Materials

20 pages, 8996 KiB

Open AccessEditor’s ChoiceArticle

Photothermal-Controlled Release of IL-4 in IL-4/PDA-Immobilized Black Titanium Dioxide (TiO₂) Nanotubes Surface to Enhance Osseointegration: An In Vivo Study

by Bo Chen, Yu Liang, Yunjia Song, Yunkai Liang, Jian Jiao, Hong Bai and Ying Li

Materials 2022, 15(17), 5962; https://doi.org/10.3390/ma15175962 - 29 Aug 2022

Cited by 7 | Viewed by 2582

Abstract

Host immune response has gradually been accepted as a critical factor in achieving successful implant osseointegration. The aim of this study is to create a favorable immune microenvironment by the dominant release of IL-4 during the initial few days after implant insertion to [...] Read more.

Host immune response has gradually been accepted as a critical factor in achieving successful implant osseointegration. The aim of this study is to create a favorable immune microenvironment by the dominant release of IL-4 during the initial few days after implant insertion to mitigate early inflammatory reactions and facilitate osseointegration. Herein, the B-TNT/PDA/IL-4 substrate was established by immobilizing an interleukin-4 (IL-4)/polydopamine (PDA) coating on a black TiO₂ nanotube (B-TNT) surface, achieving on-demand IL-4 release under near infrared (NIR) irradiation. Gene Ontology (GO) enrichment analyses based on high-throughput DNA microarray data revealed that IL-4 addition inhibited osteoclast differentiation and function. Animal experiment results suggested that the B-TNT/PDA/IL-4+Laser substrate induced the least inflammatory, tartrate-resistant acid phosphatase, inducible nitric oxide synthase and the most CD163 positive cells, compared to the Ti group at 7 days post-implantation. In addition, 28 days post-implantation, micro-computed tomography results showed the highest bone volume/total volume, trabecular thickness, trabecular number and the lowest trabecular separation, while Hematoxylin-eosin and Masson-trichrome staining revealed the largest amount of new bone formation for the B-TNT/PDA/IL-4+Laser group. This study revealed the osteoimmunoregulatory function of the novel B-TNT/PDA/IL-4 surface by photothermal release of IL-4 at an early period post-implantation, thus paving a new way for dental implant surface modification. Full article

(This article belongs to the Special Issue Dental Materials and Devices: Volume II)

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24 pages, 6512 KiB

Open AccessEditor’s ChoiceReview

Irradiation-Induced Amorphous-to-Crystalline Phase Transformations in Ceramic Materials

by Cyrus Koroni, Tristan Olsen, Janelle P. Wharry and Hui Xiong

Materials 2022, 15(17), 5924; https://doi.org/10.3390/ma15175924 - 27 Aug 2022

Cited by 15 | Viewed by 3800

Abstract

Amorphous ceramics are a unique class of materials with unusual properties and functionalities. While these materials are known to crystallize when subjected to thermal annealing, they have sometimes been observed to crystallize athermally when exposed to extreme irradiation environments. Because irradiation is almost [...] Read more.

Amorphous ceramics are a unique class of materials with unusual properties and functionalities. While these materials are known to crystallize when subjected to thermal annealing, they have sometimes been observed to crystallize athermally when exposed to extreme irradiation environments. Because irradiation is almost universally understood to introduce disorder into materials, these observations of irradiation-induced ordering or crystallization are unusual and may partially explain the limited research into this phenomenon. However, the archival literature presents a growing body of evidence of these irradiation-induced amorphous-to-crystalline (a-to-c) phase transformations in ceramics. In this perspective, the summary and review of examples from the literature of irradiation-induced a-to-c transformations for various classifications of ceramics are provided. This work will highlight irradiation conditions and material parameters that appear most influential for activating a-to-c transformations, identify trends, examine possible mechanisms, and discuss the impact of a-to-c transformations on material properties. Finally, future research directions that will enable researchers to harness a-to-c transformations to tailor materials behaviors will be provided. Full article

(This article belongs to the Special Issue Radiation Damage in Materials: Coupled Extreme Environments)

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12 pages, 5764 KiB

Open AccessEditor’s ChoiceArticle

Role of Metallic Adlayer in Limiting Ge Incorporation into GaN

by Henryk Turski, Pawel Wolny, Mikolaj Chlipala, Marta Sawicka, Anna Reszka, Pawel Kempisty, Leszek Konczewicz, Grzegorz Muziol, Marcin Siekacz and Czeslaw Skierbiszewski

Materials 2022, 15(17), 5929; https://doi.org/10.3390/ma15175929 - 27 Aug 2022

Cited by 3 | Viewed by 2252

Abstract

Atomically thin metal adlayers are used as surfactants in semiconductor crystal growth. The role of the adlayer in the incorporation of dopants in GaN is completely unexplored, probably because n-type doping of GaN with Si is relatively straightforward and can be scaled [...] Read more.

Atomically thin metal adlayers are used as surfactants in semiconductor crystal growth. The role of the adlayer in the incorporation of dopants in GaN is completely unexplored, probably because n-type doping of GaN with Si is relatively straightforward and can be scaled up with available Si atomic flux in a wide range of dopant concentrations. However, a surprisingly different behavior of the Ge dopant is observed, and the presence of atomically thin gallium or an indium layer dramatically affects Ge incorporation, hindering the fabrication of GaN:Ge structures with abrupt doping profiles. Here, we show an experimental study presenting a striking improvement in sharpness of the Ge doping profile obtained for indium as compared to the gallium surfactant layer during GaN-plasma-assisted molecular beam epitaxy. We show that the atomically thin indium surfactant layer promotes the incorporation of Ge in contrast to the gallium surfactant layer, which promotes segregation of Ge to the surface and Ge crystallite formation. Understanding the role of the surfactant is essential to control GaN doping and to obtain extremely high n-type doped III-nitride layers using Ge, because doping levels >10²⁰ cm⁻³ are not easily available with Si. Full article

(This article belongs to the Special Issue Advanced Materials and Devices for Applied System Innovation)

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10 pages, 3987 KiB

Open AccessEditor’s ChoiceArticle

Hilbert-Coding Metasurface for Diverse Electromagnetic Controls

by Jianjiao Hao, Fuju Ye, Ying Ruan, Lei Chen and Haoyang Cui

Materials 2022, 15(17), 5913; https://doi.org/10.3390/ma15175913 - 26 Aug 2022

Cited by 1 | Viewed by 2034

Abstract

Metamaterials, or metasurfaces, allow the flexible and efficient manipulation of electromagnetic (EM) wave. Although the passive coding metasurfaces have achieved a great deal of functionality, they also need a complex design process. In this paper, we propose Hilbert-coding metasurfaces for flexible and convenient [...] Read more.

Metamaterials, or metasurfaces, allow the flexible and efficient manipulation of electromagnetic (EM) wave. Although the passive coding metasurfaces have achieved a great deal of functionality, they also need a complex design process. In this paper, we propose Hilbert-coding metasurfaces for flexible and convenient EM regulation by arranging Hilbert-coding metamaterial units of different orders. To demonstrate this behavior, we designed 12 metasurfaces, then fabricated and measured 6 samples. Validation results on 6 Hilbert-coding metasurfaces show the deflection angles of the four single beam patterns obtained are about 21°, 13°, 12°, and 39°, with energy values of 7.75 dB, 7.3 dB, 7.2 dB, and 7.7 dB, respectively, and the deflection angles of the dual-beam patterns are 28.5° and 20° with energy values of 10.05 dB and 11.4 dB, respectively. The results are quite consistent with the simulation data, further confirming the feasibility of our idea. In addition, there are potential applications in Wireless Communications and Radar-imaging, like EM beam scanning and EM field energy distribution control in communication and imaging scenarios. Full article

(This article belongs to the Special Issue Metamaterials and Metasurfaces: Fundamentals and Applications)

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16 pages, 4141 KiB

Open AccessEditor’s ChoiceArticle

Activated Biocarbons Obtained from Plant Biomass as Adsorbents of Heavy Metal Ions

by Małgorzata Wiśniewska, Magdalena Marciniak, Marlena Gęca, Karolina Herda, Robert Pietrzak and Piotr Nowicki

Materials 2022, 15(17), 5856; https://doi.org/10.3390/ma15175856 - 25 Aug 2022

Cited by 10 | Viewed by 2073

Abstract

This paper deals with the adsorption of heavy metal ions on the surface of carbonaceous materials obtained via the chemical activation of biomass. Waste plum stones, pine sawdust and horsetail herb were used as the precursors of carbonaceous adsorbents. The effect of the [...] Read more.

This paper deals with the adsorption of heavy metal ions on the surface of carbonaceous materials obtained via the chemical activation of biomass. Waste plum stones, pine sawdust and horsetail herb were used as the precursors of carbonaceous adsorbents. The effect of the precursor type and preparation procedure on the physicochemical properties of activated biocarbons and their sorption abilities towards Pb(II) and Cu(II) ions have been checked. The obtained micro-mesoporous activated biocarbons were characterized by determination of elemental composition and ash content, the number of surface functional groups and pH of water extracts as well as textural study based on low temperature nitrogen adsorption/desorption and scanning electron microscopy. Additionally, the electrokinetic studies including solid surface charge density and zeta potential determination were performed. Moreover, the adsorption data modelling (equilibrium and kinetics), XPS results analysis and comparison of parameters characterizing electrical double layer formed at the solid-liquid interface enabled the specification of the mechanism of heavy metals binding with the activated biocarbons surface. The maximum adsorption capacity towards copper and lead ions (177.5 and 178.1 mg/g, respectively) was found for plum stone-based activated biocarbon. For all carbonaceous materials, better fit to the experimental data was achieved with a Langmuir isotherm than a Freundlich one. In turn, a better fit of the kinetics data was obtained using the pseudo-second order model. Full article

(This article belongs to the Special Issue Advances in Eco-Friendly Adsorbent Materials for Removal of Inorganic and Organic Pollutants (Volume II))

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8 pages, 2735 KiB

Open AccessEditor’s ChoiceArticle

High-κ van der Waals Oxide MoO₃ as Efficient Gate Dielectric for MoS₂ Field-Effect Transistors

by Junfan Wang, Haojie Lai, Xiaoli Huang, Junjie Liu, Yueheng Lu, Pengyi Liu and Weiguang Xie

Materials 2022, 15(17), 5859; https://doi.org/10.3390/ma15175859 - 25 Aug 2022

Cited by 14 | Viewed by 3138

Abstract

Two-dimensional van der Waals crystals (2D vdW) are recognized as one of the potential materials to solve the physical limits caused by size scaling. Here, vdW metal oxide MoO₃ is applied with the gate dielectric in a 2D field-effect transistor (FET). Due [...] Read more.

Two-dimensional van der Waals crystals (2D vdW) are recognized as one of the potential materials to solve the physical limits caused by size scaling. Here, vdW metal oxide MoO₃ is applied with the gate dielectric in a 2D field-effect transistor (FET). Due to its high dielectric constant and the good response of MoS₂ to visible light, we obtained a field effect transistor for photodetection. In general, the device exhibits a threshold voltage near 0 V, Ion/Ioff ratio of 10⁵, electron mobility about 85 cm² V⁻¹ s⁻¹ and a good response to visible light, the responsivity is near 5 A/W at low laser power, which shows that MoO₃ is a potential material as gate dielectric. Full article

(This article belongs to the Special Issue Synthesis, Structure and Applications of 2D Heterostructures)

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16 pages, 7635 KiB

Open AccessEditor’s ChoiceArticle

Dye-Sensitized Solar Cell Based on TiO₂ Anode Thin Film with Three-Dimensional Web-like Structure

by Yang Liu, Jinzhu Chen, Zhihua Tian and Jianxi Yao

Materials 2022, 15(17), 5875; https://doi.org/10.3390/ma15175875 - 25 Aug 2022

Cited by 2 | Viewed by 1662

Abstract

TiO₂ films with a three-dimensional web-like porous structure were prepared using the photo polymerization-induced phase separation method integrated with the pulling coating process. By adjusting the ratio of the substance in the precursor sol and the coating times, the relationships between the [...] Read more.

