Cross-linked Type Research Articles

Plasma-Polymerised Antibacterial Coating of Ovine Tendon Collagen Type I (OTC) Crosslinked with Genipin (GNP) and Dehydrothermal-Crosslinked (DHT) as a Cutaneous Substitute for Wound Healing

Tissue engineering products have grown in popularity as a therapeutic approach for chronic wounds and burns. However, some drawbacks include additional steps and a lack of antibacterial capacities, both of which need to be addressed to treat wounds effectively. This study aimed to develop an acellular, ready-to-use ovine tendon collagen type I (OTC-I) bioscaffold with an antibacterial coating for the immediate treatment of skin wounds and to prevent infection post-implantation. Two types of crosslinkers, 0.1% genipin (GNP) and dehydrothermal treatment (DHT), were explored to optimise the material strength and biodegradability compared with a non-crosslinked (OTC) control. Carvone plasma polymerisation (ppCar) was conducted to deposit an antibacterial protective coating. Various parameters were performed to investigate the physicochemical properties, mechanical properties, microstructures, biodegradability, thermal stability, surface wettability, antibacterial activity and biocompatibility of the scaffolds on human skin cells between the different crosslinkers, with and without plasma polymerisation. GNP is a better crosslinker than DHT because it demonstrated better physicochemical properties (27.33 ± 5.69% vs. 43 ± 7.64% shrinkage), mechanical properties (0.15 ± 0.15 MPa vs. 0.07 ± 0.08 MPa), swelling (2453 ± 419.2% vs. 1535 ± 392.9%), biodegradation (0.06 ± 0.06 mg/h vs. 0.15 ± 0.16 mg/h), microstructure and biocompatibility. Similarly, its ppCar counterpart, GNPppCar, presents promising results as a biomaterial with enhanced antibacterial properties. Plasma-polymerised carvone on a crosslinked collagen scaffold could also support human skin cell proliferation and viability while preventing infection. Thus, GNPppCar has potential for the rapid treatment of healing wounds.

Healable carbon fiber reinforced epoxy composites: Synchronous healing of matrix and interface damage

AbstractThermosetting composites are a range of high‐performance materials with important applications in multiple fields. However, inaccessible damage such as microcracks ingress from the environment may appear with long term use. Over time, the micro‐damage further expands and leads to material failure. The damage includes the interface damage and the matrix damage. Therefore, the healing technology of composites needs to respond and heal the micro‐damage of the interface and resin in the composites synchronously. In this work, siloxane dynamic bond was introduced into matrix and interface respectively. Specifically, a new type of crosslinker containing polysiloxane was synthesized and used to cure epoxy resin. Polyhedral oligomeric silsesquioxane was modified on the surface of carbon fibers (CFs) by sizing method. The prepared resin showed great mechanical properties and thermal stability, while the mechanical strength and surface activity of the CFs were also improved. Due to siloxane chain exchange reaction, matrix and interface could healing synchronously with good healing efficiency. Furthermore, the composites could retain about 65% of their original mechanical properties after healing multiple times. Composites realized synchronous healing of the resin matrix and the interface and laid foundation for extending the service life and performance of advanced resin‐based composites.

Super high gas separation performance membranes derived from a brominated alternative PIM by thermal induced crosslinking and carbonization at low temperature

