Search Results (2,369)

Bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) play a pivotal role in promoting osteogenesis and angiogenesis that concurrently take place during bone regeneration. The rapid degradation and diffusion of these growth factors, combined with the potential side effects associated with their exogenous insertion, limit their applications. To overcome these shortcomings, we developed a controlled release system for BMP-2 and VEGF on microspheres comprising gelatin (Gel) and polyvinyl alcohol (PVA). We fabricated Gel–PVA microspheres using a constant Gel concentration of 10% w/v and a varied PVA concentration of 0, 5, and 10% w/v (Gel–PVA0%, Gel–PVA5%, and Gel–PVA10%, respectively). The microspheres were loaded with the model protein bovine serum albumin (BSA) first. The Gel–PVA10% microspheres demonstrated significantly higher loading capacity and encapsulation efficiency, as well as lower cumulative release rate, compared to the Gel–PVA5% ones when loaded with BSA. Thus, the microspheres with the Gel–PVA10% composition were selected for loading with BMP-2 and VEGF. Kinetic studies of BMP-2 and VEGF loaded into Gel–PVA10% microspheres indicated similar results to those with BSA. The microsphere concentration with the optimal cytocompatibility was 0.5 mg/mL, and it was applied for the assessment of the osteogenic differentiation using bone marrow-derived mesenchymal stem cells (MSCs), and for the angiogenic differentiation in Wharton jelly and adipose-derived MSCs. Alkaline phosphatase activity, collagen secretion, and calcium mineralization were significantly upregulated in the presence of BMP-2-loaded microspheres, while tubular formation and PECAM-1 secretion were significantly higher in VEGF-loaded microspheres compared to the unloaded control, demonstrating their effectiveness as drug delivery carriers. Full article

Background/Objectives: The medial meniscus is crucial for load transmission and knee stability. Meniscal tears disrupt joint biomechanics, increasing the risk of cartilage degeneration. However, few studies have quantitatively compared how different tear types affect stress and contact mechanics using finite element analysis (FEA). This study aims to analyze stress distributions for various meniscal tear types and develop a predictive model for meniscal stress behavior. This study investigates how stress distributions differ between healthy and torn medial menisci under identical loading conditions. The study examines which meniscal tear type produces the highest stress concentrations. The effects of different tear types on penetration, gap formation, pressure distribution, and sliding distance at the meniscus interface are also analysed. Materials and Methods: The FEA model of the knee joint, including femoral and tibial cartilage and the medial meniscus, was developed. Simulations were conducted for a healthy meniscus and for menisci with radial, horizontal and complex tears. Stress, penetration, gap, pressure, and sliding distance were calculated, and a mathematical model describing their relationships was established. Results: All torn menisci exhibited significantly higher stresses than the healthy meniscus (p < 0.001). Radial tears generated the highest stress concentrations (p < 0.001). Pressure was mainly influenced by meniscal geometry, while the gap remained nearly constant. Penetration increased slightly (p < 0.05). The predictive model demonstrated a strong correlation between meniscal stress and interface parameters (R² > 0.9). In a healthy meniscus, stress distribution is homogeneous (≈26 MPa). Stress concentration increases depending on the tear type: limited in a horizontal tear (≈26.5 MPa), significant in a vertical tear (≈30.8 MPa), and highest in a radial tear (≈40.6 MPa). These results indicate that as the tear progresses, the load-bearing capacity of the meniscus decreases, and stresses concentrate at the tear edges. Conclusions: Meniscal tears, especially radial ones, substantially alter knee biomechanics and elevate tissue stress. These biomechanical insights highlight the importance of early diagnosis and targeted rehabilitation strategies to prevent further cartilage damage and osteoarthritis progression. Full article