TiO₂ films with a three-dimensional web-like porous structure were prepared using the photo polymerization-induced phase separation method integrated with the pulling coating process. By adjusting the ratio of the substance in the precursor sol and the coating times, the relationships between the sol ratio, the coating times, the film structure, and the performance of the DSC were studied. The optimal film structure was found and a detailed description is given. The performance of the DSC was further improved by introducing the barrier layer and the surface-modified layer of the TiO₂ coating. This promoted the short-circuit current density and the photoelectric conversion efficiency of the DSC, the mechanism of which was also investigated. Ultimately, the photoelectric conversion efficiency of the DSC based on the TiO₂ anode films with a three-dimensional web-like structure was stabilized at a higher level as a result of the structural improvement. Full article

(This article belongs to the Special Issue Nanocatalysts for Dye-Sensitized Solar Cells)

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16 pages, 9590 KiB

Open AccessEditor’s ChoiceArticle

Electrospinning of Poly (Acrylamide), Poly (Acrylic Acid) and Poly (Vinyl Alcohol) Nanofibers: Characterization and Optimization Study on the Effect of Different Parameters on Mean Diameter Using Taguchi Design of Experiment Method

by Tannaz Soltanolzakerin Sorkhabi, Mehrab Fallahi Samberan, Krzysztof Adam Ostrowski, Paulina Zajdel, Agata Stempkowska and Tomasz Gawenda

Materials 2022, 15(17), 5876; https://doi.org/10.3390/ma15175876 - 25 Aug 2022

Cited by 12 | Viewed by 3378

Abstract

In this study, nanofibers of poly (acrylic acid) (PAAc), polyacrylamide (PAAm) and poly (vinyl alcohol) (PVOH) were prepared using the electrospinning technique. Based on the Taguchi DOE (design of experiment) method, the effects of electrospinning parameters, i.e., needle tip to collector distance, polymer [...] Read more.

In this study, nanofibers of poly (acrylic acid) (PAAc), polyacrylamide (PAAm) and poly (vinyl alcohol) (PVOH) were prepared using the electrospinning technique. Based on the Taguchi DOE (design of experiment) method, the effects of electrospinning parameters, i.e., needle tip to collector distance, polymer solution concentration, applied voltage, polymer solution feed rate and polymer type, on the diameter and morphology of polymer nanofibers were evaluated. Analyses of the experiments for the diameters of the polymer nanofibers showed that the type of polymer was the most significant factor. The optimal combination to obtain the smallest diameters with minimum deviations for electrospun polymer nanofibers was also determined. For this purpose, the appropriate factor levels were determined as follows: polymer PAAm, applied voltage 10 kV, delivery rate 0.1 mL/h, needle tip to collector distance 10 cm, and polymer solution concentration 8%, to obtain the thinnest nanofibers. This combination was further validated by conducting a confirmation experiment, and the average diameter of the polymer nanofibers was found to be close to the optimal conditions estimated by the Taguchi DOE method. Full article

(This article belongs to the Section Advanced Nanomaterials and Nanotechnology)

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16 pages, 4687 KiB

Open AccessEditor’s ChoiceReview

A Mini Review on Persulfate Activation by Sustainable Biochar for the Removal of Antibiotics

by Mengxue Li, Peng Li, Qi Zhou and Stephanie Ling Jie Lee

Materials 2022, 15(17), 5832; https://doi.org/10.3390/ma15175832 - 24 Aug 2022

Cited by 20 | Viewed by 3483

Abstract

Antibiotic contamination in water bodies poses ecological risks to aquatic organisms and humans and is a global environmental issue. Persulfate-based advanced oxidation processes (PS-AOPs) are efficient for the removal of antibiotics. Sustainable biochar materials have emerged as potential candidates as persulfates (Peroxymonosulfate (PMS) [...] Read more.

Antibiotic contamination in water bodies poses ecological risks to aquatic organisms and humans and is a global environmental issue. Persulfate-based advanced oxidation processes (PS-AOPs) are efficient for the removal of antibiotics. Sustainable biochar materials have emerged as potential candidates as persulfates (Peroxymonosulfate (PMS) and Peroxydisulfate (PDS)) activation catalysts to degrade antibiotics. In this review, the feasibility of pristine biochar and modified biochar (non-metal heteroatom-doped biochar and metal-loaded biochar) for the removal of antibiotics in PS-AOPs is evaluated through a critical analysis of recent research. The removal performances of biochar materials, the underlying mechanisms, and active sites involved in the reactions are studied. Lastly, sustainability considerations for future biochar research, including Sustainable Development Goals, technical feasibility, toxicity assessment, economic and life cycle assessment, are discussed to promote the large-scale application of biochar/PS technology. This is in line with the global trends in ensuring sustainable production. Full article

(This article belongs to the Special Issue Progress in Carbon-Based Materials)

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16 pages, 3527 KiB

Open AccessEditor’s ChoiceArticle

Novel SrO-Containing Glass-Ceramic Sealants for Solid Oxide Electrolysis Cells (SOEC): Their Design and Characterization under Relevant Conditions

by Hassan Javed, Elisa Zanchi, Fabiana D’Isanto, Chiara Bert, Domenico Ferrero, Massimo Santarelli and Federico Smeacetto

Materials 2022, 15(17), 5805; https://doi.org/10.3390/ma15175805 - 23 Aug 2022

Cited by 4 | Viewed by 2453

Abstract

This study presents results on the development of strontium oxide (SrO) containing glass sealants used to join Crofer22APU to yttria-stabilized zirconia (3YSZ), in which the main glass components, that is, silicon oxide (SiO₂), strontium oxide (SrO), calcium oxide (CaO) and aluminum [...] Read more.

This study presents results on the development of strontium oxide (SrO) containing glass sealants used to join Crofer22APU to yttria-stabilized zirconia (3YSZ), in which the main glass components, that is, silicon oxide (SiO₂), strontium oxide (SrO), calcium oxide (CaO) and aluminum oxide (Al₂O₃), have been varied appropriately. Certain properties, such as the crystallization behavior, the coefficient of thermal expansion, adhesion, and reactivity of the sealants in contact with Crofer22APU, have been reviewed and discussed. The optimized glass composition (with CTE in the 9.8–10.3 × 10⁻⁶ K⁻¹ range) results in a good joining behavior by hindering the formation of undesirable strontium chromate (SrCrO₄) on contact with the Crofer22APU steel after 1000 h. at 850 °C. High specific resistivity values of about 10⁶ Ohm.cm have been obtained, thus demonstrating good insulating properties at 850 °C under an applied voltage of 1.6 V. A negligible degradation in the electrical resistivity trend was measured during the test up to 1000 h, thus excluding the presence of detrimental reactions of the glass-ceramic sealant in contact with Crofer22APU under a dual atmosphere, as confirmed using SEM-EDS post-mortem analyses. Full article

(This article belongs to the Special Issue Feature Papers in the Section Advanced and Functional Ceramics and Glasses)

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16 pages, 5613 KiB

Open AccessEditor’s ChoiceArticle

A Novel Physical Mechanism to Model Brownian Yet Non-Gaussian Diffusion: Theory and Application

by Francisco E. Alban-Chacón, Erick A. Lamilla-Rubio and Manuel S. Alvarez-Alvarado

Materials 2022, 15(17), 5808; https://doi.org/10.3390/ma15175808 - 23 Aug 2022

Cited by 1 | Viewed by 2837

Abstract

In the last years, a few experiments in the fields of biological and soft matter physics in colloidal suspensions have reported “normal diffusion” with a Laplacian probability distribution in the particle’s displacements (i.e., Brownian yet non-Gaussian diffusion). To model this behavior, different stochastic [...] Read more.

In the last years, a few experiments in the fields of biological and soft matter physics in colloidal suspensions have reported “normal diffusion” with a Laplacian probability distribution in the particle’s displacements (i.e., Brownian yet non-Gaussian diffusion). To model this behavior, different stochastic and microscopic models have been proposed, with the former introducing new random elements that incorporate our lack of information about the media and the latter describing a limited number of interesting physical scenarios. This incentivizes the search of a more thorough understanding of how the media interacts with itself and with the particle being diffused in Brownian yet non-Gaussian diffusion. For this reason, a comprehensive mathematical model to explain Brownian yet non-Gaussian diffusion that includes weak molecular interactions is proposed in this paper. Based on the theory of interfaces by De Gennes and Langevin dynamics, it is shown that long-range interactions in a weakly interacting fluid at shorter time scales leads to a Laplacian probability distribution in the radial particle’s displacements. Further, it is shown that a phase separation can explain a high diffusivity and causes this Laplacian distribution to evolve towards a Gaussian via a transition probability in the interval of time as it was observed in experiments. To verify these model predictions, the experimental data of the Brownian motion of colloidal beads on phospholipid bilayer by Wang et al. are used and compared with the results of the theory. This comparison suggests that the proposed model is able to explain qualitatively and quantitatively the Brownian yet non-Gaussian diffusion. Full article

(This article belongs to the Section Soft Matter)

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16 pages, 3608 KiB

Open AccessEditor’s ChoiceArticle

A Facile One-Pot Approach to the Fabrication of Nanocellulose–Titanium Dioxide Nanocomposites with Promising Photocatalytic and Antimicrobial Activity

by Roberta G. Toro, Abeer M. Adel, Tilde de Caro, Bruno Brunetti, Mona T. Al-Shemy and Daniela Caschera

Materials 2022, 15(16), 5789; https://doi.org/10.3390/ma15165789 - 22 Aug 2022

Cited by 12 | Viewed by 2662

Abstract

The combination of cellulosic materials and metal oxide semiconductors can provide composites with superior functional properties compared to cellulose. By using nanocellulose derived from agricultural waste, we propose a one-pot and environmentally friendly approach to the synthesis of nanocellulose–TiO₂ (NC–TiO₂) [...] Read more.

The combination of cellulosic materials and metal oxide semiconductors can provide composites with superior functional properties compared to cellulose. By using nanocellulose derived from agricultural waste, we propose a one-pot and environmentally friendly approach to the synthesis of nanocellulose–TiO₂ (NC–TiO₂) nanocomposites with peculiar photocatalytic activity and antibacterial effects. The as-prepared NC–TiO₂ composites were fully characterized by different techniques, such as X-ray diffraction (XRD), μ-Raman, Fourier transform infrared spectroscopy (FTIR), thermogravimetry analysis (TGA), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and diffuse reflectance spectroscopy (DRS). The results showed that well crystalline anatase TiO₂ nanoparticles of about 5–6 nm were obtained. The photocatalytic activity in particular was evaluated by using methyl orange (MO) solution as a target pollutant at different pH values. It was found that all the tested NC–TiO₂ nanocomposites showed stable photocatalytic activity, even after consecutive photocatalytic runs. In addition, NCT nanocomposites with higher TiO₂ content showed degradation efficiency of almost 99% towards MO after 180 min of UV illumination. Finally, NC–TiO₂ nanocomposites also showed intriguing antimicrobial properties, demonstrating to be effective against Gram-positive (Staphylococcus aureus, Bacillus subtilis) with 20–25 mm of inhibition zone and Gram-negative bacteria (Escherichia coli, Pseudomonas aeuroginosa) with 21–24 mm of inhibition zone, and fungi (Candida albicans) with 9–10 mm of inhibition zone. Full article

(This article belongs to the Special Issue Nanomaterials for the Environmental Remediation of Water and Soil)

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15 pages, 5328 KiB

Open AccessEditor’s ChoiceArticle

Corrosive Effect of Wood Ash Produced by Biomass Combustion on Refractory Materials in a Binary Al–Si System

by Hana Ovčačíková, Marek Velička, Jozef Vlček, Michaela Topinková, Miroslava Klárová and Jiří Burda

Materials 2022, 15(16), 5796; https://doi.org/10.3390/ma15165796 - 22 Aug 2022

Cited by 16 | Viewed by 2836

Abstract

In terms of its chemical composition, biomass is a very complex type of fuel. Its combustion leads to the formation of materials such as alkaline ash and gases, and there is evidence of the corrosive effect this process has on refractory linings, thus [...] Read more.

In terms of its chemical composition, biomass is a very complex type of fuel. Its combustion leads to the formation of materials such as alkaline ash and gases, and there is evidence of the corrosive effect this process has on refractory linings, thus shortening the service life of the combustion unit. This frequently encountered process is known as “alkaline oxidative bursting”. Corrosion is very complex, and it has not been completely described yet. Alkaline corrosion is the most common cause of furnace-lining degradation in aggregates that burn biomass. This article deals with an experiment investigating the corrosion resistance of 2 types of refractory materials in the Al₂O₃-SiO₂ binary system, for the following compositions: I. (53 wt.% SiO₂/42 wt.% Al₂O₃) and II. (28 wt.% SiO₂/46 wt.% Al₂O₃/12 wt.% SiC). These were exposed to seven types of ash obtained from one biomass combustion company in the Czech Republic. The chemical composition of the ash is a good indicator of the problematic nature of a type of biomass. The ashes were analyzed by X-ray diffraction and X-ray fluorescence. Analysis confirmed that ash composition varies. The experiment also included the calculation of the so-called “slagging/fouling index” (I/C, TA, Sr, B/A, Fu, etc.), which can be used to estimate the probability of slag formation in combustion units. The corrosive effect on refractory materials was evaluated according to the norm ČSN P CEN/TS 15418, and a static corrosion test was used to investigate sample corrosion. Full article

(This article belongs to the Special Issue Design, Manufacturing and Properties of Refractory Materials)

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11 pages, 3389 KiB

Open AccessEditor’s ChoiceArticle

Universal Dependence of Nuclear Spin Relaxation on the Concentration of Paramagnetic Centers in Nano- and Microdiamonds

by Alexander M. Panich

Materials 2022, 15(16), 5774; https://doi.org/10.3390/ma15165774 - 21 Aug 2022

Cited by 5 | Viewed by 1604

Abstract

An analysis of our data on ¹H and ¹³C spin–lattice and spin–spin relaxation times and rates in aqueous suspensions of purified nanodiamonds produced by detonation technique (DNDs), DNDs with grafted paramagnetic ions, and micro- and nanodiamonds produced by milling bulk high-temperature [...] Read more.

