Cross-linking Reaction Research Articles

Thermoplastic Phenomena and Morphological Changes upon Fast Pyrolysis of Biomass and Model Compounds

The work reports preliminary results on the morphological changes that biomass particles experience at high heating rates in a heated strip reactor (HSR) at T = 1000–1600 °C under an inert atmosphere. Samples included a natural lignocellulosic biomass (pinewood) as well as biomass components: cellulose, hemicellulose (xylan) and lignin. On top of that, reference compounds have been investigated, namely naphthalene pitch, a paraffinic wax and glucose. During the heat-up phase, the investigated biomass mainly retains the original morphology and size, while the single components exhibit different behaviors. Hemicellulose undergoes a fluid stage and eventually forms millimetric spherical char particles. Cellulose does not become fully fluid but softens and forms millimetric char aggregates of different shapes. Lignin particles hardly soften and stick together in a curved slab. Comparison with model compounds allows us to infer that the degree of melting and the viscosity of the melt are responsible for the final particle shape. In fact, naphthalene pitch and glucose appear to be more viscous during pyrolysis and lead to the formation of three-dimensional columns a few millimeters high. Wax undergoes extensive melting, but the relatively low viscosity and the absence of crosslinking reactions eventually lead only to the formation of droplets.

Thiophene-fused aromatic belts

Aromatic belts, ultrashort carbon nanotubes, and related structures, are emerging molecular entities in the fields of organic electronics and supramolecular chemistry owing to their structural rigidity, fully fused π-conjugation, and well-defined cavity. Synthesis of aromatic belts with embedded thiophene structures, which manifest significant optoelectronic and conductive properties, has not yet been achieved. Herein, we report the synthesis of thiophene-fused aromatic belts (thiophene belts) via one-step sulfur cross-linking reaction of partially fluorinated cycloparaphenylenes. Their structural features, including unidirectional columnar stacking with high dipole moment in crystals, two-dimensional layer assembly on metal surfaces, and photophysical properties, such as long-lifetime phosphorescence, are uncovered. These distinctive features of the thiophene belts should inspire a range of applications such as optoelectronic devices and polar materials.

Lysyl oxidase inhibitors in colorectal cancer progression.

The lysine oxidase (LOX) family, consisting of LOX and LOX-like-1-4 (LOXL1-LOXL4), catalyses the cross-linking reaction of collagen and elastin in the extracellular matrix (ECM). Numerous studies have demonstrated that LOX family members are dysregulated in a variety of cancers, including colorectal cancer (CRC), and play a key role in cancer cell migration, proliferation, invasion and metastasis. Targeting LOX family proteins with specific inhibitors has therefore been developed as a new therapeutic strategy for cancer. In this paper, we review the role of LOX enzymes in the development and progression of CRC. In addition, we address recent advances in the development of LOX/LOXL inhibitors, highlighting the potential use of this inhibitor as an effective and complementary treatment for CRC.

Development and structural comparison of alkaline and organosolv coconut husks lignin as an eco-friendly lignin-phenol-glyoxal (LPG) wood adhesives.

The development of eco-friendly wood adhesives have gained more interest among adhesives industries due to the concerns about using carcinogenic formaldehyde and petroleum-based phenol in commercially available adhesives. Therefore, many studies have been done by using lignin to partially replace phenol and completely substitute formaldehyde with non-toxic glyoxal in a wood adhesive formulation. This study focused on using different percentages of lignin substitution (10%, 30% and 50wt%) of alkaline and organosolv coconut husk lignin into soda lignin-phenol-glyoxal (SLPG), Kraft lignin-phenol-glyoxal (KLPG) and organosolv lignin-phenol-glyoxal (OLPG) adhesives. The adhesives were further characterized using various analyses and it showed that 50% lignin substitution was the optimum rate percentage with 50% SLPG adhesive giving the highest solid content, shorter gel time and more viscosity compared to control (PF and PG), KLPG and OLPG adhesives. Mechanical properties revealed that 50% SLPG adhesive showed an improvement performance of tensile strength (TS: 68.98 ± 0.19MPa), internal bonding (IB: 17.01 ± 1.07 Nmm-2), and cross-linking density panels (775.51 ± 8.15kgm-3) due to the higher amount of molecular weight (Mw) as well as higher phenolic-OH that improved the cross-linking reaction between phenol-glyoxal with G-type unit in lignin structure.

