Cross-linking Properties Research Articles

The Effects of Citric Acid on Thermal and Mechanical Properties of Crosslinked Starch Film

Plastic waste from film packaging is one of the major threats to environmental sustainability. The problem can be reduced by using a biodegradable raw material such as starch to replace the non-biodegradable petroleum-based plastic. However, starch is highly hydrophilic and brittle, which needs to be modified to improve these drawbacks. In this research, a mixture of tapioca starch (S) and glycerol (G) was crosslinked with citric acid (CA) at different ratios (0, 0.4, 0.6, 0.8, 1.0 wt% of dry basis). Effects of CA contents on the degree of crosslinking, thermal stability, and tensile properties were investigated. The sample that contained 0.6 wt% CA showed the highest degree of crosslinking (i.e. 56 %), good thermal stability, high modulus (10 MPa) and tensile strength (0.16 MPa), and low elongation at break (161 %) when compared with other samples. Samples that have higher CA contents (i.e. 0.8 wt% and 1.0 wt%) experienced the acid hydrolysis on the crosslinking site, reducing the degree of crosslinking, thermal stabilities, and tensile properties.

Treatment and recycling of acidic fracturing flowback fluid

ABSTRACT Acidic fracturing flowback fluid (AFFF) has the characteristics of low pH value, high chemical oxygen demand (COD), high corrosiveness and complex components. Surface discharge without treatment may contaminate the environment. However, wastewater treatment after centralized transportation has potential safety risks and requires high costs. In this study, we confirmed that calcium and magnesium could affect cross-linking property of fracturing fluid prepared by flowback fluid, and conducted a three-step process, two-stage filtration, chemical precipitation, and flocculation precipitation, on AFFF. After treatment, we made new hydraulic fracturing fluid using the treated acidic flowback fluid as base fluid and compared the quality of the new hydraulic fracturing fluid to the ones used freshwater as base fluid. The results showed when concentration of sodium carbonate, polyaluminium chloride (PAC), polyacrylamide (PAM) were 145, 1000, and 20 mg/L respectively, the treatment result was optimal. After treatment, the oil content of AFFF decreased from 7400 to 26.53 mg/L and suspended solids (SS) from 650 to 18.24 mg/L, and the removal rate of high-valence metal ions was more than 99%. The rheological properties and viscoelasticity of new fracturing fluid prepared by the treated AFFF were similar to the ones prepared by freshwater, which met the requirements of high temperature and shear resistance for ultra-deep wells.

Three-Dimensional Printing to Build Fibrous Protein Architectures.

Fibrous proteins are promising bioinks for three-dimensional printing techniques to fabricate sophisticated structures that find applications in both biomedical engineering and materials science. The critical point of manufacturing these fibrous protein inks is to adjust the cross-linking and rheology properties of proteins that matching the requirements of various printing techniques. In recent years, 3D printing techniques such as extrusion-based printing, droplet-based printing, and light-assisted printing techniques have widely been applied to build sophisticated fibrous protein architectures. In this regard, a series of fibrous protein-based bioinks have been developed, such as bioinks prepared from silk fibroin, collagen, fibrin, gelatin, and recombinant spider silk. In this chapter, we present the protocols to make various fibrous protein inks, as well as how to use these bioinks to print 3D structures via different printing techniques.

Denatured pre-treatment assisted polyphenol oxidase-catalyzed cross-linking: effects on the cross-linking potential, structure, allergenicity and functional properties of OVA.

To evaluate the impacts of denatured pre-treatments (heating and denaturants) on cross-linking and the combined effect of pre-treatment and cross-linking on the structure, allergenicity and functional properties of OVA, OVA was pre-treated in different ways and then cross-linked. Results showed that the cross-linking reaction was obviously promoted with heating at 100 °C for 5 min or 0.5% of SDS as the pretreatment. Due to the coordinated process of pre-treatments and cross-linking, the secondary structure was changed and the gastrointestinal digestion of OVA was promoted. Meanwhile, the emulsifying properties, foaming properties, and antioxidant properties of OVA were remarkably improved. Furthermore, the IgG and IgE binding capacities of OVA, as well as the OVA-induced degranulation capacity of KU812 were all significantly decreased. However, upon comparing the cross-linking assisted by two different pre-treatments, it was seen that heating at 100 °C for 5 min was better than being treated with 0.5% of SDS in reducing the potential allergenicity of OVA. Therefore, we concluded that heat denaturation (at 100 °C for 5 min) assisted enzymatic cross-linking may provide a new cross-linking method to develop hypoallergenic foods with good functional properties.