An analysis of our data on ¹H and ¹³C spin–lattice and spin–spin relaxation times and rates in aqueous suspensions of purified nanodiamonds produced by detonation technique (DNDs), DNDs with grafted paramagnetic ions, and micro- and nanodiamonds produced by milling bulk high-temperature high-pressure diamonds is presented. It has been established that in all the studied materials, the relaxation rates depend linearly on the concentration of diamond particles in suspensions, the concentration of grafted paramagnetic ions, and surface paramagnetic defects produced by milling, while the relaxation times exhibit a hyperbolic dependence on the concentration of paramagnetic centers. This is a universal law that is valid for suspensions, gels, and solids. The results obtained will expand the understanding of the properties of nano- and microdiamonds and will be useful for their application in quantum computing, spintronics, nanophotonics, and biomedicine. Full article

(This article belongs to the Section Materials Physics)

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11 pages, 2194 KiB

Open AccessEditor’s ChoiceArticle

Template Method for Synthesizing Hierarchically Porous MIL-101(Cr) for Efficient Removal of Large Molecular Dye

by Minmin Zou, Hexin Zhu, Ming Dong and Tian Zhao

Materials 2022, 15(16), 5763; https://doi.org/10.3390/ma15165763 - 20 Aug 2022

Cited by 4 | Viewed by 1980

Abstract

As one of the most important prototypical chromium-based MOFs, MIL-101(Cr) is well-studied and widely employed in various scientific fields. However, due to its small capture window sizes and curved internal apertures, its application in large molecular removal is quite limited, and given its [...] Read more.

As one of the most important prototypical chromium-based MOFs, MIL-101(Cr) is well-studied and widely employed in various scientific fields. However, due to its small capture window sizes and curved internal apertures, its application in large molecular removal is quite limited, and given its high stability and high synthetic temperature (>200 °C), it is difficult to achieve hierarchically porous MIL-101(Cr). In our study, hierarchically porous MIL-101(Cr) involving a high macro-/meso-/micropores ratio was designed and synthesized using acetic acid as an additive and silicon dioxide (SiO₂) nanoparticles as a template. The optimal hierarchically porous MIL-101(Cr) (A-4) possessed a high specific surface area (2693 m² g⁻¹) and an abundant macro-/mesoporous structure with the addition of SiO₂ of 200 mg. Compared with the control sample (A-0) with a less macro-/mesoporous structure, A-4 showed good adsorption properties for both coomassie brilliant blue R-250 (CBB, 82.1 mg g⁻¹) and methylene blue (MB, 34.3 mg g⁻¹) dyes, which were 1.36 times and 9.37 times higher than those of A-0. Moreover, A-4 also had good recyclability, and the removal rate of CBB was still higher than 85% after five cycles of adsorption. Full article

(This article belongs to the Special Issue Advanced Nanomaterials for Biological, Medical and Environmental Applications)

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17 pages, 7581 KiB

Open AccessEditor’s ChoiceArticle

Influence of Filler Metal on Electrochemical Characteristics of a Laser-Welded CoCrMoW Alloy Used in Prosthodontics

by Lukasz Reimann, Zbigniew Brytan and Grzegorz Jania

Materials 2022, 15(16), 5721; https://doi.org/10.3390/ma15165721 - 19 Aug 2022

Cited by 5 | Viewed by 2053

Abstract

This paper sought to determine corrosion resistance changes in the artificial saliva of a CoCrMoW-based alloy used for dental prostheses under Nd:YAG laser welding with CoCr alloy and stainless steel wire filler metals. The paper presents the corrosion characteristics of such joints, including [...] Read more.

This paper sought to determine corrosion resistance changes in the artificial saliva of a CoCrMoW-based alloy used for dental prostheses under Nd:YAG laser welding with CoCr alloy and stainless steel wire filler metals. The paper presents the corrosion characteristics of such joints, including the next stage of porcelain-fused-to-metal (PFM) firing. Corrosion tests were performed by electrochemical methods registering anodic polarization curves and electrochemical impedance spectroscopy (EIS). The microstructures were assessed by scanning microscopy (SEM) and chemical composition analysis (EDS) at the connection and heat-affected zones. Welding CoCrMoW alloy with and without a filler material increased the open circuit potential of the samples by 40–100 mV compared to unwelded base alloy. At the same time, a potentiodynamic test showed a polarization resistance R_pol reduction in welded samples, both for CoCr and stainless steel wires, as compared to the base CoCrMoW material. On the other hand, when comparing the current density and polarization resistance between materials welded with two different filler metals, better results were obtained for samples welded with stainless steel wire. The polarization resistance R_pol for the base alloy was 402 kΩ·cm², for the CoCr wire weld it was 436 kΩ·cm², and the value was 452 kΩ·cm² for stainless steel wire welds. Comparing polarization resistance R_pol from the Tafel analysis and the total charge transfer resistance from Rp_(EIS) from EIS, the CoCrMoW alloy welded with a stainless steel wire after heat treatment equaled or even slightly exceeded the corrosion resistance of the base alloy and alloy welded with dedicated CoCr wire after heat treatment. These results indicated the possibility of using stainless steel wire for the laser welding of CoCrMoW alloys dental prostheses, including the next stage of PFM, without sacrificing the corrosion resistance of such connections, and this was confirmed by most electrochemical parameters. Full article

(This article belongs to the Special Issue Corrosion Resistance of Alloy and Coating Materials)

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26 pages, 8974 KiB

Open AccessEditor’s ChoiceArticle

Microstructural Modification of TiAl6V4 Alloy to Avoid Detrimental Effects Due to Selective In Vivo Crevice Corrosion

by Maria Herbster, Karsten Harnisch, Paulina Kriegel, Andreas Heyn, Manja Krüger, Christoph H. Lohmann, Jessica Bertrand and Thorsten Halle

Materials 2022, 15(16), 5733; https://doi.org/10.3390/ma15165733 - 19 Aug 2022

Cited by 4 | Viewed by 1996

Abstract

TiAl6V4 wrought alloy is a standard material used for endoprostheses due to its ideal characteristics in terms of osseointegration. However, the insufficient wear and crevice corrosion resistance of TiAl6V4 are limiting factors that can cause clinical problems. Therefore, the objective of this study [...] Read more.

TiAl6V4 wrought alloy is a standard material used for endoprostheses due to its ideal characteristics in terms of osseointegration. However, the insufficient wear and crevice corrosion resistance of TiAl6V4 are limiting factors that can cause clinical problems. Therefore, the objective of this study was to analyze and identify suitable phases and microstructural states of TiAl6V4 alloy with advantageous implant properties by thermal treatments. By varying the temperature and cooling rate, four heat treatment strategies were derived that produced different microstructural states that differed in morphology, arrangement and proportions of phases present. All TiAl6V4 modifications were characterized regarding their microstructure, mechanical, corrosive and tribological properties, as well as cell adhesion. The acicular, martensitic microstructure achieves a significant hardness increase by up to 63% and exhibits improved corrosion and wear resistance compared to the forged condition. Whereas the modified microstructures showed similar electrochemical properties in polarization tests using different electrolytes (PBS with H₂O₂ and HCl additives), selective α or β phase dissolution occurred under severe inflammatory crevice conditions after four weeks of exposure at 37 °C. The microstructurally selective corrosion processes resemble the damage patterns of retrieved Ti-based implants and provide a better understanding of clinically relevant in vivo crevice corrosion mechanisms. Furthermore, a microstructural effect on cell attachment was determined and is correlated to the size of the vanadium-rich β phase. These key findings highlight the relevance of an adapted processing of TiAl6V4 alloy to increase the longevity of implants. Full article

(This article belongs to the Special Issue Corrosion of Metals for Biomedical Applications)

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22 pages, 5346 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of the Usefulness of Sorbents in the Remediation of Soil Exposed to the Pressure of Cadmium and Cobalt

by Jadwiga Wyszkowska, Agata Borowik, Magdalena Zaborowska and Jan Kucharski

Materials 2022, 15(16), 5738; https://doi.org/10.3390/ma15165738 - 19 Aug 2022

Cited by 18 | Viewed by 2257

Abstract

An undesirable side effect of economic progress is increasingly severe pollution with heavy metals, responsible for the degradation of ecosystems, including soil resources. Hence, this research focused on examining six adsorbents in order to distinguish a reactive mineral with the highest capacity to [...] Read more.

An undesirable side effect of economic progress is increasingly severe pollution with heavy metals, responsible for the degradation of ecosystems, including soil resources. Hence, this research focused on examining six adsorbents in order to distinguish a reactive mineral with the highest capacity to remediate soils contaminated with heavy metals. To this end, the soil was polluted with Co²⁺ and Cd²⁺ by applying the metals in concentrations of 100 mg kg⁻¹ d.m. The extent of soil equilibrium disturbances was assessed by evaluating the response of the soil microbiome, activity of seven soil enzymes, and the yields of Helianthus annuus L. Six sorbents were evaluated: a molecular sieve, expanded clay (ExClay), halloysite, zeolite, sepiolite and biochar. Co²⁺ and Cd²⁺ proved to be significant inhibitors of the soil’s microbiological and biochemical parameters. Organotrophic bacteria among the analysed groups of microorganisms and dehydrogenases among the soil enzymes were most sensitive to the effects of the metals. Both metals significantly distorted the growth and development of sunflower, with Co²⁺ having a stronger adverse impact on the synthesis of chlorophyll. The molecular sieve and biochar were the sorbents that stimulated the multiplication of microorganisms and enzymatic activity in the contaminated soil. The activity of enzymes was also stimulated significantly by zeolite and sepiolite, while the growth of Helianthus annuus L. biomass was stimulated by the molecular sieve, which can all be considered the most useful reactive materials in the remediation of soils exposed to Co²⁺ and Cd²⁺. Full article

(This article belongs to the Special Issue Advances in Eco-Friendly Adsorbent Materials for Removal of Inorganic and Organic Pollutants)

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18 pages, 5546 KiB

Open AccessEditor’s ChoiceArticle

Microwave Absorption Properties of Multi-Walled Carbon Nanotubes/Carbonyl Iron Particles/Polyurethane Foams

by Xuegong Huang, Danping Yu and Simin Wang

Materials 2022, 15(16), 5690; https://doi.org/10.3390/ma15165690 - 18 Aug 2022

Cited by 13 | Viewed by 3209

Abstract

In order to improve the microwave absorption performance of absorbing materials, the composite foam absorbing materials with different multi-walled carbon nanotube (MWCNT) contents were prepared using polyurethane foam as the substrate and MWCNTs and flaked carbonyl iron powder as absorbers. The electromagnetic properties [...] Read more.

In order to improve the microwave absorption performance of absorbing materials, the composite foam absorbing materials with different multi-walled carbon nanotube (MWCNT) contents were prepared using polyurethane foam as the substrate and MWCNTs and flaked carbonyl iron powder as absorbers. The electromagnetic properties of the materials were characterized and analyzed. Then, CST electromagnetic simulation software was used to simulate the electromagnetic shielding effect of absorbing materials on mechatronics products under a strong electromagnetic irradiation environment, and, finally, it was verified by irradiation experiment. The results show that the materials have good microwave absorption properties, in which the composites containing 1.5 wt.% MWCNTs exhibit good microwave absorption properties. The minimum reflectivity reaches −29 dB when the thickness is 3 mm and −15.6 dB when the thickness is 1.5 mm, with a bandwidth of 5.7 GHz for reflectivity less than −10 dB. The good microwave absorption performance of the material is due to the synergistic effect of MWCNTs particles and good impedance matching. The simulation and experimental results show that the mechatronics product with absorbing materials can protect against strong electromagnetic interference and ensure the normal operation of the mechatronics product circuits. Full article

(This article belongs to the Special Issue Advances in Smart Materials and Applications)

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18 pages, 10683 KiB

Open AccessEditor’s ChoiceArticle

Design and Manufacturing of a Metal-Based Mechanical Metamaterial with Tunable Damping Properties

by Konstantin Kappe, Jan P. Wahl, Florian Gutmann, Silviya M. Boyadzhieva, Klaus Hoschke and Sarah C. L. Fischer

Materials 2022, 15(16), 5644; https://doi.org/10.3390/ma15165644 - 17 Aug 2022

Cited by 11 | Viewed by 3346

Abstract

In the present work, a novel concept for metallic metamaterials is presented, motivated by the creation of next-generation reversible damping systems that can be exposed to various environmental conditions. For this purpose, a unit cell is designed that consists of a parallel arrangement [...] Read more.