Beeswax-based nanoconstructs enriched dual responsive hydrogel for diabetic foot ulcers in streptozotocin-induced diabetic rats.

Diabetic foot ulcer (DFU) is a complicated pathophysiological process, and there is now no recognized treatment. Hyperglycemia, neuropathy, impaired angiogenesis, reactive oxygen species, and advanced glycation end products construct the distinctive wound environment of diabetic wounds. This study aimed to develop naringenin-ferulic acid beeswax-based nanoconstructs enriched dual-responsive hydrogel (NAR-FA NLC HG) for topical application for DFU. The pH- and temperature-responsive hydrogel was formulated via a chemical cross-linking reaction of carboxymethyl chitosan and poloxamer 407 and loaded with NAR-FA NLC using the swelling-loading method. SEM, FTIR, and XRD observed the morphology and characterization of the prepared hydrogel. The in vitro release study showed controlled release during 48h. Antibacterial activity significantly inhibits B. subtilis and E. coli compared to NLC and control groups (p<0.05). Cell line studies show that hydrogel is compatible with HaCaT cells and 92.4±4.9% of wound contraction after 48h of scratch wound assay. The wound closure rate with NAR FA NLC HG in STZ-induced diabetic rats reached 93.2±3.4% by day 15 with significant (p<0.001) increases in the VEGF level and decreasing ICAM-1 level. Hence, the smart hydrogel established in this study has the potential to serve as a promising topical therapy for DFU with inherent antimicrobial activity components, including beeswax, NAR, and FA.

Amino-functionalized cellulose beads supporting laccase: A dual-function catalyst for simultaneous adsorption and enzymatic conversion of tetracycline.

In this study, a novel cellulose-derived support of amino-functionalized cellulose beads (ACBs) for laccase immobilization was successfully developed using cellulose beads (CBs) and polyethyleneimine by glutaraldehyde crosslinking reaction. The covalent immobilization of laccase on ACBs was achieved via a Schiff base reaction. The obtained enzyme catalysts (Lac-ACBs) were applied for simultaneous adsorption and enzymatic conversion of tetracycline (TC) from water. The structure and properties of all samples were characterized by SEM-EDS, FT-IR, XRD, BET, and EA. Furthermore, the Lac-ACBs exhibited excellent stability and reusability: after 15 cycles of catalysis, they maintained 72 % of their original activity. The Lac-ACBs were applied for the removal of TC from water with simultaneous adsorption and enzymatic conversion, achieving an 82 % removal efficiency. The enzymatic conversion products were examined to investigate the mechanism of the conversion. The data illustrated that oxidation, dehydrogenation, and demethylation are major reactions in that process.

Modification of Polyamide Resins by Addition of Polyvinylpyrrolidone

The effect of the addition of polyvinylpyrrolidone (PVP) to polyamide resins was studied using polyamide 6 (PA6) and an amide copolymer with a low melting point (PA-L). For the PA6/PVP blends, the crosslinking reaction occurred during rheology measurements in the molten state. The blends did not show a phase-separated structure. Furthermore, the crystallization of PA6 was greatly inhibited by PVP addition. These results suggest that the PVP chains were dissolved in PA6 in the molten state, although the effect of the crosslinking reaction on the structure development is unknown. In the case of the PA-L/PVP blends, melt-mixing and the rheology measurements were performed at low temperature to avoid the crosslinking reaction. It was found that PVP was miscible with PA-L in the molten state when the PVP content was 10 and 15 wt%. The intermolecular interaction between the polyamide resins and PVP was detected from the peak shift of the infrared absorbance. PVP addition enhanced the moisture content in both polyamide resins and decreased the contact angle with water droplets. These results suggested that the surface properties and mechanical properties of polyamide resins, which are affected by the moisture content, are modified by PVP addition.

