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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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16 pages, 6122 KiB  
Article
Application of Innovative Ropes from Textile Waste as an Anti-Erosion Measure
by Giang Nguyen, Joanna Grzybowska-Pietras and Jan Broda
Materials 2021, 14(5), 1179; https://doi.org/10.3390/ma14051179 - 3 Mar 2021
Cited by 5 | Viewed by 2119
Abstract
Using materials from recycling is a key part of decreasing present-day waste. It is optimal for recycled material to be used in environmental protection. This paper presents the application of geotextile ropes in erosion protection of a slope of a gravel pit. To [...] Read more.
Using materials from recycling is a key part of decreasing present-day waste. It is optimal for recycled material to be used in environmental protection. This paper presents the application of geotextile ropes in erosion protection of a slope of a gravel pit. To protect the slope, thick ropes with a diameter of 120 mm made from wool and a mixture of recycled natural and synthetic fibers were used. After 47 months from installation, soil and rope specimens were taken from the slope parts with inclinations 1:1 and 1:1.8, and their physical and mechanical properties were determined. Direct shear tests were applied to determine the soil shear strength parameters in state at sampling and at Ic = 0 (unconsolidated and consolidated). Based on the obtained soil shear strength parameters, the loads on the ropes were determined, taking into account also unfavorable hydraulic conditions and compared to rope strength. It was shown that even after 47 months from installation, rope tension strength was higher as tension forces were induced in the ropes in every case. At present, whole slopes in protected sections are stabilized, without rills and gullies. Full article
(This article belongs to the Special Issue Innovative Materials in the Building Industry: Reducing Building Energy and Minimising Environmental Impacts)
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25 pages, 30911 KiB  
Review
Laser Powder Bed Fusion of Polymers: Quantitative Research Direction Indices
by Ihsan Murat Kusoglu, Carlos Doñate-Buendía, Stephan Barcikowski and Bilal Gökce
Materials 2021, 14(5), 1169; https://doi.org/10.3390/ma14051169 - 2 Mar 2021
Cited by 34 | Viewed by 4175
Abstract
Research on Laser Powder Bed Fusion (L-PBF) of polymer powder feedstocks has raised over the last decade due to the increased utilization of the fabricated parts in aerospace, automotive, electronics, and healthcare applications. A total of 600 Science Citation Indexed articles were published [...] Read more.
Research on Laser Powder Bed Fusion (L-PBF) of polymer powder feedstocks has raised over the last decade due to the increased utilization of the fabricated parts in aerospace, automotive, electronics, and healthcare applications. A total of 600 Science Citation Indexed articles were published on the topic of L-PBF of polymer powder feedstocks in the last decade, being cited more than 10,000 times leading to an h-index of 46. This study statistically evaluates the 100 most cited articles to extract reported material, process, and as-built part properties to analyze the research trends. PA12, PEEK, and TPU are the most employed polymer powder feedstocks, while size, flowability, and thermal behavior are the standardly reported material properties. Likewise, process properties such as laser power, scanning speed, hatch spacing, powder layer thickness, volumetric energy density, and areal energy density are extracted and evaluated. In addition, material and process properties of the as-built parts such as tensile test, flexural test, and volumetric porosity contents are analyzed. The incorporation of additives is found to be an effective route to enhance mechanical and functional properties. Carbon-based additives are typically employed in applications where mechanical properties are essential. Carbon fibers, Ca-phosphates, and SiO2 are the most reported additives in the evaluated SCI-expanded articles for L-PBF of polymer powder feedstocks. A comprehensive data matrix is extracted from the evaluated SCI-index publications, and a principal component analysis (PCA) is performed to explore correlations between reported material, process, and as-built parts. Full article
(This article belongs to the Special Issue Specialty Polymers for Additive Manufacturing)
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11 pages, 1817 KiB  
Article
Comparison of Transmission Measurement Methods of Elastic Waves in Phononic Band Gap Materials
by Maximilian Wormser, Daniel A. Kiefer, Stefan J. Rupitsch and Carolin Körner
Materials 2021, 14(5), 1133; https://doi.org/10.3390/ma14051133 - 28 Feb 2021
Cited by 1 | Viewed by 2268
Abstract
Periodic cellular structures can exhibit metamaterial properties, such as phononic band gaps. In order to detect these frequency bands of strong wave attenuation experimentally, several devices for wave excitation and measurement can be applied. In this work, piezoelectric transducers are utilized to excite [...] Read more.
Periodic cellular structures can exhibit metamaterial properties, such as phononic band gaps. In order to detect these frequency bands of strong wave attenuation experimentally, several devices for wave excitation and measurement can be applied. In this work, piezoelectric transducers are utilized to excite two additively manufactured three-dimensional cellular structures. For the measurement of the transmission factor, we compare two methods. First, the transmitted waves are measured with the same kind of piezoelectric transducer. Second, a laser Doppler vibrometer is employed to scan the mechanical vibrations of the sample on both the emitting and receiving surfaces. The additional comparison of two different methods of spatial averaging of the vibrometer data, that is, the quadratic mean and arithmetic mean, provides insight into the way the piezoelectric transducers convert the transmitted signal. Experimental results are supported by numerical simulations of the dispersion relation and a simplified transmission simulation. Full article
(This article belongs to the Special Issue Advances in Mechanical Metamaterials)
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13 pages, 2400 KiB  
Article
Study of Radiation Characteristics of Intrinsic Josephson Junction Terahertz Emitters with Different Thickness of Bi2Sr2CaCu2O8+δ Crystals
by Takanari Kashiwagi, Takumi Yuasa, Genki Kuwano, Takashi Yamamoto, Manabu Tsujimoto, Hidetoshi Minami and Kazuo Kadowaki
Materials 2021, 14(5), 1135; https://doi.org/10.3390/ma14051135 - 28 Feb 2021
Cited by 4 | Viewed by 2211
Abstract
The radiation intensity from the intrinsic Josephson junction high-Tc superconductor Bi2Sr2CaCu2O8+δ terahertz emitters (Bi2212-THz emitters) is one of the most important characteristics for application uses of the device. In principle, it would [...] Read more.
The radiation intensity from the intrinsic Josephson junction high-Tc superconductor Bi2Sr2CaCu2O8+δ terahertz emitters (Bi2212-THz emitters) is one of the most important characteristics for application uses of the device. In principle, it would be expected to be improved with increasing the number of intrinsic Josephson junctions N in the emitters. In order to further improve the device characteristics, we have developed a stand alone type of mesa structures (SAMs) of Bi2212 crystals. Here, we understood the radiation characteristics of our SAMs more deeply, after we studied the radiation characteristics from three SAMs (S1, S2, and S3) with different thicknesses. Comparing radiation characteristics of the SAMs in which the number of intrinsic Josephson junctions are N∼ 1300 (S1), 2300 (S2), and 3100 (S3), respectively, the radiation intensity, frequency as well as the characteristics of the device working bath temperature are well understood. The strongest radiation of the order of few tens of microwatt was observed from the thickest SAM of S3. We discussed this feature through the N2-relationship and the radiation efficiency of a patch antenna. The thinner SAM of S1 can generate higher radiation frequencies than the thicker one of S3 due to the difference of the applied voltage per junctions limited by the heat-removal performance of the device structures. The observed features in this study are worthwhile designing Bi2212-THz emitters with better emission characteristics for many applications. Full article
(This article belongs to the Special Issue Superconducting and Quantum Metamaterials, Metacircuits, and Metadevices)
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15 pages, 3882 KiB  
Article
Evaluation of the Effects of Cement and Lime with Rice Husk Ash as an Additive on Strength Behavior of Coastal Soil
by Zahraalsadat Eliaslankaran, Nik Norsyahariati Nik Daud, Zainuddin Md. Yusoff and Vahid Rostami
Materials 2021, 14(5), 1140; https://doi.org/10.3390/ma14051140 - 28 Feb 2021
Cited by 19 | Viewed by 2630
Abstract
Coastal accretion and erosion are unavoidable processes as some coastal sediments undergo modification and stabilization. This study was conducted to investigate the geotechnical behavior of soil collected from Bagan Lalang coast and treated with lime, cement, and rice husk ash (RHA) to design [...] Read more.
Coastal accretion and erosion are unavoidable processes as some coastal sediments undergo modification and stabilization. This study was conducted to investigate the geotechnical behavior of soil collected from Bagan Lalang coast and treated with lime, cement, and rice husk ash (RHA) to design a low-cost alternative mixture with environmentally friendly characteristics. Laboratory tests were carried out to analyze the physical properties of the soil (Atterberg limits and compaction properties), together with mechanical characteristics (direct shear and unconfined compressive strength (UCS) tests) to determine the effect of different ratios of stabilizer/pozzolan on the coastal soil and the optimum conditions for each mixture. Part of the purpose of this study was also to analyze the shear behavior of the coastal soil and monitor the maximum axial compressive stress that the treated specimens can bear under zero confining pressure. Compared to the natural soil, the soil treated with lime and rice husk ash (LRHA) in the ratio of 1:2 (8% lime content) showed a tremendous increase in shear stress under the normal stress of 200 kPa. The strength parameters such as the cohesion (c) and internal friction angle (ϕ) values showed a significant increase. Cohesion values increased considerably in samples cured for 90 days compared to specimens cured for 7 days with additional LRHA in the ratio of 1:2 (28%). Full article
(This article belongs to the Special Issue Silica and Silica-based Materials for Biotechnology, Polymer Composites and Environmental Protection)
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14 pages, 13758 KiB  
Article
Porosity Analysis of Additive Manufactured Parts Using CAQ Technology
by Peter Pokorný, Štefan Václav, Jana Petru and Michaela Kritikos
Materials 2021, 14(5), 1142; https://doi.org/10.3390/ma14051142 - 28 Feb 2021
Cited by 7 | Viewed by 2243
Abstract
Components produced by additive technology are implemented in various spheres of industry, such as automotive or aerospace. This manufacturing process can lead to making highly optimized parts. There is not enough information about the quality of the parts produced by additive technologies, especially [...] Read more.
Components produced by additive technology are implemented in various spheres of industry, such as automotive or aerospace. This manufacturing process can lead to making highly optimized parts. There is not enough information about the quality of the parts produced by additive technologies, especially those made from metal powder. The research in this article deals with the porosity of components produced by additive technologies. The components used for the research were manufactured by the selective laser melting (SLM) method. The shape of these components is the same as the shape used for the tensile test. The investigated parts were printed with orientation in two directions, Z and XZ with respect to the machine platform. The printing strategy was “stripe”. The material used for printing of the parts was SS 316L-0407. The printing parameters were laser power of 200 W, scanning speed of 650 mm/s, and the thickness of the layer was 50 µm. A non-destructive method was used for the components’ porosity evaluation. The scanning was performed by CT machine METROTOM 1500. The radiation parameters used for getting 3D scans were voltage 180 kV, current 900 µA, detector resolution 1024 × 1024 px, voxel size 119.43 µm, number of projections 1050, and integration time 2000 ms. This entire measurement process responds to the computer aided quality (CAQ) technology. VG studio MAX 3.0 software was used to evaluate the obtained data. The porosity of the parts with Z and XZ orientation was also evaluated for parts’ thicknesses of 1, 2, and 3 mm, respectively. It has been proven by this experimental investigation that the printing direction of the part in the additive manufacturing process under question affects its porosity. Full article
(This article belongs to the Special Issue The Science and Technology of 3D Printing)
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25 pages, 4815 KiB  
Review
Sustainable End-of-Life Management of Wind Turbine Blades: Overview of Current and Coming Solutions
by Leon Mishnaevsky
Materials 2021, 14(5), 1124; https://doi.org/10.3390/ma14051124 - 27 Feb 2021
Cited by 69 | Viewed by 12963
Abstract
Various scenarios of end-of-life management of wind turbine blades are reviewed. “Reactive” strategies, designed to deal with already available, ageing turbines, installed in the 2000s, are discussed, among them, maintenance and repair, reuse, refurbishment and recycling. The main results and challenges of “pro-active [...] Read more.
