Materials

2608 KiB

Open AccessArticle

Phase Changes of Monosulfoaluminate in NaCl Aqueous Solution

by Seyoon Yoon, Juyoung Ha, Sejung Rosie Chae, David A. Kilcoyne, Yubin Jun, Jae Eun Oh and Paulo J.M. Monteiro

Materials 2016, 9(5), 401; https://doi.org/10.3390/ma9050401 - 21 May 2016

Cited by 40 | Viewed by 7469

Abstract

Monosulfoaluminate (Ca₄Al₂(SO₄)(OH)₁₂∙6H₂O) plays an important role in anion binding in Portland cement by exchanging its original interlayer ions (SO₄²⁻ and OH⁻) with chloride ions. In this study, scanning transmission [...] Read more.

Monosulfoaluminate (Ca₄Al₂(SO₄)(OH)₁₂∙6H₂O) plays an important role in anion binding in Portland cement by exchanging its original interlayer ions (SO₄²⁻ and OH⁻) with chloride ions. In this study, scanning transmission X-ray microscope (STXM), X-ray absorption near edge structure (XANES) spectroscopy, and X-ray diffraction (XRD) were used to investigate the phase change of monosulfoaluminate due to its interaction with chloride ions. Pure monosulfoaluminate was synthesized and its powder samples were suspended in 0, 0.1, 1, 3, and 5 M NaCl solutions for seven days. At low chloride concentrations, a partial dissolution of monosulfoaluminate formed ettringite, while, with increasing chloride content, the dissolution process was suppressed. As the NaCl concentration increased, the dominant mechanism of the phase change became ion exchange, resulting in direct phase transformation from monosulfoaluminate to Kuzel’s salt or Friedel’s salt. The phase assemblages of the NaCl-reacted samples were explored using thermodynamic calculations and least-square linear combination (LC) fitting of measured XANES spectra. A comprehensive description of the phase change and its dominant mechanism are discussed. Full article

(This article belongs to the Section Advanced Composites)

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2219 KiB

Open AccessArticle

Water Uptake Behavior and Young Modulus Prediction of Composites Based on Treated Sisal Fibers and Poly(Lactic Acid)

by Ander Orue, Arantxa Eceiza, Cristina Peña-Rodriguez and Aitor Arbelaiz

Materials 2016, 9(5), 400; https://doi.org/10.3390/ma9050400 - 21 May 2016

Cited by 21 | Viewed by 5947

Abstract

The main aim of this work was to study the effect of sisal fiber surface treatments on water uptake behavior of composites based on untreated and treated fibers. For this purpose, sisal fibers were treated with different chemical treatments. All surface treatments delayed [...] Read more.

The main aim of this work was to study the effect of sisal fiber surface treatments on water uptake behavior of composites based on untreated and treated fibers. For this purpose, sisal fibers were treated with different chemical treatments. All surface treatments delayed the water absorption of fibers only for a short time of period. No significant differences were observed in water uptake profiles of composites based on fibers with different surface treatments. After water uptake period, tensile strength and Young modulus values of sisal fiber/poly(lactic acid) (PLA) composites were decreased. On the other hand, composites based on NaOH + silane treated fibers showed the lowest diffusion coefficient values, suggesting that this treatment seemed to be the most effective treatment to reduce water diffusion rate into the composites. Finally, Young modulus values of composites, before water uptake period, were predicted using different micromechanical models and were compared with experimental data. Full article

(This article belongs to the Special Issue Advances in Functionalization of Lignocellulosic Materials)

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23863 KiB

Open AccessArticle

Experimental and Numerical Evaluation of the Mechanical Behavior of Strongly Anisotropic Light-Weight Metallic Fiber Structures under Static and Dynamic Compressive Loading

by Olaf Andersen, Matej Vesenjak, Thomas Fiedler, Ulrike Jehring and Lovre Krstulović-Opara

Materials 2016, 9(5), 398; https://doi.org/10.3390/ma9050398 - 21 May 2016

Cited by 7 | Viewed by 7307

Abstract

Rigid metallic fiber structures made from a variety of different metals and alloys have been investigated mainly with regard to their functional properties such as heat transfer, pressure drop, or filtration characteristics. With the recent advent of aluminum and magnesium-based fiber structures, the [...] Read more.

Rigid metallic fiber structures made from a variety of different metals and alloys have been investigated mainly with regard to their functional properties such as heat transfer, pressure drop, or filtration characteristics. With the recent advent of aluminum and magnesium-based fiber structures, the application of such structures in light-weight crash absorbers has become conceivable. The present paper therefore elucidates the mechanical behavior of rigid sintered fiber structures under quasi-static and dynamic loading. Special attention is paid to the strongly anisotropic properties observed for different directions of loading in relation to the main fiber orientation. Basically, the structures show an orthotropic behavior; however, a finite thickness of the fiber slabs results in moderate deviations from a purely orthotropic behavior. The morphology of the tested specimens is examined by computed tomography, and experimental results for different directions of loading as well as different relative densities are presented. Numerical calculations were carried out using real structural data derived from the computed tomography data. Depending on the direction of loading, the fiber structures show a distinctively different deformation behavior both experimentally and numerically. Based on these results, the prevalent modes of deformation are discussed and a first comparison with an established polymer foam and an assessment of the applicability of aluminum fiber structures in crash protection devices is attempted. Full article

(This article belongs to the Special Issue Metal Foams: Synthesis, Characterization and Applications)

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11759 KiB

Open AccessArticle

Titanium Carbide Nanofibers-Reinforced Aluminum Compacts, a New Strategy to Enhance Mechanical Properties

by Khalil Abdelrazek Khalil, El-Sayed M. Sherif, A. M. Nabawy, Hany S. Abdo, Wagih W. Marzouk and Hamad F. Alharbi

Materials 2016, 9(5), 399; https://doi.org/10.3390/ma9050399 - 20 May 2016

Cited by 26 | Viewed by 7028

Abstract

TiC nanofibers reinforced Al matrix composites were produced by High Frequency Induction Heat Sintering (HFIHS).The titanium carbide nanofibers with an average diameter of 90 nm are first prepared by electrospinning technique and high temperature calcination process. A composite solution containing polyacrylonitrile and titanium [...] Read more.

