Search Results (920)

Lightweight materials that combine high mechanical strength, insulation, and fire resistance are of great interest to many industries. This work explores the properties of environmentally friendly alginate aerogel composites as potential sustainable alternatives to petroleum-based materials. This study analyzes the effects of two additives (tannic acid and montmorillonite clay), the orientation that results during casting, and the crosslinking of the biopolymer with glutaraldehyde on the properties of the aerogel composites. The prepared aerogels exhibited high porosities between 90% and 97% and densities in the range of 0.059–0.191 g/cm³. Crosslinking increased the density and resulted in excellent performance under loading conditions. In combination with axial orientation, Young’s modulus and yield strength reached values as high as 305 MPa·cm³/g and 7 MPa·cm³/g, respectively. Moreover, the alginate-based aerogels exhibited very low thermal conductivities, ranging from 0.038 W/m·K to 0.053 W/m·K. Compared to pristine alginate, the aerogel composites’ thermal degradation rate decreased substantially, enhancing thermal stability. Although glutaraldehyde promoted combustion, the non-crosslinked aerogel composites demonstrated high fire resistance. No flame was observed in these samples under cone calorimeter radiation, and a minuscule peak of heat release of 21 kW/m² was emitted as a result of their highly efficient graphitization and fire suppression. The combination of properties of these bio-based aerogels demonstrates their potential as substituents for their fossil-based counterparts. Full article

Four-dimensional-printed smart materials have a wide range of applications in areas such as biomedicine, aerospace, and soft robotics. Among 3D printing technologies, fused deposition molding (FDM) is economical, simple, and apply to thermoplastics. Cross-linked polyethylene (XLPE) forms a stable chemical cross-linking structure and shows good shape-memory properties, but the sample is not soluble or fusible, which makes it hard to be applied in FDM printing. Therefore, in this work, a new idea of printing followed by irradiation was developed to prepare 4D-printed XLPE. First, low-density polyethylene (LDPE) was used to print the products using FDM technology and then cross-linked by gamma irradiation was used. The printing parameters were optimized, and the gel content, mechanical properties, and shape-memory behaviors were characterized. After gamma irradiation, the samples showed no new peak in FTIR spectra. And the samples exhibited good shape-memory capabilities. Increasing the irradiation dose increased the cross-linking degree and tensile strength and improved the shape-memory properties. However, it also decreased the elongation at break, and it did not affect the crystallization or melting behaviors of LDPE. With 120 kGy of irradiation, the shape recovery and fixity ratios (R_r and R_f) of the samples were 97.69% and 98.65%, respectively. After eight cycles, R_r and R_f remained at 96.30% and 97.76%, respectively, indicating excellent shape-memory performance. Full article

To improve the stability of high-temperature water electrolysis, I prepared membrane electrode assemblies (MEAs) using a decal method and investigated their water electrolysis properties. Nafion 115 and crosslinked sulfonated polyphenylsulfone (CSPPSU) membranes were used. IrO₂ was used as the oxygen evolution reaction (OER) catalyst, and Pt/C was used as the hydrogen evolution reaction (HER) catalyst. The conductivity of the CSPPSU membrane at 80 °C and 90% RH (relative humidity) is about four times lower than that of the Nafion 115 membrane. Single-cell water electrolysis was performed while measuring the current density and performing electrochemical impedance spectroscopy (EIS) at cell temperatures from 80 to 150 °C and the stability of the current density over time at 120 °C and 1.7 V. The current density of water electrolysis using Nafion 115 and CSPPSU membranes at 150 °C and 2 V was 1.2 A/cm² for both. The current density of the water electrolysis using the CSPPSU membrane at 120 °C and 1.7 V was stable for 40 h. The decal method improved the contact between the CSPPSU membrane and the catalyst electrode, and a stable current density was obtained. Full article

Skin wounds often form scar tissue during healing. Early intervention with tissue-engineered materials and cell therapies may promote scar-free healing. Exosomes and extracellular vesicles (EV) secreted by mesenchymal stromal cells (MSC) are believed to have high regenerative capacity. EV bioactivity is preserved after lyophilization and storage to enable use in remote and typically resource-constrained environments. We developed a bioprinted bandage containing reconstituted EVs that can be fabricated at the point-of-need. An alginate/carboxymethyl cellulose (CMC) biomaterial ink was prepared, and printability and mechanical properties were assessed with rheology and compression testing. Three-dimensional printed constructs were evaluated for Young’s modulus relative to infill density and crosslinking to yield material with stiffness suitable for use as a wound dressing. We purified EVs from human MSC-conditioned media and characterized them with nanoparticle tracking analysis and mass spectroscopy, which gave a peak size of 118 nm and identification of known EV proteins. Fluorescently labeled EVs were mixed to form bio-ink and bioprinted to characterize EV release. EV bandages were bioprinted on both a commercial laboratory bioprinter and a custom ruggedized 3D printer with bioprinting capabilities, and lyophilized EVs, biomaterial ink, and thermoplastic filament were deployed to an austere Arctic environment and bioprinted. This work demonstrates that EVs can be bioprinted with an alginate/CMC hydrogel and released over time when in contact with a skin-like substitute. The technology is suitable for operational medical applications, notably in resource-limited locations, including large-scale natural disasters, humanitarian crises, and combat zones. Full article

