovery to the maximum extent. The test results show that the crack appeared at the tip of the aggregate firstly, and then the broken boundary was applied in the direction of the applied load and around the pores. Finally, the crack was selectively expanded under the axial force. During the loading process, the minor principal stress was normally distributed. As the porosity and loading time increased, the heterogeneity increased. Full article
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Open AccessArticle
Formability of Ultrasonically Additive Manufactured Ti-Al Thin Foil Laminates
Materials 2019, 12(20), 3402; https://doi.org/10.3390/ma12203402 (registering DOI) - 17 Oct 2019
Abstract
This study investigates the effect of strain rates and temperatures on the mechanical behavior of ultrasonically consolidated Titanium–Aluminum thin foils to understand and characterize their formability. To this goal, laminated composite samples with a distinct number of layers were bonded using ultrasonic consolidation. [...] Read more.
This study investigates the effect of strain rates and temperatures on the mechanical behavior of ultrasonically consolidated Titanium–Aluminum thin foils to understand and characterize their formability. To this goal, laminated composite samples with a distinct number of layers were bonded using ultrasonic consolidation. Then, tensile and biaxial hydraulic bulge tests at different strain rates and temperature conditions were conducted. The effect of the sample orientation on the mechanical response was also examined. Tensile and hydraulic bulge tests results were compared to observe differences in ultimate tensile strength and strain levels under uniaxial and biaxial loading conditions. The effects of loading condition, strain rate, and temperature on the material response were analyzed and discussed on the basis of test results. In general, it was concluded that the maximum elongation values attained were higher for the samples subtracted along the sonotrode movement direction compared to those obtained from the normal to sonotrode movement direction. The elongation was obtained as high as 46% for seven bi-layered samples at high-temperature ranges of 200–300 °C. Hydraulic bulge test results showed that elongation improved as the number of bi-layers increased, yet the ultimate strength values did not change significantly indicating an expansion of the formability window. Full article
Open AccessArticle
Three-Dimensional Vibration Analysis of a Functionally Graded Sandwich Rectangular Plate Resting on an Elastic Foundation Using a Semi-Analytical Method
Materials 2019, 12(20), 3401; https://doi.org/10.3390/ma12203401 (registering DOI) - 17 Oct 2019
Abstract
The three-dimensional vibration of a functionally graded sandwich rectangular plate on an elastic foundation with normal boundary conditions was analyzed using a semi-analytical method based on three-dimensional elasticity theory. The material properties of the sandwich plate varied with thickness according to the power [...] Read more.
The three-dimensional vibration of a functionally graded sandwich rectangular plate on an elastic foundation with normal boundary conditions was analyzed using a semi-analytical method based on three-dimensional elasticity theory. The material properties of the sandwich plate varied with thickness according to the power law distribution. Two types of functionally graded material (FGM) sandwich plates were investigated in this paper: one with a homogeneous core and FGM facesheets, and another with homogeneous panels and an FGM core. Various displacements of the plates were created using an improved Fourier series consisting of a standard Fourier cosine series along with a certain number of closed-form auxiliary functions satisfying the essential boundary conditions. The vibration behavior of the FGM sandwich plate, including the natural frequencies and mode shapes, was obtained using the Ritz method. The effectiveness and accuracy of the suggested technique were fully verified by comparing the natural frequencies of sandwich plates with results from investigations of other functionally graded sandwich rectangular plates in the literature. A parametric study, including elastic parameters, foundation parameters, power law exponents, and layer thickness ratios, was performed, and some new results are presented. Full article
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Open AccessArticle
A Vitronectin-Derived Bioactive Peptide Improves Bone Healing Capacity of SLA Titanium Surfaces
Materials 2019, 12(20), 3400; https://doi.org/10.3390/ma12203400 (registering DOI) - 17 Oct 2019
Abstract
In this study, we evaluated early bone responses to a vitronectin-derived, minimal core bioactive peptide, RVYFFKGKQYWE motif (VnP-16), both in vitro and in vivo, when the peptide was treated on sandblasted, large-grit, acid-etched (SLA) titanium surfaces. Four surface types of titanium discs and [...] Read more.
In this study, we evaluated early bone responses to a vitronectin-derived, minimal core bioactive peptide, RVYFFKGKQYWE motif (VnP-16), both in vitro and in vivo, when the peptide was treated on sandblasted, large-grit, acid-etched (SLA) titanium surfaces. Four surface types of titanium discs and of titanium screw-shaped implants were prepared: control, SLA, scrambled peptide-treated, and VnP-16-treated surfaces. Cellular responses, such as attachment, spreading, migration, and viability of human osteoblast-like HOS and MG63 cells were evaluated in vitro on the titanium discs. Using the rabbit tibia model with the split plot design, the implants were inserted into the tibiae of four New Zealand white rabbits. After two weeks of implant insertion, the rabbits were sacrificed, the undecalcified specimens were prepared for light microscopy, and the histomorphometric data were measured. Analysis of variance tests were used for the quantitative evaluations in this study. VnP-16 was non-cytotoxic and promoted attachment and spreading of the human osteoblast-like cells. The VnP-16-treated SLA implants showed no antigenic activities at the interfaces between the bones and the implants and indicated excellent bone-to-implant contact ratios, the means of which were significantly higher than those in the SP-treated implants. VnP-16 reinforces the osteogenic potential of the SLA titanium dental implant. Full article
(This article belongs to the Special Issue Dental Implant Materials 2019)
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Open AccessArticle
Antibacterial Activity and Biodegradation of Cellulose Fiber Blends with Incorporated ZnO
Materials 2019, 12(20), 3399; https://doi.org/10.3390/ma12203399 (registering DOI) - 17 Oct 2019
Abstract
This research aimed to study the influence of lyocell with incorporated ZnO (CLY) for antibacterial activity and biodegradation of fiber blends composed of viscose (CV), flax (LI), and CLY. Fiber blended samples with an increased weight fraction of CLY fibers were composed, and [...] Read more.