In Situ-Forming, Adhesive, and Antioxidant Chitosan Hydrogels for Accelerated Wound Healing.

Antioxidant hydrogels that can provide a moist environment and scavenge reactive oxygen species have emerged as highly potential wound dressing materials. In situ-forming and good tissue adhesiveness will make them more desirable, as they can fill the irregular wound defect, stick to the wound, and offer intimate contact with the wound. Herein, a hydrogel dressing combining in situ-forming, good tissue adhesiveness, and excellent antioxidant capabilities was developed by simply conjugating dopamine onto carboxymethyl chitosan. The introduction of dopamine allows in situ gelation of the polymer under mild conditions using an HRP-catalyzed cross-linking reaction. The introduction of dopamine also endows the hydrogels with suitable tissue-adhesion properties. Excellent antioxidant properties were also imparted as a result of the introduction of dopamine. Thanks to the favorable moist environment provided by the hydrogel and the effectively mitigated oxidative stress at wound sites, accelerated healing and reduced scar formation were observed in a rat full-thickness skin wound model.

Regio-Selective Mechanical Enhancement of Polymer-Grafted Nanoparticle Composites via Light-Mediated Crosslinking.

Polymer-brush-grafted nanoparticles (PGNPs) that can be covalently crosslinked post-processing enable the fabrication of mechanically robust and chemically stable polymer nanocomposites with high inorganic filler content. Modifying PGNP brushes to append UV-activated crosslinkers along the polymer chains would permit a modular crosslinking strategy applicable to a diverse range of nanocomposite compositions. Further, light-activated crosslinking reactions enable spatial control of crosslink density to program intentionally inhomogeneous mechanical responses. Here, a method of synthesizing composites using UV-crosslinkable brush-coated nanoparticles (referred to as UV-XNPs) is introduced that can be applied to various monomer compositions by incorporating photoinitiators into the polymer brushes. UV crosslinking of processed UV-XNP structures can increase their tensile modulus up to 15-fold without any noticeable alteration to their appearance or shape. By using photomasks to alter UV intensity across a sample, intentionally designed inhomogeneities in crosslink density result in predetermined anisotropic shape changes under strain. This unique capability of UV-XNP materials is applied to stiffness-patterned flexible electronic substrates that prevent the delamination of rigid components under deformation. The potential of UV-XNPs as functional, soft device components is further demonstrated by wearable devices that can be modified post-fabrication to customize their performance, permitting the ability to add functionality to existing device architectures.

Film characteristics of atmospheric pressure plasma-treated chitosan solution

Chitosan (Cs) is a biopolymer that can be used to create films with high swelling capacity. Its application, however, is restricted by its weak mechanical strength. To address this limitation, atmospheric pressure plasma (APP) treatment was integrated into the Cs film synthesis. This was done by exposing the Cs solution to air plasma at varying times—2, 4, and 6 min. Improved dissolution of Cs was observed in the scanning electron microscope images where no traces of excess Cs particles were found on the surface. Spectroscopic techniques such as optical emission spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy suggested that chain scission and cross-linking synergistically occurred to establish the network of the Cs films. This possible reaction mechanism of film formation was manifested as changes in the peak intensities of the different Cs attributes such as the pyranose ring, –OH, the C–O–C glycosidic, and the amide linkages. Shorter treatment time (2 min) resulted in the dominance of degradation where scission occurred to open the Cs rings. When using a longer treatment time (&amp;gt;4 min), cross-linking reactions occurred along the scission sites, which acted as initiation points. As a result, the hydrophilicity and swelling behavior of the Cs films were influenced by the APP treatment. The fabricated Cs films were generally hydrophilic. However, utilizing a longer treatment time decreased the hydrophilic nature of the film. A decreased swelling capacity for APP-treated Cs films also accompanied the decreased hydrophilicity. This observed phenomenon was attributed to the addition of Cs chains possibly caused by cross-linking. The study revealed that the water absorption ability of the Cs films was based on the relaxation of the Cs chains upon interaction with water. The integration of APP treatment for film synthesis may provide easier processing of Cs films.