The inadequate disposal of tires poses a significant threat to human health and requires effective recycling solutions. The crosslinked structure of rubber, formed through sulfur bridges during vulcanization, presents a major challenge for recycling because it prevents the rubber scraps from being reshaped thermoplastically. Reclaiming or devulcanization aims to reverse this crosslinking, allowing waste rubber to be transformed into products that can be reprocessed and revulcanized, thereby saving costs and preserving resources. Microwave technology shows promise for devulcanization due to its ability to break sulfur crosslinks. In this study, we investigate the devulcanization of ground tire rubber (GTR) through a combined process applied to samples from both car and truck tires subjected to varying periods of microwave irradiation (0, 3, 5 and 10 min). The devulcanized GTR was then blended with natural rubber (NR) and underwent a new vulcanization process, simulating recycling for novel applications. The GTR was mixed with NR in proportions of 0, 10, 30 and 50 parts per hundred rubber (phr). This study also examines the differences between the GTR from car tires and GTR from truck tires. The results showed that the treatment effectively breaks the crosslinks in the GTR, creating double bonds (C=C) and improving the mechanical properties of the revulcanized samples. The crosslinking density and related properties of the samples increased with treatment time, reaching a maximum at 5 min of microwave treatment, followed by a decrease at 10 min. Additionally, the incorporation of GTR enhanced the thermal stability of the resulting materials. Full article

A new series of flexible polyamide (PA) aerogels was synthesized using terephthaloyl chloride (TPC), 2,2′-dimethylbenzidine (DMBZ) and cross-linked with an inexpensive, commercially available tri-isocyanate (Desmodur N3300A) at polymer concentrations of 6–8 wt.% total solids and repeating units, n, from 30 to 60. The cross-linked DMBZ-based polyamide aerogels obtained, after supercritically drying using liquid CO₂, had shrinkages of 19–27% with densities ranging from 0.12 g/cm³ to 0.22 g/cm³, porosity and surface areas up to 91% and 309 m²/g, respectively, and modulus values ranging from 20.6 to 109 MPa. Evidence suggests that a higher flexibility could be achieved using DMBZ in the polyamide backbone with N3300A as a cross-linker, when compared to previously reported TPC-mPDA-BTC PA aerogels, N3300A-polyimide aerogels, and N3300-reinforced silica aerogels. Full article

Herein, we simultaneously prepared borax-crosslinked starch-based hydrogels with enhanced mechanical properties and self-healing ability via a simple one-pot method. The focus of this work is to study the effects of the amylose/amylopectin ratio of starch on the grafting reactions and the performance of the resulting borax-crosslinked hydrogels. An increase in the amylose/ amylopectin ratio increased the gel fraction and grafting ratio but decreased the swelling ratio and pore diameter. Compared with hydrogels prepared from low-amylose starches, hydrogels prepared from high-amylose starches showed pronouncedly increased network strength, and the maximum storage modulus increased by 8.54 times because unbranched amylose offered more hydroxyl groups to form dynamic borate ester bonds with borate ions and intermolecular hydrogen bonds, leading to an enhanced crosslink density. In addition, all the hydrogels exhibited a uniformly interconnected network structure. Furthermore, owing to the dynamic borate ester bonds and hydrogen bonds, the hydrogel exhibited excellent recovery behavior under continuous step strain, and it also showed thermal responsiveness. Full article

Due to the increasing prevalence of articular cartilage diseases and limitations faced by current therapeutic methodologies, there is an unmet need for new materials to replace damaged cartilage. In this work, poly(vinyl alcohol) (PVA) hydrogels were reinforced with different amounts of Nomex^® (known for its high mechanical toughness, flexibility, and resilience) and sterilized by gamma irradiation. Samples were studied concerning morphology, chemical structure, thermal behavior, water content, wettability, mechanical properties, and rheological and tribological behavior. Overall, it was found that the incorporation of aramid nanostructures improved the hydrogel’s mechanical performance, likely due to the reinforcement’s intrinsic strength and hydrogen bonding to PVA chains. Additionally, the sterilization of the materials also led to superior mechanical properties, possibly related to the increased crosslinking density through the hydrogen bonding caused by the irradiation. The water content, wettability, and tribological performance of PVA hydrogels were not compromised by either the reinforcement or the sterilization process. The best-performing composite, containing 1.5% wt. of Nomex^®, did not induce cytotoxicity in human chondrocytes. Plugs of this hydrogel were inserted in porcine femoral heads and tested in an anatomical hip simulator. No significant changes were observed in the hydrogel or cartilage, demonstrating the material’s potential to be used in cartilage replacement. Full article