In the present work, a novel concept for metallic metamaterials is presented, motivated by the creation of next-generation reversible damping systems that can be exposed to various environmental conditions. For this purpose, a unit cell is designed that consists of a parallel arrangement of a spring and snap-fit mechanism. The combination of the two concepts enables damping properties one order of magnitude higher than those of the constituting metal material. The spring element stores elastic energy while the snap-fit allows to absorb and dissipate energy and to reach a second stable state. Different configurations of single unit cells and connected cell assemblies are manufactured by laser powder bed fusion using Ti6Al4V powder. The dimensioning is supported by finite element modelling and the characteristic properties of the unit cells are studied in cyclic compression experiments. The metamaterial exhibits damping properties in the range of polymeric foams while retaining its higher environmental resistance. By variation of selected geometrical parameters, either bistable or self-recovering characteristics are achieved. Therefore, a metamaterial as an assembly of the described unit cells could offer a high potential as a structural element in future damping or energy storage systems operating at elevated temperatures and extreme environmental conditions. Full article

(This article belongs to the Special Issue Mechanical Metamaterials: Optimization and New Design Ideas)

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18 pages, 8929 KiB

Open AccessEditor’s ChoiceArticle

Tunable Compact Metamaterial-Based Double-Negative/Near-Zero Index Resonator for 6G Terahertz Wireless Applications

by Alya Ali Musaed, Samir Salem Al-Bawri, Mohammad Tariqul Islam, Ahmed Jamal Abdullah Al-Gburi and Mandeep Jit Singh

Materials 2022, 15(16), 5608; https://doi.org/10.3390/ma15165608 - 16 Aug 2022

Cited by 18 | Viewed by 2423

Abstract

This paper introduces the tunability performance, concept, and analysis of a unique and miniaturized metamaterial (MTM) unit cell covering the upcoming 6G applications. The proposed metamaterial consists of two metallic star-shaped split-ring resonators (SRR). It has a line segment placed in the middle [...] Read more.

This paper introduces the tunability performance, concept, and analysis of a unique and miniaturized metamaterial (MTM) unit cell covering the upcoming 6G applications. The proposed metamaterial consists of two metallic star-shaped split-ring resonators (SRR). It has a line segment placed in the middle of the structure, which can feature tunable characteristics. The proposed design provides dual resonances of transmission coefficient S21 at 0.248 and 0.383 THz with a significant operating frequency span of 0.207–0.277 and 0.382–0.390 THz, respectively. Moreover, wide-range achievement, negative permittivity, double-negative (DNG) refractive index, and near-zero permeability characteristics have been exhibited in two (z and y) principal wave propagation axes. The resonance frequencies are selective and modified by adjusting the central slotted-strip line length. Furthermore, the metamaterial is constituted on a polyimide substrate while the overall dimensions are 160 × 160 μm². A numerical simulation of the proposed design is executed in CST microwave studio and has been compared with advanced design software (ADS) to generate the proposed MTM’s equivalent circuit, which exhibits a similar transmission coefficient (S21). Full article

(This article belongs to the Special Issue Design and Analysis of Novel Materials and Structures in the THz Frequencies)

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10 pages, 2809 KiB

Open AccessEditor’s ChoiceArticle

Intermodal Four-Wave Mixing Process in Strain-Induced Birefringent Multimode Optical Fibers

by Michał Kwaśny, Paweł Mergo, Marek Napierała, Krzysztof Markiewicz and Urszula A. Laudyn

Materials 2022, 15(16), 5604; https://doi.org/10.3390/ma15165604 - 15 Aug 2022

Cited by 3 | Viewed by 1734

Abstract

Our study investigated the partially degenerate intermodal four-wave mixing (IM-FWM) process in nonlinear multimode optical fibers with strain-induced birefringence. The difference in the refractive index along the two orthogonal directions was due to the photoelastic effect that occurred when the fiber under test [...] Read more.

Our study investigated the partially degenerate intermodal four-wave mixing (IM-FWM) process in nonlinear multimode optical fibers with strain-induced birefringence. The difference in the refractive index along the two orthogonal directions was due to the photoelastic effect that occurred when the fiber under test (FUT) was subjected to uniformly applied diameter stress caused by winding on a cylinder of a given diameter. Our work analyzed how the nonlinear frequency conversion and the output modal field profiles depended on the degree of birefringence in FUT. The experimental results significantly affected the order of the excited moduli in fiber sections characterized by different amounts of birefringence. We also checked the efficiency of the FWM process for different polarizations of the pump beam to determine those for which the FWM process was most effective for the 532 nm sub-nanosecond pulses. More than 30% conversion efficiency was obtained for the FUTs with a length of tens of centimeters. Full article

(This article belongs to the Section Optical and Photonic Materials)

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21 pages, 11656 KiB

Open AccessEditor’s ChoiceArticle

Bond Modification of Carbon Rovings through Profiling

by Paul Penzel, Maximilian May, Lars Hahn, Silke Scheerer, Harald Michler, Marko Butler, Martin Waldmann, Manfred Curbach, Chokri Cherif and Viktor Mechtcherine

Materials 2022, 15(16), 5581; https://doi.org/10.3390/ma15165581 - 14 Aug 2022

Cited by 12 | Viewed by 2600

Abstract

The load-bearing behavior and the performance of composites depends largely on the bond between the individual components. In reinforced concrete construction, the bond mechanisms are very well researched. In the case of carbon and textile reinforced concrete, however, there is still a need [...] Read more.

The load-bearing behavior and the performance of composites depends largely on the bond between the individual components. In reinforced concrete construction, the bond mechanisms are very well researched. In the case of carbon and textile reinforced concrete, however, there is still a need for research, especially since there is a greater number of influencing parameters. Depending on the type of fiber, yarn processing, impregnation, geometry, or concrete, the proportion of adhesive, frictional, and shear bond in the total bond resistance varies. In defined profiling of yarns, we see the possibility to increase the share of the shear bond (form fit) compared to yarns with a relatively smooth surface and, through this, to reliably control the bond resistance. In order to investigate the influence of profiling on the bond and tensile behavior, yarns with various profile characteristics as well as different impregnation and consolidation parameters are studied. A newly developed profiling technique is used for creating a defined tetrahedral profile. In the article, we present this approach and the first results from tensile and bond tests as well as micrographic analysis with profiled yarns. The study shows that bond properties of profiled yarns are superior to conventional yarns without profile, and a defined bond modification through variation of the profile geometry as well as the impregnation and consolidation parameters is possible. Full article

(This article belongs to the Special Issue Repair and Strengthening of Existing Reinforced Concrete Structures)

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15 pages, 5822 KiB

Open AccessEditor’s ChoiceArticle

Impact of External Mechanical Loads on Coda Waves in Concrete

by Fabian Diewald, Niklas Epple, Thomas Kraenkel, Christoph Gehlen and Ernst Niederleithinger

Materials 2022, 15(16), 5482; https://doi.org/10.3390/ma15165482 - 9 Aug 2022

Cited by 13 | Viewed by 2206

Abstract

During their life span, concrete structures interact with many kinds of external mechanical loads. Most of these loads are considered in advance and result in reversible deformations. Nevertheless, some of the loads cause irreversible, sometimes unnoticed changes below the macroscopic scale depending on [...] Read more.

During their life span, concrete structures interact with many kinds of external mechanical loads. Most of these loads are considered in advance and result in reversible deformations. Nevertheless, some of the loads cause irreversible, sometimes unnoticed changes below the macroscopic scale depending on the type and dimension of the impact. As the functionality of concrete structures is often relevant to safety and society, their condition must be known and, therefore, assessed on a regular basis. Out of the spectrum of non-destructive monitoring methods, Coda Wave Interferometry using embedded ultrasonic sensors is one particularly sensitive technique to evaluate changes to heterogeneous media. However, there are various influences on Coda waves in concrete, and the interpretation of their superimposed effect is ambiguous. In this study, we quantify the relations of uniaxial compression and uniaxial tension on Coda waves propagating in normal concrete. We found that both the signal correlation of ultrasonic signals as well as their velocity variation directly reflect the stress change in concrete structures in a laboratory environment. For the linear elastic range up to 30% of the strength, we calculated a velocity variation of −0.97‰/MPa for compression and 0.33%/MPa for tension using linear regression. In addition, these parameters revealed even weak irreversible changes after removal of the load. Furthermore, we show the time-dependent effects of shrinkage and creep on Coda waves by providing the development of the signal parameters over time during half a year together with creep recovery. Our observations showed that time-dependent material changes must be taken into account for any comparison of ultrasonic signals that are far apart in time. The study’s results demonstrate how Coda Wave Interferometry is capable of monitoring stress changes and detecting even small-size microstructural changes. By indicating the stated relations and their separation from further impacts, e.g., temperature and moisture, we anticipate our study to contribute to the qualification of Coda Wave Interferometry for its application as an early-warning system for concrete structures. Full article

(This article belongs to the Special Issue Concrete and Concrete Structures Monitored by Ultrasound)

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56 pages, 7034 KiB

Open AccessEditor’s ChoiceReview

Color Conversion Light-Emitting Diodes Based on Carbon Dots: A Review

by Danilo Trapani, Roberto Macaluso, Isodiana Crupi and Mauro Mosca

Materials 2022, 15(15), 5450; https://doi.org/10.3390/ma15155450 - 8 Aug 2022

Cited by 21 | Viewed by 4234

Abstract

This paper reviews the state-of-the-art technologies, characterizations, materials (precursors and encapsulants), and challenges concerning multicolor and white light-emitting diodes (LEDs) based on carbon dots (CDs) as color converters. Herein, CDs are exploited to achieve emission in LEDs at wavelengths longer than the pump [...] Read more.

This paper reviews the state-of-the-art technologies, characterizations, materials (precursors and encapsulants), and challenges concerning multicolor and white light-emitting diodes (LEDs) based on carbon dots (CDs) as color converters. Herein, CDs are exploited to achieve emission in LEDs at wavelengths longer than the pump wavelength. White LEDs are typically obtained by pumping broad band visible-emitting CDs by an UV LED, or yellow–green-emitting CDs by a blue LED. The most important methods used to produce CDs, top-down and bottom-up, are described in detail, together with the process that allows one to embed the synthetized CDs on the surface of the pumping LEDs. Experimental results show that CDs are very promising ecofriendly candidates with the potential to replace phosphors in traditional color conversion LEDs. The future for these devices is bright, but several goals must still be achieved to reach full maturity. Full article

(This article belongs to the Special Issue Organic Materials for Electronic and Optoelectronic Applications)

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18 pages, 15322 KiB

Open AccessEditor’s ChoiceArticle

A High Temporal-Spatial Resolution Temperature Sensor for Simultaneous Measurement of Anisotropic Heat Flow

by Xuwen Luo and Haidong Wang

Materials 2022, 15(15), 5385; https://doi.org/10.3390/ma15155385 - 5 Aug 2022

Cited by 4 | Viewed by 2613

Abstract

The thermal measurement sensor applied to hypersonic vehicles requires characteristic size in the order of micrometers and characteristic time in the order of microseconds. The measurement criteria of localized detection, high temporal-spatial precision, and long-term stability cannot all be reached by current thermal [...] Read more.