In carbon dioxide capture and sequestration, achieving excellent performance, robustness, and reliability of gas separation membranes is a big challenge. Here, we report two novel highly crosslinked and partially carbonized molecular sieve membranes (CCMSM) that partially achieve the above goals for the first time. By thermally treating a novel bromomethyl substituted alternative intrinsic microporous polymer at relatively low temperatures of 340 °C and 350 °C, two PIM-BA-340 and PIM-BA-350 CCMSMs were obtained. They underwent the mechanism of triazine crosslinking (type I), debromomethylation induced crosslinking (type II) and partial carbonization (type III), resulting in membranes with excellent solvent resistance, thermal stability, and good mechanical strength. The PIM-BA-350 demonstrates a very small (4.1 Å) and intensive ultra-micropore (65.2%), consequently, outstanding gas separation property that outperformed various updated trade-off curves. The permeability of O2 is 145 Barrer and O2/N2 selectivity is 10.8, and further reaches unprecedented 22.2 at −20 °C. Additionally, PIM-BA-350 also shows remarkable CO2/CH4 separation property with CO2 permeability of 619 Barrer and CO2/CH4 selectivity of 124, even at a CO2/CH4 mixed-gas feeding pressure of 550 psi, there is no plasticization, and the selectivity for CO2/CH4 still reaches 106 coupled with a CO2 permeability of 306 Barrer. This low temperature formation of CCMSM paves a new path in searching for advanced membranes, and offers a great perspective in O2 and CO2 based industrial applications.

Fabrication of Fibrin/Polyvinyl Alcohol Scaffolds for Skin Tissue Engineering via Emulsion Templating

In the search for a novel and scalable skin scaffold for wound healing and tissue regeneration, we fabricated a class of fibrin/polyvinyl alcohol (PVA) scaffolds using an emulsion templating method. The fibrin/PVA scaffolds were formed by enzymatic coagulation of fibrinogen with thrombin in the presence of PVA as a bulking agent and an emulsion phase as the porogen, with glutaraldehyde as the cross-linking agent. After freeze drying, the scaffolds were characterized and evaluated for biocompatibility and efficacy of dermal reconstruction. SEM analysis showed that the formed scaffolds had interconnected porous structures (average pore size e was around 330 µm) and preserved the nano-scale fibrous architecture of the fibrin. Mechanical testing showed that the scaffolds' ultimate tensile strength was around 0.12 MPa with an elongation of around 50%. The proteolytic degradation of scaffolds could be controlled over a wide range by varying the type or degree of cross-linking and by fibrin/PVA composition. Assessment of cytocompatibility by human mesenchymal stem cell (MSC) proliferation assays shows that MSC can attach, penetrate, and proliferate into the fibrin/PVA scaffolds with an elongated and stretched morphology. The efficacy of scaffolds for tissue reconstruction was evaluated in a murine full-thickness skin excision defect model. The scaffolds were integrated and resorbed without inflammatory infiltration and, compared to control wounds, promoted deeper neodermal formation, greater collagen fiber deposition, facilitated angiogenesis, and significantly accelerated wound healing and epithelial closure. The experimental data showed that the fabricated fibrin/PVA scaffolds are promising for skin repair and skin tissue engineering.

The Relationship Between the Cross-Linker on Chitosan-Coated Magnetic Nanoparticles and the Properties of Immobilized Papain.

The immobilized enzymes' properties can be affected by cross-linkers on the surface of supports. To study how cross-linkers alter enzymes function, chitosan-coated magnetic nanoparticles (CMNPs) with immobilized papain were prepared using glutaraldehyde and or genipin, and then, the properties of the nanoparticles and the immobilized enzymes were assessed. The Scanning Electron Microscope (SEM), Fourier Transform Infrared (FTIR), and X-Ray Diffraction (XRD) results showed that the CMNPs were prepared and papain molecules were immobilized on CMNPs by glutaraldehyde (CMNP-Glu-Papain) or by genipin (CMNP-Gen-Papain). Also, the results associated with enzymes activity indicated that the immobilization by glutaraldehyde and genipin increased the pH optimum of papain from 7 to 7.5 and 9, respectively. The kinetic results indicated that the immobilization by genipin slightly affects the enzyme affinity to the substrate. The stability results showed that CMNP-Gen-Papain has more thermal stability than CMNP-Glu-Papain and papain immobilization on CMNPs by genipin leads to stabilization of the enzyme in the presence of polar solvents, probably due to the more hydroxyl groups on CMNPs activated by genipin. In conclusion, this study suggests that there is a relationship between the types of cross-linker on the surface of supports, and the mechanism of action, kinetic parameters, and the stability of immobilized papain.

Kinesin-driven active cytoskeletal composite restructuring.