This research aimed to study the influence of lyocell with incorporated ZnO (CLY) for antibacterial activity and biodegradation of fiber blends composed of viscose (CV), flax (LI), and CLY. Fiber blended samples with an increased weight fraction of CLY fibers were composed, and single CLY, CV and LI fibers were also used for comparison. Antibacterial activity was determined for the Gram-negative Escherichia coli and the Gram-positive Staphylococcus aureus bacteria. The biodegradation of fiber blends was investigated by the soil burial test. The results show that the single CLY fibers exhibited high antimicrobial activity against both E. coli and S. aureus bacteria and that the presence of LI fibers in the blended samples did not significantly affect antibacterial activity against E. coli, but drastically decreased the antibacterial activity against S. aureus. LI fibers strongly promoted the growth of S. aureus and, consequently, impaired the antimicrobial performance of ZnO against this bacterium. The presence of CLY fibers slowed down, but did not prevent, the biodegradation process of the fiber blends, even at the highest ZnO concentration. The soil that was in contact with the fiber blended samples during their burial was not contaminated to such an extent as to affect the growth of sprouts, confirming the sustainability of the fiber blends. Full article
(This article belongs to the Special Issue Antimicrobial Textile)
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Open AccessArticle
Comparative Study of Phenomenological Residual Strength Models for Composite Materials Subjected to Fatigue: Predictions at Constant Amplitude (CA) Loading
Materials 2019, 12(20), 3398; https://doi.org/10.3390/ma12203398 (registering DOI) - 17 Oct 2019
Abstract
The most popular methods of characterizing a composite’s fatigue properties and predicting its life are phenomenological, meaning the micro-mechanisms of composite structures under cyclic loading are not treated. In addition, in order to characterize the fatigue properties, only macro-parameters, namely strength and/or stiffness, [...] Read more.
The most popular methods of characterizing a composite’s fatigue properties and predicting its life are phenomenological, meaning the micro-mechanisms of composite structures under cyclic loading are not treated. In addition, in order to characterize the fatigue properties, only macro-parameters, namely strength and/or stiffness, are adopted. Residual strength models are mostly used in practice, given their strong relationship with safety and reliability. Indeed, since failure occurs when the strength degrades to the peak stress of fatigue loading, the remaining strength is used as a failure index. In this paper, based on a wide set of literature data, we summarize the capabilities of four models, namely Caprino’s, D’Amore’s, Sendekyj’s, and Kassapoglou’s models. The models are briefly described and then applied to the same data set, which is re-elaborated. The selected experimental data are recovered from a large experimental campaign carried out by the Federal Aviation Administration (FAA). Specimens of the same material were subjected to different loading in terms of peak stress, σmax, and stress ratio, R = σminmax, ranging from pure tension (0 < R < 1) to prevalent tension (−1 < R < 0) to tension-compression (R = −1) to pure compression (1 < R < ∞). The data represent a formidable test bed to comparatively evaluate the models’ capabilities and their predictive prerogatives. The models are also tested with respect to their ability to replicate the principal responses’ feature of composite materials subjected to constant amplitude (CA) loadings. It is shown that Caprino’s and D’Amore’s models are equally capable of adequately fitting the experimental fatigue life data under given loading conditions and predicting the fatigue behavior at different loading ratios, R, with two fixed parameters. Sendekyj’s model required different parameters’ sets for each loading condition, and Kassapoglou’s model was unable to fit the majority of fatigue life data. When compared on the basis of the residual strength data, only the recently developed D’Amore’s model revealed its reliability. Full article
(This article belongs to the Special Issue Fatigue Properties and Damage Mechanisms of Polymeric Composites)
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Open AccessArticle
Design, Experimental and Numerical Characterization of 3D-Printed Porous Absorbers
Materials 2019, 12(20), 3397; https://doi.org/10.3390/ma12203397 (registering DOI) - 17 Oct 2019
Abstract
The application of porous materials is a common measure for noise mitigation and in room acoustics. The prediction of the acoustic behavior applies material models, among which most are based on the Biot-parameters. Thereby, it is expected that, if more Biot-parameters [...] Read more.
The application of porous materials is a common measure for noise mitigation and in room acoustics. The prediction of the acoustic behavior applies material models, among which most are based on the Biot-parameters. Thereby, it is expected that, if more Biot-parameters are used, a better prediction can be obtained. Nevertheless, an estimation of the Biot-parameters from the geometric design of the material is possible for simple structures only. For common porous materials, the microstructure is typically unknown and characterized by homogenized quantities. This contribution introduces a methodology that enables the design and optimization of porous materials based on the Biot-parameters and connects these to microscopic geometric quantities. Therefore, artificial porous materials were manufactured using 3D-printing technology with a prescribed geometric design and the influence of different design variables was investigated. The Biot-parameters were identified with an inverse procedure and it can be shown that different Biot-parameters can be influenced by adjusting the geometric design variables. Based on these findings, a one-parameter optimization procedure of the material is set up to maximize the absorption characteristics in the frequency range of interest. Full article
(This article belongs to the Special Issue Damping Materials)
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Open AccessArticle
Waste-Based Pigments for Application in Ceramic Glazes and Stoneware Bodies
Materials 2019, 12(20), 3396; https://doi.org/10.3390/ma12203396 (registering DOI) - 17 Oct 2019
Abstract
The use of wastes, some of them hazards, as raw materials of ceramic pigments has been a way to diminish their environmental impact, to economically valorize them, and to face the depletion of virgin raw materials. In this work were prepared pigments having [...] Read more.