The thermal measurement sensor applied to hypersonic vehicles requires characteristic size in the order of micrometers and characteristic time in the order of microseconds. The measurement criteria of localized detection, high temporal-spatial precision, and long-term stability cannot all be reached by current thermal measuring techniques. This work presents a temperature sensor with excellent temporal-spatial resolution that can measure both in-plane and out-of-plane heat flow. The sensor was made of thin platinum nano-film and an aluminum nitride ceramic sheet. The sensor was calibrated using a thermostatic vacuum chamber and used for in-plane and out-of-plane heat flow measurements. The temperature measurement accuracy of the sensor was estimated to be 0.01 K. The sensor’s resolution for measuring heat flow density is more than 500 W/m² and its measurement uncertainty is roughly 3%. To ensure the structural stability of the device, the aluminum nitride ceramic sheet was chosen as the substrate of the thermal sensing unit, and the response time became longer due to the high thermal conductivity of aluminum nitride. The suspension platinum nano-film sensor can reach a sub-microsecond response time according to the theoretical derivation. Experimental results of pneumatic thermal effects of high-temperature flames using the sensor prove that the designed sensor has good sensitivity and accuracy. Full article

(This article belongs to the Special Issue Advances in Heat Transfer and Property Characterization of Nano Materials)

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15 pages, 6046 KiB

Open AccessEditor’s ChoiceArticle

Effect of Ultrafine Fly Ash and Water Glass Content on the Performance of Phosphorus Slag-Based Geopolymer

by Jin Yang, Xiaolei Yu, Xingyang He, Ying Su, Jingyi Zeng, Fei Dai and Shiyu Guan

Materials 2022, 15(15), 5395; https://doi.org/10.3390/ma15155395 - 5 Aug 2022

Cited by 12 | Viewed by 2197

Abstract

Phosphorus slag (PS), an industrial waste slag, has been used in geopolymers because it is rich in silicon and calcium. The poor performance of phosphorus slag-based geopolymer is due to its aluminum deficiency. In this work, low-calcium fly ash, treated by a wet-grinding [...] Read more.

Phosphorus slag (PS), an industrial waste slag, has been used in geopolymers because it is rich in silicon and calcium. The poor performance of phosphorus slag-based geopolymer is due to its aluminum deficiency. In this work, low-calcium fly ash, treated by a wet-grinding process, named wet-grinding ultrafine fly ash (WUFA) was used as an Al supplement to replace some of the phosphorus slag, and the wet-grinding, ultrafine fly ash-phosphorus slag (WUFA-PS)-based geopolymer was prepared. The effects of the substitution amount of WUFA and the activator dosage on the hydration properties, mechanical properties, pore structure and SEM of the WUFA-PS geopolymer were discussed in detail. The results indicate that WUFA and more activators contribute to the Al and high alkalinity environment, which positively induces the production of more geopolymer gels, thus releasing more heat and optimizing the pore structure of the matrix. The compressive strength increased by up to 28.1%. The enhanced performance of the WUFA-PS-based geopolymer may also arise from the filling effect and activity improvement of WUFA. This study has proved the feasibility of preparing a geopolymer by blending wet-grinding ultrafine fly ash and phosphorus slag and has provided references for the ratio and performance evaluation of WUFA-PS-based geopolymer concrete. Full article

(This article belongs to the Special Issue Durability and Sustainability of Cement and Concrete Composites)

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21 pages, 4521 KiB

Open AccessEditor’s ChoiceArticle

Superhydrophobic Anticorrosive Phosphonate–Siloxane Films Formed on Zinc with Different Surface Morphology

by Galina V. Redkina, Alexandra S. Sergienko, Yurii I. Kuznetsov and Oleg Yu. Grafov

Materials 2022, 15(15), 5360; https://doi.org/10.3390/ma15155360 - 4 Aug 2022

Cited by 9 | Viewed by 1883

Abstract

The composition, structure, and protective and hydrophobic properties of nanoscale films formed layer-by-layer in solutions of sodium dodecylphosphonate (SDDP) and vinyltrimethoxysilane or n-octyltriethoxysilane (OTES) on the zinc surface with different morphologies were studied by SEM, XPS, water contact angle measurements, and electrochemical [...] Read more.

The composition, structure, and protective and hydrophobic properties of nanoscale films formed layer-by-layer in solutions of sodium dodecylphosphonate (SDDP) and vinyltrimethoxysilane or n-octyltriethoxysilane (OTES) on the zinc surface with different morphologies were studied by SEM, XPS, water contact angle measurements, and electrochemical and corrosion tests. The protective, hydrophobic properties of phosphonate–siloxane films on zinc and their stability in a corrosive media are determined both by the initial surface morphology and composition of the surface oxide layer, and by the nature of inhibitors. It was shown that preliminary laser texturing of the zinc surface is preferable than chemical etching to enhance the anticorrosive properties of the resulting thin films. The most stable films with excellent superhydrophobic and protective properties in atmospheres of high humidity and salt spray are formed on the zinc surface with fractal morphology during layer-by-layer passivation with SDDP and OTES. Full article

(This article belongs to the Special Issue Corrosion Prediction and Corrosion Protection)

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14 pages, 4993 KiB

Open AccessEditor’s ChoiceArticle

An Overview of Some Nonpiezoelectric Properties of BaTiO₃ Ceramics Doped by Eu Ions

by Magdalena Krupska-Klimczak, Przemyslaw Gwizd, Irena Jankowska-Sumara, Dorota Sitko and Piotr Jeleń

Materials 2022, 15(15), 5363; https://doi.org/10.3390/ma15155363 - 4 Aug 2022

Cited by 7 | Viewed by 2273

Abstract

Ferroelectric ceramics BaTiO₃:x%Eu (x = 0, 0.1, 1, 2, 3) were synthesized by a conventional method. Structural investigation confirmed that all ceramics possessed tetragonal (P4mm) symmetries at room temperature for the undoped ceramics as well as for the [...] Read more.

Ferroelectric ceramics BaTiO₃:x%Eu (x = 0, 0.1, 1, 2, 3) were synthesized by a conventional method. Structural investigation confirmed that all ceramics possessed tetragonal (P4mm) symmetries at room temperature for the undoped ceramics as well as for the doped ceramics. Furthermore, a slight downshifting of the Curie temperature (T_C) with an increasing Eu³⁺ doping amount has been noted. The Raman spectra unveiled the existence of new modes for higher-doped BaTiO₃:x%Eu (BTEx) which are related to local disorders and defects. The ferroelectric properties were found to depend on both doping and the microstructure. The electrocaloric effect was also studied for those ceramics. It was observed that ΔT decreases with doping; however, the temperature range of its occurrence widens considerably. Full article

(This article belongs to the Special Issue Emerging Dielectric, Piezoelectric and Ferroelectric Ceramic and Crystalline Materials and Their Applications)

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16 pages, 1798 KiB

Open AccessEditor’s ChoiceArticle

Effect of Biochar Modification by Vitamin C, Hydrogen Peroxide or Silver Nanoparticles on Its Physicochemistry and Tetracycline Removal

by Agnieszka Tomczyk and Katarzyna Szewczuk-Karpisz

Materials 2022, 15(15), 5379; https://doi.org/10.3390/ma15155379 - 4 Aug 2022

Cited by 16 | Viewed by 2996

Abstract

Chemical modification of biochars can improve their adsorption capacity relative to antibiotics, posing a serious threat to the environment. Therefore, this research is aimed at the treatment of sunflower husk biochar (BC) by vitamin C, hydrogen peroxide or silver nanoparticles and the impact [...] Read more.

Chemical modification of biochars can improve their adsorption capacity relative to antibiotics, posing a serious threat to the environment. Therefore, this research is aimed at the treatment of sunflower husk biochar (BC) by vitamin C, hydrogen peroxide or silver nanoparticles and the impact of this procedure on the biochar porosity, surface chemistry, and ability to remove tetracycline (TC). During the study, BC was produced by pyrolysis of sunflower husks at 650 °C. All solids were characterized using potentiometric titration, nitrogen adsorption/desorption, Fourier transform infrared spectroscopy, etc. The experimental adsorption data was described by kinetics equations: pseudo-first order, pseudo-second order, and particle internal diffusion (IPD) models as well as by isotherms of Langmuir, Langmuir-Freundlich, and Redlich-Peterson. The obtained results indicated that the biochar upgraded by vitamin C (BCV) had the highest ability to attract antibiotic molecules and, as a result, the TC adsorption on its surface was the largest. Furthermore, the TC desorption from this material was minimal. The measured TC adsorbed amounts for the modified BCs were as follows: 47.75% (7.47 mg/g) for BCV, 37.35% (8.41 mg/g)-for biochar treated by hydrogen peroxide (BCH), and 42.04% (9.55 mg/g) for biochar modified by silver nanoparticles (BCA). The lowest adsorption level was noted for non-modified biochar, i.e., 34.17% (6.83 mg/g). Based on the presented results it can be stated that the upgraded biochars had a good potential to improve the tetracycline removal from aqueous media, e.g., groundwater. Full article

(This article belongs to the Special Issue Advances in Eco-Friendly Adsorbent Materials for Removal of Inorganic and Organic Pollutants (Volume II))

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17 pages, 6822 KiB

Open AccessEditor’s ChoiceArticle

Influence of the Additive of Ceramic and Intermetallic Powders on the Friction Properties and Temperature of the Wet Clutch Disc

by Aleksander Yevtushenko, Michal Kuciej, Piotr Grzes, Aleksander Ilyushchanka and Andrey Liashok

Materials 2022, 15(15), 5384; https://doi.org/10.3390/ma15155384 - 4 Aug 2022

Cited by 2 | Viewed by 1928

Abstract

The basic function of friction clutches is to transfer the torque in the conditions of its smooth engagement without vibrations. Hard working conditions under high thermal and mechanical loads, leading to high temperature in the contact area, intense wear, and instability of the [...] Read more.

The basic function of friction clutches is to transfer the torque in the conditions of its smooth engagement without vibrations. Hard working conditions under high thermal and mechanical loads, leading to high temperature in the contact area, intense wear, and instability of the coefficient of friction impose restrictive criteria in the design of friction materials. In this paper, the results of experimental research of the effect of ceramic and intermetallic additives to the copper-based material of the friction disc of the clutch on the thermophysical and frictional properties were presented. Next, these properties were incorporated in the proposed contact 3D numerical model of the clutch to carry out computer simulations of the heating process and subsequent cooling. Based on the obtained experimental data and transient temperature changes of the friction and steel discs, the relations between the powder additives, thermophysical properties of the five friction materials, and coefficients of friction, wear, and temperature reached were discussed. Among these, it was found that when working with the lubrication, the largest values of the coefficient of friction 0.068 and wear

13.5 μ m {km}^{- 1}

were reached when using the 3 wt.% SiC additive. Full article

(This article belongs to the Special Issue Use of Modern Materials in Technological Processes Accompanied by Frictional Heating)

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16 pages, 9579 KiB

Open AccessEditor’s ChoiceArticle

Effect of Silver Doping on the Superconducting and Structural Properties of YBCO Films Grown by PLD on Different Templates

by Ilya A. Shipulin, Aleena Anna Thomas, Sigrid Holleis, Michael Eisterer, Kornelius Nielsch and Ruben Hühne

Materials 2022, 15(15), 5354; https://doi.org/10.3390/ma15155354 - 3 Aug 2022

Cited by 5 | Viewed by 2881

Abstract

We report the local structural and superconducting properties of undoped and Ag-doped YBa₂Cu₃O_6+x (YBCO) films with a thickness of up to 1 µm prepared by pulsed laser deposition on SrTiO₃ (STO) single crystals and on ion-beam-assisted deposition [...] Read more.

We report the local structural and superconducting properties of undoped and Ag-doped YBa₂Cu₃O_6+x (YBCO) films with a thickness of up to 1 µm prepared by pulsed laser deposition on SrTiO₃ (STO) single crystals and on ion-beam-assisted deposition (IBAD) and rolling-assisted biaxially textured substrate (RABiTS)-based metal templates. X-ray diffraction demonstrates the high crystalline quality of the films on both single crystalline substrates and metal-based templates, respectively. Although there was only a slight decrease in T_c of up to 1.5 K for the Ag-doped YBCO films on all substrates, we found significant changes in their transport characteristics. The effect of the silver doping mainly depended on the concentration of silver, the type of substrate, and the temperature and magnetic field. In general, the greatest improvement in J_c over a wide range of magnetic fields and temperatures was observed for the 5%Ag-doped YBCO films on STO substrates, showing a significant increase compared to undoped films. Furthermore, a slight J_c improvement was observed for the 2%Ag-doped YBCO films on the RABiTS templates at temperatures below 65 K, whereas J_c decreased for the Ag-doped films on IBAD-MgO-based templates compared to undoped YBCO films. Using detailed electron microscopy studies, small changes in the local microstructure of the Ag-doped YBCO films were revealed; however, no clear correlation was found with the transport properties of the films. Full article

(This article belongs to the Special Issue Advances in Superconducting Materials: Characterization, Properties and Applications)

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19 pages, 4137 KiB

Open AccessEditor’s ChoiceArticle

Archaeometric Characterization of the Industrial Production of Porcelains in the Vieillard & Co. Manufactory (Bordeaux, France, 19th Century)

by Emmie Beauvoit, Nadia Cantin, Quentin Lemasson, Rémy Chapoulie and Ayed Ben Amara

Materials 2022, 15(15), 5311; https://doi.org/10.3390/ma15155311 - 2 Aug 2022

Cited by 2 | Viewed by 1797

Abstract

In this paper, we focus on the industrial production of porcelain in the Bordeaux area (France) in the 19th century. Our main objective is to assess the evolution of production technology of the same manufactory over a period of more than 40 years. [...] Read more.

