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14 pages, 2482 KB  
Article
Multiscale Structural Engineering of Cellulose Foams: Performance Characterization and Fiber Imaging
by Patricija Pevec, Urška Kavčič, Aleš Hladnik and Diana Gregor-Svetec
Polymers 2025, 17(17), 2355; https://doi.org/10.3390/polym17172355 - 29 Aug 2025
Viewed by 749
Abstract
The paper industry is always looking for possible solutions for new fiber-based products, such as protective and cushioning materials. These materials must be carefully designed to provide effective cushioning while also being lightweight to reduce transportation costs. Additionally, they need to offer protection [...] Read more.
The paper industry is always looking for possible solutions for new fiber-based products, such as protective and cushioning materials. These materials must be carefully designed to provide effective cushioning while also being lightweight to reduce transportation costs. Additionally, they need to offer protection from environmental and mechanical damage, besides having good processability to ensure proper buffering. The widely used protective and cushioning materials, such as plastic foams and expanded or extruded polystyrene, create significant disposal challenges. Therefore, there is increasing demand for biodegradable and sustainable materials for cushioning applications. The focus of our research was to develop fiber-based foams and investigate the influence of different compositions (hardwood and softwood) of cellulose fibers on the basic (mass, thickness, density) and mechanical properties (three-point bend test, tensile properties). Foams made entirely from short eucalyptus fibers (100S) exhibited the highest density (28.0 ± 0.34 kg/m3) and lowest thickness (38.82 ± 4.21 mm), resulting in superior tensile strength and elastic modulus but lower strain at break. In contrast, foams composed of long spruce fibers (100L) had the lowest density (19.0 ± 0.27 kg/m3) and highest thickness (58.52 ± 1.50 mm), with lower strength and stiffness but much higher ductility and porosity (confirmed by ~30% higher air permeability compared to 100S). Blended formulations demonstrated intermediate behavior, with the 50S50L foam showing a favorable balance of strength, stiffness, and flexibility. Visual analysis confirmed heterogeneous fiber distribution with localized agglomerates and compaction at the bottom layer due to casting. To further interpret the complex relationships within the dataset and uncover patterns, Principal Component Analysis (PCA) was applied to all experimental results. The findings of the research contribute to the broader understanding of how different fiber types and blends impact the performance of sustainable cellulose-based foams, with potential implications for the development of biodegradable packaging and lightweight construction materials. Full article
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24 pages, 3590 KB  
Article
Palmitic Acid Esterification Boosts Epigallocatechin Gallate’s Immunomodulatory Effects in Intestinal Inflammation
by Raúl Domínguez-Perles, Concepción Medrano-Padial, Cristina García-Viguera and Sonia Medina
Biomolecules 2025, 15(8), 1208; https://doi.org/10.3390/biom15081208 - 21 Aug 2025
Viewed by 735
Abstract
Lipophenols, combining phenolic and lipid moieties in a single molecule, are valuable candidates for providing enhanced bioactive properties with therapeutic potential, including anti-inflammatory functions associated with immune-mediated diseases such as intestinal bowel disease (IBD). Thus, palmitoyl–epigallocatechin gallate (PEGCG), a lipophilic derivative of epigallocatechin [...] Read more.