The use of wastes, some of them hazards, as raw materials of ceramic pigments has been a way to diminish their environmental impact, to economically valorize them, and to face the depletion of virgin raw materials. In this work were prepared pigments having in their composition only industrial wastes: Cr/Ni electroplating (ES), and sludges from the cutting of natural stones—marble (MS) and granite (GS). The prepared mixtures were calcined at three temperatures (1100, 1200, and 1300 °C) and the obtained powders were characterized by XRD and UV-vis. Their coloring strength and thermal stability were assessed by adding them to different ceramic substrates: glazes (transparent bright and opaque matte) and a stoneware paste. The CIEL*a*b* coordinates of the fired materials were measured. The developed pigments are thermally stable and exhibit good tinting power, originating nicely colored and defect-free ceramic materials. Full article
(This article belongs to the Special Issue Recent Progress in Sustainable Clay Ceramics)
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Open AccessArticle
Effect of Dentin Bonding Agents, Various Resin Composites and Curing Modes on Bond Strength to Human Dentin
Materials 2019, 12(20), 3395; https://doi.org/10.3390/ma12203395 (registering DOI) - 17 Oct 2019
Abstract
This study investigated the influence of several dentin bonding agents, resin composites and curing modes on push-out bond strength to human dentin. 360 extracted caries-free third molars were prepared, cut into slices, embedded in epoxy resin and perforated centrally. One half of the [...] Read more.
This study investigated the influence of several dentin bonding agents, resin composites and curing modes on push-out bond strength to human dentin. 360 extracted caries-free third molars were prepared, cut into slices, embedded in epoxy resin and perforated centrally. One half of the specimens (180) were treated by using one-step adhesive systems and the other half (180) with multi-step adhesive systems. Subsequently, the cavities were filled with either universal, flowable or bulk-fill resin composite according to the manufactures’ product line and cured with either turbo or soft start program. After storage the push-out test was performed. The data was analyzed using Kolmogorov-Smirnov, three- and one-way ANOVA followed by the Scheffé post-hoc test, unpaired two-sample t-test (p < 0.05). The strongest influence on push-out bond strength was exerted by the resin composite type (partial eta squared ηP2 = 0.505, p < 0.001), followed by the adhesive system (ηP2 = 0.138, p < 0.001), while the choice of the curing intensity was not significant (p = 0.465). The effect of the binary or ternary combinations of the three parameters was significant for the combinations resin composite type coupled adhesive system (ηP2 = 0.054, p < 0.001), only. The flowable resin composites showed predominantly mixed, while the universal and bulk-fill resin composite showed adhesive failure types. Cohesive failure types were not observed in any group. Multi-step adhesive systems are preferable to one-step adhesive systems due to their higher bond strength to dentin. Flowable resin composites showed the highest bond strength and should become more important as restoration material especially in cavity lining. The use of a soft start modus for polymerization of resin composites does not enhance the bond strength to dentin. Full article
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Open AccessArticle
Preparation of Small-Particle and High-Density Cobalt Carbonate Using a Continuous Carbonate Precipitation Method and Evaluation of Its Growth Mechanism
Materials 2019, 12(20), 3394; https://doi.org/10.3390/ma12203394 (registering DOI) - 17 Oct 2019
Abstract
Spherical CoCO3 powder with a small particle size and high density was successfully prepared using a continuous carbonate liquid precipitation method with a raw material of cobalt chloride solution, a precipitant of NH4HCO3, and without a template. The [...] Read more.
Spherical CoCO3 powder with a small particle size and high density was successfully prepared using a continuous carbonate liquid precipitation method with a raw material of cobalt chloride solution, a precipitant of NH4HCO3, and without a template. The effects of the concentration of ammonium carbonate, process pH, and feeding rate on the tap density and apparent density of cobalt carbonate were investigated. It was found that the apparent and tap density values of 4.4 µm of cobalt carbonate were 1.27 g/cm3 and 1.86 g/cm3, respectively, when the initial concentration of NH4HCO3 solution was 60 g/L, the pH was 7.15–7.20, and the feeding rate of cobalt chloride was 2 L/h. The anisotropic growth process of the crystal lattice plane of CoCO3 under the aforementioned optimal conditions were studied. The results demonstrated that the crystal grew fastest along the (110) facet orientation, which was the dominant growth surface, determining the final morphology of the primary particles. The scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HR-TEM) results demonstrated that the primary particle morphology of the cobalt carbonate was a nanosheet. The unit cell of cobalt carbonate, of a hexagonal structure in the horizontal direction, grew horizontally along the (110) facet orientation, while 20–35 unit cells of the carbon carbonate were stacked along the c-axis in the thickness direction. Finally, the sheet-shaped particles were agglomerated into dense spherical secondary particles, as presented through the crystal re-crystallization model. Full article
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Open AccessArticle
Radiation Synthesis of Pentaethylene Hexamine Functionalized Cotton Linter for Effective Removal of Phosphate: Batch and Dynamic Flow Mode Studies
Materials 2019, 12(20), 3393; https://doi.org/10.3390/ma12203393 (registering DOI) - 17 Oct 2019
Abstract
A quaternized cotton linter fiber (QCLF) based adsorbent for removal of phosphate was prepared by grafting glycidyl methacrylate onto cotton linter and subsequent ring-opening reaction of epoxy groups and further quaternization. The adsorption behavior of the QCLF for phosphate was evaluated in a [...] Read more.