Various scenarios of end-of-life management of wind turbine blades are reviewed. “Reactive” strategies, designed to deal with already available, ageing turbines, installed in the 2000s, are discussed, among them, maintenance and repair, reuse, refurbishment and recycling. The main results and challenges of “pro-active strategies”, designed to ensure recyclability of new generations of wind turbines, are discussed. Among the main directions, the wind turbine blades with thermoplastic and recyclable thermoset composite matrices, as well as wood, bamboo and natural fiber-based composites were reviewed. It is argued that repair and reuse of wind turbine blades, and extension of the blade life has currently a number of advantages over other approaches. While new recyclable materials have been tested in laboratories, or in some cases on small or medium blades, there are remaining technological challenges for their utilization in large wind turbine blades. Full article
(This article belongs to the Special Issue Experimental and Numerical Analysis of Innovative Engineering Structures)
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24 pages, 12311 KiB  
Article
Mesoscale Modelling of Concretes Subjected to Triaxial Loadings: Mechanical Properties and Fracture Behaviour
by Qingqing Chen, Yuhang Zhang, Tingting Zhao, Zhiyong Wang and Zhihua Wang
Materials 2021, 14(5), 1099; https://doi.org/10.3390/ma14051099 - 26 Feb 2021
Cited by 5 | Viewed by 1886
Abstract
The mechanical properties and fracture behaviour of concretes under different triaxial stress states were investigated based on a 3D mesoscale model. The quasistatic triaxial loadings, namely, compression–compression–compression (C–C–C), compression–tension–tension (C–T–T) and compression–compression–tension (C–C–T), were simulated using an implicit solver. The mesoscopic modelling with [...] Read more.
The mechanical properties and fracture behaviour of concretes under different triaxial stress states were investigated based on a 3D mesoscale model. The quasistatic triaxial loadings, namely, compression–compression–compression (C–C–C), compression–tension–tension (C–T–T) and compression–compression–tension (C–C–T), were simulated using an implicit solver. The mesoscopic modelling with good robustness gave reliable and detailed damage evolution processes under different triaxial stress states. The lateral tensile stress significantly influenced the multiaxial mechanical behaviour of the concretes, accelerating the concrete failure. With low lateral pressures or tensile stress, axial cleavage was the main failure mode of the specimens. Furthermore, the concretes presented shear failures under medium lateral pressures. The concretes experienced a transition from brittle fracture to plastic failure under high lateral pressures. The Ottosen parameters were modified by the gradient descent method and then the failure criterion of the concretes in the principal stress space was given. The failure criterion could describe the strength characteristics of concrete materials well by being fitted with experimental data under different triaxial stress states. Full article
(This article belongs to the Special Issue Concrete Technology and Mechanical Properties of Concretes)
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19 pages, 1126 KiB  
Review
Effect of UV Irradiation and TiO2-Photocatalysis on Airborne Bacteria and Viruses: An Overview
by Nina Bono, Federica Ponti, Carlo Punta and Gabriele Candiani
Materials 2021, 14(5), 1075; https://doi.org/10.3390/ma14051075 - 25 Feb 2021
Cited by 82 | Viewed by 8561
Abstract
Current COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has put a spotlight on the spread of infectious diseases brought on by pathogenic airborne bacteria and viruses. In parallel with a relentless search for therapeutics and vaccines, considerable effort [...] Read more.
Current COVID-19 pandemic caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has put a spotlight on the spread of infectious diseases brought on by pathogenic airborne bacteria and viruses. In parallel with a relentless search for therapeutics and vaccines, considerable effort is being expended to develop ever more powerful technologies to restricting the spread of airborne microorganisms in indoor spaces through the minimization of health- and environment-related risks. In this context, UV-based and photocatalytic oxidation (PCO)-based technologies (i.e., the combined action of ultraviolet (UV) light and photocatalytic materials such as titanium dioxide (TiO2)) represent the most widely utilized approaches at present because they are cost-effective and ecofriendly. The virucidal and bactericidal effect relies on the synergy between the inherent ability of UV light to directly inactivate viral particles and bacteria through nucleic acid and protein damages, and the production of oxidative radicals generated through the irradiation of the TiO2 surface. In this literature survey, we draw attention to the most effective UV radiations and TiO2-based PCO technologies available and their underlying mechanisms of action on both bacteria and viral particles. Since the fine tuning of different parameters, namely the UV wavelength, the photocatalyst composition, and the UV dose (viz, the product of UV light intensity and the irradiation time), is required for the inactivation of microorganisms, we wrap up this review coming up with the most effective combination of them. Now more than ever, UV- and TiO2-based disinfection technologies may represent a valuable tool to mitigate the spread of airborne pathogens. Full article
(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)
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14 pages, 1538 KiB  
Article
Poly(Ethylene Furanoate) along Its Life-Cycle from a Polycondensation Approach to High-Performance Yarn and Its Recyclate
by Tim Höhnemann, Mark Steinmann, Stefan Schindler, Martin Hoss, Simon König, Antje Ota, Martin Dauner and Michael R. Buchmeiser
Materials 2021, 14(4), 1044; https://doi.org/10.3390/ma14041044 - 23 Feb 2021
Cited by 18 | Viewed by 4475
Abstract
We report on the pilot scale synthesis and melt spinning of poly(ethylene furanoate) (PEF), a promising bio-based fiber polymer that can heave mechanical properties in the range of commercial poly(ethylene terephthalate) (PET) fibers. Catalyst optimization and solid state polycondensation (SSP) allowed for intrinsic [...] Read more.
We report on the pilot scale synthesis and melt spinning of poly(ethylene furanoate) (PEF), a promising bio-based fiber polymer that can heave mechanical properties in the range of commercial poly(ethylene terephthalate) (PET) fibers. Catalyst optimization and solid state polycondensation (SSP) allowed for intrinsic viscosities of PEF of up to 0.85 dL·g−1. Melt-spun multifilament yarns reached a tensile strength of up to 65 cN·tex−1 with an elongation of 6% and a modulus of 1370 cN·tex−1. The crystallization behavior of PEF was investigated by differential scanning calorimetry (DSC) and XRD after each process step, i.e., after polymerization, SSP, melt spinning, drawing, and recycling. After SSP, the previously amorphous polymer showed a crystallinity of 47%, which was in accordance with literature. The corresponding XRD diffractograms showed signals attributable to α-PEF. Additional, clearly assignable signals at 2θ > 30° are discussed. A completely amorphous structure was observed by XRD for as-spun yarns, while a crystalline phase was detected on drawn yarns; however, it was less pronounced than for the granules and independent of the winding speed. Full article
(This article belongs to the Special Issue Novel Synthetic Fibers for Textile Applications)
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19 pages, 4660 KiB  
Article
The Role of Solvents in Lithography-Based Ceramic Manufacturing of Lithium Disilicate
by Malte Hartmann, Markus Pfaffinger and Jürgen Stampfl
Materials 2021, 14(4), 1045; https://doi.org/10.3390/ma14041045 - 23 Feb 2021
Cited by 9 | Viewed by 2584
Abstract
Digital dentistry is increasingly replacing conventional methods of manually producing dental restorations. With regards to computer-aided manufacturing (CAM), milling is state of the art. Additive manufacturing (AM), as a complementary approach, has also found its way into dental practices and laboratories. Vat photo-polymerization [...] Read more.
Digital dentistry is increasingly replacing conventional methods of manually producing dental restorations. With regards to computer-aided manufacturing (CAM), milling is state of the art. Additive manufacturing (AM), as a complementary approach, has also found its way into dental practices and laboratories. Vat photo-polymerization is gaining increasing attention, because it enables the production of full ceramic restorations with high precision. One of the two predominantly used ceramic materials for these applications is lithium disilicate, Li2Si2O5. This glass ceramic exhibits a substantial fracture toughness, although possesses much lower bending strength, than the other predominantly used ceramic material, zirconia. Additionally, it shows a much more natural optical appearance, due to its inherent translucency, and therefore is considered for anterior tooth restorations. In this work, an optimized formulation for photo-reactive lithium disilicate suspensions, to be processed by vat photo-polymerization, is presented. Following the fundamental theoretical considerations regarding this processing technique, a variety of solvents was used to adjust the main properties of the suspension. It is shown that this solvent approach is a useful tool to effectively optimize a suspension with regards to refractive index, rheology, and debinding behavior. Additionally, by examining the effect of the absorber, the exposure time could be reduced by a factor of ten. Full article
(This article belongs to the Special Issue 3D-Printed Dental Materials)
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14 pages, 21007 KiB  
Article
Temperature-Dependent Photoluminescence of ZnO Thin Films Grown on Off-Axis SiC Substrates by APMOCVD
by Ivan Shtepliuk, Volodymyr Khranovskyy, Arsenii Ievtushenko and Rositsa Yakimova
Materials 2021, 14(4), 1035; https://doi.org/10.3390/ma14041035 - 22 Feb 2021
Cited by 4 | Viewed by 2322
Abstract
The growth of high-quality ZnO layers with optical properties congruent to those of bulk ZnO is still a great challenge. Here, for the first time, we systematically study the morphology and optical properties of ZnO layers grown on SiC substrates with off-cut angles [...] Read more.
The growth of high-quality ZnO layers with optical properties congruent to those of bulk ZnO is still a great challenge. Here, for the first time, we systematically study the morphology and optical properties of ZnO layers grown on SiC substrates with off-cut angles ranging from 0° to 8° by using the atmospheric pressure meta–organic chemical vapor deposition (APMOCVD) technique. Morphology analysis revealed that the formation of the ZnO films on vicinal surfaces with small off-axis angles (1.4°–3.5°) follows the mixed growth mode: from one side, ZnO nucleation still occurs on wide (0001) terraces, but from another side, step-flow growth becomes more apparent with the off-cut angle increasing. We show for the first time that the off-cut angle of 8° provides conditions for step-flow growth of ZnO, resulting in highly improved growth morphology, respectively structural quality. Temperature-dependent photoluminescence (PL) measurements showed a strong dependence of the excitonic emission on the off-cut angle. The dependences of peak parameters for bound exciton and free exciton emissions on temperature were analyzed. The present results provide a correlation between the structural and optical properties of ZnO on vicinal surfaces and can be utilized for controllable ZnO heteroepitaxy on SiC toward device-quality ZnO epitaxial layers with potential applications in nano-optoelectronics. Full article
(This article belongs to the Special Issue Progress in Optical Characterization of Semiconductor Nanomaterials and Devices)
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6 pages, 1796 KiB  
Article
Enhanced Ultraviolet Damage Resistance in Magnesium Doped Lithium Niobate Crystals through Zirconium Co-Doping
by Tengfei Kong, Yi Luo, Weiwei Wang, Hanxiao Kong, Zhiqin Fan and Hongde Liu
Materials 2021, 14(4), 1017; https://doi.org/10.3390/ma14041017 - 21 Feb 2021
Cited by 13 | Viewed by 1621
Abstract
MgO-doped LiNbO3 (LN:Mg) is famous for its high resistance to optical damage, but this phenomenon only occurs in visible and infrared regions, and its photorefraction is not decreased but enhanced in ultraviolet region. Here we investigated a series of ZrO2 co-doped [...] Read more.