Lipophenols, combining phenolic and lipid moieties in a single molecule, are valuable candidates for providing enhanced bioactive properties with therapeutic potential, including anti-inflammatory functions associated with immune-mediated diseases such as intestinal bowel disease (IBD). Thus, palmitoyl–epigallocatechin gallate (PEGCG), a lipophilic derivative of epigallocatechin gallate (EGCG), has been highlighted for its enhanced stability in lipid-rich environments and bioavailability due to improved cellular uptake. However, the contribution of lipophilic esterification to PEGCG’s capacity to inhibit inflammation and the development of harmful autoimmune responses remains underexplored. This work uncovered the differential efficiency of EGCG and its palmitoyl derivative in modulating, in vitro, the interleukin profile generated by intestinal epithelium under inflammatory conditions. Therefore, both could attenuate the immune response by lowering macrophage migration and polarisation towards pro-inflammatory (M1) or anti-inflammatory (M2) phenotypes. While the fatty acid moiety gave PEGCG a functional advantage over EGCG in adjusting the interleukin-based response of intestinal epithelium to inflammation—since both of them decreased, to a similar extent, the expression of pro-inflammatory interleukins, namely IL-6, IL-17, IL-18, IL-23, and TNF-α (which lowered by 11.2%, on average)—the former was significantly more efficient in cushioning the increase in IL-1β and IL-12p70 (by 9.2% and 10.4%, respectively). This immune modulation capacity did not significantly impact the migration and expression of costimulatory molecules featuring M1 (CD86+) or M2 (CD206+) phenotypes by THP-1-derived macrophages, for which both bioactive compounds exhibited equivalent efficiency. Nonetheless, the analysis of the pro- and anti-inflammatory interleukins secreted by differentiated macrophages allowed the identification of an advantage for PEGCG, which decreased the expression of the pro-inflammatory immune mediators IL-1β and IL-12p70, IL-23, and TNF-α more efficiently. These results suggest that lipophilisation of phenolic compounds presents exciting potential for extending their application as functional molecules by combining the effects of their polar head with their ability to interfere with membranes, conveyed by their lipophilic tail. In addition, the enhanced reactivity would confer a higher capacity to interact with cellular signalling molecules and thus inhibit or attenuate the immune response, which is of special interest for preventing the onset and severity of immune-mediated pathologies such as IBD. Full article
(This article belongs to the Special Issue Recent Advances in the Enzymatic Synthesis of Bioactive Compounds)
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13 pages, 5470 KB  
Article
Cushioning Performance of Specialized Running Socks for Enhanced Shock Absorption and Reduced Plantar Pressure
by Xia Zhou, Pui-Ling Li, Kit-Lun Yick and Annie Yu
Materials 2025, 18(13), 2941; https://doi.org/10.3390/ma18132941 - 21 Jun 2025
Viewed by 1362
Abstract
Running socks play an important role in alleviating foot impact and preventing foot injuries. Despite the variety of commercial options, their cushioning effectiveness is not well understood. This study examines three different types of running socks made of bio-based and synthetic textiles. Material [...] Read more.
Running socks play an important role in alleviating foot impact and preventing foot injuries. Despite the variety of commercial options, their cushioning effectiveness is not well understood. This study examines three different types of running socks made of bio-based and synthetic textiles. Material testing includes compression, tensile, and shock absorption, while wear tests assess plantar loading in 10 adult recreational runners on a treadmill. Results show that specialized running socks offer superior shock absorption compared to regular running socks, largely due to fabric thickness and weight. Socks made of high-performance bio-composite fibers significantly reduced maximum peak pressure and impulse in the great toe (p < 0.05) and first metatarsal head (p < 0.05) during running. Additionally, ground contact time in the forefoot (p < 0.05) area was significantly lower with specialized running socks. Compared to regular running socks, five-toed running socks can reduce the pressure load on the forefoot area. These findings can guide the design of specialized sockwear for better foot protection and improved sports performance. Full article
(This article belongs to the Special Issue Leather, Textiles and Bio-Based Materials)
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56 pages, 2756 KB  
Review
Articular Cartilage: Structure, Biomechanics, and the Potential of Conventional and Advanced Diagnostics
by Robert Karpiński, Aleksandra Prus, Jacek Baj, Sebastian Radej, Marcin Prządka, Przemysław Krakowski and Kamil Jonak
Appl. Sci. 2025, 15(12), 6896; https://doi.org/10.3390/app15126896 - 18 Jun 2025
Cited by 3 | Viewed by 4581
Abstract
Articular cartilage (AC) plays an important role in the biomechanics of synovial joints. Its task is to enable smooth movement and transfer of mechanical loads with minimised friction. AC is characterised by unique mechanical properties resulting from its complex structure, in which the [...] Read more.
