Search Results (319)

This study proposes a continuous preparation strategy for poly (l-lactic acid) (PLLA) scaffolds with oriented hierarchical microporous structures for bone repair. A PLLA-oriented multi-stage microporous bone repair scaffold (hereafter referred to as the oriented multi-stage microporous scaffold) was designed using a novel extrusion foaming technology that integrates fused deposition modeling (FDM) 3D printing with supercritical carbon dioxide (SC-CO₂) microcellular foaming technology. The influence of the 3D-printed structure on the microcellular morphology of the oriented multi-stage microporous scaffold was investigated and optimized. The combination of FDM and SC-CO₂ foaming technology enables a continuous extrusion foaming process for preparing oriented multi-stage microporous scaffolds. The mechanical strength of the scaffold reached 15.27 MPa, meeting the requirements for bone repair in a low-load environment. Notably, the formation of open pores on the surface of the oriented multi-stage microporous scaffold positively affected cell proliferation, differentiation, and activity, as well as the expression of anti-inflammatory and pro-inflammatory factors. In vitro cell experiments (such as CCK-8) showed that the cell proliferation rate in the oriented multi-stage microporous scaffold reached 100–300% after many days of cultivation. This work provides a strategy for the design and manufacture of PLLA scaffolds with hierarchical microcellular structures and biocompatibility for bone repair. Full article

Biopolyols derived from solid fats of both vegetable origin (coconut oil (P/CO) and palm oil (P/PA)) and animal origin (pork fat (P/PO) and duck fat (P/DU)) were used to produce thermal insulation polyurethane foams. The biopolyols were characterized by hydroxyl numbers in the range of 341–396 mgKOH/g, a viscosity of 60–88 mPa·s, and a functionality of 2.3–3.4. Open-cell polyurethane foams were obtained by replacing from 50 to 100 wt.% of a petrochemical polyol with the biopolyols from solid fats. The most advantageous properties were found for the materials modified with the biopolyol based on pork fat, which was attributed to its high degree of cell openness. At a low apparent density, the foam materials were characterized by good dimensional stability. The use of solid fats offers new possibilities for modifying thermal insulation polyurethane foams. Full article

Negative-pressure wound therapy (NPWT) using vacuum-assisted closure (VAC) is a well known tissue defect bridging method that applies a vacuum pump to sterile, open-cell foam dressings via suction tubes. Although it has mostly been described for soft tissue use, there are also a few studies concerning its use on hard tissue. However, as oral and maxillofacial surgery has to deal with both soft and hard tissue, which lie next to each other in these regions, there is a particular need to assess the influence of negative pressure on bone. Therefore, the effects of different negative pressure levels (530 mbar and 725 mbar) and atmospheric pressure (1013 mbar) on bone tissue cultures and osteoblast cell cultures were investigated over periods of 1, 3, and 6 weeks. During the culture period, osteoblast growth and the tissue regeneration of bone defects were studied in vitro using tissue cultures that were histologically supplemented by cytological investigations and quantitative RNA expression studies. In the bone defect model, there was a faster defect reduction using NPWT; the effect was especially strong for 530 mbar. Compared to the control group, up to 30% more newly generated bone tissue was detected. This effect on the mineralization capacity was assessed by the mRNA expression of osteogenic marker genes, as well as the receptor activator of nuclear factor κB ligand (RANKL) and osteoprotegerin (OPG), two multifaceted cytokines that regulate bone metabolism. The influence of negative pressure consequently resulted in a decreased RANKL/OPG ratio in osteoblasts. Associated with the upregulation of marker genes to up to 400%, including Col1, BMP4, OCN, and RUNX2, the decrease in the RANKL/OPG ratio to 41% indicates the stimulation of osteogenesis. Since VAC has been shown to be a safe and effective method to close wounds in general, these data suggest that patients suffering from compound bone and soft tissue defects in the maxillofacial area may benefit from an adapted therapy approach accelerating both soft and hard tissue regeneration. Full article

Commercially pure aluminum (Al) was refined through the addition of the Al-5Ti-0.25C master alloy, resulting in the formation of Al₃Ti and TiC phases, which serve as refining agents. Open-cell metallic foams were successfully produced using the replication casting technique, with pore sizes ranging from 1.00 to 3.35 mm. For the infiltration process, refined aluminum was used, while unrefined aluminum served as a baseline reference. The resultant foams underwent multiple annealing cycles at 480 °C, with the most refined and homogeneous microstructure observed after 504 h. Comprehensive microstructural characterization was conducted utilizing scanning electron microscopy and optical microscopy. Additionally, uniaxial compression tests were performed to generate stress–strain profiles for the foams, facilitating an assessment of their energy absorption capacity. The findings indicated an enhancement in energy absorption capacity by a factor of 2.4 to 3, which can be attributed to the incorporation of Al-5Ti-0.25C and the subsequent annealing process. Full article