MgO-doped LiNbO3 (LN:Mg) is famous for its high resistance to optical damage, but this phenomenon only occurs in visible and infrared regions, and its photorefraction is not decreased but enhanced in ultraviolet region. Here we investigated a series of ZrO2 co-doped LN:Mg (LN:Mg,Zr) regarding their ultraviolet photorefractive properties. The optical damage resistance experiment indicated that the resistance against ultraviolet damage of LN:Mg was significantly enhanced with increased ZrO2 doping concentration. Moreover, first-principles calculations manifested that the enhancement of ultraviolet damage resistance for LN:Mg,Zr was mainly determined by both the increased band gap and the reduced ultraviolet photorefractive center O2−/−. So, LN:Mg,Zr crystals would become an excellent candidate for ultraviolet nonlinear optical material. Full article
(This article belongs to the Special Issue Growth and Characterization of Bulk Crystals)
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13 pages, 1149 KiB  
Article
Chemical Evaluation of Energy Dispersive X-ray Spectroscopy Analysis of Different Failing Dental Implant Surfaces: A Comparative Clinical Trial
by Berceste Guler, Ahu Uraz, Hasan Hatipoğlu and Mehmet Yalım
Materials 2021, 14(4), 986; https://doi.org/10.3390/ma14040986 - 19 Feb 2021
Cited by 1 | Viewed by 1844
Abstract
The aim of the present study is to compare two different implant surface chemistries of failing dental implants. Sixteen patients (mean age: 52 ± 8.27 with eight females and eight males) and 34 implants were included in the study. Group-I implants consisted of [...] Read more.
The aim of the present study is to compare two different implant surface chemistries of failing dental implants. Sixteen patients (mean age: 52 ± 8.27 with eight females and eight males) and 34 implants were included in the study. Group-I implants consisted of a blasted/etched surface with a final process surface, while Group-II implants consisted of the sandblasted acid etching (SLA) method. The chemical surface analysis was performed by the energy dispersive X-ray spectroscopy (EDX) method from coronal, middle, and apical parts of each implant. Titanium (Ti) element values were found to be 20.22 ± 15.7 at.% in Group I and 33.96 ± 13.62 at.% in Group-II in the middle of the dental implants. Aluminum (Al) element values were found to be 0.01 ± 0.002 in Group-I and 0.17 ± 0.28 at.% in Group II in the middle of the dental implants, and statistically significant differences were found between the groups for the Al and Ti elements in the middle of the dental implants (p < 0.05). There was a statistically significant difference for the Ti, Al, O, Ca, Fe, P, and Mg elements in the coronal, middle, and apical parts of the implants in the intragroup evaluation (p < 0.05). It is reported that different parts of the implants affected by peri-implant inflammation show different surface chemistries, from coronal to apical, but there is no difference in the implants with different surfaces. Full article
(This article belongs to the Section Materials Chemistry)
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22 pages, 3798 KiB  
Article
Detection and Imaging of Damages and Defects in Fibre-Reinforced Composites by Magnetic Resonance Technique
by Carine L. Alves, Janete S. Oliveira, Alberto Tannus, Alessandra Cristina Soares P. Tarpani and José R. Tarpani
Materials 2021, 14(4), 977; https://doi.org/10.3390/ma14040977 - 19 Feb 2021
Cited by 3 | Viewed by 2653
Abstract
Defectively manufactured and deliberately damaged composite laminates fabricated with different continuous reinforcing fibres (respectively, carbon and glass) and polymer matrices (respectively, thermoset and thermoplastic) were inspected in magnetic resonance imaging equipment. Two pulse sequences were evaluated during non-destructive examination conducted in saline solution-immersed [...] Read more.
Defectively manufactured and deliberately damaged composite laminates fabricated with different continuous reinforcing fibres (respectively, carbon and glass) and polymer matrices (respectively, thermoset and thermoplastic) were inspected in magnetic resonance imaging equipment. Two pulse sequences were evaluated during non-destructive examination conducted in saline solution-immersed samples to simulate load-bearing orthopaedic implants permanently in contact with biofluids. The orientation, positioning, shape, and especially the size of translaminar and delamination fractures were determined according to stringent structural assessment criteria. The spatial distribution, shape, and contours of water-filled voids were sufficiently delineated to infer the amount of absorbed water if thinner image slices than this study were used. The surface texture of composite specimens featuring roughness, waviness, indentation, crushing, and scratches was outlined, with fortuitous artefacts not impairing the image quality and interpretation. Low electromagnetic shielding glass fibres delivered the highest, while electrically conductive carbon fibres produced the poorest quality images, particularly when blended with thermoplastic polymer, though reliable image interpretation was still attainable. Full article
(This article belongs to the Special Issue Non-Destructive Testing of Structures)
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13 pages, 7001 KiB  
Article
On the Features of Composite Coating, Based on Nickel Alloy and Aluminum–Iron Bronze, Processed by Direct Metal Deposition
by Eugene E. Feldshtein, Oleg Devojno, Marharyta Kardapolava, Nikolaj Lutsko and Justyna Patalas-Maliszewska
Materials 2021, 14(4), 957; https://doi.org/10.3390/ma14040957 - 18 Feb 2021
Cited by 1 | Viewed by 1612
Abstract
In recent years, additive manufacturing technologies have become increasingly widespread with the most intensive development being direct metal deposition (DMD), alloys, and ceramic materials on a metal substrate. This study shows the possibilities of the effective formation of coatings, based on heterogeneous metal [...] Read more.
In recent years, additive manufacturing technologies have become increasingly widespread with the most intensive development being direct metal deposition (DMD), alloys, and ceramic materials on a metal substrate. This study shows the possibilities of the effective formation of coatings, based on heterogeneous metal alloys (Ni-based alloy and Fe-Al bronze) deposited onto 1045 structural steel. Changes in the microhardness, the microstructure, and the tribological properties of the composite coating, depending on the laser spot speed and pitch during DMD processing, have been considered. It was revealed that if the components of the composite coating are chosen correctly, there are possible DMD conditions ensuring reliable and durable connection between them and with the substrate. Full article
(This article belongs to the Special Issue Precision and Ultra-Precision Subtractive and Additive Manufacturing Processes of Alloys and Steels)
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17 pages, 2760 KiB  
Article
Effect of Modification of Amorphous Silica with Ammonium Agents on the Physicochemical Properties and Hydrogenation Activity of Ir/SiO2 Catalysts
by Monika Kot, Robert Wojcieszak, Ewa Janiszewska, Mariusz Pietrowski and Michał Zieliński
Materials 2021, 14(4), 968; https://doi.org/10.3390/ma14040968 - 18 Feb 2021
Cited by 9 | Viewed by 2351
Abstract
The modification of commercial silica with solutions of NH4F or NH4Cl salts, followed by thermal treatment, enabled generation of the acidic sites in SiO2 and changed its textural properties. The use of ammonium salts solution also caused the [...] Read more.
The modification of commercial silica with solutions of NH4F or NH4Cl salts, followed by thermal treatment, enabled generation of the acidic sites in SiO2 and changed its textural properties. The use of ammonium salts solution also caused the generation of additional porosity. Using NH4F solution caused significant decrease in the specific surface area and the increase in the average pore diameter. The number and strength of resulting acid sites depend on the nature of anion in the applied ammonium salt and the concentration of salt solution. It has been found that the sample treated with NH4F presented higher total acidity (TPD–NH3) and the amount as well as the strength of acid sites increased with the concentration of the used modifier. As modified amorphous SiO2 materials used as a support for iridium (1 wt %, Ir(acac)3) nanoparticles permitted to obtain highly active catalysts for toluene hydrogenation under atmospheric pressure. The highest activity (expressed as the apparent rate and TOF) was obtained for iridium catalysts supported on silica modified by NH4F with the highest acidity. The modification of silica with NH4F favors the generation of centers able to adsorb toluene, which results in higher activity of this catalyst. Full article
(This article belongs to the Special Issue Mesoporous Silica and Their Applications)
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19 pages, 3522 KiB  
Article
Upconversion Luminescence of Silica–Calcia Nanoparticles Co-doped with Tm3+ and Yb3+ Ions
by Katarzyna Halubek-Gluchowska, Damian Szymański, Thi Ngoc Lam Tran, Maurizio Ferrari and Anna Lukowiak
Materials 2021, 14(4), 937; https://doi.org/10.3390/ma14040937 - 16 Feb 2021
Cited by 23 | Viewed by 3132
Abstract
Looking for upconverting biocompatible nanoparticles, we have prepared by the sol–gel method, silica–calcia glass nanopowders doped with different concentration of Tm3+ and Yb3+ ions (Tm3+ from 0.15 mol% up to 0.5 mol% and Yb3+ from 1 mol% up to [...] Read more.
Looking for upconverting biocompatible nanoparticles, we have prepared by the sol–gel method, silica–calcia glass nanopowders doped with different concentration of Tm3+ and Yb3+ ions (Tm3+ from 0.15 mol% up to 0.5 mol% and Yb3+ from 1 mol% up to 4 mol%) and characterized their structure, morphology, and optical properties. X-ray diffraction patterns indicated an amorphous phase of the silica-based glass with partial crystallization of samples with a higher content of lanthanides ions. Transmission electron microscopy images showed that the average size of particles decreased with increasing lanthanides content. The upconversion (UC) emission spectra and fluorescence lifetimes were registered under near infrared excitation (980 nm) at room temperature to study the energy transfer between Yb3+ and Tm3+ at various active ions concentrations. Characteristic emission bands of Tm3+ ions in the range of 350 nm to 850 nm were observed. To understand the mechanism of Yb3+–Tm3+ UC energy transfer in the SiO2–CaO powders, the kinetics of luminescence decays were studied. Full article
(This article belongs to the Special Issue Advances in Nanostructured Materials)
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19 pages, 10467 KiB  
Article
Polyurethane Foams for Domestic Sewage Treatment
by Ewa Dacewicz and Joanna Grzybowska-Pietras
Materials 2021, 14(4), 933; https://doi.org/10.3390/ma14040933 - 16 Feb 2021
Cited by 21 | Viewed by 3999
Abstract
The aim of the study was to assess the possibility of using polyurethane foams (PUF) as a filling of a foam-sand filter to directly treat domestic sewage with increased content of ammonium nitrogen and low organic carbon to nitrogen ratio (C/N). The study [...] Read more.
The aim of the study was to assess the possibility of using polyurethane foams (PUF) as a filling of a foam-sand filter to directly treat domestic sewage with increased content of ammonium nitrogen and low organic carbon to nitrogen ratio (C/N). The study compared performance of two types of flexible foams: new, cylinder-shaped material (Novel Foams, NF) and waste, scrap foams (Waste Foams, WF). The foams serving as a filling of two segments of a foam-sand filter were assessed for their hydrophobic and physical properties and were tested for their cell structure, i.e., cell diameter, cell size distribution, porosity, and specific surface area. The study accounted also for selected application-related properties, such as hydrophobicity, water absorption, apparent density, dimensional stability, amount of adsorbed biomass, and the possibility of regeneration. Cell morphology was compared in reference foams, foams after 14 months of the filter operation, and regenerated foams. The experimental outcomes indicated WF as an innovative type of biomass carrier for treating domestic sewage with low C/N ratio. SEM images showed that immobilization of microorganisms in NF and WF matrices involved the formation of multi-cellular structures attached to the inner surface of the polyurethane and attachment of single bacterial cells to the foam surface. The amount of adsorbed biomass confirmed that the foam-sand filter made up of two upper layers of waste foams (with diameters and pore content of 0.50–1.53 mm and 53.0–63.5% respectively) provided highly favorable conditions for the development of active microorganisms. Full article
(This article belongs to the Special Issue Performance Research of Polyurethane Foams and Composites)
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11 pages, 2254 KiB  
Article
Dynamic Crosslinking: An Efficient Approach to Fabricate Epoxy Vitrimer
by Yin Ran, Ling-Ji Zheng and Jian-Bing Zeng
Materials 2021, 14(4), 919; https://doi.org/10.3390/ma14040919 - 15 Feb 2021
Cited by 13 | Viewed by 3372
Abstract
Epoxy vitrimers with reprocessability, recyclability, and a self-healing performance have attracted increasingly attention, but are usually fabricated through static curing procedures with a low production efficiency. Herein, we report a new approach to fabricate an epoxy vitrimer by dynamic crosslinking in a torque [...] Read more.