Facile preparation of sulfonium peptide and protein probes for selective crosslinking of methyllysine readers.

Sulfonium is an electrophilic and biocompatible group that is widely applied in synthetic chemistry on small molecules. However, there have been few developments of peptide or protein-based sulfonium tools. We recently reported sulfonium-mediated tryptophan crosslinking and developed NleS+me2 (norleucine-dimethylsulfonium) peptides as dimethyllysine mimics that crosslink site-specific methyllysine readers. Therefore, sulfonium probes show great potential for investigating methyllysine readers and other aromatic cage-containing proteins. However, the current synthesis is not very efficient and is limited to peptide probes that, in many cases, cannot mimic protein-protein interactions. In addition to peptidyl conjugates that are valuable for reader identification, there are unavoidable methyl conjugates as side products. As a result, a robust method to prepare peptide and protein sulfonium tools with great crosslinking reactivity and selectivity is highly desirable. Here, we report a cysteine alkylation method to introduce site-specific sulfonium at protein level with excellent yield. In addition to dimethylsulfonium, we also developed cyclic sulfonium warheads that enhanced peptidyl conjugate selectivity. The method thus made it possible to prepare nucleosome probes in which LEDGF and NSD2, as H3K36 methylation readers were readily crosslinked. We thus believe this method will accelerate the development of sulfonium peptide and protein tool sets for broad applications in chemical biology studies.

Bioactive Silk Cryogel Dressing with Multiple Physical Cues to Control Cell Migration and Wound Regeneration.

Introducing multiple physical cues to control cell behaviors effectively is considered as a promising strategy in developing bioactive wound dressings. Silk nanofiber-based cryogels are developed to favor angiogenesis and tissue regeneration through tuning hydrated state, microporous structure, and mechanical property, but remained a challenge to endow with more physical cues. Here, β-sheet rich silk nanofibers are used to develop cryogels with nanopore structure. Through optimizing crosslinking time and exposing the reactive group inside the nanofibers, the crosslinking reaction is improved to induce stable cryogel formation. Besides the hydrated state and macroporous structure, the nanopore structure formed on the macroporous walls, providing hierarchical microstructures to improve cell migration. Both in vitro and in vivo results reveal quicker cell migration inside the cryogels, which then accelerates angiogenesis and wound healing. The mechanical properties can further regulate to match with skin regeneration. The wound healing study in vivo reveals lower inflammatory factor secretion in the wounds treated with softer cryogels with nanopores, which then resulted in the best angiogenesis and wound healing with less scar. Therefore, the porous cryogels with multiple physical cues can be fabricated with silk nanofibers to control cell behaviors and tissue regeneration, providing a promising approach for designing bioactive wound dressings.

Thermosetting Resin for Plug and Abandonment of Oil Wells with Reduced Environmental Impact.

Plug and abandonment of offshore oil wells is a costly and time-consuming process, yet it is necessary for the ever-increasing number of mature fields in the region of the Danish North Sea, as well as globally. Current practices ensuring durable solutions for the complete zonal isolation of oil wells have a large environmental impact. This paper proposes a novel resin that could be mixed on the platform and pumped into the tubing in a liquid state. The increased temperature inside the oil well initiates the cross-linking reaction of the liquid resin, creating a solid and impermeable barrier. The liquid resin is thermally stable up to 180 °C and can be handled for up to 20 h at room temperature, preventing setting before intended while decreasing environmental impact. The solid resin has a compressive strength of 54 MPa and a steel adhesion strength of 6.27 MPa, highlighting its ability to withstand extreme downhole conditions.

Additive Manufacturing and Functionalization of Hollow Polypropylene Sorbents for Water Remediation.