TiC nanofibers reinforced Al matrix composites were produced by High Frequency Induction Heat Sintering (HFIHS).The titanium carbide nanofibers with an average diameter of 90 nm are first prepared by electrospinning technique and high temperature calcination process. A composite solution containing polyacrylonitrile and titanium isopropoxide is first electrospun into the nanofibers, which are subsequently stabilized and then calcined to produce the desired TiC nanofibers. The X-ray diffraction pattern and transmission electron microscopy results show that the main phase of the as-synthesized nanofibers is titanium carbide. The TiC nanofibers is then mixed with the aluminum powders and introduced into high frequency induction heat sintering (HFIHS) to produce composites of TiC nanofibers reinforced aluminum matrix. The potential application of the TiC nanofibers reinforced aluminum matrix composites was systematically investigated. 99.5% relative density and around 85 HV (833 MPa) Vickers hardness of the Al reinforced with 5 wt % TiC nanofiber has been obtained. Furthermore, the sample of Al contains 5 wt % TiC, has the highest value of compression and yield strength of about 415 and 350 MPa, respectively. The ductility of the Al/5 wt % TiC showed increasing with increasing the TiC contents. Full article

(This article belongs to the Section Advanced Composites)

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4769 KiB

Open AccessArticle

Gold Nanoparticle-Mediated Delivery of Molecules into Primary Human Gingival Fibroblasts Using ns-Laser Pulses: A Pilot Study

by Judith Krawinkel, Maria Leilani Torres-Mapa, Kristian Werelius, Alexander Heisterkamp, Stefan Rüttermann, Georgios E. Romanos and Susanne Gerhardt-Szép

Materials 2016, 9(5), 397; https://doi.org/10.3390/ma9050397 - 20 May 2016

Cited by 7 | Viewed by 5485

Abstract

Interaction of gold nanoparticles (AuNPs) in the vicinity of cells’ membrane with a pulsed laser (λ = 532 nm, τ = 1 ns) leads to perforation of the cell membrane, thereby allowing extracellular molecules to diffuse into the cell. The objective of this [...] Read more.

Interaction of gold nanoparticles (AuNPs) in the vicinity of cells’ membrane with a pulsed laser (λ = 532 nm, τ = 1 ns) leads to perforation of the cell membrane, thereby allowing extracellular molecules to diffuse into the cell. The objective of this study was to develop an experimental setting to deliver molecules into primary human gingival fibroblasts (pHFIB-G) by using ns-laser pulses interacting with AuNPs (study group). To compare the parameters required for manipulation of pHFIB-G with those needed for cell lines, a canine pleomorphic adenoma cell line (ZMTH3) was used (control group). Non-laser-treated cells incubated with AuNPs and the delivery molecules served as negative control. Laser irradiation (up to 35 mJ/cm²) resulted in a significant proportion of manipulated fibroblasts (up to 85%, compared to non-irradiated cells: p < 0.05), while cell viability (97%) was not reduced significantly. pHFIB-G were perforated as efficiently as ZMTH3. No significant decrease of metabolic cell activity was observed up to 72 h after laser treatment. The fibroblasts took up dextrans with molecular weights up to 500 kDa. Interaction of AuNPs and a pulsed laser beam yields a spatially selective technique for manipulation of even primary cells such as pHFIB-G in high throughput. Full article

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704 KiB

Open AccessArticle

Modeling of Compressive Strength for Self-Consolidating High-Strength Concrete Incorporating Palm Oil Fuel Ash

by Md. Safiuddin, Sudharshan N. Raman, Md. Abdus Salam and Mohd. Zamin Jumaat

Materials 2016, 9(5), 396; https://doi.org/10.3390/ma9050396 - 20 May 2016

Cited by 40 | Viewed by 5624

Abstract

Modeling is a very useful method for the performance prediction of concrete. Most of the models available in literature are related to the compressive strength because it is a major mechanical property used in concrete design. Many attempts were taken to develop suitable [...] Read more.

Modeling is a very useful method for the performance prediction of concrete. Most of the models available in literature are related to the compressive strength because it is a major mechanical property used in concrete design. Many attempts were taken to develop suitable mathematical models for the prediction of compressive strength of different concretes, but not for self-consolidating high-strength concrete (SCHSC) containing palm oil fuel ash (POFA). The present study has used artificial neural networks (ANN) to predict the compressive strength of SCHSC incorporating POFA. The ANN model has been developed and validated in this research using the mix proportioning and experimental strength data of 20 different SCHSC mixes. Seventy percent (70%) of the data were used to carry out the training of the ANN model. The remaining 30% of the data were used for testing the model. The training of the ANN model was stopped when the root mean square error (RMSE) and the percentage of good patterns was 0.001 and ≈100%, respectively. The predicted compressive strength values obtained from the trained ANN model were much closer to the experimental values of compressive strength. The coefficient of determination (R²) for the relationship between the predicted and experimental compressive strengths was 0.9486, which shows the higher degree of accuracy of the network pattern. Furthermore, the predicted compressive strength was found very close to the experimental compressive strength during the testing process of the ANN model. The absolute and percentage relative errors in the testing process were significantly low with a mean value of 1.74 MPa and 3.13%, respectively, which indicated that the compressive strength of SCHSC including POFA can be efficiently predicted by the ANN. Full article

(This article belongs to the Section Advanced Composites)

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1852 KiB

Open AccessArticle

Effect of Na₃PO₄ on the Hydration Process of Alkali-Activated Blast Furnace Slag

by Lukáš Kalina, Vlastimil Bílek, Radoslav Novotný, Miroslava Mončeková, Jiří Másilko and Jan Koplík

Materials 2016, 9(5), 395; https://doi.org/10.3390/ma9050395 - 20 May 2016

Cited by 44 | Viewed by 6373

Abstract

In recent years, the utilization of different non-traditional cements and composites has been increasing. Alkali-activated cementitious materials, especially those based on the alkali activation of blast furnace slag, have considerable potential for utilization in the building industry. However, alkali-slag cements exhibit very rapid [...] Read more.

In recent years, the utilization of different non-traditional cements and composites has been increasing. Alkali-activated cementitious materials, especially those based on the alkali activation of blast furnace slag, have considerable potential for utilization in the building industry. However, alkali-slag cements exhibit very rapid setting times, which are too short in some circumstances, and these materials cannot be used for some applications. Therefore, it is necessary to find a suitable retarding admixture. It was shown that the sodium phosphate additive has a strong effect on the heat evolution during alkali activation and effectively retards the hydration reaction of alkali-activated blast furnace slag. The aim of the work is the suggestion of a reaction mechanism of retardation mainly based on Raman and X‑ray photoelectron spectroscopy. Full article

(This article belongs to the Special Issue Advances in Geopolymers and Alkali-Activated Materials)

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1354 KiB

Open AccessArticle

Insulation Cork Boards—Environmental Life Cycle Assessment of an Organic Construction Material

by José D. Silvestre, Nuno Pargana, Jorge De Brito, Manuel D. Pinheiro and Vera Durão

Materials 2016, 9(5), 394; https://doi.org/10.3390/ma9050394 - 20 May 2016

Cited by 62 | Viewed by 12378

Abstract

Envelope insulation is a relevant technical solution to cut energy consumption and reduce environmental impacts in buildings. Insulation Cork Boards (ICB) are a natural thermal insulation material whose production promotes the recycling of agricultural waste. The aim of this paper is to determine [...] Read more.