Epoxy vitrimers with reprocessability, recyclability, and a self-healing performance have attracted increasingly attention, but are usually fabricated through static curing procedures with a low production efficiency. Herein, we report a new approach to fabricate an epoxy vitrimer by dynamic crosslinking in a torque rheometer, using diglycidyl ether of bisphenol A and sebacic acid as the epoxy resin and curing agent, respectively, in the presence of zinc acetylacetonate as the transesterification catalyst. The optimal condition for fabricating the epoxy vitrimer (EVD) was dynamic crosslinking at 180 °C for ~11 min. A control epoxy vitrimer (EVS) was prepared by static curing at 180 °C for ~11 min. The structure, properties, and stress relaxation of the EVD and EVS were comparatively investigated in detail. The EVS did not cure completely during static curing, as evidenced by the continuously increasing gel fraction when subjected to compression molding. The gel fraction of the EVD did not change with compression molding at the same condition. The physical, mechanical, and stress relaxation properties of the EVD prepared by dynamic crosslinking were comparable to those of the EVS fabricated by static curing, despite small differences in the specific property parameters. This study demonstrated that dynamic crosslinking provides a new technique to efficiently fabricate an epoxy vitrimer. Full article
(This article belongs to the Special Issue Self-Healing Materials and Devices)
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20 pages, 5243 KiB  
Article
Research on the Thermal Properties of Fireplace Concrete Materials Containing Various Mineral Aggregates Enriched by Organic and Inorganic Fibers
by Agata Stempkowska, Joanna Mastalska-Popławska, Piotr Izak, Łukasz Wójcik, Tomasz Gawenda and Marzena Karbowy
Materials 2021, 14(4), 904; https://doi.org/10.3390/ma14040904 - 14 Feb 2021
Cited by 3 | Viewed by 1822
Abstract
This work presents a summary of research on concrete fireplace materials made of various mineral aggregates and enriched with steel and organic fibers. To determine the optimal applications of such concretes, their ability to accumulate heat and their other physicochemical parameters were tested [...] Read more.
This work presents a summary of research on concrete fireplace materials made of various mineral aggregates and enriched with steel and organic fibers. To determine the optimal applications of such concretes, their ability to accumulate heat and their other physicochemical parameters were tested and analyzed. Studies on the behavior of concrete materials during cooling are reported, and the ability of such materials to accumulate heat is evaluated using calculations. In addition, tests were performed on the loss of mass during heating, as well as on the mechanical bending strength and microstructures of these materials. Studies have shown that the behavior of concrete materials at high temperatures can be modified and adapted for specific purposes. The addition of fibers to concrete improves both the mechanical properties of mortars and the heat flow in concrete materials. Full article
(This article belongs to the Special Issue Research and Development of Modified Building Materials)
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15 pages, 5431 KiB  
Article
Stress-Dependent Particle Interactions of Magnesium Aluminometasilicates as Their Performance Factor in Powder Flow and Compaction Applications
by Pavlína Komínová, Lukáš Kulaviak and Petr Zámostný
Materials 2021, 14(4), 900; https://doi.org/10.3390/ma14040900 - 14 Feb 2021
Cited by 5 | Viewed by 2452
Abstract
In the pharmaceutical industry, silicates are commonly used excipients with different application possibilities. They are especially utilized as glidants in low concentrations, but they can be used in high concentrations as porous carriers and coating materials in oral solid drug delivery systems. The [...] Read more.
In the pharmaceutical industry, silicates are commonly used excipients with different application possibilities. They are especially utilized as glidants in low concentrations, but they can be used in high concentrations as porous carriers and coating materials in oral solid drug delivery systems. The desirable formulations of such systems must exhibit good powder flow but also good compactibility, which brings opposing requirements on inter-particle interactions. Since magnesium aluminometasilicates (MAS) are known for their interesting flow behavior reported as “negative cohesivity” yet they can be used as binders for tablet compression, the objective of this experimental study was to investigate their particle interactions within a broad range of mechanical stress from several kPa to hundreds of MPa. Magnesium aluminometasilicate (Neusilin® US2 and Neusilin® S2)-microcrystalline cellulose (Avicel® PH102) physical powder mixtures with varying silicate concentrations were prepared and examined during their exposure to different pressures using powder rheology and compaction analysis. The results revealed that MAS particles retain their repulsive character and small contact surface area under normal conditions. If threshold pressure is applied, the destruction of MAS particles and formation of new surfaces leading to particle interactions are observed. The ability of MAS particles to form interactions intensifies with increasing pressure and their amount in a mixture. This “function switching” makes MAS suitable for use as multifunctional excipients since they can act as a glidant or a binder depending on the applied pressure. Full article
(This article belongs to the Special Issue Silica and Silica-based Materials for Biotechnology, Polymer Composites and Environmental Protection)
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16 pages, 2770 KiB  
Review
Fibre Bragg Grating Based Acoustic Emission Measurement System for Structural Health Monitoring Applications
by Sagar Jinachandran and Ginu Rajan
Materials 2021, 14(4), 897; https://doi.org/10.3390/ma14040897 - 13 Feb 2021
Cited by 28 | Viewed by 3595
Abstract
Fiber Bragg grating (FBG)-based acoustic emission (AE) detection and monitoring is considered as a potential and emerging technology for structural health monitoring (SHM) applications. In this paper, an overview of the FBG-based AE monitoring system is presented, and various technologies and methods used [...] Read more.
Fiber Bragg grating (FBG)-based acoustic emission (AE) detection and monitoring is considered as a potential and emerging technology for structural health monitoring (SHM) applications. In this paper, an overview of the FBG-based AE monitoring system is presented, and various technologies and methods used for FBG AE interrogation systems are reviewed and discussed. Various commercial FBG AE sensing systems, SHM applications of FBG AE monitoring, and market potential and recent trends are also discussed. Full article
(This article belongs to the Special Issue Recent Advances in Photonic Sensors)
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29 pages, 6545 KiB  
Article
Multiphysics and Multiscale Modeling of Coupled Transport of Chloride Ions in Concrete
by Amit Jain and Bora Gencturk
Materials 2021, 14(4), 885; https://doi.org/10.3390/ma14040885 - 13 Feb 2021
Cited by 7 | Viewed by 2196
Abstract
Chloride ions (Cl−)-induced corrosion is one of the main degradation mechanisms in reinforced concrete (RC) structures. In most situations, the degradation initiates with the transport of Cl− from the surface of the concrete towards the reinforcing steel. The accumulation of [...] Read more.
Chloride ions (Cl−)-induced corrosion is one of the main degradation mechanisms in reinforced concrete (RC) structures. In most situations, the degradation initiates with the transport of Cl− from the surface of the concrete towards the reinforcing steel. The accumulation of Cl− at the steel-concrete interface could initiate reinforcement corrosion once a threshold Cl− concentration is achieved. An accurate numerical model of the Cl− transport in concrete is required to predict the corrosion initiation in RC structures. However, existing numerical models lack a representation of the heterogenous concrete microstructure resulting from the varying environmental conditions and the indirect effect of time dependent temperature and relative humidity (RH) on the water adsorption and Cl− binding isotherms. In this study, a numerical model is developed to study the coupled transport of Cl− with heat, RH and oxygen (O2) into the concrete. The modeling of the concrete microstructure is performed using the Virtual Cement and Concrete Testing Laboratory (VCCTL) code developed by the U.S. National Institute of Standards and Technology (NIST). The concept of equivalent maturation time is utilized to eliminate the limitation of simulating concrete microstructure using VCCTL in specific environmental conditions such as adiabatic. Thus, a time-dependent concrete microstructure, which depends on the hydration reactions coupled with the temperature and RH of the environment, is achieved to study the Cl− transport. Additionally, Cl− binding isotherms, which are a function of the pH of the concrete pore solution, Cl− concentration, and weight fraction of mono-sulfate aluminate (AFm) and calcium-silicate-hydrate (C-S-H), obtained from an experimental study by the same authors are utilized to account for the Cl− binding of cement hydration products. The temperature dependent RH diffusion was considered to account for the transport of Cl− with moisture transport. The temperature and RH diffusion in the concrete domain, composite theory, and Cl− binding and water adsorption isotherms are used in combination, to estimate the ensuing Cl− diffusion field within the concrete. The coupled transport process of heat, RH, Cl−, and O2 is implemented in the Multiphysics Object-Oriented Simulation Environment (MOOSE) developed by the U.S. Idaho National Laboratory (INL). The model was verified and validated using data from multiple experimental studies with different concrete mixture proportions, curing durations, and environmental conditions. Additionally, a sensitivity analysis was performed to identify that the water-to-cement (w/c) ratio, the exposure duration, the boundary conditions: temperature, RH, surface Cl− concentration, Cl− diffusion coefficient in the capillary water, and the critical RH are the important parameters that govern the Cl− transport in RC structures. In a case study, the capabilities of the developed numerical model are demonstrated by studying the complex 2D diffusion of Cl− in a RC beam located in two different climatic regions: warm and humid weather in Galveston, Texas, and cold and dry weather in North Minnesota, Minnesota, subjected to time varying temperature, RH, and surface Cl− concentrations. Full article
(This article belongs to the Special Issue Advances in Construction and Building Materials)
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30 pages, 2017 KiB  
Article
Numerically Exploring the Potential of Abating the Energy Flow Peaks through Tough, Single Network Hydrogel Vibration Isolators with Chemical and Physical Cross-Links
by Leif Kari
Materials 2021, 14(4), 886; https://doi.org/10.3390/ma14040886 - 13 Feb 2021
Cited by 3 | Viewed by 2344
Abstract
Traditional vibration isolation systems, using natural rubber vibration isolators, display large peaks for the energy flow from the machine source and into the receiving foundation, at the unavoidable rigid body resonance frequencies. However, tough, doubly cross-linked, single polymer network hydrogels, with both chemical [...] Read more.
Traditional vibration isolation systems, using natural rubber vibration isolators, display large peaks for the energy flow from the machine source and into the receiving foundation, at the unavoidable rigid body resonance frequencies. However, tough, doubly cross-linked, single polymer network hydrogels, with both chemical and physical cross-links, show a high loss factor over a specific frequency range, due to the intensive adhesion–deadhesion activities of the physical cross-links. In this study, vibration isolators, made of this tough hydrogel, are theoretically applied in a realistic vibration isolation system, displaying several rigid body resonances and various energy flow transmission paths. A simulation model is developed, that includes a suitable stress–strain model, and shows a significant reduction of the energy flow peaks. In particular, the reduction is more than 30 times, as compared to the corresponding results using the natural rubber. Finally, it is shown that a significant reduction is possible, also without any optimization of the frequency for the maximum physical loss modulus. This is a clear advantage for polyvinyl alcohol hydrogels, that are somewhat missing the possibility to alter the frequency for the maximum physical loss, due to the physical cross-link system involved—namely, that of the borate esterification. Full article
(This article belongs to the Special Issue Advanced Materials for Aerospace Engineering)
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15 pages, 3130 KiB  
Article
Preparation and Characterization of Nanoparticle-Doped Polymer Inclusion Membranes. Application to the Removal of Arsenate and Phosphate from Waters
by Enriqueta Anticó, Ruben Vera, Francisco Vázquez, Clàudia Fontàs, Changyong Lu and Josep Ros
Materials 2021, 14(4), 878; https://doi.org/10.3390/ma14040878 - 12 Feb 2021
Cited by 15 | Viewed by 2364
Abstract
Nanoparticle-doped polymer inclusion membranes (NP-PIMs) have been prepared and characterized as new materials for the removal of arsenate and phosphate from waters. PIMs are made of a polymer, cellulose triacetate (CTA), and an extractant, which interacts with the compound of interest. We have [...] Read more.