Until recently, recycling thermoset polyurethanes (PUs) was limited to degrading methods. The development of covalent adaptable networks (CANs), to which PUs can be assigned, has opened novel possibilities for actual recycling. Most efforts in this area have been directed toward inventing new materials that can benefit from CAN theory; presently, little or nothing has been applied to industrially producible materials. In this study, both an industrially available polyol (Sovermol780^®) and isocyanate (Tolonate X FLO 100^®) with percentages of bioderived components were employed, resulting in a potentially scalable and industrially producible material. The resultant network could be reworked up to three times, maintaining the crosslinked structure without significantly changing the thermal properties. Improvements in mechanical parameters were observed when comparing the pristine material to the material exposed to three rework processes, with gains of roughly 50% in elongation at break and 20% in tensile strength despite a 25% decrease in Young’s modulus and crosslink density. Thus, it was demonstrated that theory may be profitably applied even to materials that are not designed including additional bonds but instead rely just on the dynamic urethane bond that is naturally present in the network. Full article

In vitro cell activation through specific IgE bound to high-affinity receptors on the basophil surface is a widely used strategy for the evaluation of IgE-mediated immediate hypersensitivity reactions to betalactams. Cellular activation requires drug conjugation to a protein to form a large enough structure displaying a certain distance between haptens to allow the cross-linking of two IgE antibodies bound to the basophil’s surface, triggering their degranulation. However, no information about the size and composition of these conjugates is available. Routine in vitro diagnosis using the basophil activation test uses free amoxicillin, which is assumed to conjugate to a carrier present in blood. To standardize the methodology, we propose the use of well-controlled and defined nanomaterials functionalized with amoxicilloyl. Silica nanoparticles decorated with PAMAM–dendrimer–amoxicilloyl conjugates (NpDeAXO) of different sizes and amoxicilloyl densities (50–300 µmol amoxicilloyl/gram nanoparticle) have been prepared and chemically characterized. Two methods of synthesis were performed to ensure reproducibility and stability. Their functional effect on basophils was measured using an in-house basophil activation test (BAT) that determines CD63⁺ or CD203c^high activation markers. It was observed that NpDeAXO nanocomposites are not only able to specifically activate basophils but also do so in a more effective way than free amoxicillin, pointing to a translational potential diagnosis. Full article

The effects of aging on the healing capacity of maxillofacial bone defects have not been studied. The aim of this study was to evaluate the effects of aging on the regeneration of round bony defects in the mandible. We created a round-shaped bony defect in the mandibular angle area in rats of different ages (2-[2 M], 10-[10 M], and 20-month-old [20 M]) and evaluated new bone regeneration in these groups. Changes in bone turnover markers such as alkaline phosphatase, procollagen type I N-terminal propeptide (PINP), cross-linked C-telopeptide of type I collagen, and tartrate-resistant acid phosphatase 5B (TRAP5b) were investigated. The bone volume/total volume and bone mineral density of the 20 M group were significantly higher than those of the 2 M group (p = 0.029, 0.019). A low level of the bone formation marker PINP was observed in the 20 M group, and a high level of the bone resorption marker TRAP5b was observed in the 10 M and 20 M groups. Micro-computed tomography (µ-CT) results showed that older rats had significantly higher bone formation than younger rats, with lower serum levels of PINP and higher levels of TRAP5b. The local environment of the old rat bone defects, surrounded by thickened bone, may have affected the results of our study. In conclusion, old rats showed greater new bone regeneration and healing capacity for round mandibular bone defects. This result was related to the fact that the bone defects in the 20 M rat group provided more favorable conditions for new bone regeneration. Full article