A quaternized cotton linter fiber (QCLF) based adsorbent for removal of phosphate was prepared by grafting glycidyl methacrylate onto cotton linter and subsequent ring-opening reaction of epoxy groups and further quaternization. The adsorption behavior of the QCLF for phosphate was evaluated in a batch and column experiment. The batch experiment demonstrated that the adsorption process followed pseudo-second-order kinetics with an R2 value of 0.9967, and the Langmuir model with R2 value of 0.9952. The theoretical maximum adsorption capacity reached 152.44 mg/g. The experimental data of the fixed-bed column were well fitted with the Thomas and Yoon–Nelson models, and the adsorption capacity of phosphate at 100 mg/L and flow rate 1 mL/min reached 141.58 mg/g. The saturated QCLF could be regenerated by eluting with 1 M HCl. Full article
(This article belongs to the Special Issue Environmentally Friendly Polymeric Blends from Renewable Sources)
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Open AccessCommunication
Mechanical Behavior of Entangled Metallic Wire Materials under Quasi-Static and Impact Loading
Materials 2019, 12(20), 3392; https://doi.org/10.3390/ma12203392 (registering DOI) - 17 Oct 2019
Abstract
In this paper, the stiffness and damping property of entangled metallic wire materials (EMWM) under quasi-static and low-velocity impact loading were investigated. The results reveal that the maximum deformation of the EMWM mainly depends on the maximum load it bears, and that air [...] Read more.
In this paper, the stiffness and damping property of entangled metallic wire materials (EMWM) under quasi-static and low-velocity impact loading were investigated. The results reveal that the maximum deformation of the EMWM mainly depends on the maximum load it bears, and that air damping is the main way to dissipate impact energy. The EMWM can absorb more energy (energy absorption rate is over 60%) under impact conditions. The EMWM has excellent characteristics of repetitive energy absorption. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle
Characterization and Analysis of Collective Cellular Behaviors in 3D Dextran Hydrogels with Homogenous and Clustered RGD Compositions
Materials 2019, 12(20), 3391; https://doi.org/10.3390/ma12203391 (registering DOI) - 17 Oct 2019
Abstract
The interactions between substrate materials and cells usually play an important role in the hydrogel-based 3D cell cultures. However, the hydrogels that are usually used could not be parametrically regulated, especially for quantitatively regulating the spatial distribution of the adhesion sites for cells [...] Read more.
The interactions between substrate materials and cells usually play an important role in the hydrogel-based 3D cell cultures. However, the hydrogels that are usually used could not be parametrically regulated, especially for quantitatively regulating the spatial distribution of the adhesion sites for cells in 3D. Here, we employed the semisynthetic hydrogel consisting of maleimide-dextran, Arg-Gly-Asp (RGD) peptides, and cell degradable crosslinkers to biochemically characterize the evolutionary behaviors of NIH–3T3 fibroblasts and C2C12 cells in 3D. Moreover, by comparing the cell-adhesive efficacy of 3D dextran hydrogels with four different RGD clustering rates, we explored the underlying regulation law of C2C12 connections and 3T3 aggregations. The results showed that mal-dextran hydrogel could promise cells stable viability and continuous proliferation, and induce more self-organized multicellular structures relative to 2D culture. More importantly, we found that RGD-clustered mal-dextran hydrogel has the advantage of enhancing C2C12 cell elongation and the breadthwise-aggregated connection, and promoting the 3T3 cell aggregating degree compared to that with homogenous RGD. Further, the advantages of RGD clustering hydrogel could be amplified by appropriately reducing RGD concentration. Such RGD-composition controllable mal-dextran hydrogel can function as a regulator of the collective cellular behaviors, which provides useful information for quantitatively designing the tailored hydrogel system and exploiting advanced biomaterials. Full article
(This article belongs to the Section Biomaterials)
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Open AccessArticle
A Finite Element Model for the Vibration Analysis of Sandwich Beam with Frequency-Dependent Viscoelastic Material Core
Materials 2019, 12(20), 3390; https://doi.org/10.3390/ma12203390 (registering DOI) - 17 Oct 2019
Abstract
In this work, a finite element model was developed for vibration analysis of sandwich beam with a viscoelastic material core sandwiched between two elastic layers. The frequency-dependent viscoelastic dynamics of the sandwich beam were investigated by using finite element analysis and experimental validation. [...] Read more.