In this paper, we focus on the industrial production of porcelain in the Bordeaux area (France) in the 19th century. Our main objective is to assess the evolution of production technology of the same manufactory over a period of more than 40 years. A multi-analytical approach was used to investigate glazes and bodies of thirty-four sherds of biscuit and porcelain found in an archaeological context. The microstructural, chemical, and mineralogical characterization was performed using a combination of scanning electron microscopy, coupled with energy dispersive spectroscopy (SEM-EDS), particles induced X-ray and gamma emission (PIXE-PIGE), and X-ray diffraction (XRD). Results obtained on the characterization of the ceramic production technologies and on the chemical modification over time contributes to investigate this industrial production, which is not well documented by the written archives. The examination of the biscuits, rare artifacts, showed that the porcelain bodies were produced by mixing kaolinitic clays, quartz, and potassium feldspars. The mineralogical analysis of the ceramic supports allowed hypotheses to be put forward on the temperatures of the biscuit firing (around 950 °C) and the second firing (over 1200 °C). Furthermore, the treatment of the compositional data, including both glazes and bodies, using multivariate statistical analysis, revealed different types of production corresponding to the different chronological periods of production at Bordeaux throughout the 19th century. These results will enable us to consider the possibility of authenticating non-stamped and undecorated pieces. Full article

(This article belongs to the Special Issue Science and Technology of Porcelain: History, Processing, Structure and Properties)

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24 pages, 9840 KiB

Open AccessEditor’s ChoiceArticle

Effect of Polycarboxylate-Silane Modified Graphene Oxide Composite on the Properties of Cement Pastes

by Shuang Liu, Shiyu Li, Qin Wang, Ruifeng Zhang and Xiao Liu

Materials 2022, 15(15), 5313; https://doi.org/10.3390/ma15155313 - 2 Aug 2022

Cited by 4 | Viewed by 1984

Abstract

As a nano-carbon material with excellent properties, Graphene oxide (GO) has been widely used in cement-based materials, and the negative effect of paste workability caused by GO agglomeration has also been widely concerning. In this study, a polycarboxylate-silane modified graphene oxide composite (PSG) [...] Read more.

As a nano-carbon material with excellent properties, Graphene oxide (GO) has been widely used in cement-based materials, and the negative effect of paste workability caused by GO agglomeration has also been widely concerning. In this study, a polycarboxylate-silane modified graphene oxide composite (PSG) was prepared by coupling polycarboxylate molecules to the surface of graphene oxide (GO) via a reaction with vinyl triethoxysilane. The effects of GO and PSG on the cement paste and the mechanisms underpinning these effects were investigated using fluidity and rheological parameter measurements, and ion concentration and zeta potential analyses. It was found that, in the aqueous phase of the paste, the polycarboxylate molecular chains on the surface of the PSG complexed with calcium ions (Ca²⁺), thereby preventing Ca²⁺ from bridging the GO sheets, and thus stabilizing the surface potential and the electrostatic repulsion. This prevented the PSG from forming an agglomerate structure such as that formed by GO under the same conditions, thereby substantially enhancing workability of paste with nano-carbon material. This study provides some new foundations and ideas for the further application of graphene oxide materials in cement-based materials. Full article

(This article belongs to the Special Issue Development and Characterization of Novel Cement Materials)

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16 pages, 5950 KiB

Open AccessEditor’s ChoiceArticle

Zirconia versus Titanium Implants: 8-Year Follow-Up in a Patient Cohort Contrasted with Histological Evidence from a Preclinical Animal Model

by Warwick J. Duncan, Sunyoung Ma, Allauddin Siddiqi and Reham B. Osman

Materials 2022, 15(15), 5322; https://doi.org/10.3390/ma15155322 - 2 Aug 2022

Cited by 4 | Viewed by 3169

Abstract

Zirconia ceramic (ZC) implants are becoming more common, but comparisons between preclinical histology and long-term clinical trials are rare. This investigation comprised (1) 8-year clinical follow-up of one-piece ZC or titanium (Ti) implants supporting full overdentures and (2) histomorphometric analysis of the same [...] Read more.

Zirconia ceramic (ZC) implants are becoming more common, but comparisons between preclinical histology and long-term clinical trials are rare. This investigation comprised (1) 8-year clinical follow-up of one-piece ZC or titanium (Ti) implants supporting full overdentures and (2) histomorphometric analysis of the same implants in an animal model, comparing implants with various surface treatments. Methods: (1) Clinical trial: 24 completely edentulous participants (2 groups of N = 12) received 7 implants (one-piece ball-abutment ZC or Ti; maxilla N = 4, mandible N = 3) restored with implant overdentures. Outcomes after 8-years included survival, peri-implant bone levels, soft-tissue responses, and prosthodontic issues. (2) Preclinical trial: 10 New Zealand sheep received 4 implants bilaterally in the femoral condyle: Southern Implants ZC or Ti one-piece implants, identical to the clinical trial, and controls: Southern ITC^® two-piece implants with the same surface or Nobel (NBC) anodised (TiUnite™) surface. %Bone-implant contact (%BIC) was measured after 12 weeks of unloaded healing. Results: 8 of 24 participants (33%) of an average age of 75 ± 8 years were recalled; 21% of original participants had died, and 46% could not be contacted. 80.4% of implants survived; excluding palatal sites, 87.5% of Ti and 79% of ZC implants survived. All failed implants were in the maxilla. Three ZC implants had fractured. Bone loss was similar for Ti vs. ZC; pocket depths (p = 0.04) and attachment levels (p = 0.02) were greater for Ti than ZC implants. (1.7 ± 1.6 mm vs. 1.6 ± 1.3 mm). All implants in sheep femurs survived. %BIC was not statistically different for one-piece blasted surface Ti (80 ± 19%) versus ZC (76 ± 20%) or ITC^® (75 ± 16 mm); NBC had significantly higher %BIC than ITC (84 ± 17%, p = 0.4). Conclusion: Short-term preclinical results for ZC and Ti one-piece implants showed excellent bone-implant contact in unloaded femoral sites. This differed from the long-term clinical results in older-aged, edentulous participants. While ZC and Ti implants showed equivalent performance, the risks of peri-implantitis and implant loss in older, completely edentulous patients remain a significant factor. Full article

(This article belongs to the Special Issue Zirconia Implants: Current Status and Future Prospects)

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10 pages, 1250 KiB

Open AccessEditor’s ChoiceArticle

Injectable Click Fibroin Bioadhesive Derived from Spider Silk for Accelerating Wound Closure and Healing Bone Fracture

by Woong-Jin Lee, Kyoungjoo Cho, Aaron-Youngjae Kim and Gyung-Whan Kim

Materials 2022, 15(15), 5269; https://doi.org/10.3390/ma15155269 - 30 Jul 2022

Cited by 5 | Viewed by 2729

Abstract

Wound closure is a critical step in postoperative wound recovery. Substantial advancements have been made in many different means of facilitating wound closure, including the use of tissue adhesives. Compared to conventional methods, such as suturing, tissue bioadhesives better accelerate wound closure. However, [...] Read more.

Wound closure is a critical step in postoperative wound recovery. Substantial advancements have been made in many different means of facilitating wound closure, including the use of tissue adhesives. Compared to conventional methods, such as suturing, tissue bioadhesives better accelerate wound closure. However, several existing tissue adhesives suffer from cytotoxicity, inadequate tissue adhesive strength, and high costs. In this study, a series of bioadhesives was produced using non-swellable spider silk-derived silk fibroin protein and an outer layer of swellable polyethylene glycol and tannic acid. The gelation time of the spider silk-derived silk fibroin protein bioadhesive is less than three minutes and thus can be used during rapid surgical wound closure. By adding polyethylene glycol (PEG) 2000 and tannic acid as co-crosslinking agents to the N-Hydroxysuccinimide (NHS), and 1-Ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) reaction, the adhesive strength of the bioadhesive became 2.5 times greater than that of conventional fibrin glue adhesives. Silk fibroin bioadhesives do not show significant cytotoxicity in vitro compared with other bioadhesives. In conclusion, silk fibroin bioadhesive is promising as a new medical tool for more effective and efficient surgical wound closure, particularly in bone fractures. Full article

(This article belongs to the Special Issue Development and Application of Silk-Proteins Based Biomaterials)

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28 pages, 7705 KiB

Open AccessEditor’s ChoiceArticle

Topology Optimization and Multiobjective Optimization for Drive Axle Housing of a Rear Axle Drive Truck

by Bin Zheng, Shengyan Fu and Jilin Lei

Materials 2022, 15(15), 5268; https://doi.org/10.3390/ma15155268 - 30 Jul 2022

Cited by 9 | Viewed by 4374

Abstract

As one of the important load-bearing components of a truck, the drive axle housing must meet the requirements of stiffness and strength. The traditional design method uses redundancy design to meet the performance requirements. The joint design between the three-dimensional mathematical model and [...] Read more.

As one of the important load-bearing components of a truck, the drive axle housing must meet the requirements of stiffness and strength. The traditional design method uses redundancy design to meet the performance requirements. The joint design between the three-dimensional mathematical model and finite element model is adopted, and the optimal design of the drive axle housing is realized based on topology optimization and multiobjective optimization. Firstly, the static analysis of the drive axle housing of a rear axle drive truck was carried out with four typical working conditions. It was concluded that the four working conditions all operate under the yield limit of the material, and it was found that the maximum equivalent stress of the four working conditions occurs at the step of the half-shaft casing. Among the four working conditions, the most critical one is the maximum vertical force working condition. Then, based on the maximum vertical force working condition, the fatigue life analysis is conducted, and the minimum fatigue life appears at the transition position of the half-shaft sleeve and the arc transition position of the main reducer chamber. The remaining parts can meet the design requirements. The overall safety factor of the drive axle housing is mainly between 1 and 5 when operating under this working condition. Then, through modal analysis, the first to sixth natural frequency and vibration modes of the drive axle housing are extracted. Based on the modal analysis, the dynamic characteristics of the drive axle housing are further studied by harmonic response analysis and random vibration analysis. Finally, two kinds of lightweight optimization schemes for the drive axle housing are given. Topology optimization reduces the mass of the drive axle housing by 17.4%, but the overall performance slightly decreases. Then, the five dimensional parameters of the drive axle housing are selected as design variables. The mass, maximum deformation, equivalent stress, service life, and the first-, second- and third-order natural frequencies are defined as objective functions. Through the optimal space-filling design method, the experimental designs are performed and the sample points are obtained. Based on the results of experiment design, the multiobjective genetic algorithm and response surface method are combined to optimize the objective functions. The analysis results show that the mass is reduced by 4.35%, the equivalent stress is reduced by 21.05%, the minimum life is increased by 72.28%, and the first-, second-, and third-order natural frequency are also increased to varying degrees. Two different optimization strategies are provided for the design of the drive axle housing. Full article

(This article belongs to the Special Issue Finite Element Analysis of Mechanical Behaviors and Properties of Engineering Materials and Structures)

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12 pages, 6330 KiB

Open AccessEditor’s ChoiceArticle

Self-Powered Photodetector Based on FTO/n-TiO₂/p-CuMnO₂ Transparent Thin Films

by Carmen Lazau, Mircea Nicolaescu, Corina Orha, Viorel Şerban and Cornelia Bandas

Materials 2022, 15(15), 5229; https://doi.org/10.3390/ma15155229 - 28 Jul 2022

Cited by 5 | Viewed by 2508

Abstract

A self-powered photodetector with the FTO/n-TiO₂/p-CuMnO₂ configuration, representing the novelty of the work, was successfully achieved for the first time and presumes two steps: deposition of the n-type semiconductor (TiO₂) by the doctor [...] Read more.