Envelope insulation is a relevant technical solution to cut energy consumption and reduce environmental impacts in buildings. Insulation Cork Boards (ICB) are a natural thermal insulation material whose production promotes the recycling of agricultural waste. The aim of this paper is to determine and evaluate the environmental impacts of the production, use, and end-of-life processing of ICB. A “cradle-to-cradle” environmental Life Cycle Assessment (LCA) was performed according to International LCA standards and the European standards on the environmental evaluation of buildings. These results were based on site-specific data and resulted from a consistent methodology, fully described in the paper for each life cycle stage: Cork oak tree growth, ICB production, and end-of-life processing-modeling of the carbon flows (i.e., uptakes and emissions), including sensitivity analysis of this procedure; at the production stage—the modeling of energy processes and a sensitivity analysis of the allocation procedures; during building operation—the expected service life of ICB; an analysis concerning the need to consider the thermal diffusivity of ICB in the comparison of the performance of insulation materials. This paper presents the up-to-date “cradle-to-cradle” environmental performance of ICB for the environmental categories and life-cycle stages defined in European standards. Full article

(This article belongs to the Section Biomaterials)

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10679 KiB

Open AccessArticle

Contrastive Numerical Investigations on Thermo-Structural Behaviors in Mass Concrete with Various Cements

by Wei Zhou, Chuqiao Feng, Xinghong Liu, Shuhua Liu, Chao Zhang and Wei Yuan

Materials 2016, 9(5), 378; https://doi.org/10.3390/ma9050378 - 20 May 2016

Cited by 8 | Viewed by 4957

Abstract

This work is a contrastive investigation of numerical simulations to improve the comprehension of thermo-structural coupled phenomena of mass concrete structures during construction. The finite element (FE) analysis of thermo-structural behaviors is used to investigate the applicability of supersulfated cement (SSC) in mass [...] Read more.

This work is a contrastive investigation of numerical simulations to improve the comprehension of thermo-structural coupled phenomena of mass concrete structures during construction. The finite element (FE) analysis of thermo-structural behaviors is used to investigate the applicability of supersulfated cement (SSC) in mass concrete structures. A multi-scale framework based on a homogenization scheme is adopted in the parameter studies to describe the nonlinear concrete behaviors. Based on the experimental data of hydration heat evolution rate and quantity of SSC and fly ash Portland cement, the hydration properties of various cements are studied. Simulations are run on a concrete dam section with a conventional method and a chemo-thermo-mechanical coupled method. The results show that SSC is more suitable for mass concrete structures from the standpoint of temperature control and crack prevention. Full article

(This article belongs to the Section Advanced Materials Characterization)

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8316 KiB

Open AccessArticle

Investigation on Polylactide (PLA)/Poly(butylene adipate-co-terephthalate) (PBAT)/Bark Flour of Plane Tree (PF) Eco-Composites

by Qiang Dou and Jun Cai

Materials 2016, 9(5), 393; https://doi.org/10.3390/ma9050393 - 19 May 2016

Cited by 25 | Viewed by 6503

Abstract

Polylactide (PLA)/poly(butylene adipate-co-terephthalate) (PBAT)/bark flour of plane tree (PF) eco-composites were prepared via melt blending. The morphologies, mechanical properties, crystal structures and melting and crystallization behaviors of the eco-composites were investigated by means of scanning electron microscopy (SEM), mechanical tests, polarized light microscopy [...] Read more.

Polylactide (PLA)/poly(butylene adipate-co-terephthalate) (PBAT)/bark flour of plane tree (PF) eco-composites were prepared via melt blending. The morphologies, mechanical properties, crystal structures and melting and crystallization behaviors of the eco-composites were investigated by means of scanning electron microscopy (SEM), mechanical tests, polarized light microscopy (PLM), wide angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC), respectively. It is shown that the interfacial adhesion between PLA matrix and PF is weak and the mechanical properties of PLA/PF eco-composites are poor. The titanate treatment improves the adhesion between the matrix and the filler and enhances the stiffness of the eco-composites. The toughness is improved by PBAT and ductile fractured surfaces can be found. The spherulitic size of PLA is decreased by the addition of PF. The α crystalline form of PLA remains in the composites. Compared with PF, T-PF (PF treated by a titanate coupling agent) and PBAT have negative effects on the crystallization of PLA. Full article

(This article belongs to the Special Issue Polymer Blends and Compatibilization)

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2156 KiB

Open AccessArticle

Optimising Ambient Setting Bayer Derived Fly Ash Geopolymers

by Evan Jamieson, Catherine S. Kealley, Arie Van Riessen and Robert D. Hart

Materials 2016, 9(5), 392; https://doi.org/10.3390/ma9050392 - 19 May 2016

Cited by 16 | Viewed by 5310

Abstract

The Bayer process utilises high concentrations of caustic and elevated temperature to liberate alumina from bauxite, for the production of aluminium and other chemicals. Within Australia, this process results in 40 million tonnes of mineral residues (Red mud) each year. Over the same [...] Read more.

The Bayer process utilises high concentrations of caustic and elevated temperature to liberate alumina from bauxite, for the production of aluminium and other chemicals. Within Australia, this process results in 40 million tonnes of mineral residues (Red mud) each year. Over the same period, the energy production sector will produce 14 million tonnes of coal combustion products (Fly ash). Both industrial residues require impoundment storage, yet combining some of these components can produce geopolymers, an alternative to cement. Geopolymers derived from Bayer liquor and fly ash have been made successfully with a compressive strength in excess of 40 MPa after oven curing. However, any product from these industries would require large volume applications with robust operational conditions to maximise utilisation. To facilitate potential unconfined large-scale production, Bayer derived fly ash geopolymers have been optimised to achieve ambient curing. Fly ash from two different power stations have been successfully trialled showing the versatility of the Bayer liquor-ash combination for making geopolymers. Full article

(This article belongs to the Special Issue Advances in Geopolymers and Alkali-Activated Materials)

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2874 KiB

Open AccessArticle

The Structure and Mechanical Properties of High-Strength Bulk Ultrafine-Grained Cobalt Prepared Using High-Energy Ball Milling in Combination with Spark Plasma Sintering

by Ivo Marek, Dalibor Vojtěch, Alena Michalcová and Tomáš František Kubatík

Materials 2016, 9(5), 391; https://doi.org/10.3390/ma9050391 - 19 May 2016

Cited by 14 | Viewed by 5532

Abstract

In this study, bulk ultrafine-grained and micro-crystalline cobalt was prepared using a combination of high-energy ball milling and subsequent spark plasma sintering. The average grain sizes of the ultrafine-grained and micro-crystalline materials were 200 nm and 1 μm, respectively. Mechanical properties such as [...] Read more.

In this study, bulk ultrafine-grained and micro-crystalline cobalt was prepared using a combination of high-energy ball milling and subsequent spark plasma sintering. The average grain sizes of the ultrafine-grained and micro-crystalline materials were 200 nm and 1 μm, respectively. Mechanical properties such as the compressive yield strength, the ultimate compressive strength, the maximum compressive deformation and the Vickers hardness were studied and compared with those of a coarse-grained as-cast cobalt reference sample. The bulk ultrafine-grained sample showed an ultra-high compressive yield strength that was greater than 1 GPa, which is discussed with respect to the preparation technique and a structural investigation. Full article

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8324 KiB

Open AccessArticle

Influence of Hybridizing Flax and Hemp-Agave Fibers with Glass Fiber as Reinforcement in a Polyurethane Composite

by Pankaj Pandey, Dilpreet Bajwa, Chad Ulven and Sreekala Bajwa

Materials 2016, 9(5), 390; https://doi.org/10.3390/ma9050390 - 19 May 2016

Cited by 8 | Viewed by 8396

Abstract

In this study, six combinations of flax, hemp, and glass fiber were investigated for a hybrid reinforcement system in a polyurethane (PU) composite. The natural fibers were combined with glass fibers in a PU composite in order to achieve a better mechanical reinforcement [...] Read more.