In this work, a finite element model was developed for vibration analysis of sandwich beam with a viscoelastic material core sandwiched between two elastic layers. The frequency-dependent viscoelastic dynamics of the sandwich beam were investigated by using finite element analysis and experimental validation. The stiffness and damping of the viscoelastic material core is frequency-dependent, which results in complex vibration modes of the sandwich beam system. A third order seven parameter Biot model was used to describe the frequency-dependent viscoelastic behavior, which was then incorporated with the finite elements of the sandwich beam. Considering the parameters identification, a strategy to determine the parameters of the Biot model has been outlined, and the curve fitting results closely follow the experiment. With identified model parameters, numerical simulations were carried out to predict the vibration and damping behavior in the first three vibration modes, and the results showed that the finite model presented here had good accuracy and efficiency in the specific frequency range of interest. The experimental testing on the viscoelastic sandwich beam validated the numerical predication. The experimental results also showed that the finite element modeling method of sandwich beams that was proposed was correct, simple and effective. Full article
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Open AccessArticle
An Active Absorbent for Cleanup of High-Concentration Strong Acid and Base Solutions
Materials 2019, 12(20), 3389; https://doi.org/10.3390/ma12203389 (registering DOI) - 17 Oct 2019
Abstract
There is significant interest in developing novel absorbents for hazardous material cleanup. Iron oxide-coated melamine formaldehyde sponge (MFS/IO) absorbents with various IO layer thicknesses were synthesized. Various other absorbents were also synthesized and compared to evaluate the absorption capability of the MFS/IO absorbents [...] Read more.
There is significant interest in developing novel absorbents for hazardous material cleanup. Iron oxide-coated melamine formaldehyde sponge (MFS/IO) absorbents with various IO layer thicknesses were synthesized. Various other absorbents were also synthesized and compared to evaluate the absorption capability of the MFS/IO absorbents for strong acid (15%, v/v) and base (50%, m/m) solutions. Specifically, absorbent and solution drop tests, dust tests, and droplet fragment tests were performed. Among the various absorbents, MFS/IO absorbents possessing a needlelike surface morphology showed several unique characteristics not observed in other absorbents. The MFS/IO absorbents naturally absorbed a strong base solution (absorption time: 0.71–0.5 s, absorption capacity: 10,000–34,000%) without an additional external force and immediately absorbed a strong acid solution (0.31–0.43 s, 9830–10,810%) without absorption delay/overflow during absorbent and solution drop tests, respectively. The MFS/IO absorbents were also demonstrated to be ideal absorbents that generated fewer dust particles (semiclass 1 (ISO 3) level of 280 piece/L) than the level of a clean room (class 100). Furthermore, the MFS/IO absorbents were able to prevent the formation of droplet fragments and solution overflow during the solution drop test due to their unique surface morphology and extremely high absorption speed/capacity, respectively. Full article
(This article belongs to the Special Issue Smart Nanomaterials for Environmental Remediation)
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Open AccessArticle
High-Efficiency p-Type Si Solar Cell Fabricated by Using Firing-Through Aluminum Paste on the Cell Back Side
Materials 2019, 12(20), 3388; https://doi.org/10.3390/ma12203388 (registering DOI) - 17 Oct 2019
Abstract
Firing-through paste used for rear-side metallization of p-type monocrystalline silicon passivated emitter and rear contact (PERC) solar cells was developed. The rear-side passivation Al2O3 layer and the SiNx layer can be effectively etched by the firing-through paste. Ohmic contact [...] Read more.
Firing-through paste used for rear-side metallization of p-type monocrystalline silicon passivated emitter and rear contact (PERC) solar cells was developed. The rear-side passivation Al2O3 layer and the SiNx layer can be effectively etched by the firing-through paste. Ohmic contact with a contact resistivity between 1 to 10 mΩ·cm2 was successfully fabricated. Aggressive reactive firing-through paste would introduce non-uniform etching and high-density recombination centers at the Si/paste interface. Good balance between low resistive contact formation and relatively high open-circuit voltage can be achieved by adjusting glass frit and metal powder content in the paste. Patterned dot back contacts formed by firing-through paste can further decrease recombination density at the Si/paste interface. A P-type solar cell with an area of 7.8 × 7.8 cm2 with a Voc of 653.4 mV and an efficiency of 19.61% was fabricated. Full article
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Open AccessArticle
Temperature Monitoring and Material Flow Characteristics of Friction Stir Welded 2A14-t6 Aerospace Aluminum Alloy
Materials 2019, 12(20), 3387; https://doi.org/10.3390/ma12203387 (registering DOI) - 17 Oct 2019
Abstract
Aiming at the problems that the temperature in the welding area of friction stir welding (FSW) is difficult to measure and the joints are prone to defects. Hence, it is particularly important to study the material flow in the welding area and improve [...] Read more.
Aiming at the problems that the temperature in the welding area of friction stir welding (FSW) is difficult to measure and the joints are prone to defects. Hence, it is particularly important to study the material flow in the welding area and improve the welding quality. The temperature of the tool shoulder and the tool pin was monitored by the wireless temperature measuring system. The finite element model of friction stir welding was established and the welding conditions were numerically simulated. The flow law of material of the friction stir welding process was studied by numerical simulation. The material flow model was established by combining the microstructure analysis results, and the forming mechanism of the defects was analyzed. The results show that the temperature in the welding zone is the highest at 1300 rpm, and the temperature at the tool shoulder is significantly higher than that at the tool pin in the welding stage. When high-rotation speeds (HRS) are chosen, the material beneath the tool shoulder tends to be extruded into the pin stirred zone (PSZ) after flowing back to the advancing side. This will cause turbulence phenomenon in the advancing side of the joint, which will easily lead to the formation of welding defects. In the future, temperature monitoring methods and the flow model of material can be used to optimize the welding parameters. Full article
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Open AccessReview
Ethylcellulose–A Pharmaceutical Excipient with Multidirectional Application in Drug Dosage Forms Development
Materials 2019, 12(20), 3386; https://doi.org/10.3390/ma12203386 (registering DOI) - 17 Oct 2019
Abstract
Polymers constitute the most important group of excipients utilized in modern pharmaceutical technology, playing an essential role in the development of drug dosage forms. Synthetic, semisynthetic, and natural polymeric materials offer opportunities to overcome different formulative challenges and to design novel dosage forms [...] Read more.