A self-powered photodetector with the FTO/n-TiO₂/p-CuMnO₂ configuration, representing the novelty of the work, was successfully achieved for the first time and presumes two steps: deposition of the n-type semiconductor (TiO₂) by the doctor blade method and of the p-type semiconductor (CuMnO₂) by the spin coating technique, respectively. Investigation techniques of the structural and morphological characteristics of the as-synthesized heterostructures, such as XRD, UV-VIS analysis, and SEM/EDX and AFM morphologies, were used. The I-t measurements of the photodetector showed that the responsivity in the self-powered mode was 2.84 × 10⁷ A W⁻¹ cm² and in the 1 V bias mode it was 1.82 × 10⁶ A W⁻¹ cm². Additionally, a self-powered current of 14.2 nA was generated under UV illumination with an intensity of 0.1 mW/cm². Furthermore, under illumination conditions, the response time (t_res) and the recovery time (t_rec) of the sensor exhibited a good response; thus, t_res = 7.30 s and t_rec = 0.4 s for the self-powered mode, and in the 1 V bias mode, these were t_res = 15.16 s and t_rec = 2.18 s. The above results show that the transparent heterojunction device of n-TiO₂/p-CuMnO₂ exhibited a self-powered ultraviolet photodetector with high sensitivity. Full article

(This article belongs to the Special Issue Nano-Engineering of Functional Oxides: Synthesis, Functional Properties and Applications)

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19 pages, 14590 KiB

Open AccessEditor’s ChoiceArticle

Performance of 3D-Printed Bionic Conch-Like Composite Plate under Low-Velocity Impact

by Mincen Wan, Dayong Hu and Baoqing Pei

Materials 2022, 15(15), 5201; https://doi.org/10.3390/ma15155201 - 27 Jul 2022

Cited by 11 | Viewed by 2796

Abstract

Biological armors can provide an effective protection against predators. In this study, inspired by conch shell, beetle exoskeleton, and nacre, three different types of bionic composites plates were fabricated: Bio-S, Bio-B, and Bio-N, as well as an equivalent monolithic plate formed from the [...] Read more.

Biological armors can provide an effective protection against predators. In this study, inspired by conch shell, beetle exoskeleton, and nacre, three different types of bionic composites plates were fabricated: Bio-S, Bio-B, and Bio-N, as well as an equivalent monolithic plate formed from the same stiff material designed and manufactured by additive manufacturing, respectively. Low velocity impact tests using drop tower were conducted to study their impact resistance. Experimental findings indicated that the Bio-S composite had superior impact resistance compared with the other bionic composites and the monolithic plate. Furthermore, the influence of the ply angle on the impact resistance of the Bio-S composite plate was investigated. The (0°/30°/0°/30°) arrangement was able to provide the highest impact resistance. Finally, the crack propagation mode in Bio-S composites plates was analyzed, enhancing our understanding of the underlying mechanisms during impact. Such findings may lead to the development of superior lightweight protective structures with improved anti-impact performance. Full article

(This article belongs to the Special Issue Advanced Composite Material Design and Manufacturing Technology for Aerospace Engineering)

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16 pages, 4627 KiB

Open AccessEditor’s ChoiceArticle

Compression Deformation Prediction of Chiral Metamaterials: A Compression–Shear Coupling Model

by Xin Zhou, Xi Liang, Zeliang Liu, Chenglin Tao and Huijian Li

Materials 2022, 15(15), 5180; https://doi.org/10.3390/ma15155180 - 26 Jul 2022

Cited by 4 | Viewed by 1904

Abstract

A category of metamaterials consisting of chiral cytosolic elements assembled periodically, in which the introduction of a rotatable annular structure gives metamaterials the ability to deform in compression–shear, has been a focus of research in recent years. In this paper, a compression–shear coupling [...] Read more.

A category of metamaterials consisting of chiral cytosolic elements assembled periodically, in which the introduction of a rotatable annular structure gives metamaterials the ability to deform in compression–shear, has been a focus of research in recent years. In this paper, a compression–shear coupling model is developed to predict the compressive deformation behaviour of chiral metamaterials. This behaviour will be analysed by coupling the rotation of the annular node and the bending characteristics of ligament beam, which are obtained as a function of the length of ligament beam and the angle of rotation at the end of the beam. The shape function of the ligament beam under large deformation is obtained based on the elliptic integral theory; the function characterises the potential relationship between key parameters such as displacement and rotation angle at any point on the ligament beam. By simulating the deformation of cells under uniaxial compression, the reasonableness of the large deformation model of the ligament beam is verified. On this basis, a chiral cell-compression mechanical model considering the ductile deformation of the annular node is established. The compression–shear deformation of two-dimensional planar chiral metamaterials and three-dimensional cylindrical-shell chiral metamaterials was predicted; the offset displacements and torsion angles agreed with the experimental and finite element simulation results with an error of less than 10%. The developed compression–shear coupling model provides a theoretical basis for the design of chiral metamaterials, which meet the need for the precise control of shapes and properties. Full article

(This article belongs to the Section Mechanics of Materials)

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9 pages, 1962 KiB

Open AccessEditor’s ChoiceCommunication

Energy-Resolved Ultrafast Spectroscopic Investigation on the Spin-Coupled Electronic States in Multiferroic Hexagonal HoMnO₃

by Wei-Hong Huang, Hao-Keng Wei, Nguyen Nhat Quyen, Pei-Tsung Yang, Yi-Cheng Cheng, Yu-Ting Wang, Ying-Kuan Ko, Chien-Ming Tu, Atsushi Yabushita and Chih-Wei Luo

Materials 2022, 15(15), 5188; https://doi.org/10.3390/ma15155188 - 26 Jul 2022

Cited by 1 | Viewed by 1861

Abstract

A complete temperature-dependent scheme of the Mn³⁺ on-site d-d transitions in multiferroic hexagonal HoMnO₃ (h-HoMnO₃) thin films was unveiled by energy-resolved ultrafast spectroscopy. The results unambiguously revealed that the ultrafast responses of the e_1g and e [...] Read more.

A complete temperature-dependent scheme of the Mn³⁺ on-site d-d transitions in multiferroic hexagonal HoMnO₃ (h-HoMnO₃) thin films was unveiled by energy-resolved ultrafast spectroscopy. The results unambiguously revealed that the ultrafast responses of the e_1g and e_2g states differed significantly in the hexagonal HoMnO₃. We demonstrated that the short-range antiferromagnetic and ferroelectric orderings are more relevant to the e_2g state, whereas the long-range antiferromagnetic ordering is intimately coupled to both the e_2g and e_1g states. Moreover, the primary thermalization times of the e_2g and e_1g states were 0.34 ± 0.08 ps and 0.38 ± 0.08 ps, respectively. Full article

(This article belongs to the Special Issue Application of Emerging Materials for Advanced Imaging and Sensing)

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27 pages, 14051 KiB

Open AccessEditor’s ChoiceArticle

Modified Micro-Mechanics Based Multiscale Model for Damage Analysis of Open-Hole Composite Laminates under Compression

by Meng Wang and Xiaochen Hang

Materials 2022, 15(15), 5105; https://doi.org/10.3390/ma15155105 - 22 Jul 2022

Cited by 4 | Viewed by 2320

Abstract

The multiscale model based on micro-mechanics failure theory is modified to consider complex internal structures, including a fiber random arrangement pattern and interface with the clustering method. Then, a feed-forward-neural-network (FFNN)-based damage evolution method is developed to evaluate the macroscale property degradation. The [...] Read more.

The multiscale model based on micro-mechanics failure theory is modified to consider complex internal structures, including a fiber random arrangement pattern and interface with the clustering method. Then, a feed-forward-neural-network (FFNN)-based damage evolution method is developed to evaluate the macroscale property degradation. The progressive damage analysis of open-hole laminates under compression is conducted to validate the modified multiscale method. The predicted results reveal that the interface results in the premature initiation of damage, and the fiber random arrangement pattern contributes to the decrease in the predicted compression responses. The developed FFNN-based method aimed at degradation results in an increase in the predicted compression strength. For the fiber random distribution pattern, the increase in percentage of predicted compressive strength is 6.0%, which is much larger than the value for the fiber diamond distribution pattern. Full article

(This article belongs to the Special Issue Analytical and Computational Methods in Material and Mechanical Engineering)

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15 pages, 1194 KiB

Open AccessEditor’s ChoiceArticle

Clinical and Microbiological Evaluation of a Chlorhexidine-Modified Glass Ionomer Cement (GIC-CHX) Restoration Placed Using the Atraumatic Restorative Treatment (ART) Technique

by Jithendra Ratnayake, Arthi Veerasamy, Hassan Ahmed, David Coburn, Carolina Loch, Andrew R. Gray, Karl M. Lyons, Nicholas C. K. Heng, Richard D. Cannon, Marcus Leung and Paul A. Brunton

Materials 2022, 15(14), 5044; https://doi.org/10.3390/ma15145044 - 20 Jul 2022

Cited by 7 | Viewed by 2679

Abstract

The aims of this study were to investigate the clinical effectiveness and patient acceptability of a modified glass ionomer cement placed using the atraumatic restorative treatment (ART) technique to treat root caries, and to carry out microbiological analysis of the restored sites. Two [...] Read more.

The aims of this study were to investigate the clinical effectiveness and patient acceptability of a modified glass ionomer cement placed using the atraumatic restorative treatment (ART) technique to treat root caries, and to carry out microbiological analysis of the restored sites. Two clinically visible root surface carious lesions per participant were restored using ART. One was restored with commercial glass ionomer cement (GIC) (ChemFil^® Superior, DENTSPLY, Konstonz, Germany) which acted as the control. The other carious root lesion was restored with the same GIC modified with 5% chlorhexidine digluconate (GIC-CHX; test). Patient acceptability and restoration survival rate were evaluated at baseline and after 6 months. Plaque and saliva samples around the test and control restorations were collected, and microbiological analysis for selected bacterial and fungal viability were completed at baseline, and after 1, 3, and 6 months. In total, 52 restorations were placed using GIC and GIC-CHX in 26 participants; 1 patient was lost to follow-up. After reviewing the restorations during their baseline appointments, participants indicated that they were satisfied with the appearance of the restorations (n = 25, 96%) and did not feel anxious during the procedure (n = 24, 92%). Forty-eight percent (n = 12) of the GIC-CHX restorations were continuous with the existing anatomic form as opposed to six for the GIC restorations (24%), a difference which was statistically significant (p = 0.036). There was no statistically significant reduction in the mean count of the tested microorganisms in plaque samples for either type of restorations after 1, 3, or 6 months. Restoration of carious root surfaces with GIC-CHX resulted in higher survival rates than the control GIC. ART using GIC-CHX may therefore be a viable approach for use in outreach dental services to restore root surface carious lesions where dental services are not readily available, and for older people and special needs groups. Full article

(This article belongs to the Special Issue Bioinspired Materials for Dentistry)

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8 pages, 1581 KiB

Open AccessEditor’s ChoiceArticle

Stretchable and Conductive Cellulose/Conductive Polymer Composite Films for On-Skin Strain Sensors

by Joo Won Han, Jihyun Park, Jung Ha Kim, Siti Aisyah Nurmaulia Entifar, Ajeng Prameswati, Anky Fitrian Wibowo, Soyeon Kim, Dong Chan Lim, Jonghee Lee, Myoung-Woon Moon, Min-Seok Kim and Yong Hyun Kim

Materials 2022, 15(14), 5009; https://doi.org/10.3390/ma15145009 - 19 Jul 2022

Cited by 11 | Viewed by 2791

Abstract

Conductive composite materials have attracted considerable interest of researchers for application in stretchable sensors for wearable health monitoring. In this study, highly stretchable and conductive composite films based on carboxymethyl cellulose (CMC)-poly (3,4-ethylenedioxythiopehe):poly (styrenesulfonate) (PEDOT:PSS) (CMC-PEDOT:PSS) were fabricated. The composite films achieved excellent [...] Read more.

Conductive composite materials have attracted considerable interest of researchers for application in stretchable sensors for wearable health monitoring. In this study, highly stretchable and conductive composite films based on carboxymethyl cellulose (CMC)-poly (3,4-ethylenedioxythiopehe):poly (styrenesulfonate) (PEDOT:PSS) (CMC-PEDOT:PSS) were fabricated. The composite films achieved excellent electrical and mechanical properties by optimizing the lab-synthesized PEDOT:PSS, dimethyl sulfoxide, and glycerol content in the CMC matrix. The optimized composite film exhibited a small increase of only 1.25-fold in relative resistance under 100% strain. The CMC-PEDOT:PSS composite film exhibited outstanding mechanical properties under cyclic tape attachment/detachment, bending, and stretching/releasing tests. The small changes in the relative resistance of the films under mechanical deformation indicated excellent electrical contacts between the conductive PEDOT:PSS in the CMC matrix, and strong bonding strength between CMC and PEDOT:PSS. We fabricated highly stretchable and conformable on-skin sensors based on conductive and stretchable CMC-PEDOT:PSS composite films, which can sensitively monitor subtle bio-signals and human motions such as respiratory humidity, drinking water, speaking, skin touching, skin wrinkling, and finger bending. Because of the outstanding electrical properties of the films, the on-skin sensors can operate with a low power consumption of only a few microwatts. Our approach paves the way for the realization of low-power-consumption stretchable electronics using highly stretchable CMC-PEDOT:PSS composite films. Full article

(This article belongs to the Special Issue Advanced Materials and Systems for Biomedical Application)

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10 pages, 1784 KiB

Open AccessEditor’s ChoiceArticle

Application of Genetically Encoded Photoconvertible Protein SAASoti for the Study of Enzyme Activity in a Single Live Cell by Fluorescence Correlation Microscopy

by Ilya D. Solovyev, Liliya G. Maloshenok and Alexander P. Savitsky

Materials 2022, 15(14), 4962; https://doi.org/10.3390/ma15144962 - 16 Jul 2022

Cited by 6 | Viewed by 1937

Abstract

Fluorescent Correlation Spectroscopy (FCS) allows us to determine interactions of labeled proteins or changes in the oligomeric state. The FCS method needs a low amount of fluorescent dye, near nanomolar concentrations. To control the amount of fluorescent dye, we used new photoconvertible FP [...] Read more.