In this study, six combinations of flax, hemp, and glass fiber were investigated for a hybrid reinforcement system in a polyurethane (PU) composite. The natural fibers were combined with glass fibers in a PU composite in order to achieve a better mechanical reinforcement in the composite material. The effect of fiber hybridization in PU composites was evaluated through physical and mechanical properties such as water absorption (WA), specific gravity (SG), coefficient of linear thermal expansion (CLTE), flexural and compression properties, and hardness. The mechanical properties of hybridized samples showed mixed trends compared to the unhybridized samples, but hybridization with glass fiber reduced water absorption by 37% and 43% for flax and hemp-agave PU composites respectively. Full article

(This article belongs to the Special Issue Bio- and Natural-Fiber Composites)

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2539 KiB

Open AccessFeature PaperArticle

Determination of Specific Heat Capacity on Composite Shape-Stabilized Phase Change Materials and Asphalt Mixtures by Heat Exchange System

by Biao Ma, Xue-yan Zhou, Jiang Liu, Zhanping You, Kun Wei and Xiao-feng Huang

Materials 2016, 9(5), 389; https://doi.org/10.3390/ma9050389 - 19 May 2016

Cited by 53 | Viewed by 9608

Abstract

Previous research has shown that composite shape-stabilized phase change material (CPCM) has a remarkable capacity for thermal storage and stabilization, and it can be directly applied to highway construction without leakage. However, recent studies on temperature changing behaviors of CPCM and asphalt mixture [...] Read more.

Previous research has shown that composite shape-stabilized phase change material (CPCM) has a remarkable capacity for thermal storage and stabilization, and it can be directly applied to highway construction without leakage. However, recent studies on temperature changing behaviors of CPCM and asphalt mixture cannot intuitively reflect the thermoregulation mechanism and efficiency of CPCM on asphalt mixture. The objective of this paper is to determine the specific heat capacity of CPCM and asphalt mixtures mixed with CPCM using the heat exchange system and the data acquisition system. Studies have shown that the temperature-rise curve of 5 °C CPCM has an obvious temperature plateau, while an asphalt mixture mixed with 5 °C CPCM does not; with increasing temperature, the specific heat capacities of both 5 °C CPCM and asphalt mixture first increase and then decrease, while the variation rate of 5 °C CPCM is larger than that of the asphalt mixture, and the maximum specific heat capacity of 5 °C CPCM appears around the initial phase change temperature. It is concluded that the temperature intervals of 5 °C CPCM are −18 °C–7 °C, 7 °C–25 °C and 25 °C–44 °C, respectively, and that of the asphalt mixture are −18 °C~10 °C, −10 °C~5 °C and 5 °C~28 °C. A low dosage of 5 °C CPCM has little influence on the specific heat capacity of asphalt mixture. Finally, the functions of specific heat capacities and temperature for CPCM and asphalt mixture mixed with CPCM were recommended by the sectional regression method. Full article

(This article belongs to the Special Issue Development and Characterisation of Encapsulated PCM: Nano-, Micro-, and Macro-Encapsulation)

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5197 KiB

Open AccessCommunication

Evaluation of Microstructure and Transport Properties of Deteriorated Cementitious Materials from Their X-ray Computed Tomography (CT) Images

by Michael Angelo B. Promentilla, Shermaine M. Cortez, Regina Anne DC. Papel, Bernadette M. Tablada and Takafumi Sugiyama

Materials 2016, 9(5), 388; https://doi.org/10.3390/ma9050388 - 19 May 2016

Cited by 40 | Viewed by 7627

Abstract

Pore structure, tortuosity and permeability are considered key properties of porous materials such as cement pastes to understand their long-term durability performance. Three-dimensional image analysis techniques were used in this study to quantify pore size, effective porosity, tortuosity, and permeability from the X-ray [...] Read more.

Pore structure, tortuosity and permeability are considered key properties of porous materials such as cement pastes to understand their long-term durability performance. Three-dimensional image analysis techniques were used in this study to quantify pore size, effective porosity, tortuosity, and permeability from the X-ray computed tomography (CT) images of deteriorated pastes that were subjected to accelerated leaching test. X-ray microtomography is a noninvasive three-dimensional (3D) imaging technique which has been recently gaining attention for material characterization. Coupled with 3D image analysis, the digitized pore can be extracted and computational simulation can be applied to the pore network to measure relevant microstructure and transport properties. At a spatial resolution of 0.50 μm, the effective porosity (ψ_e) was found to be in the range of 0.04 to 0.33. The characteristic pore size (d) using a local thickness algorithm was found to be in the range of 3 to 7 μm. The geometric tortuosity (τ_g) based on a 3D random walk simulation in the percolating pore space was found to be in the range of 2.00 to 7.45. The water permeability values (K) using US NIST Permeability Stokes Solver range from an order of magnitudes of 10⁻¹⁴ to 10⁻¹⁷ m². Indications suggest that as effective porosity increases, the geometric tortuosity increases and the permeability decreases. Correlation among these microstructure and transport parameters is also presented in this study. Full article

(This article belongs to the Special Issue Image Analysis and Processing for Cement-based Materials)

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1715 KiB

Open AccessFeature PaperReview

Innate Immune Response in Implant-Associated Infections: Neutrophils against Biofilms

by Ulrike Dapunt, Gertrud Maria Hänsch and Carla Renata Arciola

Materials 2016, 9(5), 387; https://doi.org/10.3390/ma9050387 - 18 May 2016

Cited by 14 | Viewed by 6098

Abstract

Biofilm has been recognized as a well-protected form of living for bacteria, contributing to bacterial pathogenicity, particularly for opportunistic species. Biofilm-associated infections are marked by their persistence. Extensive research has been devoted to the formation and composition of biofilms. The immune response against [...] Read more.

Biofilm has been recognized as a well-protected form of living for bacteria, contributing to bacterial pathogenicity, particularly for opportunistic species. Biofilm-associated infections are marked by their persistence. Extensive research has been devoted to the formation and composition of biofilms. The immune response against biofilms remains rather unexplored, but there is the notion that bacteria within a biofilm are protected from host defences. Here we glance at the mechanisms by which neutrophils recognize and face biofilms in implant infections and discuss the implications of this interplay, as well as speculate on its significance. Full article

(This article belongs to the Special Issue Anti-Infective Materials in Medicine and Technology)

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6981 KiB

Open AccessArticle

Streamlined Membrane Proteome Preparation for Shotgun Proteomics Analysis with Triton X-100 Cloud Point Extraction and Nanodiamond Solid Phase Extraction

by Minh D. Pham, Ting-Chun Wen, Hung-Cheng Li, Pei-Hsuan Hsieh, Yet-Ran Chen, Huan-Cheng Chang and Chau-Chung Han

Materials 2016, 9(5), 385; https://doi.org/10.3390/ma9050385 - 18 May 2016

Cited by 15 | Viewed by 8179

Abstract

While mass spectrometry (MS) plays a key role in proteomics research, characterization of membrane proteins (MP) by MS has been a challenging task because of the presence of a host of interfering chemicals in the hydrophobic protein extraction process, and the low protease [...] Read more.