The high-temperature corrosion behavior of A1, T22, and T91 steels was investigated in molten nitrate salts at 400, 500, and 600 °C during 100 h of exposure. The combined influence of temperature and chromium content on corrosion kinetics and oxide-scale stability was evaluated using open-circuit potential (OCP), linear polarization resistance (Rp), electrochemical impedance spectroscopy (EIS), scanning electron microscopy, X-ray diffraction, and cross-sectional elemental mapping. OCP measurements showed a progressive shift toward more negative potential with increasing temperature, indicating enhanced oxidation tendency. Electrochemical measurements revealed a systematic decrease in Rp and impedance magnitude as temperature increased, confirming accelerated corrosion kinetics and reduced interfacial resistance. EIS spectra exhibited two characteristic time constants associated with the outer corrosion products and the inner metal/oxide interface. Significant differences in scale growth were observed depending on alloy composition. At 600 °C, oxide thickness reached approximately 700–800 μm for A1, ~100 μm for T22, and ~10 μm for T91. Chromium-containing steels promoted the formation of a compact Cr-rich inner oxide layer that improved scale adhesion and suppressed the exfoliation phenomena observed in A1 steel. Overall, temperature controls corrosion kinetics, whereas chromium content governs oxide-scale compactness and long-term stability in molten nitrate environments. Full article

CoFe₂O₄ nanoparticles were prepared using a hydrothermal method. All the studied samples were single-phase and were crystallized in a cubic Fd-3m structure. XRD and TEM analyses revealed that the particles had average sizes between 5 and 22 nm. It has been shown that, by using the PVP of different molecular masses, trends of growth and crystallization can be established, obtaining elongated 40 k, cubical 58 k, and rhomboidal 360 kg/mol nanoparticles. While using Ethylene glycol as solvent, the formation of separated “raspberry”-like nanostructures was revealed. The saturation magnetizations are somewhat smaller compared with crystalline CoFe₂O₄ saturation magnetization, but are high enough to have possible biomedical applications. FC and ZFC measurements show that the blocking temperature was around 100 K for the CF5 sample and around 20 K for the FC6 sample. The calculated anisotropy constants were between 7 and 10 kJ/m³, being close to previously reported values. The calculated blocking temperatures are in good agreement with experimental ones. The M_r/Ms ratio at room temperature was lower than 0.5, confirming the predominance of magnetostatic interactions. This paper serves as a good starting point for researchers seeking to synthesize a CoFe₂O₄ system with a desired size and growth tendency at the nanometer scale. Full article

This study presents a comparative analysis of batch and continuous lubricant supply strategies in internal combustion engines (ICEs), focusing on precursor consumption and material efficiency. A phenomenological model based on mass balance equations was developed to describe the dynamics of lubricant precursor depletion, film formation, and film removal under both supply strategies. The results demonstrate that the continuous supply strategy achieves a steady-state condition that ensures stable film thickness and a significant reduction in precursor consumption compared with the batch strategy. Sensitivity analyses reveal that both the kinetic constant and the film removal rate strongly influence lubricant make-up requirements, defining a feasibility region for system operation. Under supercritical conditions, the batch strategy exhibits rapid precursor overconsumption; in contrast, the continuous strategy maintains minimal excess. The proposed framework provides a system-level tool for evaluating lubrication strategies based on precursor utilization efficiency. The findings suggest that continuous lubrication strategies can improve material efficiency and environmental performance, with associated economic benefits, when properly designed and operated within feasible kinetic and mechanical limits. Full article

Developing efficient and durable electrocatalysts for the alkaline hydrogen evolution reaction (HER) remains challenging due to intrinsically sluggish reaction kinetics and the limited long-term stability of many non-noble metal catalysts under continuous operation. Herein, a nickel-doped polypyrrole/chitosan composite electrode on stainless steel (PPy/Chi/Ni) was fabricated via electrodeposition as a low-cost and scalable method. Benefiting from the combined effects of Ni incorporation and the conductive polymer–biopolymer composite framework, the optimized PPy/Chi/Ni electrode exhibits enhanced HER activity in alkaline environment, delivering a low overpotential of η₁₀ = 78 mV at a current density of 10 mA·cm⁻² and a reduced Tafel slope of 93 mV·dec⁻¹, indicative of accelerated reaction kinetics. Structural and morphological characterizations by XRD, FTIR, and FESEM indicate the formation of the composite structure. FESEM images suggest that the deposited layer forms a relatively uniform coating on the stainless steel substrate. EIS further reveals improved interfacial charge-transfer characteristics upon Ni doping. Additionally, long-term stability tests confirm the structural integrity of the composite electrode and its electrochemical stability under HER conditions by demonstrating stable HER performance for 15 h with only a 22 mV potential change at a constant current density. By providing a conductive interface and numerous catalytic sites, the Ni-doped electrocatalyst coating activates the stainless steel substrate, leading to a 79% reduction in overpotential compared to bare stainless steel and thereby significantly improving its HER performance. Full article