Polymers constitute the most important group of excipients utilized in modern pharmaceutical technology, playing an essential role in the development of drug dosage forms. Synthetic, semisynthetic, and natural polymeric materials offer opportunities to overcome different formulative challenges and to design novel dosage forms for controlled release or for site-specific drug delivery. They are extensively used to design therapeutic systems, modify drug release, or mask unpleasant drug taste. Cellulose derivatives are characterized by different physicochemical properties, such as swellability, viscosity, biodegradability, pH dependency, or mucoadhesion, which determine their use in industry. One cellulose derivative with widespread application is ethylcellulose. Ethylcellulose is used in pharmaceutical technology as a coating agent, flavoring fixative, binder, filler, film-former, drug carrier, or stabilizer. The aim of this article is to provide a broad overview of ethylcellulose utilization for pharmaceutical purposes, with particular emphasis on its multidirectional role in the development of oral and topical drug dosage forms. Full article
(This article belongs to the Special Issue Advanced Materials in Drug Release and Drug Delivery Systems)
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Open AccessArticle
Investigation on Compression Mechanical Properties of Rigid Polyurethane Foam Treated under Random Vibration Condition: An Experimental and Numerical Simulation Study
Materials 2019, 12(20), 3385; https://doi.org/10.3390/ma12203385 (registering DOI) - 17 Oct 2019
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Abstract
The mechanical failure properties of rigid polyurethane foam treated under random vibration were studied experimentally and by numerical simulation. The random vibration treatments were carried out in the frequency range of 5–500 Hz, 500–1000 Hz, and 1000–1500 Hz, respectively. The influence of the [...] Read more.
The mechanical failure properties of rigid polyurethane foam treated under random vibration were studied experimentally and by numerical simulation. The random vibration treatments were carried out in the frequency range of 5–500 Hz, 500–1000 Hz, and 1000–1500 Hz, respectively. The influence of the vibration frequency, mass block and acceleration on the mechanical performance of rigid polyurethane foam was further investigated by compression testing. The experimental results showed that the compression performance and energy absorption of foams decreased the least between 500–1000 Hz. In addition, in the 5–500 Hz range, the reduction rate of compression performance and energy absorption increased with the increase of the vibration mass block and acceleration. The resulting simulation indicated that the deformation degree of the sample was the most serious under the condition of 5–500 Hz. With the increase of deformation, the damage of the sample during the vibration process increased, which led to the decrease of compression property and energy absorption of rigid polyurethane foam. This further explained the variation mechanism of the compression test performance. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle
Dynamic Simulation of a Fe-Ga Energy Harvester Prototype Through a Preisach-Type Hysteresis Model
Materials 2019, 12(20), 3384; https://doi.org/10.3390/ma12203384 (registering DOI) - 17 Oct 2019
Abstract
This paper presents the modeling of an Fe–Ga energy harvester prototype, within a large range of values of operating parameters (mechanical preload, amplitude and frequency of dynamic load, electric load resistance). The simulations, based on a hysteretic Preisach-type model, employ a voltage-driven finite [...] Read more.
This paper presents the modeling of an Fe–Ga energy harvester prototype, within a large range of values of operating parameters (mechanical preload, amplitude and frequency of dynamic load, electric load resistance). The simulations, based on a hysteretic Preisach-type model, employ a voltage-driven finite element formulation using the fixed-point technique, to handle the material nonlinearities. Due to the magneto–mechanical characteristics of Fe–Ga, a preliminary tuning must be performed for each preload to individualize the fixed point constant, to ensure a good convergence of the method. This paper demonstrates how this approach leads to good results for the Fe–Ga prototype. The relative discrepancies between experimental and computational values of the output power remain lower than 5% in the entire range of operating parameters considered. Full article
(This article belongs to the Special Issue Smart Materials and Devices for Energy Harvesting)
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Open AccessArticle
Experimental Research and Analysis on Fatigue Life of Carbon Fiber Reinforced Polymer (CFRP) Tendons
Materials 2019, 12(20), 3383; https://doi.org/10.3390/ma12203383 - 16 Oct 2019
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Abstract
The fatigue life of carbon fiber reinforced polymer (CFRP) tendons was studied in this paper. A new wedge-type anchorage system was applied to the fatigue test of CFRP tendons and demonstrated an excellent fatigue resistance. In the test and analytical data, the fatigue [...] Read more.