This study explored the innovative foaming behavior of a novel biodegradable polymer blend consisting of polylactic acid/poly(butylene succinate)/poly(butylene adipate-co-terephthalate) (PLA/PBS/PBAT) enhanced with nanohydroxyapatite (nHA), using supercritical carbon dioxide (SCCO₂) as an environmentally friendly physical foaming agent. The aim was to investigate the effects of various foaming strategies on the resulting cell structure, aiming for potential applications in tissue engineering. Eight foaming strategies were examined, starting with a basic saturation process at high temperature and pressure, followed by rapid decompression to ambient conditions, referred to as the (1T-1P) strategy. Intermediate temperature and pressure variations were introduced before the final decompression to evaluate the impact of operating parameters further. These strategies included intermediate-temperature cooling (2T-1P), intermediate-temperature cooling with rapid intermediate decompression (2T-2P), and intermediate-temperature cooling with gradual intermediate decompression (2T-2P, stepwise ΔP). SEM imaging revealed that the (2T-2P, stepwise ΔP) strategy produced a bimodal cell structure featuring small cells ranging from 105 to 164 μm and large cells between 476 and 889 μm. This study demonstrated that cell size was influenced by the regulation of intermediate pressure reduction and the change in intermediate temperature. The results were interpreted based on classical nucleation theory, the gas solubility principle, and the effect of polymer melt strength. Foaming results of average cell size, cell density, expansion ratio, porosity, and opening cell content are reported. The hydrophilicity of various foamed polymer blends was evaluated by measuring the water contact angle. Typical compressive stress–strain curves obtained using DMA showed a consistent trend reflecting the effect of foam stiffness. Full article

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

In the maritime industry, hydrogen fuel cell ships demonstrate significant potential for development due to their environmental friendliness and high efficiency. However, the risks of fire and explosion caused by hydrogen leakage pose severe challenges to their safety. To enhance the safety of hydrogen fuel cell ships and mitigate the explosion hazards caused by leakage, this study employs the XiFoam solver in the OpenFOAM v9 to establish an explosion model for a full-scale hydrogen fuel cell compartment within a hydrogen fuel cell ship. The model simulates the transient explosion process following high-pressure hydrogen leakage under varying initial hydrogen concentrations and premixed fuel conditions. By analyzing the temporary evolution of temperature distribution, flame front propagation, and explosion pressure, the study provides a comprehensive understanding of the safety implications of hydrogen leakage at different locations within the fuel cell. Specifically, increasing the hydrogen concentration from ΦH₂ = 0.10 to ΦH₂ = 0.18 and ΦH₂ = 0.20 significantly elevates the overpressure peak and accelerates the flame speed from 250 m/s to 370 m/s, with local pressure gradients approaching the deflagration to detonation transition threshold. The simulation results contribute valuable insights into optimizing hydrogen fuel cell design, formulating effective fire safety strategies, and improving overall ship safety. Full article

Modern tissue engineering requires not only degradable materials promoting cell growth and differentiation, but also vascularization of the engineered tissue. Porous polylactide/polycaprolactone (PLA/PCL, ratio 3/5) foam scaffolds were prepared by a combined porogen leaching and freeze-drying technique using NaCl (crystal size 250–500 µm) and a water-soluble cellulose derivative (Klucel^TM E; 10–100% w/w relative to the total PLA/PCL concentration) as porogens. Scanning electron microscopy, micro-CT, and Brunauer–Emmett–Teller analysis showed that all scaffolds contained a trimodal range of pore sizes, i.e., macropores (average diameter 298–539 μm), micropores (100 nm to 10 μm), and nanopores (mostly around 3.0 nm). All scaffolds had an open porosity of about 90%, and the pores were interconnected. The size of the macropores and the nanoporosity were higher in the scaffolds prepared with Klucel. Nanoporosity increased water uptake by the scaffolds, while macroporosity promoted cell ingrowth, which was most evident in scaffolds prepared with 25% Klucel. Human adipose-derived stem cells co-cultured with endothelial cells formed pre-vascular structures in the scaffolds, which was further enhanced in a dynamic cell culture system. The scaffolds are promising for the engineering of pre-vascularized soft tissues (relatively pliable 10% Klucel scaffolds) and hard tissues (mechanically stronger 25% and 50% Klucel scaffolds). Full article