Levoglucosan (LG), a tracer of biomass-burning air pollution, was measured in PM₁₀ particulate matter during a year-long study at an urban background site in Zagreb, Croatia. It is known that the atmospheric lifetime of LG is not constant and undergoes degradation through reactions with hydroxyl radicals, ozone, photooxidation, etc. In this study, daily variations in LG were examined and evaluated in relation to NO₂, O₃, and meteorological conditions, including temperature, relative humidity, solar irradiance, UV index, and wind characteristics. The annual mean PM₁₀ concentration was 22 µg m⁻³, while LG average was 0.312 µg m⁻³, both exhibiting pronounced seasonal variability. Elevated LG levels occurred during winter and autumn, consistent with residential wood combustion and stable atmospheric conditions, whereas markedly lower concentrations were observed in spring and summer. Moderate correlations of LG with PM₁₀ and NO₂ indicate contributions from combustion sources, while weak wind speeds and limited dispersion favored pollutant accumulation. In contrast, significant negative relationships were found between LG and ozone, temperature, and UV index. The results revealed non-linear behavior and an exponential decrease in LG with increasing oxidant levels, suggesting pseudo–first-order degradation driven by enhanced photochemical activity and hydroxyl radical formation. These findings highlight the importance of considering both emission patterns and atmospheric processing when using levoglucosan as a tracer of biomass burning in urban environments. Full article

Charge-trapping memory (CTM) exhibits significant potential in high-density memory, yet reliability degradation resulting from the coupling of program/erase (P/E) cycles and electrical stress remains a key bottleneck for large-scale commercialization. This study focuses on a Au/Al₂O₃/TiO₂/p-Si CTM device, systematically investigating the device failure mechanism under continuously operating P/E cycles and constant voltage stress (CVS), with emphasis on elucidating the synergistic effect of bulk and interface defects on performance decay. Mechanistically, oxygen vacancies in TiO₂ serve as defect precursors, which form Frenkel pairs under electric field stress and further promote the formation of new defect precursors, thereby driving a self-sustaining defect evolution process. Interface traps, by contrast, arise from the cleavage of interfacial Si-H bonds triggered by electric field stress, resulting in a net elevation of the interface state density. The passive effects from the bulk and interface defects may give rise to issues, such as threshold voltage drift and decreased P/E speed. This work provides in-depth insights into the device failure mechanism of CTM, offering critical theoretical support for optimizing fabrication processes and enhancing long-term reliability. Full article

Given the therapeutic potential of bioactive cordycepin in medical and healthcare products, precision fermentation using an engineered strain of Aspergillus oryzae was performed to enhance cordycepin production. To understand and predict the dynamics of cell growth and cordycepin production in this fungal strain, mathematical modeling of submerged fermentation was applied. The effects of different nitrogen sources (yeast extract, peptone, (NH₄)₂SO₄, NH₄Cl, NaNO₃, and KNO₃) and carbon sources (glucose and cassava starch hydrolysate, CSH) on cell growth and cordycepin production were evaluated under submerged fermentation conditions. The results showed that organic nitrogen sources significantly enhanced biomass formation and cordycepin production compared with inorganic nitrogen sources. Among them, yeast extract provided the best performance, yielding the highest biomass (13.63–15.99 g/L) and cordycepin titer (1.24–1.72 g/L). In contrast, nitrate-based nitrogen sources supported cell growth but resulted in negligible cordycepin production. Under optimized conditions in a bioreactor, both glucose and CSH supported fungal growth, although CSH promoted higher biomass formation while glucose favored cordycepin biosynthesis. The kinetic model demonstrated that the growth of engineered A. oryzae was well described by the logistic growth model (R² > 0.88). The cordycepin production profiles were well fitted by the Luedeking–Piret model (R² > 0.99), indicating a mixed growth-associated product with kinetic constants α and β representing growth-associated and non-growth-associated production, respectively. Overall, the developed kinetic model provides a quantitative framework for describing cell growth, substrate utilization, and cordycepin formation, offering guidance for process optimization and scale-up of cordycepin production in engineered fungal systems. Full article