The cytoskeleton is an intricate dynamic network that enables vital processes in the cell such as mitosis, movement, and growth. It is composed of protein filaments including semi-flexible actin filaments and rigid microtubules, as well as motor proteins, such as kinesin. The versatile restructurability of the cytoskeleton makes it highly intriguing for designing materials that combine tunability, flexibility, and resilience. Applications can span from soft tissue repair to biodegradable plastics and rubbers. Here, we create actin-microtubule composites, driven by kinesin motors, and adapted by different types of cross-linkers. We observe a range of restructuring of the composites, from formation of homogeneous clusters to heterogeneous threadlike networks. We quantify dynamics of our active composites by using particle image velocimetry (PIV) on time series videos of fluorescently labeled actin and microtubules, and by performing single particle tracking (SPT) on fluorescently labeled NeutrAvidin. Additionally, by imaging spherical hydrogels in the networks, then measuring the deformation of the spheres, we are able to measure forces generated by actin-microtubule composites being reconfigured by kinesin motors.

Design and characterization of matrix metalloproteinase-responsive hydrogels for the treatment of inflammatory skin diseases.

Enzyme-responsive hydrogels, formed by step growth photopolymerization of biscysteine peptide linkers with alkene functionalized polyethylene glycol, provide interesting opportunities as biomaterials and drug delivery systems. In this study, we developed stimuli-responsive, specific, and cytocompatible hydrogels for delivery of anti-inflammatory drugs for the treatment of inflammatory skin diseases. We designed peptide linkers with optimized sensitivity towards matrix metalloproteinases, a family of proteolytic enzymes overexpressed in the extracellular matrix of the skin during inflammation. The peptide linkers were crosslinked with branched 4-arm and 8-arm polyethylene glycols by thiol-norbornene photopolymerization, leading to the formation of a hydrogel network, in which the anti-inflammatory Janus kinase inhibitor tofacitinib citrate was incorporated. The hydrogels were extensively characterized by physical properties, in vitro release studies, cytocompatibility with fibroblasts, and anti-inflammatory efficacy testing in both an atopic dermatitis-like keratinocyte assay and an activated T-cell assay. The drug release was studied after single and multiple-time exposure to matrix metalloproteinase 9 to mimic inflammatory flare-ups. Drug release was found to be triggered by matrix metalloproteinase 9 and to depend on type of crosslinker and of the polyethylene glycol polymer, due to differences in architecture and swelling behavior. Moreover, swollen hydrogels showed elastic properties similar to those of extracellular matrix proteins in the dermis. Cell studies revealed limited cytotoxicity when fibroblasts and keratinocytes were exposed to the hydrogels or their enzymatic cleavage products. Taken together, our results suggest multi-arm polyethylene glycol hydrogels as promising matrix metalloproteinase-responsive drug delivery systems, with potential in the treatment of inflammatory skin disease. STATEMENT OF SIGNIFICANCE: Smart responsive drug delivery systems such as matrix metalloproteinase-responsive hydrogels are excellent candidates for the treatment of inflammatory skin diseases including psoriasis. Their release profile can be optimized to correspond to the patient's individual disease state by tuning formulation parameters and disease-related stimuli, providing personalized treatment solutions. However, insufficient cross-linking efficiency, low matrix metalloproteinase sensitivity, and undesirable drug release kinetics remain major challenges in the development of such drug delivery systems. In this study, we address shortcomings of previous work by designing peptide linkers with optimized sensitivity towards matrix metalloproteinases and high cross-linking efficiencies. We further provide a proof-of-concept for the usability of the hydrogels in inflammatory skin conditions by employing a drug release set-up simulating inflammatory flare-ups.