Articular cartilage (AC) plays an important role in the biomechanics of synovial joints. Its task is to enable smooth movement and transfer of mechanical loads with minimised friction. AC is characterised by unique mechanical properties resulting from its complex structure, in which the dominant components are type II collagen, proteoglycans and water. Healthy articular cartilage shows elasticity in compression, viscoelastic properties, and the ability to relax stresses under the influence of cyclic loads. In response to different loading modes, it shows anisotropic and non-uniform behaviour, which translates into its cushioning and protective function for the subchondral bone. Significant changes occur in the structure and mechanical properties of cartilage with age as a result of mechanical overload or degenerative diseases, such as osteoarthritis. This results in a deterioration of the cushioning and mechanical function, which leads to progressive degradation of joint tissues. Understanding the mechanical properties of AC is crucial for developing effective diagnostic methods. Analysis of changes in mechanical properties contributes to the early detection of pathological changes. The aim of this paper is to review the current state of knowledge regarding the structure and biomechanical properties of articular cartilage, and to analyse conventional and alternative diagnostic methods in the context of their suitability for assessing the state of AC, particularly in the early stages of degenerative processes. Full article
(This article belongs to the Special Issue Orthopaedics and Joint Reconstruction: Latest Advances and Prospects)
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20 pages, 5810 KB  
Article
The Effects of the Substrate Length and Cultivation Time on the Physical and Mechanical Properties of Mycelium-Based Cushioning Materials from Salix psammophila and Peanut Straw
by Xiaowen Song, Shuoye Chen, Jianxin Wu, Ziyi Cai, Yanfeng Zhang, Risu Na, He Lv, Cong He, Tingting Wu and Xiulun Wang
Biomimetics 2025, 10(6), 371; https://doi.org/10.3390/biomimetics10060371 - 5 Jun 2025
Viewed by 891
Abstract
Mycelium-based biocomposites represent a novel class of environmentally friendly materials. This study investigated the potential of using Salix psammophila and peanut straw as substrates for cultivating Pleurotus ostreatus and Ganoderma lucidum, respectively, to fabricate mycelium-based cushioning materials. The results demonstrated that the [...] Read more.
Mycelium-based biocomposites represent a novel class of environmentally friendly materials. This study investigated the potential of using Salix psammophila and peanut straw as substrates for cultivating Pleurotus ostreatus and Ganoderma lucidum, respectively, to fabricate mycelium-based cushioning materials. The results demonstrated that the Pleurotus ostreatus-based cushion material using Salix psammophila (POSM) outperformed the Ganoderma lucidum-based cushion material using peanut straw (GLPM) in terms of overall performance. Both materials presented optimal comprehensive properties when the cultivation period reached 30 days. Increasing the substrate length enhanced most of the material properties. The resulting density ranged from 0.13 to 0.16 g/cm3, which was higher than that of polystyrene foam. The contact angles of both materials exceeded 120°, whereas their elastic springback rates reached 50.2% and 43.2%, and their thermal conductivities were 0.049 W/m·K and 0.051 W/m·K, respectively. Additionally, thermogravimetric analysis revealed that both materials exhibited similar thermal degradation behavior and relatively high thermal stability. These findings align with those of previous studies on mycelium composites and indicate that the physical and mechanical properties of the materials are largely comparable to those of expanded polystyrene (EPS). In conclusion, the developed mycelium-based cushioning materials promote the efficient utilization of agricultural residues and hold promise as a sustainable alternative to EPS, offering broad application prospects in the transportation and packaging sectors. Full article
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11 pages, 2006 KB  
Article
Physicomechanical Properties of Tissue Conditioner Reinforced with Glass Fibers
by Aftab Ahmed Khan, Abdulaziz Abdullah AlKhureif, Eraj Humayun Mirza, Raghad Khalid AlHassoun, Aisha Wasi and Jukka Matinlinna
Bioengineering 2025, 12(5), 515; https://doi.org/10.3390/bioengineering12050515 - 13 May 2025
Viewed by 706
Abstract
Tissue conditioners are temporary lining materials applied to dentures to soothe and cushion inflamed or traumatized oral tissues, typically resulting from ill-fitting dentures. This laboratory study aimed to evaluate the physicomechanical properties of a clinical tissue conditioner with 0.5 and 1 wt.% of [...] Read more.