Microporous metal materials have promising applications in the high-temperature industry for their high heat exchange efficiency. However, due to their complex internal structure, analyzing the heat transfer mechanisms presents a great challenge. This I confirm work introduces a mathematical model to accurately calculate the radiative thermal conductivity of microporous open-cell metal materials. The finite element and lattice Boltzmann methods were employed to calculate the thermal conduction and thermal radiation conductivities separately and validated for aluminum foams, with the relative errors all less than 9.3%. The results show that the thermal conductivity of microporous metal materials mainly increased with an increase in temperature and volume-specific surface area but decreased with an increase in porosity. Analysis of the spectral radiation characteristics shows that the surface plasmon polariton resonance and the magnetic polariton resonance appearing at the gas–solid interface of the metal foam significantly increase the dissipation effect of the gas–solid interface, further reducing the metal foam’s heat transfer efficiency. This indicates the potential of this work for use in the design of specific microporous metal materials like energy management devices or heat transfer exchangers in the aerospace industry. Full article

We aimed to evaluate the effects of unit cell design and the volume fraction of 3D-printed lattice structures with relative densities of 30% or 45% on compressive response and orthopedics screw pullout strength. All 3D lattice models were created using FLatt Pack software (version 3.31.0.0). The unit cell size of sheet-based triply periodic minimal surfaces (TPMSs)—Gyroid and Schwarz Diamond—was 5.08 mm, whereas that of skeletal TPMS—Skeletal Gyroid, Skeletal Schwarz Diamond, and Skeletal Schoen I-Wrapped Package—was scaled down to 3.175 and 2.54 mm. Two photopolymer resin types—Rigid 10k and Standard Grey—were used. In uniaxial compression tests, Rigid 10k resin lattices failed at relatively lower strains (<0.11), while Standard Grey lattices endured higher strains (>0.60) and experienced less softening effects, resulting in stress–strain curve plateauing followed by lattice densification. ANOVA revealed significant effects of design and volume fraction at p < 0.001 on compressive modulus, screw pullout strength, and screw withdrawal stiffness of the 3D-printed lattice. The pullout load from 3D-printed lattices (61.00–2839.42 N) was higher than that from open-cell polyurethane foam (<50 N) and lower than that of human bone of similar volume fraction (1134–2293 N). These findings demonstrate that 3D-printed lattices can be tailored to approximate different bone densities, enabling more realistic orthopedic and dental training models. Full article

Biomass carbon foams are extensively utilized across various fields due to their favorable properties and cost-effectiveness. In this study, triethylene glycol (TEG), nylon 66 (PA66), and 3-glycidyl-oxypropyl-trimethoxy-silane (KH560) were incorporated into pine wood liquefaction resin to successfully prepare three novel modified carbon foams (MCFs), and their characteristics were investigated. The results indicate that the compressive strength and specific surface area of the three MCFs were significantly enhanced. Specifically, the compressive strength increased by 37%, 46%, and 89% following modification with TEG, PA66, and KH560, respectively, while the specific surface areas ranged from 383.4 to 499.3 m²/g. Additionally, the cell structures of the three MCFs exhibited greater uniformity, with larger average pore sizes, thinner ligament thicknesses, and increased opening porosities. Notably, the opening porosity of KH560-modified carbon foam (KH560-PLP-PF-CF) reached its maximum value at 87.95%. XPS analysis confirmed the successful introduction of Si-containing molecular bonds, including Si-OH-Si, Si-OH, and Si-CH, into KH560-PLP-PF-CF. Furthermore, FT-IR analysis revealed characteristic Si-O vibration peaks, PA66 amide peaks, and TEG ether bond absorption peaks in the three MCFs. The incorporation of flexible functional groups effectively enhanced their compressive properties. The findings of this study expand the potential for utilizing biomass waste to partially replace phenol in the development of novel carbon foams. Full article