Fluorescent Correlation Spectroscopy (FCS) allows us to determine interactions of labeled proteins or changes in the oligomeric state. The FCS method needs a low amount of fluorescent dye, near nanomolar concentrations. To control the amount of fluorescent dye, we used new photoconvertible FP SAASoti. This work is devoted to the proof of principle of using photoconvertible proteins to measure caspase enzymatic activity in a single live cell. The advantage of this approach is that partial photoconversion of the FP makes FCS measurements possible when studying enzymatic reactions. To investigate the process, in vivo we used HeLa cell line expressing the engineered FRET sensor, SAASoti-23-KFP. This FRET sensor has a cleavable (DEVD) sequence in the linker between two FPs for the detection of one of the key enzymes of apoptosis, caspase-3. Caspase-3 activity was detected by registering the increase in the fluorescent lifetimes of the sensor, whereas the diffusion coefficient of SAASoti decreased. This can be explained by an increase in the total cell viscosity during apoptosis. We can suppose that in the moment of detectible caspase-3 activity, cell structure already has crucial changes in viscosity. Full article

(This article belongs to the Special Issue Feature Paper in Optical and Photonic Materials)

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24 pages, 14705 KiB

Open AccessEditor’s ChoiceArticle

Vibration-Based Fatigue Analysis of Octet-Truss Lattice Infill Blades for Utilization in Turbine Rotors

by Sajjad Hussain, Wan Aizon W. Ghopa, S. S. K. Singh, Abdul Hadi Azman, Shahrum Abdullah, Zambri Harun and Hawa Hishamuddin

Materials 2022, 15(14), 4888; https://doi.org/10.3390/ma15144888 - 14 Jul 2022

Cited by 7 | Viewed by 2568

Abstract

Vibration fatigue characteristics are critical for rotating machinery components such as turbine rotor blades. Lattice structures are gaining popularity in engineering applications due to their unique ability to reduce weight and improve the mechanical properties. This study is an experimental investigation of octet-truss [...] Read more.

Vibration fatigue characteristics are critical for rotating machinery components such as turbine rotor blades. Lattice structures are gaining popularity in engineering applications due to their unique ability to reduce weight and improve the mechanical properties. This study is an experimental investigation of octet-truss lattice structure utilization in turbine rotor blades for weight reduction and to improve vibration fatigue characteristics. One completely solid and three lattice infilled blades with variable strut thickness were manufactured via additive manufacturing. Both free and forced experimental vibration analyses were performed on the blades to investigate their modal and vibration fatigue characteristics. The blades were subjected to random vibration using a vibration shaker. The response was measured using a triaxial accelerometer in terms of vibration acceleration time histories in the X, Y, and Z directions. Results indicate a weight reduction of up to 24.91% and enhancement in the first natural frequency of up to 5.29% were achieved using lattice infilled blades. The fatigue life of the blades was investigated using three frequency domain approaches, namely, Lalanne, Dirlik and narrow band. The fatigue life results indicate that the 0.25 mm lattice blade exhibits the highest fatigue life, while the solid blade exhibits the lowest fatigue life of all four blades. The fatigue life of the 0.25 mm lattice blade was 1822-, 1802-, and 1819- fold higher compared to that of the solid blade, using the Lalanne, Dirlik, and narrow-band approaches, respectively. These results can serve as the first step towards the utilization of lattice structures in turbine blades, with thermal analysis as the next step. Therefore, apart from being light weight, the octet-truss lattice infilled blades exhibited superior vibration fatigue characteristics to vibration loads, thereby making them a potential replacement for solid blades in turbine rotors. Full article

(This article belongs to the Section Mechanics of Materials)

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14 pages, 2924 KiB

Open AccessEditor’s ChoiceArticle

Synthesis and Processing Parameter Optimization of Nano-Belite via One-Step Combustion Method

by Hongfang Sun, Weixing Lian, Xiaogang Zhang, Wei Liu, Feng Xing and Jie Ren

Materials 2022, 15(14), 4913; https://doi.org/10.3390/ma15144913 - 14 Jul 2022

Cited by 6 | Viewed by 1923

Abstract

This paper proposes a new chemical combustion method for the synthesis of nano-low-carbon belite cement via a simple one-step process without using any oxidizers, and related mechanisms are briefly introduced. The starting materials used, including micro-silica (silica fume) as a byproduct of the [...] Read more.

This paper proposes a new chemical combustion method for the synthesis of nano-low-carbon belite cement via a simple one-step process without using any oxidizers, and related mechanisms are briefly introduced. The starting materials used, including micro-silica (silica fume) as a byproduct of the metallurgic industry and CaCO₃ powders, are of great abundance, and the processing parameters involved were optimized using a series of systematic experiments based on X-ray diffraction (XRD) and the Rietveld fitting method. Besides, the properties of the synthesized belite cement were characterized by the Brunauer–Emmett–Teller (BET) technique and scanning electron microscopy (SEM). Experimental results revealed that the optimized fuel agent was urea with a dosage of 4.902 times that of the starting materials by mass, and the corresponding holding temperature and time were 1150 °C and 2 h, respectively. In addition, the CaO/(SiO₂ + CaO) for the starting materials should be set at 62.5% by mass ratio. BET and SEM results showed that the obtained belite cement had a specific surface area of 11.17 m²/g and a size of around 500 nm or even smaller in spherical shapes, suggesting that this method was successfully implemented. Thus, it can be a promising approach for the synthesis of nano-belite particles as a low-carbon construction material, which could be used more in the near future, such as for low-carbon concrete productions. Full article

(This article belongs to the Section Construction and Building Materials)

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17 pages, 5833 KiB

Open AccessEditor’s ChoiceArticle

Evaluation of Solidified Wastewater Treatment Sludge as a Potential SCM in Pervious Concrete Pavements

by Ognjen Govedarica, Marina Aškrabić, Milica Hadnađev-Kostić, Tatjana Vulić, Branislava Lekić, Vladana Rajaković-Ognjanović and Dimitrije Zakić

Materials 2022, 15(14), 4919; https://doi.org/10.3390/ma15144919 - 14 Jul 2022

Cited by 12 | Viewed by 2709

Abstract

Waste and recycled materials have recently been used in the construction industry to comply with the principles of circular economy and sustainable development. The aim of this paper is to examine the potentials of solidified wastewater treatment sludge (SWWTS) as a supplementary cementitious [...] Read more.

Waste and recycled materials have recently been used in the construction industry to comply with the principles of circular economy and sustainable development. The aim of this paper is to examine the potentials of solidified wastewater treatment sludge (SWWTS) as a supplementary cementitious material (SCM) in the production of lightweight pervious concrete pavers (LWPCP) suitable for pedestrian trails and rooftops (green) that comply with EU standards. Detailed characterization of SWWTS was performed, in order to understand its properties related to application as SCM, which led to the conclusion that it may be applied only as a filler, having 89.5% of Ca(OH)₂. After thorough characterization, LWPCP samples were prepared and testing of physical and mechanical properties was conducted. The research showed that partial replacement of cement with SWWTS led to the decrease of all mechanical properties, ranging between 3.91 and 5.81 MPa for compressive strength and 0.97 to 1.23 MPa for flexural strength. However, all of the investigated mixtures showed a value higher than 3.5 MPa, which was defined as the lowest compressive strength in the range of pervious concrete properties. The addition of SWWTS led to a slight decrease in bulk density of the mixtures and an increase in water absorption. This could be explained by the reduction in hydration products that would fill in the micropores of the matrix, since SWWTS showed no pozzolanic reactivity. Pore sizes that prevail in the tested binder matrices are in accordance with the results measured on ordinary pervious concrete (the largest fraction of pores had a diameter between 0.02 and 0.2 μm). Low thermal conductivity nominates produced pavers as potential rooftop elements. Full article

(This article belongs to the Special Issue Industrial Symbiosis and Development of New Materials or Products in Building Sector)

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15 pages, 3530 KiB

Open AccessEditor’s ChoiceArticle

Promotion Effect of Carboxymethyl Chitosan on Dental Caries via Intrafibrillar Mineralization of Collagen and Dentin Remineralization

by Qi Zhang, Jiaxin Guo, Zihua Huang and Sui Mai

Materials 2022, 15(14), 4835; https://doi.org/10.3390/ma15144835 - 12 Jul 2022

Cited by 15 | Viewed by 3261

Abstract

Objective: To observe ultrastructural changes during the process of carboxymethyl chitosan (CMC)-mediated intrafibrillar mineralization, we evaluated the biomimetic remineralization potential of CMC in type-I collagen fibrils and membranes, and further explored the bond strength as well as the bond interfacial integrity of the [...] Read more.

Objective: To observe ultrastructural changes during the process of carboxymethyl chitosan (CMC)-mediated intrafibrillar mineralization, we evaluated the biomimetic remineralization potential of CMC in type-I collagen fibrils and membranes, and further explored the bond strength as well as the bond interfacial integrity of the biomimetic remineralized artificial caries-affected dentin (ACAD). Methods: A mineralized solution containing 200 μg/mL CMC was used to induce type-I collagen biomimetic remineralization in ACAD, while traditional mineralization without CMC was used as a control. The process and pattern of mineralization were investigated by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) as well as structured illumination microscopy (SIM). The Vickers hardness test was used to quantify the dentin hardness, while the microtensile bond strength (µTBS) test was used to assess the bond strength and durability. The bond interfacial integrity was evaluated by a confocal laser scanning microscope (CLSM). Results: TEM, SEM, and SIM images showed that CMC had a positive effect on stabilizing amorphous calcium phosphate (ACP) and promoting intrafibrillar mineralization, while extrafibrillar mineralization was formed without CMC. Furthermore, hardness evaluation and µTBS proved that CMC significantly increased dentin hardness and bond strength. CLSM indicated that CMC could create a significantly better bond interfacial integrity with less of a micro-gap in ACAD. Significance: CMC possessed the ability to promote intrafibrillar mineralization and remineralization in demineralized caries dentin lesions, as well as improve bond performance, which implied its potential in carious dentin demineralization or dentin hypersensitivity and possibly even as a possible material for indirect pulp-capping, to deal with deep caries. Highlights: CMC possessed the ability to induce intrafibrillar mineralization effectively; the bond strength and bond durability of demineralized caries dentin were improved via CMC-induced remineralization; the CMC-induced remineralization complex is a potential material for indirect pulp-capping, to deal with deep caries. Full article

(This article belongs to the Special Issue New Materials and Their Applications: Perspectives in Restorative Dentistry and Endodontics)

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23 pages, 2784 KiB

Open AccessEditor’s ChoiceReview

Comparison between Piezoelectric and Piezoresistive Wearable Gait Monitoring Techniques

by Zhiyuan Zhang, Zhenyu Xu, Wenbin Chen and Shuo Gao

Materials 2022, 15(14), 4837; https://doi.org/10.3390/ma15144837 - 12 Jul 2022

Cited by 9 | Viewed by 3566

Abstract

Insole plantar stress detection (PSD) techniques play an important role in gait monitoring. Among the various insole PSD methods, piezoelectric- and piezoresistive-based architectures are broadly used in medical scenes. Each year, a growing number of new research outcomes are reported. Hence, a deep [...] Read more.

Insole plantar stress detection (PSD) techniques play an important role in gait monitoring. Among the various insole PSD methods, piezoelectric- and piezoresistive-based architectures are broadly used in medical scenes. Each year, a growing number of new research outcomes are reported. Hence, a deep understanding of these two kinds of insole PSD sensors and state-of-the-art work would strongly benefit the researchers in this highly interdisciplinary field. In this context, this review article is composed of the following aspects. First, the mechanisms of the two techniques and corresponding comparisons are explained and discussed. Second, advanced materials which could enhance the performance of current piezoelectric and piezoresistive insole prototypes are introduced. Third, suggestions for designing insole PSD prototypes/products for different diseases are offered. Last, the current challenge and potential future trends are provided. Full article

(This article belongs to the Special Issue Functional Materials Based Human-Machine Interactivities)

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