Cross-linked polymers synthesized through inverse vulcanization of unsaturated vegetable oils (biopolymers) were used as matrices for incorporating gentamicin (GEN) to form a biocomposite that can amplify GEN antimicrobial activity against Pseudomonas aeruginosa. Two different biopolymers were synthesized using soybean (PSB) and sunflower (PSF) oils by inverse vulcanization cross-linked with sulfur in a 1:1 weight ratio. The study involves the synthesis and characterization of these biopolymers using FTIR and SEM as well as measurements of density and hydrophobicity. The results reveal the formation of biopolymers, wherein triglyceride molecules undergo cross-linking with sulfur chains through a reaction with the unsaturated groups present in the oil. Additionally, both polymers exhibit a porous structure and display hydrophobic behavior (contact angle higher than 120°). The biopolymers swell more in GEN solution (PSB 127.7% and PSF 174.4%) than in pure water (PSB 88.7% and PSF 109.1%), likely due to hydrophobic interactions. The kinetics of GEN sorption and release within the biopolymer matrices were investigated. The antibacterial efficacy of the resulting biocomposite was observed through the analysis of inhibition growth halos and the assessment of P. aeruginosa viability. A notable enhancement of the growth inhibition halo of GEN (13.1 ± 1.1 mm) compared to encapsulated GEN (PSF-GEN 21.1 ± 1.3 and PSB-GEN 21.45 ± 1.0 mm) is observed. Also, significant bactericidal activity is observed in PSF-GEN and PSB-GEN as a reduction in the number of colonies (CFU/mL), more than 2 log₁₀ compared to control, PSF, and PSB, highlighting the potential of these biopolymers as effective carriers for gentamicin in combating bacterial infections. Full article

This study investigates the crosslinking dynamics and swelling properties of pH-responsive poly(ethylene glycol) (PEG)/poly(acrylic acid) (PAA) interpenetrating polymer network (IPN) hydrogels. These hydrogels feature denser crosslinked networks compared to PEG single network (SN) hydrogels. Fabrication involved a two-step UV curing process: First, forming PEG-SN hydrogels using poly(ethylene glycol) diacrylate (PEGDA) through UV-induced free radical polymerization and crosslinking reactions, then immersing them in PAA solutions with two different molar ratios of acrylic acid (AA) monomer and poly(ethylene glycol) dimethacrylate (PEGDMA) crosslinker. A subsequent UV curing step created PAA networks within the pre-fabricated PEG hydrogels. The incorporation of AA with ionizable functional groups imparted pH sensitivity to the hydrogels, allowing the swelling ratio to respond to environmental pH changes. Rheological analysis showed that PEG/PAA IPN hydrogels had a higher storage modulus (G′) than PEG-SN hydrogels, with PEG/PAA-IPN5 exhibiting the highest modulus. Thermal analysis via thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicated increased thermal stability for PEG/PAA-IPN5 compared to PEG/PAA-IPN1, due to higher crosslinking density from increased PEGDMA content. Consistent with the storage modulus trend, PEG/PAA-IPN hydrogels demonstrated superior mechanical properties compared to PEG-SN hydrogels. The tighter network structure led to reduced water uptake and a higher gel modulus in swollen IPN hydrogels, attributed to the increased density of active network strands. Below the pK_a (4.3) of acrylic acid, hydrogen bonds between PEG and PAA chains caused the IPN hydrogels to contract. Above the pKa, ionization of PAA chains induced electrostatic repulsion and osmotic forces, increasing water absorption. Adjusting the crosslinking density of the PAA network enabled fine-tuning of the IPN hydrogels’ properties, allowing comprehensive comparison of single network and IPN characteristics. Full article

Cellulose aerogels are considered as ideal thermal insulation materials owing to their excellent properties such as a low density, high porosity, and low thermal conductivity. However, they still suffer from poor mechanical properties and low flame retardancy. In this study, mullite-fibers-reinforced bagasse cellulose (Mubce) aerogels are designed using bagasse cellulose as the raw material, mullite fibers as the reinforcing agent, glutaraldehyde as the cross-linking agent, and chitosan as the additive. The resulted Mubce aerogels exhibit a low density of 0.085 g/cm³, a high porosity of 93.2%, a low thermal conductivity of 0.0276 W/(m∙K), superior mechanical performances, and an enhanced flame retardancy. The present work offers a novel and straightforward strategy for creating high-performance aerogels, aiming to broaden the application of cellulose aerogels in thermal insulation. Full article

Ethylene–vinyl acetate copolymer (EVA), a crucial elastomeric resin, finds extensive application in the footwear industry. Conventional chemical foaming agents, including azodicarbonamide and 4,4′-oxybis(benzenesulfonyl hydrazide), have been identified as environmentally problematic. Hence, this study explores the potential of physical foaming of EVA using supercritical nitrogen as a sustainable alternative, garnering considerable interest in both academia and industry. The EVA formulations and processing parameters were optimized and EVA foams with densities between 0.15 and 0.25 g/cm³ were produced. Key findings demonstrate that physical foaming not only reduces environmental impact but also enhances product quality by a uniform cell structure with small cell size (50–100 μm), a wide foaming temperature window (120–180 °C), and lower energy consumption. The research further elucidates the mechanisms of cell nucleation and growth within the crosslinked EVA network, highlighting the critical role of blowing agent dispersion and localized crosslinking around nucleated cells in defining the foam’s cellular morphology. These findings offer valuable insights for producing EVA foams with a more controllable cellular structure, utilizing physical foaming techniques. Full article