Nucleoside-Based Cross-Linkers for Hydrogels with Tunable Properties

Herein, we report bioderived cross-linkers to create biopolymer-based hydrogels with tunable properties. Nucleosides (inosine and uridine) and ribose (pentose sugar lucking the nitrogenous base) were partially oxidized to yield inosine dialdehyde (IdA), uridine dialdehyde (UdA), and ribose dialdehyde (RdA). The dialdehydes were further used as cross-linkers with polysaccharide chitosan to form hydrogels. Depending on the cross-linker type and concentration, the hydrogels showed tunable rheological, mechanical, and liquid holding properties allowing the preparation of injectable, soft, and moldable hydrogels. Computational modeling and molecular dynamics simulations shed light on hydrogel formation and revealed that, in addition to covalent bonding, noncovalent interactions (π-π stacking, cation-π, and H-bonding) also significantly contributed to the cross-linking process. To demonstrate various application possibilities, the prepared hydrogels were used as a growth platform for plant cells, as injectable inks for layer-by-layer 3D printing applications, and as moldable hydrogels for soft lithography to replicate the microstructure of the plant. These findings suggest that the obtained tunable biocompatible hydrogels have the potential to be good candidates for various biotechnological applications.

Circulating levels of endotrophin and cross-linked type III collagen reflect liver fibrosis in people with HIV

Background and aimsLiver-associated complications still frequently lead to mortality in people with HIV (PWH), even though combined antiretroviral treatment (cART) has significantly improved overall survival. The quantification of circulating collagen fragments released during collagen formation and degradation correlate with the turnover of extracellular matrix (ECM) in liver disease. Here, we analysed the levels of ECM turnover markers PC3X, PRO-C5, and PRO-C6 in PWH and correlated these with hepatic fibrosis and steatosis.MethodsThis monocentre, retrospective study included 141 PWH. Liver stiffness and liver fat content were determined using transient elastography (Fibroscan) with integrated CAP function. Serum levels of formation of cross-linked type III collagen (PC3X), formation of type V collagen (PRO-C5) and formation type VI collagen (PRO-C6), also known as the hormone endotrophin, were measured with ELISA.ResultsTwenty-five (17.7%) of 141 PWH had clinical significant fibrosis with liver stiffness ≥ 7.1 kPa, and 62 PWH (44.0%) had steatosis with a CAP value > 238 dB/m. Study participants with fibrosis were older (p = 0.004) and had higher levels of AST (p = 0.037) and lower number of thrombocytes compared to individuals without fibrosis (p = 0.0001). PC3X and PRO-C6 were markedly elevated in PWH with fibrosis. Multivariable cox regression analysis confirmed PC3X as independently associated with hepatic fibrosis. PRO-C5 was significantly elevated in participants with presence of hepatic steatosis.ConclusionSerological levels of cross-linked type III collagen formation and endotrophin were significantly associated with liver fibrosis in PWH receiving cART and thus may be suitable as a non-invasive evaluation of liver fibrosis in HIV disease.

Multiple oxidative post-translational modifications of human glutamine synthetase mediate peroxynitrite-dependent enzyme inactivation and aggregation

Glutamine synthetase (GS), which catalyzes the ATP-dependent synthesis of L-glutamine from L-glutamate and ammonia, is a ubiquitous and conserved enzyme that plays a pivotal role in nitrogen metabolism across all life domains. In vertebrates, GS is highly expressed in astrocytes, where its activity sustains the glutamate-glutamine cycle at glutamatergic synapses and is thus essential for maintaining brain homeostasis. In fact, decreased GS levels or activity have been associated with neurodegenerative diseases, with these alterations attributed to oxidative post-translational modifications of the protein, in particular tyrosine nitration. In this study, we expressed and purified human GS (HsGS) and performed an in-depth analysis of its oxidative inactivation by peroxynitrite (ONOO-) invitro. We found that ONOO- exposure led to a dose-dependent loss of HsGS activity, the oxidation of cysteine, methionine, and tyrosine residues and also the nitration of tryptophan and tyrosine residues. Peptide mapping by LC-MS/MS through combined H216O/H218O trypsin digestion identified up to 10 tyrosine nitration sites and five types of dityrosine cross-links; these modifications were further scrutinized by structural analysis. Tyrosine residues 171, 185, 269, 283, and 336 were the main nitration targets; however, tyrosine-to-phenylalanine HsGS mutants revealed that their sole nitration was not responsible for enzyme inactivation. In addition, we observed that ONOO- induced HsGS aggregation and activity loss. Thiol oxidation was a key modification to elicit aggregation, as it was also induced by hydrogen peroxide treatment. Taken together, our results indicate that multiple oxidative events at various sites are responsible for the inactivation and aggregation of human GS.