As the demand for clean water intensifies, developing effective methods for removing pollutants from contaminated sources becomes increasingly crucial. This work establishes a method for additive manufacturing of functional polymer sorbents with hollow porous features, designed to enhance interactions with organic micropollutants. Specifically, core-shell filaments are used as the starting materials, which contain polypropylene (PP) as the shell and poly(acrylonitrile-co-butadiene-co-styrene)as the core, to fabricate 3-dimensional (3D) structures on-demand via material extrusion. After 3D printing, the cores of the printed roads are removed through solvent extraction, creating hollow structures that increase accessible surface area for adsorption. Subsequently, a sulfonation-induced crosslinking reaction installs sulfonic acid functionalities into the PP backbones, while enhancing their chemical stability. It is found that larger voids, and thinner polymer shells, enable improved structural retention during the sulfonation through limiting reaction-induced stresses. The hollow sulfonated PP sorbents exhibit a strong affinity againstcationic pollutants. Specifically, larger voids within these structures not only improve structural integrity but also result in accelerated adsorption kinetics by maximizing accessible surface area, thereby enhancing pollutant removal efficiency. This work provides a promising solution for advanced structured sorbent fabrication with hollow architectures, leading to more effective solutions for water contaminant removal in the future.

Removal of Tetracycline Antibiotic as a Hospital Waste by pH‐Sensitive Degradable Composite Hydrogel Using Fenton‐Like System

ABSTRACTFenton‐like hydrogels crosslinked with imine bond were prepared for the removal of tetracycline. Initially, the oxidation process of carboxymethyl cellulose (CMC) was performed, and it was named OX‐CMC. The confirmations were then obtained using NMR and FTIR analyses. The degree of CMC oxidation was investigated in relation to reaction time, and optimal time of 4 h was selected. In the second part, a pH‐sensitive hydrogel with imine bond was prepared from the crosslinking reaction between OX‐CMC and chitosan. The formation of the hydrogel through imine crosslinking was confirmed by FTIR spectroscopy. By increasing ratio of OX‐CMC to chitosan, the swelling rate for the hydrogel decreased. Turbidity measurements showed that a higher OX‐CMC to chitosan weight ratio resulted in slower hydrogel degradation in acidic environments. In the third part, Fe3O4 nanoparticles with concentrations of 5 and 10 wt% were incorporated into the hydrogel structure. TEM studies revealed a spherical morphology and uniform distribution of nanoparticles within the hydrogel network. SEM images revealed a porous structure which composed of interconnected pores in the hydrogel. The results of UV–visible spectroscopy indicated that the degradation of magnetic hydrogels would augment as magnetic nanoparticle content increases, pH decreases, and the hydrogen peroxide content increases.

Design of the Multi-Bioactive Graphene-Oxide/Gelatin/Alginate Scaffolds as Dual ECM-Mimetic and Specific Wound Healing Phase-Target Therapeutic Concept for Advanced Wound Healing.

Objectives: To develop and evaluate graphene oxide/gelatin/alginate scaffolds for advanced wound therapy capable of mimicking the native extracellular matrix (ECM) and bio-stimulating all specific phases of the wound healing process, from inflammation and proliferation to the remodeling of damaged skin tissue in three dimensions. Methods: The scaffolds were engineered as interpenetrating polymeric networks by the crosslinking reaction of gelatin in the presence of alginate and characterized by structural, morphological, mechanical, swelling properties, porosity, adhesion to the skin tissue, wettability, and in vitro simultaneous release of the active agents. Biocompatibility of the scaffolds were evaluated in vitro by MTT test on fibroblasts (MRC5 cells) and in vivo using Caenorhabditis elegans assay. Results: The scaffolds exhibited a highly porous interconnected morphology with adjustable porosity (93-96%) and mechanical strength (1.10-2.90 MPa), hydrophilic nature with high capacity to absorb physiological fluids, and stable adhesion to the skin tissue. The obtained results of MRC5 cell viability indicate that the scaffolds are safe for biomedical applications. No mortality was detected among the Caenorhabditis elegans throughout the incubation period, indicating that the scaffolds are not toxic. The results of in vitro release study of allantoin, quercetin, and caffeic acid confirm the scaffolds' significant potential for simultaneous release. Conclusion: The graphene oxide/gelatin/alginate scaffolds are promising candidates for non-invasive, dual ECM-mimetic, and multi-target wound therapy, offering an innovative strategy to address the complexities of wound healing process.