The growing demand for gold in various high-technology applications necessitates the development of efficient and selective methods for its recovery and analysis, which can be achieved using such macrocyclic ligands as crown esters and their aza-substituted derivatives. The present paper reports on the equilibrium constants for the formation of gold(III) complexes with 18-crown-6, 1-aza-18-crown-6, 1,10-diaza-18-crown-6, and the cryptand 4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]hexacosane (Kryptofix 222) in aqueous solution at T = 298.2 K, p = 0.1 MPa, I → 0. The equilibrium constants (log β) for the substitution of chloride ions by macrocycles were determined to be 4.52 ± 0.04, 9.15 ± 0.03, 9.08 ± 0.07, and 11.51 ± 0.08, respectively. Equilibrium constants for protonated and polyligand species are also provided. The complexation mechanism was elucidated using a combination of spectroscopic techniques. UV-Vis and IR spectroscopy confirm the substitution of chloride ligands by the nitrogen donor atoms of the aza-macrocycles within the tetrachloroaurate(III) ion. Furthermore, ¹H NMR analysis reveals that the diaza-substituted ligands can form both inclusion complexes, where the gold cation is encapsulated within the macrocyclic cavity, and exclusion complexes. These findings provide a quantitative foundation for the design of novel macrocycle-based extractants and sensors for gold(III). Full article

This study evaluates the effectiveness of microfine cement (MF) to seal two laboratory-fabricated wellbore microannuli. The samples were characterized with their hydraulic apertures (158 and 85 µm). A rough cement surface paired with a transparent acrylic plate, acting as a steel surrogate, formed the basis of the experimental setup, with the acrylic enabling direct visual monitoring of MF behavior throughout the tests. Hydraulic aperture measurements were taken before and after each repair attempt, with MF injected at constant pressure and a 24 h curing period allowed between successive injections. Four injection cycles were completed per sample. The MF cement had a d₉₅ = ~14 µm and a w/c of 1.45. Results show progressive reduction in hydraulic aperture from 158 µm to 20 µm and from 85 µm to 8 µm, but complete sealing was not achieved. Visual observations revealed that bleeding and filtration (plug formation) were the primary mechanisms limiting repair efficiency. These findings highlight the challenges of sealing rough microannuli with MF and suggest that aperture variability and particle filtration strongly influence repair outcomes. Higher injection pressures or alternative materials may be required for complete sealing. Full article

Titanium dioxide (TiO₂) is a versatile material that exhibits a high refractive index, strong light-scattering capability, effective UV-absorption, wide band gap semiconductor behavior (3.0–3.2 eV), and excellent chemical stability. Owing to this unique combination of properties, TiO₂ is widely used in applications such as cosmetic and healthcare products, architectural and automotive coatings, and photocatalytic degradation of environmental pollutants. In photocatalytic applications, the crystal structure, phase composition and electronic properties of TiO₂ play a critical role in determining its performance. In the present study, TiO₂ nanotubes were synthesized by anodization of Ti° coatings deposited via a semi-industrial arc-PVD process. A post-anodization heat treatment was carried out at 430 °C for 1 h to promote the formation of the anatase phase within the TiO₂ nanotube structures. The structural characterization of the synthesized film was performed using X-ray diffraction (XRD) and Rietveld refinement. This methodology enabled the identification of the formed oxide phases, structure, and crystalline, confirming the formation of mixed oxides in the coating. To address the difficulty of refinement of these crystalline phases, the Le Bail method was applied. This refinement strategy allowed the identification of the crystalline phases that are present in the Ti_xO_y coating, including a hexagonal structure characteristic of α-Ti (space group P63/mmc, No. 194), the tetragonal anatase TiO₂ (space group I41/amd, No. 141) phase, and the trigonal Ti₂O₃ phase (space group R-3/c No. 167). Key crystallographic parameters such as lattice constants, bond lengths and angles, crystallite sizes, unit cell distortion and electron density were systematically evaluated for each phase. In addition, the Wyckoff positions and interatomic distances of the constitutive atoms were calculated, providing a comprehensive description of the TiO₂+Ti₂O₃/Ti° crystallographic system. The topographic and surface oxidation states were recorded by using profilometry and X-ray photoelectron spectroscopy, respectively. Full article