Tissue conditioners are temporary lining materials applied to dentures to soothe and cushion inflamed or traumatized oral tissues, typically resulting from ill-fitting dentures. This laboratory study aimed to evaluate the physicomechanical properties of a clinical tissue conditioner with 0.5 and 1 wt.% of silanized, micron-sized, E-glass fibers. The experimental tissue conditioners were characterized based on their molecular structure, surface roughness, contact angle, tensile strength, dimensional stability, water sorption, and solubility. The results were analyzed by two-way ANOVA (factors: material composition and aging) and the post hoc Tukey’s test. FTIR analysis revealed characteristic peaks at 1710–1720 cm−1, 2800–3000 cm−1, and 1400 cm−1, indicating a strong interaction between the tissue conditioner and the micron-sized glass fibers. Tensile strength was highest at baseline but declined in all groups after 14 days of aging, with the 0.5 wt.% glass fiber group showing the least reduction. Linear dimensional changes remained consistent across all groups. Surface roughness increased in all groups after 14 days, though the 0.5 wt.% glass fiber group exhibited the smallest increase. Water contact angles ranged from 71° to 92°, suggesting adequate surface wettability for clinical use. The experimental groups consistently demonstrated lower water sorption and solubility values. The 0.5 wt.% glass fiber formulation showed the potential to improve clinical performance by its reduced water sorption and solubility. However, long-term studies and clinical trials are necessary to validate the clinical effectiveness of this formulation. Full article
(This article belongs to the Special Issue Biomaterials for Oral Health Maintenance: A Translational Approach)
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21 pages, 14800 KB  
Article
Robust Continuous Sliding-Mode-Based Assistive Torque Control for Series Elastic Actuator-Driven Hip Exoskeleton
by Rui Wang, Xiaoou Lin, Changwei Yin, Zhongtao Liu, Yang Zhang, Wenping Liu and Fuxin Du
Actuators 2025, 14(5), 239; https://doi.org/10.3390/act14050239 - 9 May 2025
Cited by 1 | Viewed by 1169
Abstract
In this paper, a real-time assistive torque controller based on sliding-mode control is proposed for a Series Elastic Actuator (SEA)-driven lower limb assistive exoskeleton. To address the problem of the lack of buffering properties and the uneven torque output in traditional exoskeletons, a [...] Read more.
In this paper, a real-time assistive torque controller based on sliding-mode control is proposed for a Series Elastic Actuator (SEA)-driven lower limb assistive exoskeleton. To address the problem of the lack of buffering properties and the uneven torque output in traditional exoskeletons, a novel SEA is designed for the hip joint lower-limb exoskeleton. This structure features excellent cushioning properties and smooth torque output. On this basis, to enhance the torque tracking performance of the hip joint exoskeleton, in this study, a robust composite control strategy is proposed, which can maintain accuracy in the presence of unknown external disturbances and model parameter inaccuracies. The strategy consists of an adaptive phase oscillator for outputting the phase of the gait, a single-peak curve to provide a reference assistive torque, and a low-level controller to track the torque. The low-level controller employs Continuous Sliding-Mode Control (CSMC) to obtain a continuous control law and utilizes an Extended State Observer (ESO) to estimate the lumped disturbance. It ensures that the tracking error is asymptotically convergent with minimized chatter. The closed-loop stability of the system is theoretically proven by the Lyapunov method. The validity of the proposed algorithm is validated on a designed exoskeleton. Full article
(This article belongs to the Section Actuators for Robotics)
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14 pages, 4910 KB  
Article
Enhanced Compression Properties of Open-Cell Foams Reinforced with Shear-Thickening Fluids and Shear-Stiffening Polymers
by Jian Li, Yaoguang Zhou, Mohammad Rauf Sheikhi and Selim Gürgen
Polymers 2025, 17(9), 1218; https://doi.org/10.3390/polym17091218 - 29 Apr 2025
Cited by 3 | Viewed by 1022
Abstract
Open-cell PU foams have a wide range of industrial applications due to their excellent cushioning, impact protection, packaging, thermal insulation, and sound reduction benefits. The foams absorb impact energy while deforming under compressing and are ideal for applications with severe and repeated loading [...] Read more.