While mass spectrometry (MS) plays a key role in proteomics research, characterization of membrane proteins (MP) by MS has been a challenging task because of the presence of a host of interfering chemicals in the hydrophobic protein extraction process, and the low protease digestion efficiency. We report a sample preparation protocol, two-phase separation with Triton X-100, induced by NaCl, with coomassie blue added for visualizing the detergent-rich phase, which streamlines MP preparation for SDS-PAGE analysis of intact MP and shot-gun proteomic analyses. MP solubilized in the detergent-rich milieu were then sequentially extracted and fractionated by surface-oxidized nanodiamond (ND) at three pHs. The high MP affinity of ND enabled extensive washes for removal of salts, detergents, lipids, and other impurities to ensure uncompromised ensuing purposes, notably enhanced proteolytic digestion and down-stream mass spectrometric (MS) analyses. Starting with a typical membranous cellular lysate fraction harvested with centrifugation/ultracentrifugation, MP purities of 70%, based on number (not weight) of proteins identified by MS, was achieved; the weight-based purity can be expected to be much higher. Full article

(This article belongs to the Special Issue The Properties and Applications of Nanodiamonds)

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2658 KiB

Open AccessReview

Nanoparticles for Control of Biofilms of Acinetobacter Species

by Richa Singh, Shradhda Nadhe, Sweety Wadhwani, Utkarsha Shedbalkar and Balu Ananda Chopade

Materials 2016, 9(5), 383; https://doi.org/10.3390/ma9050383 - 18 May 2016

Cited by 33 | Viewed by 8878

Abstract

Biofilms are the cause of 80% of microbial infections. Acinetobacter species have emerged as multi- and pan-drug-resistant bacteria and pose a great threat to human health. These act as nosocomial pathogens and form excellent biofilms, both on biotic and abiotic surfaces, leading to [...] Read more.

Biofilms are the cause of 80% of microbial infections. Acinetobacter species have emerged as multi- and pan-drug-resistant bacteria and pose a great threat to human health. These act as nosocomial pathogens and form excellent biofilms, both on biotic and abiotic surfaces, leading to severe infections and diseases. Various methods have been developed for treatment and control of Acinetobacter biofilm including photodynamic therapy, radioimmunotherapy, prophylactic vaccines and antimicrobial peptides. Nanotechnology, in the present scenario, offers a promising alternative. Nanomaterials possess unique properties, and multiple bactericidal mechanisms render them more effective than conventional drugs. This review intends to provide an overview of Acinetobacter biofilm and the significant role of various nanoparticles as anti-biofouling agents, surface-coating materials and drug-delivery vehicles for biofilm control and treatment of Acinetobacter infections. Full article

(This article belongs to the Special Issue Biofilm and Materials Science)

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4152 KiB

Open AccessArticle

Molecular Dynamics Study of Self-Assembly of Aqueous Solutions of Poly[9,9-bis(4-Sulfonylbutoxyphenylphenyl) Fluorene-2,7-diyl-2,2’-Bithiophene] (PBS-PF2T) in the Presence of Pentaethylene Glycol Monododecyl Ether (C₁₂E₅)

by Beverly Stewart and Hugh Douglas Burrows

Materials 2016, 9(5), 379; https://doi.org/10.3390/ma9050379 - 18 May 2016

Cited by 5 | Viewed by 4657

Abstract

Results are presented using molecular dynamics (MD) of the self-assembly of the conjugated polyelectrolyte poly[9,9-bis(4-sulfonylbutoxyphenylphenyl) fluorene-2,7-diyl-2,2’-bithiophene] (PBS-PF2T) with 680 mM pentaethylene glycol monododecyl ether (C₁₂E₅) in water. Simulations are used to examine the interaction between PBS-PF2T and C₁₂ [...] Read more.

Results are presented using molecular dynamics (MD) of the self-assembly of the conjugated polyelectrolyte poly[9,9-bis(4-sulfonylbutoxyphenylphenyl) fluorene-2,7-diyl-2,2’-bithiophene] (PBS-PF2T) with 680 mM pentaethylene glycol monododecyl ether (C₁₂E₅) in water. Simulations are used to examine the interaction between PBS-PF2T and C₁₂E₅ and suggest a break-up of PBS-PF2T aggregates in solution. These systems are dominated by the formation of cylindrical phases at temperatures between 0 °C and 20 °C and also between 45 °C and 90 °C. More diffuse phases are seen to occur between 20 °C and 45 °C and also above 90 °C. Simulations are related to previous computational and experimental studies on PBS-PF2T aggregation in the presence of tetraethylene glycol monododecyl ether (C₁₂E₄) in bulk and thin films. Full article

(This article belongs to the Special Issue Surface Forces and Thin Liquid Films)

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2095 KiB

Open AccessArticle

Microwave-Assisted Synthesis of Arene Ru(II) Complexes Induce Tumor Cell Apoptosis Through Selectively Binding and Stabilizing bcl-2 G-Quadruplex DNA

by Yanhua Chen, Qiong Wu, Xicheng Wang, Qiang Xie, Yunyun Tang, Yutao Lan, Shuangyan Zhang and Wenjie Mei

Materials 2016, 9(5), 386; https://doi.org/10.3390/ma9050386 - 17 May 2016

Cited by 13 | Viewed by 5691

Abstract

A series of arene Ru(II) complexes coordinated with phenanthroimidazole derivatives, [(η⁶-C₆H₆)Ru(l)Cl]Cl(1b L = p-ClPIP = 2-(4-Chlorophenyl)imidazole[4,5f] 1,10-phenanthroline; 2b L = m-ClPIP = 2-(3-Chlorophenyl)imidazole[4,5f] 1,10-phenanthroline; 3b L = p-NPIP = 2-(4-Nitrophenyl)imidazole[4,5f] 1,10-phenanthroline; 4b [...] Read more.