Boron coatings were deposited by RF magnetron sputtering in an Ar atmosphere at a constant power of 80 W, varying the working pressure in the 0.6–5 Pa range. Plasma diagnostics were performed by means of a Langmuir probe to determine the electron temperature and electron density under different operating conditions. Within the investigated pressure range, the deposition rate remained nearly constant, whereas a significant decrease in coating mass density was observed with increasing pressure. The coatings display a columnar structure at all investigated pressures, with no significant differences in bulk morphology. Pressure primarily affects the surface features, leading to an increase in the density, lateral dimensions, and height of surface agglomerates with increasing pressure. Compositional analysis by EDX revealed a substantial oxygen incorporation in the films, with the lowest oxygen content (~11 at.%) measured for the coating deposited at 0.6 Pa. XPS depth profiling confirmed the presence of oxygen and evidenced the formation of boron oxide species, while the boron concentration exceeded 80 at.% in all samples. These results highlight the strong sensitivity of boron film density and oxygen uptake to sputtering pressure. Full article

This study clarifies the catalytic role of chloride ions on the corrosion performance of SS316L alloy immersed in molten LiNaK carbonate salt at 700 °C. Accordingly, isothermal static immersion corrosion tests were systematically conducted under different experimental conditions. Our results revealed that the presence of Cl significantly accelerates the corrosion process: the rate constant of the corroded samples increased from 11.3 × 10⁻² mg/cm² to 13.8 × 10⁻² mg/cm² with the addition of Cl. Continuous migration of Cl₂ and volatile metal chlorides leads to the formation of obvious pores, transverse cracks along grain boundaries, surface wrinkles, and partial spalling of the oxide scale, thereby severely aggravating substrate degradation. Notably, no chlorine-containing compounds or chlorine-rich regions were detected in the corroded samples, confirming that chlorine is not consumed in the corrosion process, rather it acts as an autocatalyst through the cyclic process of “oxidation–diffusion–reaction–regeneration”. Full article

The current study explored the martensite structures of Fe₃Pt alloys, specifically $Cmmm$-Fe₃Pt, $P{6}_3/mmc$-Fe₃Pt, $P4/mmm$-Fe₃Pt, and $R\overline{3}m$-Fe₃Pt, aiming to provide a comprehensive understanding of the mechanisms that govern their physical and chemical properties. We have focused on their structural, thermodynamical, magnetic, electronic, mechanical, and dynamical characteristics, utilizing the density functional theory (DFT) technique. Our study revealed that in addition to the previously reported austenitic cubic $Pm\overline{3}m$-Fe₃Pt and martensite tetragonal $I4/mmm$-Fe₃Pt with L1₂ structure, there exist additional Fe₃Pt phases that exhibit excellent structural, thermodynamic, magnetic, and mechanical properties. The calculated enthalpies of formation were found to be negative and less than −0.39 eV in all the structures considered, indicating thermodynamic stability and formation under experimental synthetic conditions. Moreover, the computed magnetic moments are in the range 2.94 to 3.04 ${\mathsf{\mu }}_{\mathrm{B}}$, which is relatively comparable to 3.24 ${\mathsf{\mu }}_{\mathrm{B}}$ of the widely reported $Pm\overline{3}m$-Fe₃Pt alloy. The analysis of the electronic structure also revealed strong magnetism due to the presence of asymmetry in the spin-up and -down states of the density of states (DOS) plots. To determine the mechanical response of Fe₃Pt structures under loading conditions, we computed the independent elastic constants, macroscopic properties, and stress–strain relationship under hydrostatic stress. All four phases were studied, but the hypothetical $P{6}_3/mmc$-Fe₃Pt showed excellent mechanical stability at ambient conditions and exceptional hardness and resistance to compression in the elastic region 0% ≤ strain ≤ 10%. This evidence is provided by satisfying the Born necessary stability conditions, large bulk modulus, and a strong linear relationship fit ($R^2$) of greater than 0.94. Moreover, the phonon dispersion curves revealed dynamical stability for $Cmmm$-Fe₃Pt and $R\overline{3}m$-Fe₃Pt, and metastability for $P4/mmm$-Fe₃Pt, while the hypothetical $P{6}_3/mmc$-Fe₃Pt is unstable. Full article