Open-cell PU foams have a wide range of industrial applications due to their excellent cushioning, impact protection, packaging, thermal insulation, and sound reduction benefits. The foams absorb impact energy while deforming under compressing and are ideal for applications with severe and repeated loading conditions. Enhancing and improving their compressive durability is a vital area of ongoing research. We investigated the effect of incorporating shear-stiffening polymers (SSPs) and shear-thickening fluids (STFs) on the compression properties of open-cell foams. Rheological properties of STFs and SSPs prepared for incorporation into the foams confirmed the shear-thickening and shear-stiffening characteristics. Quasi-static compression tests performed at different speeds (6, 60, 120, 180, and 240 mm/s), as well as load-unload compression tests (6 and 24 mm/s), showed that the SSP-filled foam exhibited the most pronounced improvement in the elastic, plateau, and densification regions compared to the neat foam. While the STF-filled foam also improved performance over the neat foam, its advantages over the SSP-filled foam were less pronounced. The performance of the SSP-filled foam improved with increasing compression speeds, while the performance of the STF-filled foam remained relatively stable between 60 and 240 mm/s of load-unload tests. Post-test compression evaluations showed that neat and STF-filled foams quickly regained their original shape, while SSP-filled foams required more time before recovery. This research shows that combining SSP and STF smart materials with open-cell foams substantially improves their compressive performance, especially at high compression rates and load-unloading scenarios, increasing their functional life. Full article
(This article belongs to the Special Issue Mechanical Behaviors and Properties of Polymer Materials, 2nd Edition)
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41 pages, 35264 KB  
Article
A New Method and Set of Parameters for Evaluating the Cushioning Effect of Shoe Heels, Revealing the Inadvertent Design of Running Shoes
by Franz Konstantin Fuss, Tizian Scharl and Niko Nagengast
Bioengineering 2025, 12(5), 467; https://doi.org/10.3390/bioengineering12050467 - 28 Apr 2025
Cited by 1 | Viewed by 7006
Abstract
According to standards, the heel soles of running shoes are currently tested with an energy absorption of 5 J. This study offers an alternative method to improve the measurement of cushioning properties. The new method uses the ratio of absorbed energy to applied [...] Read more.
According to standards, the heel soles of running shoes are currently tested with an energy absorption of 5 J. This study offers an alternative method to improve the measurement of cushioning properties. The new method uses the ratio of absorbed energy to applied force and determines the maximum of this ratio (optimum or shoulder point) and the associated optimal force, energy, and displacement. This method was applied to 112 shoe models using compression testing. The method was found to be insensitive to strain rates and identified shoes that were over-, well-, or under-designed (running before, at, or after the shoulder point, respectively) relative to the range of the first ground reaction force peak (0.700–2 kN). The optimum ratio was between 0.6 J/kN (barefoot shoes) and 11.2 J/kN (Puma RuleBreaker), the optimal energy was between 0.5 and 40.6 J, the optimal force was between 0.1 and 4.6 kN, and the optimal displacement was between 3 and 23 mm. Participants ran at or near the shoulder point (within the design forgiveness range) unless they were too heavy and ran at their preferred running speed. This study proposes replacing current standards with the new method, allowing consumers to make informed decisions regarding injury prevention while running. Full article
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34 pages, 13428 KB  
Review
Materials and Structures Inspired by Human Heel Pads for Advanced Biomechanical Function
by Zhiqiang Zhuang, Congtian Gu, Shunlin Li, Hu Shen, Ning Liu, Ziwei Li, Dakai Wang, Cong Wang, Linpeng Liu, Kaixian Ba, Bin Yu and Guoliang Ma
Biomimetics 2025, 10(5), 267; https://doi.org/10.3390/biomimetics10050267 - 27 Apr 2025
Cited by 1 | Viewed by 998
Abstract
The heel pad, located under the calcaneus of the human foot, is a hidden treasure that has been subjected to harsh mechanical conditions such as impact, vibration, and cyclic loading. This has resulted in a unique compartment structure and material composition, endowed with [...] Read more.