Synthesis of p(HEMA-co-AETAC) nanocomposite hydrogel with vinyl-function montmorillonite nanoparticles and effective removal of methyl orange from aqueous solution

It has become crucial to develop new adsorbents to remove toxic dye wastes from wastewater to protect our existing aquatic ecosystem. Here, to remove methyl orange azo dye from aqueous solutions, a new p(HEMA-co-AETAC)/VMt nanocomposite hydrogel was prepared by using 2-hydroxyethyl methacrylate and [2-(acryloyloxy)ethyl]trimethylammonium chloride monomers using vinyl-based montmorillonite crosslinker. Obtained new types of crosslinker and nanocomposite hydrogels have been characterized by various analysis methods. In addition, the effects of crosslinker amount, monomer amount and pH on the swelling behavior of nanocomposite hydrogel were investigated. The effects of essential parameters such as contact time, initial dye concentration, pH effect of the solution, adsorbent amount, and temperature on adsorption were evaluated. It was determined that there was no significant change in the adsorption ability of the nanocomposite hydrogel in the pH range of 3–10. Experimental results showed that the Langmuir isotherm model fit better, and the calculated maximum adsorption capacity was 961.54 mg/g. In addition, it was determined that vinyl-based montmorillonite used as a crosslinker supported MO adsorption. p(HEMA-co-AETAC)/VMt nanocomposite hydrogel may be a new type of adsorbent to remove toxic synthetic dye residues from aqueous media.

Utilization of palm oil as an alternative processing oil in carbon black-filled natural rubber compounds

Due to the toxicity of distillate aromatic extract (DAE), palm oil (PO) being environmental friendliness, renewability, and sustainability, was used as an alternative processing oil in this study. The properties of carbon black-filled natural rubber compounds containing PO were investigated and compared with the DAE-added rubber compound. The results revealed that the presence of PO in the rubber compound gave the same degree of filler–filler interactions but higher filler-rubber interactions compared with the one with DAE. Payne effect as referred to filler-filler interactions of the rubber compounds with DAE and PO was 191 and 189 kPa, respectively. In addition, the presence of PO not only accelerated the vulcanization reaction but also reduced the crosslink density within the rubber matrix. The crosslinking type of PO-added rubber compounds consisted only of polysulfidic linkages, whereas the DAE-added rubber compound contained various crosslinking types, i.e., mono-, di-, and polysulfidic linkages. On the other hand, the presence of PO in rubber compounds promoted a positive effect on elastic properties, as indicated by the temperature scanning stress relaxation (TSSR) index and tan δ at 60 °C. The TSSR index of rubber compounds with DAE and PO was 0.69 and 0.71, respectively. Given the low tan δ at 60 °C of the PO-added rubber compounds, PO promoted a low rolling resistance when applied in tire applications, providing tires with safe energy.

Understanding the (dis)-assembly of in situ forming hydrogel coatings in a 2D model system