The shift toward sustainable energy sources is essential to curb greenhouse gas emissions and satisfy energy demands. Among renewable options, carbon-based materials—such as agricultural residues and municipal solid waste—provide a dual advantage by generating energy and fuels while also reducing landfill waste. A notable innovation is transforming plastic waste into methane-rich streams via catalytic hydrogasification, a process in which carbon-based feedstocks interact with hydrogen using a selective catalyst. In this study, a structured catalyst was developed, characterized, and tested for converting plastic waste samples. The thermal degradation properties of plastic waste were first studied using thermogravimetric analysis. The catalyst was prepared using an Oxygen Bonded Silicon Carbide (OBSiC) open-cell foam as the carrier, coated with γ-Al₂O₃-based washcoat, CeO₂, and Ni layers. It was characterized in terms of specific surface area, coating adhesion, pore distribution, acidity, and the strength of its active sites. Experimental tests revealed that a hydrogen-enriched atmosphere significantly enhances CH₄ formation. Specifically, during catalytic hydrogasification, methane selectivity reached approximately 59%, compared to 6.7%, 13.7%, and 7.8% observed during pyrolysis, catalyzed pyrolysis, and non-catalyzed hydrogasification tests, respectively. This study presents a novel and effective approach for converting plastic waste using a structured catalyst, a method rarely explored in literature. Full article

The volume of fluid (VoF) method is widely used in multiphase flow simulations to track and locate the interface between two immiscible fluids. The relative volume fraction in each cell is used to recover the interface properties (i.e., normal, location, and curvature). Accurate computation of the local interface curvature is essential for evaluation of the surface tension force at the interface. However, this interface reconstruction step is a major bottleneck of the VoF method due to its high computational cost and low accuracy on unstructured grids. Recent attempts to apply data-driven approaches to this problem have outperformed conventional methods in many test cases. However, these machine learning-based methods are restricted to computations on structured grids. In this work, we propose a machine learning-enhanced VoF method based on graph neural networks (GNNs) to accelerate interface reconstruction on general unstructured meshes. We first develop a methodology for generating a synthetic dataset based on paraboloid surfaces discretized on unstructured meshes to obtain a dataset akin to the configurations encountered in industrial settings. We then train an optimized GNN architecture on this dataset. Our approach is validated using analytical solutions and comparisons with conventional methods in the OpenFOAM framework on a canonical test. We present promising results for the efficiency of GNN-based approaches for interface reconstruction in multiphase flow simulations in the industrial context. Full article

The acoustic product development process, crucial for effective noise control, emphasises efficient testing and validation of materials for sound absorption in the R&D phase. Balancing cost-effectiveness, speed, and sustainability, the focus is on minimising excess materials. While strides have been made in reducing sample sizes for estimating random-incident absorption, challenges persist, particularly in establishing validity thresholds for smaller samples with increasing thickness, susceptible to potential overestimation due to edge effects. This study delves into analysing the absorption coefficients of widely used acoustic absorber types—polyester, fibreglass, and open-cell foam—in a full-scale reverberation chamber at Ventac, Blessington, and Wicklow. Demonstrating significant absorption above 500 Hz, these porous absorbers exhibit diminished effectiveness at lower frequencies. The strategic combination of these absorbers with different facings enhances their theoretical broadband absorption characteristics in practical applications. Moreover, the study assesses the validity threshold for reduced sample sizes, employing statistical analysis against ISO 354:2003 standard control samples of the absorber types. Analysis of Variance (ANOVA) on material groups underscores the significant influence of frequency components and sample sizes on the absorption coefficient. The determined validity threshold for 12.8 sqm ISO 354 standard control size is 7.7 sqm for the 25 mm open-cell foam. Similarly, the validity threshold of the 12 sqm ISO 354 standard control size is 9.6 sqm for the 20 mm 800 gsm polyester, 7.2 sqm for the 25 mm fibreglass, and the vinyl black on 25 mm fibreglass. Full article

This paper concerns research into the use of 3D-printed gyroid structures as a modern thermal insulation material in construction. The study focuses on the analysis of open-cell gyroid structures and their effectiveness in insulating external building envelopes. Gyroid composite samples produced using DLP 3D-printing technology were tested to determine key parameters such as thermal conductivity (λ), thermal resistance (R) and heat transfer coefficient (U) according to ISO 9869-1:2014. In addition, the authors carried out a comprehensive analysis of the annual energy balance of four different residential buildings, including older and modern structures, using Arcadia software v9.0. The results showed that 100 mm-thick multi-layer gyroid structures achieve exceptionally low thermal conductivity (approximately 0.023 W/(m·K)), significantly outperforming traditional materials such as mineral wool or polystyrene foam in terms of insulation efficiency. These structures also have high mechanical strength and low density, making them both lightweight and highly durable. As a result of these properties, the structures studied represent a promising solution for designing energy-efficient buildings, effectively reducing heating energy demand and improv the overall energy balance of buildings. Full article