Changes in rheological properties and structure of wheat gluten proteins induced by transglutaminase.

To elucidate the effect of transglutaminase (TG) on the rheological properties of wheat gluten, this study investigates the underlying mechanisms by analyzing changes in gluten structure. The results demonstrated that the TG-treated gluten samples had higher storage modulus (G') and loss modulus (G″) compared to the control, conversely, creep and recovery strains followed an opposite trend. Notably, the most pronounced effects were observed with adding 2U/g TG for 20-30min. Size exclusion/reversed phase-high performance liquid chromatography profiles revealed that the treatment with TG elevated the levels of glutenin subunits, alongside reduced α- and γ-gliadins, promoting gluten aggregation. Moreover, the extractability of gluten gradually decreased due to TG-induced oxidation of sulfhydryl groups, which formed new disulfide bonds and cross-linked products. This structural modification reduced surface hydrophobic regions and promoted the aggregation of low molecular weight proteins into larger molecular weight aggregates. Microstructural analysis further confirmed that TG enhanced gluten network stability through covalent cross-linking. Overall, this study demonstrates that TG enhances the rheological characteristics of wheat gluten by facilitating the formation of a more robust network structure, driven by cross-linking reactions and disulfide bond formation.

Intrinsically photosensitive polyimide photoresist and its double crosslinking mechanism.

A new negative-working photoinitiator-free polyimide was developed for photolithographic processes. The polyimide introduced a photosensitive benzophenone unit into the backbone and a cross-linking group (methacrylate) into the side chains. A novel pre-functionalized diamine monomer was designed to avoid using corrosive sulfonyl chloride in the polyimide side-chain introduction step. Mechanistic studies revealed that benzophenone initiates various cross-linking reactions under i-line (UV 365 nm) irradiation, resulting in excellent photolithography performance of polyimide, with a resolution of 10 μm.

Vat photopolymerization printing by thermal polymerisation utilising carbon nanotubes as photothermal converters

ABSTRACT Traditional printing compositions for stereolithography (SLA), a vat photopolymerization technology, rely on light-sensitive photoinitiators (PIs) to initiate cross-linking reactions. Here, we propose a new approach for printing in which the polymerisation occurs locally with carbon nanotubes (CNTs), which function as photothermal converters combined with low-cost thermal initiators (TIs). The irradiation is performed at near-infrared (NIR), which enables deep light penetration, and polymerisation in black compositions, thus increasing the printing throughput. We demonstrate the control over polymerisation kinetics, printing resolution and cure depth, achieving very large printable layer thickness. The CNT photoconvertors can be used in both nonaqueous and aqueous systems, while the latter addresses the limited availability of water-soluble PIs for printing in water. The CNT enables dual use, initiating polymerisation and printing composite materials. This approach presents an advancement in SLA-based technologies, avoiding the use of conventional PIs and thus broadening the scope of 3D printing applications.

Humidity-Activated Ammonia Sensor Based on Carboxylic Functionalized Cross-Linked Hydrogel.

Owing to its extensive use and intrinsic toxicity, NH3 detection is very crucial. Moisture can cause significant interference in the performance of sensors, and detecting NH3 in high humidity is still a challenge. In this work, a humidity-activated NH3 sensor was prepared by urocanic acid (URA) modifying poly (ethylene glycol) diacrylate (PEGDA) via a thiol-ene click cross-linking reaction. The optimized sensor achieved a response of 70% to 50 ppm NH3 at 80% RH, with a response time of 105.6 s and a recovery time of 346.8 s. The sensor was improved for response and recovery speed. In addition, the prepared sensor showed excellent selectivity to NH3 in high-humidity environments, making it suitable for use in some areas with high humidity all the year round or in high-humidity areas such as the detection of respiratory gas. A detailed investigation of the humidity-activated NH3-sensing mechanism was conducted using complex impedance plot (CIP) measurements.