HypothesisInjectable hydrogels are important in situ forming implants for tissue regeneration at damaged sites. Understanding the behavior of these systems in a complex in vivo environment remains a challenge. Ultrathin films as 2D model systems are expected to provide fundamental insights into formation and (bio)degradation at material-liquid interfaces, and are also applicable as bioresponsive coatings. ExperimentsHydrogel ultrathin films are prepared by covalently cross-linking four-arm PEG macromers with maleimide end-groups (PEG4MAL) at alkaline pH using two different types of dithiol-bearing cross-linkers – thio-depsipeptide (TDP) or 3,6-Dioxa-1,8-octanedithiol (DODT). This thiol-Michael addition “click” reaction is carried out at the air-water interface using the Langmuir technique. Morphological observation in real time is carried out by Brewster angle microscopy (BAM) and in coatings using atomic force microscopy (AFM). Stability against enzymatic and oxidative degradation is evaluated in the same setup. FindingsNon-cross-linked PEG or PEG incubated with cross-linkers at slightly acidic pH desorbs from the interface over time. Cross-linking of PEG at alkaline pH renders 2D hydrogel networks (thickness <1 nm) that are stable against desorption. They are easily transferrable onto solid mica surfaces, forming homogenous coatings as revealed by AFM. The type of dithiol cross-linker used to form the branching centers influences the degradability of these 2D hydrogel networks in the presence of lipase, peroxides, or bases. For example, enzymatic degradation of the 2D hydrogel networks can be switched “on” or “off” depending on the cleavable sites in the cross-linkers.

Выбор ускорителей вулканизации для резин на основе эпихлоргидринового каучука

The effect of vulcanization accelerators on the structure and properties of rubbers based on Hydrin T6000 epichlorohydrin rubber has been studied. Mercaptobenzthiazole (MBT) in the amount of 1.5 pts.wt., tetramethylthiuram disulfide (TMTD) — 0.5 – 1.5 pst.wt. were used as accelerators and N,N’-diphenylguanidine (DPG) — 0.5 – 1.5 pst.wt., which represent a triple system of accelerators. The choice of accelerators is based on the possibility of obtaining a vulcanization spatial structure of different sulfide content: thiuram group accelerators promote the formation of mono-, disulfide bonds; guanidine — polysulfide bonds, and thiazole groups — from carbon-carbon to polysulfide with varying degrees of sulfide. According to the results of the study of physical and mechanical properties, the determination of the parameters of the spatial grid and the study of the dynamic behavior of rubber, differences were revealed due to the formation of a spatial structure with different types of cross-links and density. It is shown that rubber containing 1.5 pst. wt. MBT, 0.5 pst. wt. DFG and 0.5 – 1.0 pst.wt. TMTD due to the manifestation of a synergistic effect on the formation of a vulcanization network of a certain density and the ratio of poly-, di- and monosulfide cross-links. Thus, the use of a group of accelerators with different functional effects makes it possible to obtain vulcanizates with an optimal set of technological and operational properties.

Advancing mesoporous carbon synthesis for supercapacitors: a systematic investigation of cross-linking agent effects on pore structure and functionality.

Soft-templating synthesis provides an effective route to prepare ordered mesoporous carbons (MCs) that can be used for supercapacitors. During this process, the cross-linking of carbon precursors is critical to obtain tailored pore structural MCs, thus careful selection of appropriate cross-linking agents is required. Despite the shift from the prevailing cross-linker formaldehyde to its more environmentally friendly alternatives, detailed understanding on the influence of different cross-linking agents on templating synthesis is still lacking. Therefore, it remains challenging to draw a conclusion regarding which cross-linker can effectively enable an ideal cross-linking and a robust templating synthesis of ordered MCs. This work presents a systematic study, by comparing three typical cross-linkers (formaldehyde, glyoxal, and glyoxylic acid), on the pore architecture, surface functionality, and electrochemical performance of resulting MCs. Both the type of cross-linker and its ratio with precursor monomer were found to be crucial for the pore architecture and electrochemical performance of resulting MCs. Glyoxal showed to be a promising cross-linker for easily generating ordered mesopores between 3.3-6.1 nm when the molar ratio between cross-linker and carbon precursor ranged from 1 to 2, whereas glyoxylic acid and formaldehyde induced interrupted or disordered mesopores. When the resulting MCs were used as supercapacitor electrodes, those cross-linked with glyoxal also led to overall higher capacitance in both 6 M KOH aqueous and ionic liquid [N2220][NTf2]/acetonitrile electrolytes thanks to the dominance of ordered mesopore channels, especially MC prepared at glyoxal/precursor molar ratio of 1.5. These findings on the effect of cross-linking on templating synthesis can be used to guide the customisation of MCs for supercapacitors and other applications by smartly choosing a suitable cross-linking agent and its ratio with the precursor.