Nanoparticle-doped polymer inclusion membranes (NP-PIMs) have been prepared and characterized as new materials for the removal of arsenate and phosphate from waters. PIMs are made of a polymer, cellulose triacetate (CTA), and an extractant, which interacts with the compound of interest. We have used the ionic liquid (IL) trioctylmethylammonium chloride (Aliquat 336) as the extractant and have investigated how the addition of nanoparticles can modify membrane properties. To this end, inorganic nanoparticles, such as ferrite (Fe3O4), SiO2 and TiO2, and multiwalled carbon nanotubes (MWCNTs), were blended with the polymer/extractant mixture. Scanning electron microscopy (SEM), infrared spectroscopy (FT-IR), and contact angle measurements have been used to characterize the material. Moreover, PIM stability was checked by measuring the mass loss during the experiments. Since Aliquat 336 acts as an anion exchanger, the NP-PIMs have been explored in two different applications: (i) as sorbent materials for the extraction of arsenate and phosphate anions; (ii) as an organic phase for the separation of arsenate and phosphate in a three-phase system. The presence of oleate-coated ferrite NP in the PIM formulation represents an improvement in the efficiency of NP-PIMs used as sorbents; nevertheless, a decrease in the transport efficiency for arsenate but not for phosphate was obtained. The ease with which the NP-PIMs are prepared suggests good potential for future applications in the treatment of polluted water. Future work will address three main aspects: firstly, the implementation of the Fe3O4-PIMs for the removal of As(V) in real water containing complex matrices; secondly, the study of phosphate recovery with other cell designs that allow large volumes of contaminated water to be treated; and thirdly, the investigation of the role of MWCNTs in PIM stability. Full article
(This article belongs to the Special Issue New Materials and Technologies for Wastewater Treatment)
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24 pages, 3616 KiB  
Article
Assessment of Mechanical and Thermal Properties of Hemp-Lime Mortar
by Eliana Parcesepe, Rosa Francesca De Masi, Carmine Lima, Gerardo Maria Mauro, Maria Rosaria Pecce and Giuseppe Maddaloni
Materials 2021, 14(4), 882; https://doi.org/10.3390/ma14040882 - 12 Feb 2021
Cited by 12 | Viewed by 2429
Abstract
The use of renewable and natural materials characterized by the low environmental impact is nowadays a key issue for the sustainable development of the construction industry. For this reason, the interest for natural fibers, to be used as reinforcement in composites as an [...] Read more.
The use of renewable and natural materials characterized by the low environmental impact is nowadays a key issue for the sustainable development of the construction industry. For this reason, the interest for natural fibers, to be used as reinforcement in composites as an alternative to other fibers, is continuously growing. In this paper, the use of hemp for reinforcing lime mortar used as plaster is considered with a multidisciplinary approach, taking into consideration the structural and thermal performance. Natural fibers have several advantages compared to industrial ones, such as low cost, low environmental impact, biodegradability, renewable nature. Moreover, these can show remarkable mechanical performance in relation to specific weight, and sometimes, as in the case of hemp fibers, these can improve the thermal insulation capacity of the plaster. However, the experimental results on the mechanical features are still lacking, especially to assess their durability, and the variability of thermal parameters with the mechanical characteristics. Therefore, this paper proposes an experimental program, developed at Laboratory of Materials and Structures (LAMAS) of the University of Sannio (Italy), aimed at investigating the main mechanical properties (compression strength, flexural strength) of lime mortar reinforced by hemp fibers and subjected to various environmental exposures and aging processes. The characterization is completed with the measurement for the produced samples of the thermal conductivity by means of the standardized guarded hot plate technique. Full article
(This article belongs to the Special Issue State-of-the-Art Construction Materials in Italy: Challenges for Sustainable, Safe, and Resilient Buildings)
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10 pages, 2254 KiB  
Article
Dentin Phosphophoryn-Derived Peptide Promotes Odontoblast Differentiation In Vitro and Dentin Regeneration In Vivo
by Bayarchimeg Altankhishig, Mohammad Ali Akbor Polan, Youjing Qiu, Md Riasat Hasan and Takashi Saito
Materials 2021, 14(4), 874; https://doi.org/10.3390/ma14040874 - 12 Feb 2021
Cited by 6 | Viewed by 1852
Abstract
The purpose of the present study was to investigate the effect of a peptide (i.e., SESDNNSSSRGDASYNSDES) derived from dentin phosphophoryn (DPP) with arginine-glycine-aspartic acid (RGD) motifs on odontoblast differentiation in vitro and to compare it with calcium hydroxide—a material used conventionally for vital [...] Read more.
The purpose of the present study was to investigate the effect of a peptide (i.e., SESDNNSSSRGDASYNSDES) derived from dentin phosphophoryn (DPP) with arginine-glycine-aspartic acid (RGD) motifs on odontoblast differentiation in vitro and to compare it with calcium hydroxide—a material used conventionally for vital pulp therapy—in terms of reparative dentin formation and pulp inflammation in vivo. Alkaline phosphatase activity assay and alizarin red S staining were performed to evaluate odontoblast-differentiation in cell culturing experiments. To observe the reparative dentin formation and pulp inflammation animal experiment was performed and examined by histological methods. The difference between the experimental group and the control group was analyzed statistically using a one-way ANOVA test. The results revealed that the DPP-derived RGD-containing peptide triggered odontoblast differentiation and mineralization in vitro. In rats undergoing direct pulp capping, the DPP-derived RGD-containing peptide was found to induce intensively formed reparative dentin with high compactness at week 4. On histological and morphometrical examinations, a smaller degree of pulpitis was observed in the specimens treated with the peptide than in those treated with calcium hydroxide. This study suggests that the DPP-derived RGD-containing peptide is a biocompatible, biodegradable and bioactive material for dentin regeneration. Full article
(This article belongs to the Special Issue Current Developments in Additive Manufacturing for Tissue Engineering and Regenerative Medicine)
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19 pages, 3824 KiB  
Article
A Comparative Analysis of Laser Additive Manufacturing of High Layer Thickness Pure Ti and Inconel 718 Alloy Materials Using Finite Element Method
by Sapam Ningthemba Singh, Sohini Chowdhury, Yadaiah Nirsanametla, Anil Kumar Deepati, Chander Prakash, Sunpreet Singh, Linda Yongling Wu, Hongyu Y. Zheng and Catalin Pruncu
Materials 2021, 14(4), 876; https://doi.org/10.3390/ma14040876 - 12 Feb 2021
Cited by 22 | Viewed by 3487
Abstract
Investigation of the selective laser melting (SLM) process, using finite element method, to understand the influences of laser power and scanning speed on the heat flow and melt-pool dimensions is a challenging task. Most of the existing studies are focused on the study [...] Read more.
Investigation of the selective laser melting (SLM) process, using finite element method, to understand the influences of laser power and scanning speed on the heat flow and melt-pool dimensions is a challenging task. Most of the existing studies are focused on the study of thin layer thickness and comparative study of same materials under different manufacturing conditions. The present work is focused on comparative analysis of thermal cycles and complex melt-pool behavior of a high layer thickness multi-layer laser additive manufacturing (LAM) of pure Titanium (Ti) and Inconel 718. A transient 3D finite-element model is developed to perform a quantitative comparative study on two materials to examine the temperature distribution and disparities in melt-pool behaviours under similar processing conditions. It is observed that the layers are properly melted and sintered for the considered process parameters. The temperature and melt-pool increases as laser power move in the same layer and when new layers are added. The same is observed when the laser power increases, and opposite is observed for increasing scanning speed while keeping other parameters constant. It is also found that Inconel 718 alloy has a higher maximum temperature than Ti material for the same process parameter and hence higher melt-pool dimensions. Full article
(This article belongs to the Special Issue Modeling, Simulation and Data Processing for Additive Manufacturing)
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18 pages, 5512 KiB  
Article
A Facile and Scalable Approach in the Fabrication of Tailored 3D Graphene Foam via Freeze Drying
by Tony Thomas and Arvind Agarwal
Materials 2021, 14(4), 864; https://doi.org/10.3390/ma14040864 - 11 Feb 2021
Cited by 12 | Viewed by 3849
Abstract
One of the challenges in the processing of advanced composite materials with 2D reinforcement is their extensive agglomeration in the matrix. 3D architecture of 2D graphene sheets into a Graphene Foam (GrF) assembly has emerged as an effective way to overcome agglomeration. The [...] Read more.
One of the challenges in the processing of advanced composite materials with 2D reinforcement is their extensive agglomeration in the matrix. 3D architecture of 2D graphene sheets into a Graphene Foam (GrF) assembly has emerged as an effective way to overcome agglomeration. The highly reticulated network of branches and nodes of GrF offers a seamless pathway for photon and electron conduction in the matrix along with improved mechanical properties. 3D GrF nano-filler is often fabricated by chemical vapor deposition (CVD) technique, which demands high energy, slow deposition rate, and restricting production to small scale. This work highlights freeze-drying (FD) technique to produce 3D graphene nanoplatelets (GNP) foam with a similar hierarchical structure to the CVD GrF. The FD technique using water as the main chemical in 3D GNP foam production is an added advantage. The flexibility of the FD in producing GNP foams of various pore size and morphology is elucidated. The simplicity with which one can engineer thermodynamic conditions to tailor the pore shape and morphology is presented here by altering the GNP solid loading and mold geometry. The FD 3D GNP foam is mechanically superior to CVD GrF as it exhibited 1280 times higher elastic modulus. However, thermal diffusivity of the FD GNP foam is almost 0.5 times the thermal diffusivity of the CVD GrF due to the defects in GNP particles and pore architecture. The versatility in GNP foam scalability and compatibility to form foam of other 1D and 2D material systems (e.g., carbon nanotubes, boron nitride nanotubes, and boron nitride nanoplatelets) brings a unique dimensionality to FD as an advanced engineering foam development process. Full article
(This article belongs to the Special Issue Graphene Foam Based Composites)
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3 pages, 170 KiB  
Editorial
Special Issue: “Microstructures and Durability of Cement-Based Materials”
by Jeong Gook Jang and Solmoi Park
Materials 2021, 14(4), 866; https://doi.org/10.3390/ma14040866 - 11 Feb 2021
Cited by 3 | Viewed by 1525
Abstract
Cement-based materials play an irreplaceable role in building and sustaining our society by meeting the performance demand imposed on structures and sustainability. Cement-based materials are no longer limited to derivatives of Portland cement, and appreciate a wider range of binders that come from [...] Read more.
Cement-based materials play an irreplaceable role in building and sustaining our society by meeting the performance demand imposed on structures and sustainability. Cement-based materials are no longer limited to derivatives of Portland cement, and appreciate a wider range of binders that come from various origins. It is therefore of utmost importance for understanding and expanding the relevant knowledge on their microstructure and likely durability performance. This Special Issue “Microstructures and Durability of Cement-Based Materials” presents recent studies reporting microstructural and durability investigation revealing the characteristics of cement-based materials. Full article
(This article belongs to the Special Issue Microstructures and Durability of Cement-Based Materials)
11 pages, 4488 KiB  
Article
Thermal Nonlinear Klein–Gordon Equation for Nano-/Micro-Sized Metallic Particle–Attosecond Laser Pulse Interaction
by Mihai Oane, Muhammad Arif Mahmood, Andrei C. Popescu, Alexandra Bănică, Carmen Ristoscu and Ion N. Mihăilescu
Materials 2021, 14(4), 857; https://doi.org/10.3390/ma14040857 - 10 Feb 2021
Cited by 1 | Viewed by 2005
Abstract
In this study, a rigorous analytical solution to the thermal nonlinear Klein–Gordon equation in the Kozłowski version is provided. The Klein–Gordon heat equation is solved via the Zhukovsky “state-of-the-art” mathematical techniques. Our study can be regarded as an initial approximation of attosecond laser–particle [...] Read more.