The fatigue life of carbon fiber reinforced polymer (CFRP) tendons was studied in this paper. A new wedge-type anchorage system was applied to the fatigue test of CFRP tendons and demonstrated an excellent fatigue resistance. In the test and analytical data, the fatigue stress ranged from 200 MPa to 800 MPa, and maximum stresses from 0.37 to 1.0 fu (fu = ultimate tensile strength of CFRP tendons) were determined. The main work and results were that the stress range and stress level (maximum stress) were two key parameters affecting the fatigue life of CFRP tendons. A bilinear equation and a linear equation considering the fatigue life of CFRP tendons jointly affected by the stress range and the maximum stress were established. The error of predicted results and test results was 0.038 and 0.083, respectively, both representing good prediction accuracy. The predicted results of Whitney's method showed that, at a 95% confidence level, when the stress range was 200 MPa, 400 MPa, and 600 MPa, the maximum stress limit of CFRP tendons, which were not broken in a fatigue test of 2 million times, was 63.9% fu, 53.0% fu, and 36.8% fu, respectively. Full article
Open AccessArticle
Direct Pulp Capping: Which is the Most Effective Biomaterial? A Retrospective Clinical Study
Materials 2019, 12(20), 3382; https://doi.org/10.3390/ma12203382 - 16 Oct 2019
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Abstract
(1) Background: Recently, tricalcium silicate cements, such as Biodentine™, have emerged. This biomaterial has a calcium hydroxide base and characteristics like mineral aggregate trioxide cements, but has tightening times that are substantially more suitable for their application and other clinical advantages. (2) Methods: [...] Read more.
(1) Background: Recently, tricalcium silicate cements, such as Biodentine™, have emerged. This biomaterial has a calcium hydroxide base and characteristics like mineral aggregate trioxide cements, but has tightening times that are substantially more suitable for their application and other clinical advantages. (2) Methods: A retrospective clinical study was conducted with 20 patients, which included a clinical evaluation of the presence or absence of pulp inflammation compatible symptoms, radiographic evaluation of the periapical tissues, and structural alterations of the coronary restoration that supports pulp capping therapies with Biodentine™ and WhiteProRoot®MTA. (3) Results: This clinical study revealed similar success rates between mineral trioxide cement and tricalcium silicates cements at 6 months, with 100% and 95% success rates, respectively. There were no statistically significant differences between both biomaterials and between these and the various clinical circumstances, namely the absolute isolation of the operating field, exposure size, the aetiology of exposure, and even the type of restorative material used. (4) Conclusions: Biodentine™ demonstrated a therapeutic effect on the formation of a dentin bridge accompanied by slight inflammatory signs, with a high clinical success rate, indicating the possibility of its effective and safe use in dental pulp direct capping in humans, similar to the gold standard material. Full article
(This article belongs to the Special Issue Current and Future Trends in Dental Materials)
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Open AccessArticle
Controlling Fluid Diffusion and Release through Mixed-Molecular-Weight Poly(ethylene) Glycol Diacrylate (PEGDA) Hydrogels
Materials 2019, 12(20), 3381; https://doi.org/10.3390/ma12203381 - 16 Oct 2019
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Abstract
Due to their inherent ability to swell in the presence of aqueous solutions, hydrogels offer a means for the delivery of therapeutic agents in a range of applications. In the context of designing functional tissue-engineering scaffolds, their role in providing for the diffusion [...] Read more.
Due to their inherent ability to swell in the presence of aqueous solutions, hydrogels offer a means for the delivery of therapeutic agents in a range of applications. In the context of designing functional tissue-engineering scaffolds, their role in providing for the diffusion of nutrients to cells is of specific interest. In particular, the facility to provide such nutrients over a prolonged period within the core of a 3D scaffold is a critical consideration for the prevention of cell death and associated tissue-scaffold failure. The work reported here seeks to address this issue via fabrication of hybrid 3D scaffolds with a component fabricated from mixed-molecular-weight hydrogel formulations capable of storing and releasing nutrient solutions over a predetermined time period. To this end, poly(ethylene) glycol diacrylate hydrogel blends comprising mixtures of PEGDA-575 Mw and PEGDA-2000 Mw were prepared via UV polymerization. The effects of addition of the higher-molecular-weight component and the associated photoinitiator concentration on mesh size and corresponding fluid permeability have been investigated by diffusion and release measurements using a Theophylline as an aqueous nutrient model solution. Fluid permeability across the hydrogel films has also been determined using a Rhodamine B solution and associated fluorescence measurements. The results indicate that addition of PEGDA-2000 Mw to PEGDA-575 Mw coupled with the use of a specific photoinitiator concentration provides a means to change mesh size in a hydrogel network while still retaining an overall microporous material structure. The range of mesh sizes created and their distribution in a 3D construct provides for the conditions required for a more prolonged nutrient release profile for tissue-engineering applications. Full article
(This article belongs to the Special Issue Smart Hydrogels in Biomedical Applications)
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Open AccessArticle
FEM Simulation and Verification of Brazing SiC Ceramic with Novel Zr-Cu Filler Metal
Materials 2019, 12(20), 3380; https://doi.org/10.3390/ma12203380 - 16 Oct 2019
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Abstract
Zr-Cu filler metal is proposed for SiC ceramic under special working conditions, as a novel type of the active filler metal, the difference of physical and chemical properties between SiC ceramic and Zr-Cu filler metal leads to greater residual stress in the joint, [...] Read more.