A series of arene Ru(II) complexes coordinated with phenanthroimidazole derivatives, [(η⁶-C₆H₆)Ru(l)Cl]Cl(1b L = p-ClPIP = 2-(4-Chlorophenyl)imidazole[4,5f] 1,10-phenanthroline; 2b L = m-ClPIP = 2-(3-Chlorophenyl)imidazole[4,5f] 1,10-phenanthroline; 3b L = p-NPIP = 2-(4-Nitrophenyl)imidazole[4,5f] 1,10-phenanthroline; 4b L = m-NPIP = 2-(3-Nitrophenyl) imidazole [4,5f] 1,10-phenanthroline) were synthesized in yields of 89.9%–92.7% under conditions of microwave irradiation heating for 30 min to liberate four arene Ru(II) complexes (1b, 2b, 3b, 4b). The anti-tumor activity of 1b against various tumor cells was evaluated by MTT assay. The results indicated that this complex blocked the growth of human lung adenocarcinoma A549 cells with an IC₅₀ of 16.59 μM. Flow cytometric analysis showed that apoptosis of A549 cells was observed following treatment with 1b. Furthermore, the in vitro DNA-binding behaviors that were confirmed by spectroscopy indicated that 1b could selectively bind and stabilize bcl-2 G-quadruplex DNA to induce apoptosis of A549 cells. Therefore, the synthesized 1b has impressive bcl-2 G-quadruplex DNA-binding and stabilizing activities with potential applications in cancer chemotherapy. Full article

(This article belongs to the Special Issue Microwave Materials Processing)

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4133 KiB

Open AccessArticle

Fabrication of a Delaying Biodegradable Magnesium Alloy-Based Esophageal Stent via Coating Elastic Polymer

by Tianwen Yuan, Jia Yu, Jun Cao, Fei Gao, Yueqi Zhu, Yingsheng Cheng and Wenguo Cui

Materials 2016, 9(5), 384; https://doi.org/10.3390/ma9050384 - 17 May 2016

Cited by 29 | Viewed by 6993

Abstract

Esophageal stent implantation can relieve esophageal stenosis and obstructions in benign esophageal strictures, and magnesium alloy stents are a good candidate because of biodegradation and biological safety. However, biodegradable esophageal stents show a poor corrosion resistance and a quick loss of mechanical support [...] Read more.

Esophageal stent implantation can relieve esophageal stenosis and obstructions in benign esophageal strictures, and magnesium alloy stents are a good candidate because of biodegradation and biological safety. However, biodegradable esophageal stents show a poor corrosion resistance and a quick loss of mechanical support in vivo. In this study, we chose the elastic and biodegradable mixed polymer of Poly(ε-caprolactone) (PCL) and poly(trimethylene carbonate) (PTMC) as the coated membrane on magnesium alloy stents for fabricating a fully biodegradable esophageal stent, which showed an ability to delay the degradation time and maintain mechanical performance in the long term. After 48 repeated compressions, the mechanical testing demonstrated that the PCL-PTMC-coated magnesium stents possess good flexibility and elasticity, and could provide enough support against lesion compression when used in vivo. According to the in vitro degradation evaluation, the PCL-PTMC membrane coated on magnesium was a good material combination for biodegradable stents. During the in vivo evaluation, the proliferation of the smooth muscle cells showed no signs of cell toxicity. Histological examination revealed the inflammation scores at four weeks in the magnesium-(PCL-PTMC) stent group were similar to those in the control group (p > 0.05). The α-smooth muscle actin layer in the media was thinner in the magnesium-(PCL-PTMC) stent group than in the control group (p < 0.05). Both the epithelial and smooth muscle cell layers were significantly thinner in the magnesium-(PCL-PTMC) stent group than in the control group. The stent insertion was feasible and provided reliable support for at least four weeks, without causing severe injury or collagen deposition. Thus, this stent provides a new stent for the treatment of benign esophageal stricture and a novel research path in the development of temporary stents in other cases of benign stricture. Full article

(This article belongs to the Special Issue Biological and Synthetic Organic–Inorganic Composite Materials)

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Open AccessArticle

Microstructural Anisotropy of Magnetocaloric Gadolinium Cylinders: Effect on the Mechanical Properties of the Material

by Darja Steiner Petrovič, Roman Šturm, Iztok Naglič, Boštjan Markoli and Tomaž Pepelnjak

Materials 2016, 9(5), 382; https://doi.org/10.3390/ma9050382 - 17 May 2016

Cited by 2 | Viewed by 5405

Abstract

The development of advanced materials and technologies based on magnetocaloric Gd and its compounds requires an understanding of the dependency of mechanical properties on their underlying microstructure. Therefore, the aim of the study was to characterize microstructural inhomogeneities in the gadolinium that can [...] Read more.

The development of advanced materials and technologies based on magnetocaloric Gd and its compounds requires an understanding of the dependency of mechanical properties on their underlying microstructure. Therefore, the aim of the study was to characterize microstructural inhomogeneities in the gadolinium that can be used in magnetocaloric refrigeration systems. Microstructures of magnetocaloric gadolinium cylinders were investigated by light microscopy and FE-SEM (Field Emission Scanning Electron Microscopy), EDS (Energy-dispersive X-ray Spectroscopy), and BSE (Back-scattered Electrons) in both the extrusion and the extrusion-transversal directions. XRD (X-ray Diffraction) analyses were performed to reveal the presence of calcium- and fluorine-based compounds. Metallographic characterization showed an oxidized and inhomogeneous microstructure of the cross-sections. The edges and the outer parts of the cylinders were oxidized more intensively on the surfaces directly exposed to the processing tools. Moreover, a significant morphological anisotropy of the non-metallic inclusions was observed. CaF inclusions act as active nucleation sites for internal oxidation. The non-metallic, Ca- and F-containing inclusions can be classified as complex calciumoxyfluorides. The solubility of Er and Yb in the CaF was negligible compared to the Gd matrix and/or the oxide phase. Lower mechanical properties of the material are a consequence of the lower structural integrity due to selective oxidation of surfaces and interfaces. Full article

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17388 KiB

Open AccessFeature PaperArticle

Higher Ratios of Hyaluronic Acid Enhance Chondrogenic Differentiation of Human MSCs in a Hyaluronic Acid–Gelatin Composite Scaffold

by Christian G. Pfeifer, Arne Berner, Matthias Koch, Werner Krutsch, Richard Kujat, Peter Angele, Michael Nerlich and Johannes Zellner

Materials 2016, 9(5), 381; https://doi.org/10.3390/ma9050381 - 17 May 2016

Cited by 34 | Viewed by 7105

Abstract

Mesenchymal stem cells (MSCs) seeded on specific carrier materials are a promising source for the repair of traumatic cartilage injuries. The best supportive carrier material has not yet been determined. As natural components of cartilage’s extracellular matrix, hyaluronic acid and collagen are the [...] Read more.

Mesenchymal stem cells (MSCs) seeded on specific carrier materials are a promising source for the repair of traumatic cartilage injuries. The best supportive carrier material has not yet been determined. As natural components of cartilage’s extracellular matrix, hyaluronic acid and collagen are the focus of biomaterial research. In order to optimize chondrogenic support, we investigated three different scaffold compositions of a hyaluronic acid (HA)-gelatin based biomaterial. Methods: Human MSCs (hMSCs) were seeded under vacuum on composite scaffolds of three different HA-gelatin ratios and cultured in chondrogenic medium for 21 days. Cell-scaffold constructs were assessed at different time points for cell viability, gene expression patterns, production of cartilage-specific extracellular matrix (ECM) and for (immuno-)histological appearance. The intrinsic transforming growth factor beta (TGF-beta) uptake of empty scaffolds was evaluated by determination of the TGF-beta concentrations in the medium over time. Results: No significant differences were found for cell seeding densities and cell viability. hMSCs seeded on scaffolds with higher ratios of HA showed better cartilage-like differentiation in all evaluated parameters. TGF-beta uptake did not differ between empty scaffolds. Conclusion: Higher ratios of HA support the chondrogenic differentiation of hMSCs seeded on a HA-gelatin composite scaffold. Full article

(This article belongs to the Special Issue Regenerative Materials)

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10269 KiB

Open AccessArticle

Effects of Laser Power Level on Microstructural Properties and Phase Composition of Laser-Clad Fluorapatite/Zirconia Composite Coatings on Ti6Al4V Substrates

by Chi-Sheng Chien, Cheng-Wei Liu and Tsung-Yuan Kuo

Materials 2016, 9(5), 380; https://doi.org/10.3390/ma9050380 - 17 May 2016

Cited by 29 | Viewed by 6038

Abstract

Hydroxyapatite (HA) is one of the most commonly used materials for the coating of bioceramic titanium (Ti) alloys. However, HA has poor mechanical properties and a low bonding strength. Accordingly, the present study replaces HA with a composite coating material consisting of fluorapatite [...] Read more.