In this study, a rigorous analytical solution to the thermal nonlinear Klein–Gordon equation in the Kozłowski version is provided. The Klein–Gordon heat equation is solved via the Zhukovsky “state-of-the-art” mathematical techniques. Our study can be regarded as an initial approximation of attosecond laser–particle interaction when the prevalent phenomenon is photon–electron interaction. The electrons interact with the laser beam, which means that the nucleus does not play a significant role in temperature distribution. The particle is supposed to be homogenous with respect to thermophysical properties. This theoretical approach could prove useful for the study of metallic nano-/micro-particles interacting with attosecond laser pulses. Specific applications for Au “nano” particles with a 50 nm radius and “micro” particles with 110, 130, 150, and 1000 nm radii under 100 attosecond laser pulse irradiation are considered. First, the cross-section is supposed to be proportional to the area of the particle, which is assumed to be a perfect sphere of radius R or a rotation ellipsoid. Second, the absorption coefficient is calculated using a semiclassical approach, taking into account the number of atoms per unit volume, the classical electron radius, the laser wavelength, and the atomic scattering factor (10 in case of Au), which cover all the basic aspects for the interaction between the attosecond laser and a nanoparticle. The model is applicable within the 100–2000 nm range. The main conclusion of the model is that for a range inferior to 1000 nm, a competition between ballistic and thermal phenomena occurs. For values in excess of 1000 nm, our study suggests that the thermal phenomena are dominant. Contrastingly, during the irradiation with fs pulses, this value is of the order of 100 nm. This theoretical model’s predictions could be soon confirmed with the new EU-ELI facilities in progress, which will generate pulses of 100 as at a 30 nm wavelength. Full article
(This article belongs to the Special Issue Materials Thermal Behavior during Laser or Electron Beam Irradiation)
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26 pages, 6859 KiB  
Article
Anticancer Molecular Mechanism of Protocatechuic Acid Loaded on Folate Coated Functionalized Graphene Oxide Nanocomposite Delivery System in Human Hepatocellular Carcinoma
by Kalaivani Buskaran, Saifullah Bullo, Mohd Zobir Hussein, Mas Jaffri Masarudin, Mohamad Aris Mohd Moklas and Sharida Fakurazi
Materials 2021, 14(4), 817; https://doi.org/10.3390/ma14040817 - 9 Feb 2021
Cited by 22 | Viewed by 2564
Abstract
Liver cancer is listed as the fifth-ranked cancer, responsible for 9.1% of all cancer deaths globally due to its assertive nature and poor survival rate. To overcome this obstacle, efforts have been made to ensure effective cancer therapy via nanotechnology utilization. Recent studies [...] Read more.
Liver cancer is listed as the fifth-ranked cancer, responsible for 9.1% of all cancer deaths globally due to its assertive nature and poor survival rate. To overcome this obstacle, efforts have been made to ensure effective cancer therapy via nanotechnology utilization. Recent studies have shown that functionalized graphene oxide (GO)-loaded protocatechuic acid has shown some anticancer activities in both passive and active targeting. The nanocomposites’ physicochemical characterizations were conducted. A lactate dehydrogenase experiment was conducted to estimate the severity of cell damage. Subsequently, a clonogenic assay was carried out to examine the colony-forming ability during long-term exposure of the nanocomposites. The Annexin V/ propidium iodide analysis showed that nanocomposites induced late apoptosis in HepG2 cells. Following the intervention of nanocomposites, cell cycle arrest was ascertained at G2/M phase. There was depolarization of mitochondrial membrane potential and an upregulation of reactive oxygen species when HepG2 cells were induced by nanocomposites. Finally, the proteomic profiling array and quantitative reverse transcription polymerase chain reaction revealed the expression of pro-apoptotic and anti-apoptotic proteins induced by graphene oxide conjugated PEG loaded with protocatechuic acid drug folic acid coated nanocomposite (GOP–PCA–FA) in HepG2 cells. In conclusion, GOP–PCA–FA nanocomposites treated HepG2 cells exhibited significant anticancer activities with less toxicity compared to pristine protocatechuic acid and GOP–PCA nanocomposites, due to the utilization of a folic acid-targeting nanodrug delivery system. Full article
(This article belongs to the Special Issue Nanomaterials Design towards Biomedical Applications)
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19 pages, 4697 KiB  
Article
Between-the-Holes Cryogenic Cooling of the Tool in Hole-Making of Ti-6Al-4V and CFRP
by Asif Iqbal, Guolong Zhao, Juliana Zaini, Munish Kumar Gupta, Muhammad Jamil, Ning He, Malik Muhammad Nauman, Tadeusz Mikolajczyk and Danil Yurievich Pimenov
Materials 2021, 14(4), 795; https://doi.org/10.3390/ma14040795 - 8 Feb 2021
Cited by 32 | Viewed by 2410
Abstract
Lightweight materials are finding plentiful applications in various engineering sectors due to their high strength-to-weight ratios. Hole-making is an inevitable requirement for their structural applications, which is often marred by thermal damages of the drill causing unacceptable shortening of tool life. Efficient cooling [...] Read more.
Lightweight materials are finding plentiful applications in various engineering sectors due to their high strength-to-weight ratios. Hole-making is an inevitable requirement for their structural applications, which is often marred by thermal damages of the drill causing unacceptable shortening of tool life. Efficient cooling of the tool is a prime requirement for enhancing the process viability. The current work presents a novel technique of cooling only the twist drill between drilling of holes with no effect of the applied cryogenic coolant transferred to the work material. The technique is applied in the drilling of two commonly used high-strength lightweight materials: carbon fibers reinforced polymer (CFRP) and an alloy of titanium (Ti-6Al-4V). The efficacy of the cooling approach is compared with those of conventionally applied continuous cryogenic cooling and no-cooling. The effectiveness is quantified in terms of tool wear, thrust force, hole quality, specific cutting energy, productivity, and consumption of the cryogenic fluid. The experimental work leads to a finding that between-the-holes cryogenic cooling possesses a rich potential in curbing tool wear, reducing thrust force and specific energy consumption, and improving hole quality in drilling of CFRP. Regarding the titanium alloy, it yields a much better surface finish and lesser consumption of specific cutting energy. Full article
(This article belongs to the Special Issue Additive and Subtractive Manufacturing of Advanced Materials: Applications, Future Trends and Perspectives of Industry 4.0)
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14 pages, 4374 KiB  
Article
Effect of Moisture Distribution on Velocity and Waveform of Ultrasonic-Wave Propagation in Mortar
by Shinichiro Okazaki, Hiroma Iwase, Hiroyuki Nakagawa, Hidenori Yoshida and Ryosuke Hinei
Materials 2021, 14(4), 790; https://doi.org/10.3390/ma14040790 - 7 Feb 2021
Cited by 4 | Viewed by 1976
Abstract
Considering that the ultrasonic method is applied for the quality evaluation of concrete, this study experimentally and numerically investigates the effect of inhomogeneity caused by changes in the moisture content of concrete on ultrasonic wave propagation. The experimental results demonstrate that the propagation [...] Read more.
Considering that the ultrasonic method is applied for the quality evaluation of concrete, this study experimentally and numerically investigates the effect of inhomogeneity caused by changes in the moisture content of concrete on ultrasonic wave propagation. The experimental results demonstrate that the propagation velocity and amplitude of the ultrasonic wave vary for different moisture content distributions in the specimens. In the analytical study, the characteristics obtained experimentally are reproduced by modeling a system in which the moisture content varies between the surface layer and interior of concrete. Full article
(This article belongs to the Special Issue Research on Non-destructive Testing in Civil Engineering Materials)
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16 pages, 7606 KiB  
Article
Effects of Ti and Cu Addition on Inclusion Modification and Corrosion Behavior in Simulated Coarse-Grained Heat-Affected Zone of Low-Alloy Steels
by Yuhang Wang, Xian Zhang, Wenzhui Wei, Xiangliang Wan, Jing Liu and Kaiming Wu
Materials 2021, 14(4), 791; https://doi.org/10.3390/ma14040791 - 7 Feb 2021
Cited by 7 | Viewed by 2075
Abstract
In this paper, the effects of Ti and Cu addition on inclusion modification and corrosion behavior in the simulated coarse-grained heat-affected zone (CGHAZ) of low-alloy steels were investigated by using in-situ scanning vibration electrode technique (SVET), scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDS), and [...] Read more.
In this paper, the effects of Ti and Cu addition on inclusion modification and corrosion behavior in the simulated coarse-grained heat-affected zone (CGHAZ) of low-alloy steels were investigated by using in-situ scanning vibration electrode technique (SVET), scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDS), and electrochemical workstation. The results demonstrated that the complex inclusions formed in Cu-bearing steel were (Ti, Al, Mn)-Ox-MnS, which was similar to that in base steel. Hence, localized corrosion was initiated by the dissolution of MnS. However, the main inclusions in Ti-bearing steels were modified into TiN-Al2O3/TiN, and the localized corrosion was initiated by the dissolution of high deformation region at inclusion/matrix interface. With increased interface density of inclusions in steels, the corrosion rate increased in the following order: Base steel ≈ Cu-bearing steel < Ti-bearing steel. Owing to the existence of Cu-enriched rust layer, the Cu-bearing steel shows a similar corrosion resistance with base steel. Full article
(This article belongs to the Special Issue Corrosion Properties and Mechanism of Steels)
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23 pages, 5366 KiB  
Article
Mechanical Properties of Hardened 3D Printed Concretes and Mortars—Development of a Consistent Experimental Characterization Strategy
by Maximilian Meurer and Martin Classen
Materials 2021, 14(4), 752; https://doi.org/10.3390/ma14040752 - 5 Feb 2021
Cited by 38 | Viewed by 4452
Abstract
Today, it is already foreseeable that additive manufacturing of mortar and concrete has groundbreaking potential and will revolutionize or at least fundamentally change the way we build. In recent years, 3D concrete printing (3DCP) with extrusion-based deposition methods has been pushed forward by [...] Read more.
Today, it is already foreseeable that additive manufacturing of mortar and concrete has groundbreaking potential and will revolutionize or at least fundamentally change the way we build. In recent years, 3D concrete printing (3DCP) with extrusion-based deposition methods has been pushed forward by a growing research community. Albeit being regarded one of the most promising innovations in construction industry, a consistent characterization methodology for assessing the constitutive behavior of 3D printed, hardened cementitious materials is missing, so far, which hinders its widespread use in engineering practice. The major objective of this paper is to fill this gap by developing a new experimental framework that can thoroughly describe the mechanical properties of 3D printed cementitious materials. Based on both a review of state-of-the-art test setups and a comprehensive experimental campaign, the present paper proposes a set of easy-to-use experimental methods that allow us to assess flexural, tensile, shear and compressive strength as well as fracture energy of 3D printed concretes and mortars in a reliable and reproducible manner. The experimental results revealed anisotropic material behavior for flexural, tensile, shear and compressive loading. Furthermore, they confirm that interval time (time gap between deposition of subsequent layers) has a crucial effect on investigated material properties leading to a severe reduction in strength and fracture energy for longer interval times. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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13 pages, 2445 KiB  
Article
pH-Sensitive Dairy-Derived Hydrogels with a Prolonged Drug Release Profile for Cancer Treatment
by Oksana A. Mayorova, Ben C. N. Jolly, Roman A. Verkhovskii, Valentina O. Plastun, Olga A. Sindeeva and Timothy E. L. Douglas
Materials 2021, 14(4), 749; https://doi.org/10.3390/ma14040749 - 5 Feb 2021
Cited by 10 | Viewed by 2341
Abstract
A novel versatile biocompatible hydrogel of whey protein isolate (WPI) and two types of tannic acid (TAs) was prepared by crosslinking of WPI with TAs in a one-step method at high temperature for 30 min. WPI is one common protein-based preparation which is [...] Read more.