Recent progress in structural modification of polymer gel electrolytes for use in solid-state zinc-ion batteries.

Zinc-ion batteries are one of the promising energy storage devices, which have the advantages of environmental friendliness, high safety and low price and are expected to be used in large-scale battery application fields. However, four prominent water-induced adverse reactions, including zinc dendrite formation, zinc corrosion, passivation and the hydrogen evolution reaction in aqueous systems, seriously shorten the cycling life of zinc-ion batteries and greatly hinder their development. Based on this, polymer gel electrolytes have been developed to alleviate these issues due to their unique network structure, which can reduce water activity and suppress water-induced side reactions. Based on the challenges of polymer gel electrolytes, this review systematically summarizes the latest research progress in the use of additives in them and explores new perspectives in response to the existing problems with polymer electrolytes. In order to expand the performance of polymer gel electrolytes in zinc-ion batteries, a range of different types of additives are added via physical/chemical crosslinking, such as organic or inorganic substances, natural plants, etc. In addition, different types of additives and polymerization crosslinking from different angles essentially improve the ionic conductivity of the gel electrolyte, inhibit the growth of zinc dendrites, and reduce hydrogen evolution and oxygen-absorbed corrosion. After these modifications of polymer gel electrolytes, a more stable and superior electrochemical performance of zinc-ion batteries can be obtained, which provides some strategies for solid-state zinc-ion batteries.

Effect of Crosslinker Types on Temporary Plugging Performance of Degradable Preformed Particle Gels for Unconventional Petroleum Reservoir Development

Temporary plugging agents (TPAs) have been widely used in unconventional petroleum reservoirs to increase the stimulated reservoir volume and generate an easier flow of oil and gas into the production well. The properties of particle-gel-based TPAs include a straightforward injection procedure, excellent deformation, strong plugging strength, and total self-degradation. This study prepared degradable preformed particle gel (DPPG) samples polymerized by two types of crosslinkers (i.e., alcohol ester and alkenoic acid ester) for low-temperature (less than 40 °C) reservoirs. The effects of different crosslinkers in the DPPG compositions on the temporary plugging performance were investigated. Infrared spectrum analysis, differential calorimetry scanning evaluation, static particle gel swelling and degradation performance assessment experiments, and dynamic temporary plugging performance tests were all employed. The results showed that the swelling ratio of DPPGs prepared by the crosslinker containing alcohol ester was larger than that of alkenoate acid ester, but the degradation rate was slower. Among them, when the amount of crosslinker was 0.01 g, the swelling ratio of DPPG prepared using the alcohol ester crosslinker was as high as 40 times, and the complete degradation time could be regulated between 80 and 360 h. When the type of crosslinker was the same, the influence of its molecular weight also significantly affected the performance of the particle gel. The plugging strength of DPPG prepared by different crosslinkers in cores was as high as 20 MPa. The DPPG prepared from the alcohol ester crosslinker caused less damage to the core after being self-degraded and was used as an ideal crosslinker. Infrared spectroscopy and differential scanning calorimetry analysis at the molecular level verified that different types of crosslinkers had apparent effects on the chemical structure stability of the DPPG. In this paper, the influence of the type of crosslinker on the performance of the DPPG was studied, which provides a new idea and theoretical basis for developing a particle gel-based TPA system with programmed self-degradation time at low temperatures.

Molecular and Interactions Modelling of PETase and Its Variant with Different Types of Crosslinker in Enzyme Immobilization