Hydroxyapatite (HA) is one of the most commonly used materials for the coating of bioceramic titanium (Ti) alloys. However, HA has poor mechanical properties and a low bonding strength. Accordingly, the present study replaces HA with a composite coating material consisting of fluorapatite (FA) and 20 wt % yttria (3 mol %) stabilized zirconia (ZrO₂, 3Y-TZP). The FA/ZrO₂ coatings are deposited on Ti6Al4V substrates using a Nd:YAG laser cladding system with laser powers and travel speeds of 400 W/200 mm/min, 800 W/400 mm/min, and 1200 W/600 mm/min, respectively. The experimental results show that a significant inter-diffusion of the alloying elements occurs between the coating layer (CL) and the transition layer (TL). Consequently, a strong metallurgical bond is formed between them. During the cladding process, the ZrO₂ is completely decomposed, while the FA is partially decomposed. As a result, the CLs of all the specimens consist mainly of FA, Ca₄(PO₄)₂O (TTCP), CaF₂, CaZrO₃, CaTiO₃ and monoclinic phase ZrO₂ (m-ZrO₂), together with a small amount of θ-Al₂O₃. As the laser power is increased, CaO, CaCO₃ and trace amounts of tetragonal phase ZrO₂ (t-ZrO₂) also appear. As the laser power increases from 400 to 800 W, the CL hardness also increases as a result of microstructural refinement and densification. However, at the highest laser power of 1200 W, the CL hardness reduces significantly due to the formation of large amounts of relatively soft CaO and CaCO₃ phase. Full article

(This article belongs to the Special Issue Solid-State Laser Materials)

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2938 KiB

Open AccessArticle

Stress Wave Propagation in Viscoelastic-Plastic Rock-Like Materials

by Liu Lang, KI-IL Song, Yue Zhai, Dezheng Lao and Hang-Lo Lee

Materials 2016, 9(5), 377; https://doi.org/10.3390/ma9050377 - 17 May 2016

Cited by 7 | Viewed by 5380

Abstract

Rock-like materials are composites that can be regarded as a mixture composed of elastic, plastic, and viscous components. They exhibit viscoelastic-plastic behavior under a high-strain-rate loading according to element model theory. This paper presents an analytical solution for stress wave propagation in viscoelastic-plastic [...] Read more.

Rock-like materials are composites that can be regarded as a mixture composed of elastic, plastic, and viscous components. They exhibit viscoelastic-plastic behavior under a high-strain-rate loading according to element model theory. This paper presents an analytical solution for stress wave propagation in viscoelastic-plastic rock-like materials under a high-strain-rate loading and verifies the solution through an experimental test. A constitutive equation of viscoelastic-plastic rock-like materials was first established, and then kinematic and kinetic equations were then solved to derive the analytic solution for stress wave propagation in viscoelastic-plastic rock-like materials. An experimental test using the SHPB (Split Hopkinson Pressure Bar) for a concrete specimen was conducted to obtain a stress-strain curve under a high-strain-rate loading. Inverse analysis based on differential evolution was conducted to estimate undetermined variables for constitutive equations. Finally, the relationship between the attenuation factor and the strain rate in viscoelastic-plastic rock-like materials was investigated. According to the results, the frequency of the stress wave, viscosity coefficient, modulus of elasticity, and density play dominant roles in the attenuation of the stress wave. The attenuation decreases with increasing strain rate, demonstrating strongly strain-dependent attenuation in viscoelastic-plastic rock-like materials. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Open AccessArticle

Surface Functionalization of Polyethersulfone Membrane with Quaternary Ammonium Salts for Contact-Active Antibacterial and Anti-Biofouling Properties

by Xiao Hu, Xiaohui Lin, Huabing Zhao, Zihao Chen, Jian Yang, Fan Li, Changjun Liu and Feng Tian

Materials 2016, 9(5), 376; https://doi.org/10.3390/ma9050376 - 17 May 2016

Cited by 33 | Viewed by 7737

Abstract

Biofilm is a significant cause for membrane fouling. Antibacterial-coated surfaces can inhibit biofilm formation by killing bacteria. In this study, polyethersulfone (PES) microfiltration membrane was photografted by four antibiotic quaternary ammonium compounds (QACs) separately, which were synthesized from dimethylaminoethyl methacrylate (DMAEMA) by quaternization [...] Read more.

Biofilm is a significant cause for membrane fouling. Antibacterial-coated surfaces can inhibit biofilm formation by killing bacteria. In this study, polyethersulfone (PES) microfiltration membrane was photografted by four antibiotic quaternary ammonium compounds (QACs) separately, which were synthesized from dimethylaminoethyl methacrylate (DMAEMA) by quaternization with butyl bromide (BB), octyl bromide (OB), dodecyl bromide (DB), or hexadecyl bromide (HB). XPS, ATR-FTIR, and SEM were used to confirm the surfaces’ composition and morphology. After modification, the pores on PES-g-DMAEMA-BB and PES-g-DMAEMA-OB were blocked, while PES-g-DMAEMA-DB and PES-g-DMAEMA-HB were retained. We supposed that DMAEMA-BB and DMAEMA-OB aggregated on the membrane surface due to the activities of intermolecular or intramolecular hydrogen bonds. Bacteria testing found the antibacterial activities of the membranes increased with the length of the substituted alkyl chain. Correspondingly, little bacteria were observed on PES-g-DMAEMA-DB and PES-g-DMAEMA-HB by SEM. The antifouling properties were investigated by filtration of a solution of Escherichia coli. Compared with the initial membrane, PES-g-DMAEMA-DB and PES-g-DMAEMA-HB showed excellent anti-biofouling performance with higher relative flux recovery (RFR) of 88.3% and 92.7%, respectively. Thus, surface functionalization of the PES membrane with QACs can prevent bacteria adhesion and improve the anti-biofouling activity by the contact-active antibacterial property. Full article

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16198 KiB

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Formation of Aluminum Particles with Shell Morphology during Pressureless Spark Plasma Sintering of Fe–Al Mixtures: Current-Related or Kirkendall Effect?

by Dina V. Dudina, Boris B. Bokhonov and Amiya K. Mukherjee

Materials 2016, 9(5), 375; https://doi.org/10.3390/ma9050375 - 14 May 2016

Cited by 13 | Viewed by 6226

Abstract

A need to deeper understand the influence of electric current on the structure and properties of metallic materials consolidated by Spark Plasma Sintering (SPS) stimulates research on inter-particle interactions, bonding and necking processes in low-pressure or pressureless conditions as favoring technique-specific local effects [...] Read more.