A novel versatile biocompatible hydrogel of whey protein isolate (WPI) and two types of tannic acid (TAs) was prepared by crosslinking of WPI with TAs in a one-step method at high temperature for 30 min. WPI is one common protein-based preparation which is used for hydrogel formation. The obtained WPI-TA hydrogels were in disc form and retained their integrity after sterilization by autoclaving. Two TA preparations of differing molecular weight and chemical structure were compared, namely a polygalloyl glucose-rich extract-ALSOK 02-and a polygalloyl quinic acid-rich extract-ALSOK 04. Hydrogel formation was observed for WPI solutions containing both preparations. The swelling characteristics of hydrogels were investigated at room temperature at different pH values, namely 5, 7, and 9. The swelling ability of hydrogels was independent of the chemical structure of the added TAs. A trend of decrease of mass increase (MI) in hydrogels was observed with an increase in the TA/WPI ratio compared to the control WPI hydrogel without TA. This dependence (a MI decrease-TA/WPI ratio) was observed for hydrogels with different types of TA both in neutral and acidic conditions (pH 5.7). Under alkaline conditions (pH 9), negative values of swelling were observed for all hydrogels with a high content of TAs and were accompanied by a significant release of TAs from the hydrogel network. Our studies have shown that the release of TA from hydrogels containing ALSOK04 is higher than from hydrogels containing ALSOK 02. Moreover, the addition of TAs, which display a strong anti-cancer effect, increases the cytotoxicity of WPI-TAs hydrogels against the Hep-2 human laryngeal squamous carcinoma (Hep-2 cells) cell line. Thus, WPI-TA hydrogels with prolonged drug release properties and cytotoxicity effect can be used as anti-cancer scaffolds. Full article
(This article belongs to the Special Issue Advances in Polymeric Materials for Biomedical Applications)
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17 pages, 6406 KiB  
Article
Adsorption of Pb(II) from Aqueous Solution by Mussel Shell-Based Adsorbent: Preparation, Characterization, and Adsorption Performance
by Quan Wang, Fangyuan Jiang, Xiao-Kun Ouyang, Li-Ye Yang and Yangguang Wang
Materials 2021, 14(4), 741; https://doi.org/10.3390/ma14040741 - 5 Feb 2021
Cited by 25 | Viewed by 2881
Abstract
As a natural biological adsorbent, shell powder is inexpensive, highly efficient, and does not leave any chemical residue; thus, it can be used to remove contaminants from water. In this study, we used mussel shells as a raw material to prepare an adsorbent. [...] Read more.
As a natural biological adsorbent, shell powder is inexpensive, highly efficient, and does not leave any chemical residue; thus, it can be used to remove contaminants from water. In this study, we used mussel shells as a raw material to prepare an adsorbent. Scanning electron microscopy was used to observe the surface morphology of the mussel shell powder before and after calcination, and X-ray diffraction measurements, Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray photoelectron spectroscopy, and Brunauer–Emmett–Teller measurements were performed to analyze the structure and composition of calcined mussel shell powder. Characterization of the shell powder before and after calcination revealed a change from calcium carbonate to calcium oxide, as well as the formation of a surface porous structure. Using Pb(II) as a representative contaminant, various factors affecting the adsorption were explored, and the adsorption mechanism was analyzed. It was found that the adsorption is consistent with the Freundlich adsorption isotherm and the pseudo second-order model. The calcined mussel shell powder exhibits excellent adsorption for Pb(II), with an adsorption capacity reaching 102.04 mg/g. Full article
(This article belongs to the Special Issue Materials for Heavy Metals Removal from Waters)
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10 pages, 1734 KiB  
Article
Resins for Frontal Photopolymerization: Combining Depth-Cure and Tunable Mechanical Properties
by Catharina Ebner, Julia Mitterer, Joamin Gonzalez-Gutierrez, Gisbert Rieß and Wolfgang Kern
Materials 2021, 14(4), 743; https://doi.org/10.3390/ma14040743 - 5 Feb 2021
Cited by 9 | Viewed by 2282
Abstract
Photopolymerization has undergone significant development in recent years. It enables fast and easy processing of materials with customized properties and allows precise printing of complex surface geometries. Nevertheless, photopolymerization is mainly applied to cure thin films since the low curing depth limits the [...] Read more.
Photopolymerization has undergone significant development in recent years. It enables fast and easy processing of materials with customized properties and allows precise printing of complex surface geometries. Nevertheless, photopolymerization is mainly applied to cure thin films since the low curing depth limits the fast production of large volumes. Frontal photopolymerization (FPP) is suitable to overcome these limitations so that curing of centimeter-thick (meth)acrylic layers can be accomplished within minutes by light induction only. Prerequisites, however, are the low optical density of the resin and bleaching ability of the photoinitiator. To date, tailored FPP-resins are not commercially available. This study discusses the potential of long-chain polyether dimethacrylates, offering high-temperature resistance and low optical density, as crosslinkers in photobleaching resins and investigates the mechanical properties of photofrontally-cured copolymers. Characteristics ranging from ductile to hard and brittle are observed in tensile tests, demonstrating that deep curing and versatile material properties are achieved with FPP. Analyzed components display uniform polymerization over a depth of four centimeters in Fourier transform infrared spectroscopy and swelling tests. Full article
(This article belongs to the Special Issue Structure Property Relationship of Polymeric Materials)
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15 pages, 5427 KiB  
Article
High Temperature Behaviors of a Casting Nickel-Based Superalloy Used for 815 °C
by Jiangping Yu, Donghong Wang, Jingyang Chen, Changlin Yang, Xin Hao, Jianxin Zhou, Dayong Li, Da Shu, Chengbo Xiao and Yinghong Peng
Materials 2021, 14(4), 716; https://doi.org/10.3390/ma14040716 - 4 Feb 2021
Cited by 4 | Viewed by 1684
Abstract
The hot deformation behaviors of the SJTU-1 alloy, the high-throughput scanned casting Nickel-based superalloy, was investigated by compression test in the temperature range of 900 to 1200 °C and strain rate range of 0.1–0.001 s−1. The hot processing map has been [...] Read more.
The hot deformation behaviors of the SJTU-1 alloy, the high-throughput scanned casting Nickel-based superalloy, was investigated by compression test in the temperature range of 900 to 1200 °C and strain rate range of 0.1–0.001 s−1. The hot processing map has been constructed with the instability zone. At the beginning of hot deformation, the flow stress moves rapidly to the peak value with the increased strain rates. Meanwhile, the peak stress is decreased with the increased temperature at the same strain rates. However, the peak stress shows the same tendency with the strain rates at the same temperature. The optimum hot deformation condition was determined in the temperature range of 1000–1075 °C, and the strain rate range of 0.005–0.1 s−1. The microstructure investigation indicates the strain rate significantly affects the characteristics of the microstructure. The deformation constitutive equation has also been discussed as well. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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14 pages, 2305 KiB  
Article
Sizing and Topology Optimization of Trusses Using Genetic Algorithm
by Ingrid Delyová, Peter Frankovský, Jozef Bocko, Peter Trebuňa, Jozef Živčák, Barbara Schürger and Sára Janigová
Materials 2021, 14(4), 715; https://doi.org/10.3390/ma14040715 - 3 Feb 2021
Cited by 17 | Viewed by 2608
Abstract
Genetic algorithms are a robust method for a solution of wide variety optimization problems. It explores a big space of design variables in order to find the best solution. From the point of view of a user, the algorithm requires the encoding of [...] Read more.
Genetic algorithms are a robust method for a solution of wide variety optimization problems. It explores a big space of design variables in order to find the best solution. From the point of view of a user, the algorithm requires the encoding of design variables into the form of strings and the procedure of optimization uses them for optimization. Here, for the structural engineer, it is crucial to find the form of objective function including the constraints of the task and also to avoid critical states during the solution of structural responses. This paper presents the use of genetic algorithm for solving truss structures. The use of genetic algorithm approach is shown on three cases of truss structures. Full article
(This article belongs to the Special Issue Computational and Experimental Mechanics of Engineering Materials and Structures)
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19 pages, 3988 KiB  
Article
Compacted Anthropogenic Materials as Backfill for Buried Pipes
by Andrzej Głuchowski, Raimondas Šadzevičius, Rytis Skominas and Wojciech Sas
Materials 2021, 14(4), 717; https://doi.org/10.3390/ma14040717 - 3 Feb 2021
Cited by 2 | Viewed by 1758
Abstract
Buried pipe design requires knowledge about the fill to design the backfill structure. The interaction between the backfill envelope and the pipe impacts the structural performance of the buried pipe. The backfill material and compaction level respond to the backfill’s overall strength and, [...] Read more.
Buried pipe design requires knowledge about the fill to design the backfill structure. The interaction between the backfill envelope and the pipe impacts the structural performance of the buried pipe. The backfill material and compaction level respond to the backfill’s overall strength and, therefore, for pipe-soil interaction. The strength of backfill material is described in terms of modulus of soil reaction E’ and constrained modulus Eode. As the E’ is an empirical parameter, the Eode can be measured in the laboratory by performing the oedometer tests. In this study, we have performed extensive oedometric tests on five types of anthropogenic materials (AM). Three of them are construction and demolition materials (C–D materials) namely, recycled concrete aggregate (RCA), crushed brick (CB), and recycled asphalt pavement (RAP). Two of them are industrial solid wastes (ISW) namely, fly ash and bottom slag mix (FA + BS) and blast furnace slag (BFS). The results of the tests revealed that AM behaves differently from natural aggregates (NA). In general, the Eode value for AM is lower than for NA with the same gradation. Despite that, some of AM may be used as NA substitute directly (RCA or BFS), some with special treatment like CB and some with extra compaction efforts like RAP or FA + BS. Full article
(This article belongs to the Special Issue Construction Circular Economy: Recycling Construction and Demolition Wastes)
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36 pages, 3645 KiB  
Opinion
Whither Magnetic Hyperthermia? A Tentative Roadmap
by Irene Rubia-Rodríguez, Antonio Santana-Otero, Simo Spassov, Etelka Tombácz, Christer Johansson, Patricia De La Presa, Francisco J. Teran, María del Puerto Morales, Sabino Veintemillas-Verdaguer, Nguyen T. K. Thanh, Maximilian O. Besenhard, Claire Wilhelm, Florence Gazeau, Quentin Harmer, Eric Mayes, Bella B. Manshian, Stefaan J. Soenen, Yuanyu Gu, Ángel Millán, Eleni K. Efthimiadou, Jeff Gaudet, Patrick Goodwill, James Mansfield, Uwe Steinhoff, James Wells, Frank Wiekhorst and Daniel Ortegaadd Show full author list remove Hide full author list
Materials 2021, 14(4), 706; https://doi.org/10.3390/ma14040706 - 3 Feb 2021
Cited by 78 | Viewed by 8339
Abstract
The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing [...] Read more.