&#x0D; &#x0D; &#x0D; &#x0D; Plastics are made from non-renewable resources and due to the tremendous production of plastics nowadays, they can lead to high levels of pollution. Biodegradation of plastic by utilizing enzymatic catalytic reaction is an environmentally friendly strategy that produce less or no negative carbon footprint. PETase from Ideonella sakaiensis (IsPETase) is an enzyme that able to degrade polyethylene terephthalate (PET), a building block of plastic. However, free enzyme has several limitations such as unstable in harsh conditions and lack of reusability. One of the strategies to overcome this drawback is through enzyme immobilization that able to improve the enzymatic properties. A suitable crosslinker is very important as it would determine the interactions of the enzymatic particles. Crosslinker should be chosen before performing the enzyme immobilization and this can be accomplished by molecular docking. Thus, the purpose of this research is to determine the suitability of glutaraldehyde, chitosan, dialdehyde starch (DAS) and ethylene glycol as the crosslinker for IsPETase and its variant. Three-dimensional structure of the enzymes was built and docked with different types of crosslinkers. Binding affinity and interactions between the enzymes and the crosslinkers were analyzed and it was found that chitosan has the lowest binding affinity (-7.9 kcal/mol) and the highest number of interactions. This is followed by DAS, ethylene glycol and glutaraldehyde. By using computational analysis, suitable crosslinker for IsPETase could be determine and this would a cost-effective practice in enzyme immobilization strategy. &#x0D; &#x0D; &#x0D; &#x0D;

LdtC Is a Key l,d-Transpeptidase for Peptidoglycan Assembly in Mycobacterium smegmatis.

The peptidoglycan of mycobacteria has two types of direct cross-links, classical 4-3 cross-links that occur between diaminopimelate (DAP) and alanine residues, and nonclassical 3-3 cross-links that occur between DAP residues on adjacent peptides. The 3-3 cross-links are synthesized by the concerted action of d,d-carboxypeptidases and l,d-transpeptidases (Ldts). Mycobacterial genomes encode several Ldt proteins that can be classified into six classes based upon sequence identity. As a group, the Ldt enzymes are resistant to most β-lactam antibiotics but are susceptible to carbapenem antibiotics, with the exception of LdtC, a class 5 enzyme. In previous work, we showed that loss of LdtC has the greatest effect on the carbapenem susceptibility phenotype of Mycobacterium smegmatis (also known as Mycolicibacterium smegmatis) compared to other ldt deletion mutants. In this work, we show that a M. smegmatis mutant lacking the five ldt genes other than ldtC has a wild-type phenotype with the exception of increased susceptibility to rifampin. In contrast, a mutant lacking all six ldt genes has pleiotropic cell envelope defects, is temperature sensitive, and has increased susceptibility to a variety of antibiotics. These results indicate that LdtC is capable of functioning as the sole l,d-transpeptidase in M. smegmatis and suggest that it may represent a carbapenem-resistant pathway for peptidoglycan biosynthesis. IMPORTANCE Mycobacteria have several enzymes to catalyze nonclassical 3-3 linkages in the cell wall peptidoglycan. Understanding the biology of these cross-links is important for the development of antibiotic therapies to target peptidoglycan biosynthesis. Our work provides evidence that LdtC can function as the sole enzyme for 3-3 cross-link formation in M. smegmatis and suggests that LdtC may be part of a carbapenem-resistant l,d-transpeptidase pathway.

Catechol-modified epoxy backbones for multifunctional and ultra-tough thermoset

Widely used traditional thermosets have drawn great attention due to their advantageous features such as excellent stability, mechanical reliability etc. However, brittleness is still the weak point in their extensive applications. Herein, a synthetic strategy to incorporate catechol groups into polymer structures via thiol-epoxy click chemistry was developed, the covalent and iron-catechol coordination bonds are combined to build up the material consisting of two types of crosslinks. As an important design feature of thermoset, catechol moiety provided the potential of gaining recoverable hysteretic energy dissipation through iron-catechol complexes. Favorable thermal properties comparable to commercial resin were retained, and mechanical testing revealed the thermoset exhibited high extensibility, such that it can be stretched to over 100 % with a fracture strength of 31.16 MPa, along with the tensile strength can be maintained 90.53 % after 5 cycles at the strain of 50 %. The synergistic interaction additionally providing the possibility of shape memory response to specific environmental changes, either by heat or by ultraviolet light. These behaviors further highlight the utility of dynamic coordinate bonds in the preparation of versatile thermosets, which could be potentially applied in smart devices and advanced materials.