A need to deeper understand the influence of electric current on the structure and properties of metallic materials consolidated by Spark Plasma Sintering (SPS) stimulates research on inter-particle interactions, bonding and necking processes in low-pressure or pressureless conditions as favoring technique-specific local effects when electric current passes through the underdeveloped inter-particle contacts. Until now, inter-particle interactions during pressureless SPS have been studied mainly for particles of the same material. In this work, we focused on the interactions between particles of dissimilar materials in mixtures of micrometer-sized Fe and Al powders forming porous compacts during pressureless SPS at 500–650 °C. Due to the chemical interaction between Al and Fe, necks of conventional shape did not form between the dissimilar particles. At the early interaction stages, the Al particles acquired shell morphology. It was shown that this morphology change was not related to the influence of electric current but was due to the Kirkendall effect in the Fe–Al system and particle rearrangement in a porous compact. No experimental evidence of melting or melt ejection during pressureless SPS of the Fe–Al mixtures or Fe and Al powders sintered separately was observed. Porous FeAl-based compacts could be obtained from Fe-40at.%Al mixtures by pressureless SPS at 650 °C. Full article

(This article belongs to the Collection Spark-Plasma Sintering and Related Field-Assisted Powder Consolidation Technologies)

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5323 KiB

Open AccessArticle

Fatigue Damage Monitoring of a Composite Step Lap Joint Using Distributed Optical Fibre Sensors

by Leslie Wong, Nabil Chowdhury, John Wang, Wing Kong Chiu and Jayantha Kodikara

Materials 2016, 9(5), 374; https://doi.org/10.3390/ma9050374 - 14 May 2016

Cited by 32 | Viewed by 6708

Abstract

Over the past few decades, there has been a considerable interest in the use of distributed optical fibre sensors (DOFS) for structural health monitoring of composite structures. In aerospace-related work, health monitoring of the adhesive joints of composites has become more significant, as [...] Read more.

Over the past few decades, there has been a considerable interest in the use of distributed optical fibre sensors (DOFS) for structural health monitoring of composite structures. In aerospace-related work, health monitoring of the adhesive joints of composites has become more significant, as they can suffer from cracking and delamination, which can have a significant impact on the integrity of the joint. In this paper, a swept-wavelength interferometry (SWI) based DOFS technique is used to monitor the fatigue in a flush step lap joint composite structure. The presented results will show the potential application of distributed optical fibre sensor for damage detection, as well as monitoring the fatigue crack growth along the bondline of a step lap joint composite structure. The results confirmed that a distributed optical fibre sensor is able to enhance the detection of localised damage in a structure. Full article

(This article belongs to the Special Issue Advances in Structural Health Monitoring for Aerospace Structures)

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Open AccessFeature PaperArticle

Nanoporous Monolithic Microsphere Arrays Have Anti-Adhesive Properties Independent of Humidity

by Anna Eichler-Volf, Longjian Xue, Alexander Kovalev, Elena V. Gorb, Stanislav N. Gorb and Martin Steinhart

Materials 2016, 9(5), 373; https://doi.org/10.3390/ma9050373 - 14 May 2016

Cited by 2 | Viewed by 6009

Abstract

Bioinspired artificial surfaces with tailored adhesive properties have attracted significant interest. While fibrillar adhesive pads mimicking gecko feet are optimized for strong reversible adhesion, monolithic microsphere arrays mimicking the slippery zone of the pitchers of carnivorous plants of the genus Nepenthes show anti-adhesive [...] Read more.

Bioinspired artificial surfaces with tailored adhesive properties have attracted significant interest. While fibrillar adhesive pads mimicking gecko feet are optimized for strong reversible adhesion, monolithic microsphere arrays mimicking the slippery zone of the pitchers of carnivorous plants of the genus Nepenthes show anti-adhesive properties even against tacky counterpart surfaces. In contrast to the influence of topography, the influence of relative humidity (RH) on adhesion has been widely neglected. Some previous works deal with the influence of RH on the adhesive performance of fibrillar adhesive pads. Commonly, humidity-induced softening of the fibrils enhances adhesion. However, little is known on the influence of RH on solid anti-adhesive surfaces. We prepared polymeric nanoporous monolithic microsphere arrays (NMMAs) with microsphere diameters of a few 10 µm to test their anti-adhesive properties at RHs of 2% and 90%. Despite the presence of continuous nanopore systems through which the inner nanopore walls were accessible to humid air, the topography-induced anti-adhesive properties of NMMAs on tacky counterpart surfaces were retained even at RH = 90%. This RH-independent robustness of the anti-adhesive properties of NMMAs significantly contrasts the adhesion enhancement by humidity-induced softening on nanoporous fibrillar adhesive pads made of the same material. Full article

(This article belongs to the Special Issue Bioinspired and Biomimetic Materials)

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609 KiB

Open AccessArticle

Design and Validity of Randomized Controlled Dental Restorative Trials

by Gerd Göstemeyer, Uwe Blunck, Sebastian Paris and Falk Schwendicke

Materials 2016, 9(5), 372; https://doi.org/10.3390/ma9050372 - 13 May 2016

Cited by 21 | Viewed by 5082

Abstract

Background: The evidence stemming from trials on restorative materials is shaped not only by trial findings, but also trial design and validity. We aimed to evaluate both aspects in randomized controlled dental restorative trials published from 2005–2015. Methods: Using systematic review [...] Read more.

Background: The evidence stemming from trials on restorative materials is shaped not only by trial findings, but also trial design and validity. We aimed to evaluate both aspects in randomized controlled dental restorative trials published from 2005–2015. Methods: Using systematic review methodology, we retrieved trials comparing restorative or adhesive dental materials. Two authors independently assessed design, risk of bias, registration status, and findings of trials. Descriptive and regression analyses were performed. Results: 114 studies on 15,321 restorations placed mainly in permanent teeth of 5232 patients were included. Per trial, the median number of patients was 37 (25th/75th percentiles: 30/51). Follow-up was 24 (20/48) months. Seventeen percent of trials reported on sample size calculations, 2% had been registered. Most trials (90%) used US Public Health Service (USPHS) criteria, and had a high risk of bias. More recent trials were more likely to have been registered, to have reported on sample size calculations, to be of low risk of bias, and to use other than USPHS-criteria. Twenty-three percent of trials yielded significant differences between groups. The likelihood of such differences was significantly increased in older studies, studies with potential reporting bias, published in journals with high impact factor (>2), longer follow-up periods, and not using USPHS-criteria. Conclusions: The majority of dental restorative trials published from 2005–2015 had limited validity. Risk of bias decreased in more recent trials. Future trials should aim for high validity, be registered, and use defined and appropriate sample sizes, follow-up periods, and outcome measures. Full article

(This article belongs to the Section Biomaterials)

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