The scientific community has made great efforts in advancing magnetic hyperthermia for the last two decades after going through a sizeable research lapse from its establishment. All the progress made in various topics ranging from nanoparticle synthesis to biocompatibilization and in vivo testing have been seeking to push the forefront towards some new clinical trials. As many, they did not go at the expected pace. Today, fruitful international cooperation and the wisdom gain after a careful analysis of the lessons learned from seminal clinical trials allow us to have a future with better guarantees for a more definitive takeoff of this genuine nanotherapy against cancer. Deliberately giving prominence to a number of critical aspects, this opinion review offers a blend of state-of-the-art hints and glimpses into the future of the therapy, considering the expected evolution of science and technology behind magnetic hyperthermia. Full article
(This article belongs to the Special Issue Magnetic Nanoparticles as High-Frequency Nano-Heaters)
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15 pages, 4456 KiB  
Article
Phase Formation and Thermal Stability of Reactively Sputtered YTaO4–ZrO2 Coatings
by Bastian Stelzer, Katrin Pingen, Marcus Hans, Damian M. Holzapfel, Silvia Richter, Joachim Mayer, Konda Gokuldoss Pradeep and Jochen M. Schneider
Materials 2021, 14(3), 692; https://doi.org/10.3390/ma14030692 - 2 Feb 2021
Cited by 6 | Viewed by 2818
Abstract
Y(1−x)/2Ta(1−x)/2ZrxO2 coatings with 0 to 44 mol% ZrO2 were synthesized by sputtering. Phase-pure M’-YTaO4 coatings were obtained at a substrate temperature of 900 °C. Alloying with ZrO2 resulted in the growth of [...] Read more.
Y(1−x)/2Ta(1−x)/2ZrxO2 coatings with 0 to 44 mol% ZrO2 were synthesized by sputtering. Phase-pure M’-YTaO4 coatings were obtained at a substrate temperature of 900 °C. Alloying with ZrO2 resulted in the growth of M’ along with t-Zr(Y,Ta)O2 for ≤15 mol%, while for ≥28 mol%, ZrO2 X-ray diffraction (XRD) phase-pure metastable t was formed, which may be caused by small grain sizes and/or kinetic limitations. The former phase region transformed into M’ and M and the latter to an M’ + t and M + t phase region upon annealing to 1300 and 1650 °C, respectively. In addition to M and t, T-YTa(Zr)O4 phase fractions were observed at room temperature for ZrO2 contents ≥28 mol% after annealing to 1650 °C. T phase fractions increased during in situ heating XRD at 80 °C. At 1650 °C, a reaction with the α-Al2O3 substrate resulted in the formation of AlTaO4 and an Al-Ta-Y-O compound. Full article
(This article belongs to the Section Thin Films and Interfaces)
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14 pages, 3085 KiB  
Article
Biofunctionalization of Poly(lactide-co-glycolic acid) Using Potent NorA Efflux Pump Inhibitors Immobilized on Nanometric Alpha-Zirconium Phosphate to Reduce Biofilm Formation
by Monica Pica, Nicla Messere, Tommaso Felicetti, Stefano Sabatini, Donatella Pietrella and Morena Nocchetti
Materials 2021, 14(3), 670; https://doi.org/10.3390/ma14030670 - 1 Feb 2021
Cited by 4 | Viewed by 2055
Abstract
Polymeric composites, where bioactive species are immobilized on inorganic nanostructured matrix, have received considerable attention as surfaces able to reduce bacterial adherence, colonization, and biofilm formation in implanted medical devices. In this work, potent in-house S. aureus NorA efflux pump inhibitors (EPIs), belonging [...] Read more.
Polymeric composites, where bioactive species are immobilized on inorganic nanostructured matrix, have received considerable attention as surfaces able to reduce bacterial adherence, colonization, and biofilm formation in implanted medical devices. In this work, potent in-house S. aureus NorA efflux pump inhibitors (EPIs), belonging to the 2-phenylquinoline class, were immobilized on nanometric alpha-zirconium phosphate (ZrP) taking into advantage of acid-base or intercalation reactions. The ZrP/EPI were used as filler of poly(lactide-co-glycolic acid) (PLGA) to obtain film composites with a homogeneous distribution of the ZrP/EPI fillers. As reference, PLGA films loaded with ZrP intercalated with thioridazine (TZ), that is recognized as both a NorA and biofilm inhibitor, and with the antibiotic ciprofloxacin (CPX) were prepared. Composite films were characterized by X-ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The ability of the composite films, containing ZrP/EPI, to inhibit biofilm formation was tested on Staphylococcus aureus ATCC 29213 and Staphylococcus epidermidis ATCC 12228, and it was compared with that of the composite loaded with ZrP/TZ. Finally, the antibacterial activity of CPX intercalated in ZrP was evaluated when used in combination with ZrP/EPI in the PLGA films. Full article
(This article belongs to the Section Materials Chemistry)
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20 pages, 3420 KiB  
Article
Impact of Glass Composition on Hydrolytic Degradation of Polylactide/Bioactive Glass Composites
by Inari Lyyra, Katri Leino, Terttu Hukka, Markus Hannula, Minna Kellomäki and Jonathan Massera
Materials 2021, 14(3), 667; https://doi.org/10.3390/ma14030667 - 1 Feb 2021
Cited by 9 | Viewed by 2552
Abstract
Understanding the degradation of a composite material is crucial for tailoring its properties based on the foreseen application. In this study, poly-L,DL-lactide 70/30 (PLA70) was compounded with silicate or phosphate bioactive glass (Si-BaG and P-BaG, respectively). The composite processing was carried out without [...] Read more.
Understanding the degradation of a composite material is crucial for tailoring its properties based on the foreseen application. In this study, poly-L,DL-lactide 70/30 (PLA70) was compounded with silicate or phosphate bioactive glass (Si-BaG and P-BaG, respectively). The composite processing was carried out without excessive thermal degradation of the polymer and resulted in porous composites with lower mechanical properties than PLA70. The loss in mechanical properties was associated with glass content rather than the glass composition. The degradation of the composites was studied for 40 weeks in Tris buffer solution Adding Si-BaG to PLA70 accelerated the polymer degradation in vitro more than adding P-BaG, despite the higher reactivity of the P-BaG. All the composites exhibited a decrease in mechanical properties and increased hydrophilicity during hydrolysis compared to the PLA70. Both glasses dissolved through the polymer matrix with a linear, predictable release rate of ions. Most of the P-BaG had dissolved before 20 weeks in vitro, while there was still Si-BaG left after 40 weeks. This study introduces new polymer/bioactive glass composites with tailorable mechanical properties and ion release for bone regeneration and fixation applications. Full article
(This article belongs to the Special Issue Bioactive Ceramics and Their Applications)
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16 pages, 4623 KiB  
Article
Polydopamine Ultrathin Film Growth on Mica via In-Situ Polymerization of Dopamine with Applications for Silver-Based Antimicrobial Coatings
by Zheng-Hao Huang, Shi-Wei Peng, Shu-Ling Hsieh, Rajendranath Kirankumar, Po-Feng Huang, Tsao-Ming Chang, Atul Kumar Dwivedi, Nan-Fu Chen, Hao-Ming Wu and Shuchen Hsieh
Materials 2021, 14(3), 671; https://doi.org/10.3390/ma14030671 - 1 Feb 2021
Cited by 11 | Viewed by 2910
Abstract
The development of polydopamine (PDA) coatings with a nanometer-scale thickness on surfaces is highly desirable for exploiting the novel features arising from the specific structure on the molecular level. Exploring the mechanisms of thin-film growth is helpful for attaining desirable control over the [...] Read more.
The development of polydopamine (PDA) coatings with a nanometer-scale thickness on surfaces is highly desirable for exploiting the novel features arising from the specific structure on the molecular level. Exploring the mechanisms of thin-film growth is helpful for attaining desirable control over the useful properties of materials. We present a systematic study demonstrating the growth of a PDA thin film on the surface of mica in consecutive short deposition time intervals. Film growth at each deposition time was monitored through instrumental techniques such as atomic force microscopy (AFM), water contact angle (WCA) analysis, and X-ray photoelectron spectroscopy (XPS). Film growth was initiated by adsorption of the PDA molecules on mica, with subsequent island-like aggregation, and finally, a complete molecular level PDA film was formed on the surface due to further molecular adsorption. A duration of 60−300 s was sufficient for complete formation of the PDA layer within the thickness range of 0.5−1.1 nm. An outstanding feature of PDA ultrathin films is their ability to act as a molecular adhesive, providing a foundation for constructing functional surfaces. We also explored antimicrobial applications by incorporating Ag nanoparticles into a PDA film. The Ag NPs/PDA film was formed on a surgical blade and then characterized and confirmed by SEM-EDS and XPS. The modified film inhibited bacterial growth by up to 42% on the blade after cutting through a pork meat sample. Full article
(This article belongs to the Special Issue Advances in Bio-Inspired Materials for Medical Applications)
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16 pages, 3929 KiB  
Article
Coaxial Monitoring of AISI 316L Thin Walls Fabricated by Direct Metal Laser Deposition
by Vito Errico, Sabina Luisa Campanelli, Andrea Angelastro, Michele Dassisti, Marco Mazzarisi and Cesare Bonserio
Materials 2021, 14(3), 673; https://doi.org/10.3390/ma14030673 - 1 Feb 2021
Cited by 25 | Viewed by 2808
Abstract
Direct metal laser deposition (DMLD) is an additive manufacturing technique suitable for coating and repair, which has been gaining a growing interest in 3D manufacturing applications in recent years. However, its diffusion in the manufacturing industry is still limited due to technical challenges [...] Read more.
Direct metal laser deposition (DMLD) is an additive manufacturing technique suitable for coating and repair, which has been gaining a growing interest in 3D manufacturing applications in recent years. However, its diffusion in the manufacturing industry is still limited due to technical challenges to be solved—both the sub-optimal quality of the final parts and the low repeatability of the process make the DMLD inadequate for high-value applications requiring high-performance standards. Thus, real-time monitoring and process control are indispensable requirements for improving the DMLD process. The aim of this study was the optimization of deposition strategies for the fabrication of thin walls in AISI 316L stainless steel. For this purpose, a coaxial monitoring system and image processing algorithms were employed to study the melt pool geometry. The comparison tests carried out highlighted how the region-based active contour algorithm used for image processing is more efficient and stable than others covered in the literature. The results allowed the identification of the best deposition strategy. Therefore, it is shown how this monitoring methodology proved to be suitable for designing and implementing the right building strategy for DMLD manufactured 3D components. A fast and stable image processing method was achieved, which can be considered for future closed-loop monitoring in real-time applications. Full article
(This article belongs to the Special Issue Laser Deposition Processes)
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30 pages, 7098 KiB  
Review
Silk-Based Materials for Hard Tissue Engineering
by Vanessa J. Neubauer, Annika Döbl and Thomas Scheibel
Materials 2021, 14(3), 674; https://doi.org/10.3390/ma14030674 - 1 Feb 2021
Cited by 29 | Viewed by 4260
Abstract
Hard tissues, e.g., bone, are mechanically stiff and, most typically, mineralized. To design scaffolds for hard tissue regeneration, mechanical, physico-chemical and biological cues must align with those found in the natural tissue. Combining these aspects poses challenges for material and construct design. Silk-based [...] Read more.
Hard tissues, e.g., bone, are mechanically stiff and, most typically, mineralized. To design scaffolds for hard tissue regeneration, mechanical, physico-chemical and biological cues must align with those found in the natural tissue. Combining these aspects poses challenges for material and construct design. Silk-based materials are promising for bone tissue regeneration as they fulfill several of such necessary requirements, and they are non-toxic and biodegradable. They can be processed into a variety of morphologies such as hydrogels, particles and fibers and can be mineralized. Therefore, silk-based materials are versatile candidates for biomedical applications in the field of hard tissue engineering. This review summarizes silk-based approaches for mineralized tissue replacements, and how to find the balance between sufficient material stiffness upon mineralization and cell survival upon attachment as well as nutrient supply. Full article
(This article belongs to the Special Issue Silk-Based Biomaterials)
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