Zr-Cu filler metal is proposed for SiC ceramic under special working conditions, as a novel type of the active filler metal, the difference of physical and chemical properties between SiC ceramic and Zr-Cu filler metal leads to greater residual stress in the joint, which affects the mechanical properties of brazing SiC ceramic joint. Based on the finite element method (FEM) simulation, the residual stress of the joint is simulated to guide the design of Zr-based filler metal and formulation of brazing process. The residual stress distribution of SiC ceramic joints brazed at 1200 °C with different thickness of the filler metal and cooling rate is simulated by ANSYS software. The simulation results of the residual stress are verified by brazing experiments and XRD measurements. The results show that the simulated residual stress of the joint is mainly axial compressive stress. The axial compressive stresses are the lowest when the filler metal thickness is 0.1 mm and the cooling rate is 2 °C /min, and increase with the increase of the filler metal layer thickness and cooling rate. The shear strength of the brazed SiC ceramic joint that achieves the highest with 2 °C /min is about 72 MPa, and then decreases with the increase of cooling rate. The experimental test of residual stress in different locations of the brazed SiC ceramic joint basically coincide with the FEM simulation. Full article
(This article belongs to the Section Materials Simulation and Design)
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Open AccessArticle
Bi-Material Negative Thermal Expansion Inverted Trapezoid Lattice based on A Composite Rod
Materials 2019, 12(20), 3379; https://doi.org/10.3390/ma12203379 - 16 Oct 2019
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Abstract
Negative thermal expansion (NTE) lattices are widely used in aerospace engineering where the structures experience large temperature variation. However, the available range of NTE of the current lattices is quite narrow, which severely limits their engineering application. In this paper, we report an [...] Read more.
Negative thermal expansion (NTE) lattices are widely used in aerospace engineering where the structures experience large temperature variation. However, the available range of NTE of the current lattices is quite narrow, which severely limits their engineering application. In this paper, we report an inverted trapezoid lattice (ITL) with large NTE. The NTE of the ITL is 2.6 times that of a typical triangular lattice with the same height and hypotenuse angle. Theoretically, with a pin-jointed assumption, the ITL can improve the NTE by order of magnitude if the length ratio of the composite rod is changed. In the presented ITL, a composite rod is utilized as the base of the ITL. The composite rod has large inner NTE. The inverted trapezoid structure converts the inner NTE to the vertical direction contraction and obtains an extra NTE. Finite element simulations and experimental verification by interferometric measurement were conducted to verify the large thermal expansion of the ITL. Full article
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Open AccessArticle
The Photocatalytic Degradation of Vehicle Exhausts by an Fe/N/Co–TiO2 Waterborne Coating under Visible Light
Materials 2019, 12(20), 3378; https://doi.org/10.3390/ma12203378 - 16 Oct 2019
Viewed by 86
Abstract
Based on the three-dimensional network structure of a polymer and the principle of photocatalysts, a visible-light-responsive and durable photocatalytic coating for the degradation of vehicle exhaust (VE) has been constructed using a waterborne acrylic acid emulsion as the coating substrate; Fe/N/Co–TiO2 nanoparticles [...] Read more.
Based on the three-dimensional network structure of a polymer and the principle of photocatalysts, a visible-light-responsive and durable photocatalytic coating for the degradation of vehicle exhaust (VE) has been constructed using a waterborne acrylic acid emulsion as the coating substrate; Fe/N/Co–TiO2 nanoparticles (NPs) as photocatalytic components; and water, pigments, and fillers as additives. The visible-light-responsive Fe/N/Co–TiO2 NPs with an average size of 100 nm were prepared by sol-gel method firstly. The co-doping of three elements extended the absorption range of the modified TiO2 nanoparticles to the visible light region, and showed the highest light absorption intensity, which was confirmed by the ultraviolet-visible absorption spectra (UV-Vis). X-ray diffraction (XRD) measurements showed that element doping prevents the transition from anatase to rutile and increases the transition temperature. TiO2 was successfully doped due to the reduction of the chemical binding energy of Ti, as revealed by X-ray photoelectron spectroscopy (XPS). The degradation rates of NOX, CO, and CO2 in VE by Fe/N/Co–TiO2 NPs under visible light were 71.43%, 23.79%, and 21.09%, respectively. In contrast, under the same conditions, the degradation efficiencies of coating for VE decreased slightly. Moreover, the elementary properties of the coating, including pencil hardness, adhesive strength, water resistance, salt, and alkali resistance met the code requirement. The photocatalytic coating exhibited favorable reusability and durability, as shown by the reusability and exposure test. Full article
(This article belongs to the Special Issue Materials and Coatings for Extreme Environments)
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Open AccessFeature PaperArticle
Electrochemical Detection of Solution Phase Hybridization Related to Single Nucleotide Mutation by Carbon Nanofibers Enriched Electrodes
Materials 2019, 12(20), 3377; https://doi.org/10.3390/ma12203377 - 16 Oct 2019
Viewed by 93
Abstract
In the present study, a sensitive and selective impedimetric detection of solution-phase nucleic acid hybridization related to Factor V Leiden (FV Leiden) mutation was performed by carbon nanofibers (CNF) modified screen printed electrodes (SPE). The microscopic and electrochemical characterization of CNF-SPEs was explored [...] Read more.
In the present study, a sensitive and selective impedimetric detection of solution-phase nucleic acid hybridization related to Factor V Leiden (FV Leiden) mutation was performed by carbon nanofibers (CNF) modified screen printed electrodes (SPE). The microscopic and electrochemical characterization of CNF-SPEs was explored in comparison to the unmodified electrodes. Since the FV Leiden mutation is a widespread inherited risk factor predisposing to venous thromboembolism, this study herein aimed to perform the impedimetric detection of FV Leiden mutation by a zip nucleic acid (ZNA) probe-based assay in combination with CNF-SPEs. The selectivity of the assay was then examined against the mutation-free DNA sequences as well as the synthetic PCR samples. Full article
(This article belongs to the Special Issue Nanomaterials in Health Care Diagnostics)
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