The heel pad, located under the calcaneus of the human foot, is a hidden treasure that has been subjected to harsh mechanical conditions such as impact, vibration, and cyclic loading. This has resulted in a unique compartment structure and material composition, endowed with advanced biomechanical functions including cushioning, vibration reduction, fatigue resistance, and touchdown stability, making it an ideal natural bionic prototype in the field of bionic materials. It has been shown that the highly specialized structure and material composition of the heel pad endows it with biomechanical properties such as hyperelasticity, viscoelasticity, and mechanical anisotropy. These complex biomechanical properties underpin its advanced functions. Although it is known that these properties interact with each other, the detailed influence mechanism remains unclear, which restricts its application as a bionic prototype in the field of bionic materials. Therefore, this study provides a comprehensive review of the structure, materials, biomechanical properties, and functions of the heel pad. It focuses on elucidating the relationships between the structure, materials, biomechanical properties, and functions of heel pads and proposes insights for the study of bionic materials using the heel pad as a bionic prototype. Finally, a research idea to analyze the advanced mechanical properties of heel pads by integrating sophisticated technologies is proposed, aiming to provide directions for further in-depth research on heel pads and inspiration for the innovative design of advanced bionic materials. Full article
(This article belongs to the Special Issue Bioinspired Engineered Systems)
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23 pages, 13614 KB  
Article
Study on Fatigue Characteristics of Cement-Emulsified Asphalt Mortar Under Coupled Effects of Humidity and Freeze–Thaw
by Shanshan Jin, Pengfei Liu, Zhen Wang, Daxing Zhou, Xiang Li, Zengmiao Xu, Yang Zhang, Yuling Yan and Yaodong Zhao
Coatings 2025, 15(4), 369; https://doi.org/10.3390/coatings15040369 - 21 Mar 2025
Viewed by 454
Abstract
Cement-emulsified asphalt mortar (CA mortar) is an organic–inorganic composite material composed of cement, emulsified asphalt, fine sand, water, and various admixtures. It is mainly used as the cushion layer for high-speed railway ballastless tracks. CA mortar cushion layers in North China often have [...] Read more.
Cement-emulsified asphalt mortar (CA mortar) is an organic–inorganic composite material composed of cement, emulsified asphalt, fine sand, water, and various admixtures. It is mainly used as the cushion layer for high-speed railway ballastless tracks. CA mortar cushion layers in North China often have to withstand the coupling effects of humidity and freeze–thaw, which has a very important impact on the fatigue performance of CA mortar. Based on the big data statistical results, the temperature conditions and cycle times of the CA mortar layer Freeze–Thaw cycle in North China were determined. Also, a fatigue performance test under humidity–freeze–thaw coupling conditions was designed and carried out. The fitting curve equations of fatigue stress and fatigue life under different humidity conditions and freeze–thaw coupling were established. The relationship between fatigue performance parameters K and n and humidity conditions was analyzed. This study shows that with the increase in humidity, the fatigue life of CA mortar under different humidity conditions shows an overall downward trend. The fatigue performance and fatigue life stress level sensitivity of CA mortar decrease with increasing humidity. The proportion of water damage and freeze–thaw damage to total damage increases with increasing humidity, which means that the humidity and freeze–thaw have a more significant impact on the fatigue properties of CA mortar. When the humidity is low, the fatigue cracks of CA mortar are mostly generated across the cement paste, and the macroscopic damage presents as longitudinal cracking. When the humidity is high, the fatigue cracks of CA mortar are mostly generated at the interface between aggregate and paste, and the macroscopic damage presents as oblique cracking. Based on the analysis of the damage mechanism, it is suggested that the humidity of CA mortar should be controlled below 25% in the actual project to ensure its durability. Full article
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25 pages, 29921 KB  
Article
Geological and Petrophysical Properties of Underground Gas Storage Facilities in Ukraine and Their Potential for Hydrogen and CO2 Storage
by Yuliia Demchuk, Kazbulat Shogenov, Alla Shogenova, Barbara Merson and Ceri Jayne Vincent
Sustainability 2025, 17(6), 2400; https://doi.org/10.3390/su17062400 - 9 Mar 2025
Viewed by 2957
Abstract
This article provides detailed geological and reservoir data on the existing underground gas storage (UGS) facilities in Ukraine and their prospects for hydrogen (H2) and carbon dioxide (CO2) storage. The H2 and CO2 storage issue is an [...] Read more.
This article provides detailed geological and reservoir data on the existing underground gas storage (UGS) facilities in Ukraine and their prospects for hydrogen (H2) and carbon dioxide (CO2) storage. The H2 and CO2 storage issue is an integral part of the decarbonisation of Ukraine and Europe as a whole. A detailed assessment of UGS in Ukraine was carried out in the framework of the EU Horizon 2020 project Hystories, which is about the possibility of the geological storage of H2. A database of the available geological data on reservoir and caprock properties was compiled and standardised (reservoir geometry, petrophysics, tectonics, and reservoir fluids). General environmental criteria were defined in terms of geology and surface context. The total estimated H2 energy storage capacity in 13 studied UGS facilities is about 89.8 TWh, with 459.6 and 228.2 Mt of H2 using the total (cushion and working gas) and working gas volumes, respectively. The estimated optimistic and conservative CO2 storage capacities in the 13 studied UGS facilities are about 37.6/18.8 Gt, respectively. The largest and deepest UGS facilities are favourable for H2 and CO2 storage, while shallower UGS facilities are suitable only for H2 storage. Studies could be conducted to determine if CO2 and H2 storage could be applied in synergy with CO2 being used as a cushion gas for H2 storage. The underground storage of H2 and CO2 plays key roles in reducing greenhouse gas emissions and supporting clean energy while enhancing energy security. Increasing the share of renewable energy and integrating sustainable development across various sectors of the economy is crucial for achieving climate goals. Full article
(This article belongs to the Special Issue Geological Insights for a Carbon-Free, Sustainable Environment)
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24 pages, 4606 KB  
Article
Finite Element Analysis of the Contact Pressure for Human–Seat Interaction with an Inserted Pneumatic Spring
by Xuan-Tien Tran, Van-Ha Nguyen and Duc-Toan Nguyen
Appl. Sci. 2025, 15(5), 2687; https://doi.org/10.3390/app15052687 - 3 Mar 2025
Cited by 1 | Viewed by 1540
Abstract
This study explores the integration of a custom-designed pneumatic spring into a car-seat cushion and its interaction with a simplified human body model using the Finite Element Method (FEM). A 3D half-symmetry FEM framework, developed from experimental data, ensured computational efficiency and convergence. [...] Read more.
This study explores the integration of a custom-designed pneumatic spring into a car-seat cushion and its interaction with a simplified human body model using the Finite Element Method (FEM). A 3D half-symmetry FEM framework, developed from experimental data, ensured computational efficiency and convergence. This research bridged experimental and numerical approaches by analyzing the contact pressure distributions between a seat cushion and a volunteer with representative biometric characteristics. The model incorporated two material groups: (1) human body components (bones and muscles) and (2) seat cushion materials (polyurethane foam, latex, and fabric tape). Mechanical properties were obtained from both the literature and experiments, and simulations were conducted using MSC.Marc software under realistic boundary and initial conditions. The simulation results exhibited strong agreement with experimental data, validating the model’s reliability in predicting contact pressure distribution and optimizing seat cushion designs. Contrary to the conventional notion that uniformly distributed contact pressure inherently enhances comfort, this study emphasizes that the precise localization of pressure plays a crucial role in static and long-term seating ergonomics. Both experimental and simulation results demonstrated that modulating the pneumatic spring’s internal pressure from 0 kPa to 25 kPa altered peak contact pressure by approximately 3.5 kPa (around 20%), significantly influencing pressure redistribution and mitigating high-pressure zones. By validating this FEM-based approach, this study reduces dependence on physical prototyping, lowering design costs, and accelerating the development of ergonomically optimized seating solutions. The findings contribute to a deeper understanding of human–seat interactions, offering a foundation for next-generation automotive seating innovations that enhance comfort, fatigue reduction, and adaptive pressure control. Full article
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26 pages, 7725 KB  
Review
Recent Advances in Flame-Retardant Flexible Polyurethane Foams
by Min Chen, Yao Yuan, Wei Wang and Lulu Xu
Fire 2025, 8(3), 90; https://doi.org/10.3390/fire8030090 - 23 Feb 2025
Cited by 5 | Viewed by 2541
Abstract
Flexible polyurethane foam (FPUF) is extensively applied in multiple applications, including automotive, construction, furniture cushioning, and transportation seating, due to its outstanding mechanical properties, sound absorption, breathable characteristics, and versatility. However, FPUF is highly flammable and releases significant quantities of smoke and harmful [...] Read more.
Flexible polyurethane foam (FPUF) is extensively applied in multiple applications, including automotive, construction, furniture cushioning, and transportation seating, due to its outstanding mechanical properties, sound absorption, breathable characteristics, and versatility. However, FPUF is highly flammable and releases significant quantities of smoke and harmful gases when burned, which presents considerable safety hazards and has led to extensive research into flame retardant solutions. This review covers the development of both conventional and bio-based flame-retardant agents, including reactive-type and additive-type FRs, and surface coating methods, with a focus on their preparation, characterization methods, and underlying flame retardant mechanisms. Additionally, innovative flame retardant technologies, particularly surface coatings, are discussed in terms of their impact on thermal stability, mechanical performance, and smoke toxicity reduction in the resulting FPUFs. The review also highlights future research priorities and significant challenges, including environmental concerns, cost-effectiveness, and durability. Future research will need to focus on improving flame retardant efficiency while also considering the environmental impact and recyclability of materials, aiming for the green and sustainable development of FPUFs. Full article
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19 pages, 8910 KB  
Article
Technical Advancements and Applications in Predictive Modeling of Polyurethane Foaming Height
by Chil-Chyuan Kuo, Yi-Qing Lu, Armaan Farooqui and Song-Hua Huang
Polymers 2025, 17(4), 452; https://doi.org/10.3390/polym17040452 - 8 Feb 2025
Cited by 1 | Viewed by 1250
Abstract
Various polyurethane foams (i.e., rigid, flexible, and spray polyurethane foams) offer diverse applications due to their unique properties, including thermal insulation, cushioning, and seamless gap filling. These foams provide solutions across industries such as construction, automotive, and refrigeration. However, the foaming process presents [...] Read more.
Various polyurethane foams (i.e., rigid, flexible, and spray polyurethane foams) offer diverse applications due to their unique properties, including thermal insulation, cushioning, and seamless gap filling. These foams provide solutions across industries such as construction, automotive, and refrigeration. However, the foaming process presents several challenges that may result in various defects in the final products. This work provides innovative predictive techniques for polyurethane foam expansion and applications in advanced manufacturing processes. The foaming height of the third polyurethane foaming agent (PU-3) closely aligned with the experimentally measured values. The relationship between foaming height and time is influenced by the type and concentration of catalysts, as well as the blowing agents used. However, simulations using Moldex 3D Version 2024 revealed a nonlinear relationship between foaming height and time, characterized by three distinct foaming rates. Zone B demonstrated the highest foaming rate, followed by Zone C, while Zone A showed the lowest rate. The foaming height and rate were significantly influenced by the foaming angle, with smaller angles enhancing both parameters. At a mold temperature of 30 °C and with an expansion coefficient of 35, the predicted foaming height of the polyurethane agent achieved an average accuracy of approximately 96% across four foaming angles. Based on these experimental findings, this study introduces three mechanisms involved in the foaming process of polyurethane foam components. Full article
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