A design framework for actively crosslinked filament networks

Living matter moves, deforms, and organizes itself. In cells this is made possible by networks of polymer filaments and crosslinking molecules that connect filaments to each other and that act as motors to do mechanical work on the network. For the case of highly cross-linked filament networks, we discuss how the material properties of assemblies emerge from the forces exerted by microscopic agents. First, we introduce a phenomenological model that characterizes the forces that crosslink populations exert between filaments. Second, we derive a theory that predicts the material properties of highly crosslinked filament networks, given the crosslinks present. Third, we discuss which properties of crosslinks set the material properties and behavior of highly crosslinked cytoskeletal networks. The work presented here, will enable the better understanding of cytoskeletal mechanics and its molecular underpinnings. This theory is also a first step toward a theory of how molecular perturbations impact cytoskeletal organization, and provides a framework for designing cytoskeletal networks with desirable properties in the lab.

Evaluation of anti-mold, termite resistance and physical-mechanical properties of bamboo cross-linking modified by polycarboxylic acids

Bamboo strips can be made into large-scale bamboo-based materials for construction and engineering materials, but the susceptibility of bamboo to degradation associated with moisture and microorganism attack greatly restricts its applications. In this study, chemical cross-linking modification using polycarboxylic acids [citric acid (CA) and 1,2,3,4-butanetetracarboxylic acid (BTCA)] was employed to modify the performance of bamboo strips. The results confirm the esterification reaction between CA/BTCA and bamboo components. The anti-mold property of bamboo is notably improved and achieves rating 1 mold coverings (<25%). Treated samples show high termite mortality and low mass losses, indicating good termite resistance. Owing to the cross-linking modification, the dimensional stability of bamboo is improved with anti-swelling efficiency of 29% for CA treatment and 31% for BTCA treatment. Compared with the untreated sample, polycarboxylic acids treatments cause 20–30% reduction in modulus of rupture, slight increase in modulus of elasticity, and 17–20% increase in compression strength. Moreover, the thermal stability of bamboo is enhanced by cross-linking modification. Polycarboxylic acids treatment is an eco-friendly, low-cost, and versatile method to improve bamboo properties.

The Optimization of a Novel Hydrogel-Egg White-Alginate for 2.5D Tissue Engineering of Salivary Spheroid-Like Structure.

Hydrogels have been used for a variety of biomedical applications; in tissue engineering, they are commonly used as scaffolds to cultivate cells in a three-dimensional (3D) environment allowing the formation of organoids or cellular spheroids. Egg white-alginate (EWA) is a novel hydrogel which combines the advantages of both egg white and alginate; the egg white material provides extracellular matrix (ECM)-like proteins that can mimic the ECM microenvironment, while alginate can be tuned mechanically through its ionic crosslinking property to modify the scaffold’s porosity, strength, and stiffness. In this study, a frozen calcium chloride (CaCl2) disk technique to homogenously crosslink alginate and egg white hydrogel is presented for 2.5D culture of human salivary cells. Different EWA formulations were prepared and biologically evaluated as a spheroid-like structure platform. Although all five EWA hydrogels showed biocompatibility, the EWA with 1.5% alginate presented the highest cell viability, while EWA with 3% alginate promoted the formation of larger size salivary spheroid-like structures. Our EWA hydrogel has the potential to be an alternative 3D culture scaffold that can be used for studies on drug-screening, cell migration, or as an in vitro disease model. In addition, EWA can be used as a potential source for cell transplantation (i.e., using this platform as an ex vivo environment for cell expansion). The low cost of producing EWA is an added advantage.

Study on the Effect of Zinc on the Rheological, Mechanical and Thermal Properties and Fire Hazard of Unfilled and Filled CR/BR Vulcanizates.

This paper discusses the cross-linking and functional properties of elastomer composites containing chloroprene rubber (CR) and butadiene rubber (BR) cured in the presence of zinc (Zn) and reinforced with mineral fillers. The research aimed to evaluate the effectiveness of zinc as a new cross-linking substance with the simultaneous production of elastomer materials with good mechanical properties and a reduced fire hazard. The article concerns the study and explanation of the dependencies influencing the processing and functional properties of unfilled or filled elastomer blends containing different elastomers ratio or different zinc’s amount. The following fillers were used: silica, kaolin, chalk and montmorillonite. The results revealed that the cross-linking degree of CR/BR blends decreased with the increasing amount of butadiene rubber in the blends. The mechanical properties of the cured blends depended on the proportion of elastomers in the composites, the zinc amount, and the presence and type of filler. The flammability of CR/BR/Zn vulcanizates has been investigated before and after the filling. The parameters assessed by the oxygen index method and cone calorimetry, characterizing the behavior of the tested CR/BR/Zn vulcanizates under fire conditions, have shown that they constitute a low fire hazard and can be considered as non-flammable materials.

Robust and conductive hydrogel based on mussel adhesive chemistry for remote monitoring of body signals

There is a high demand for hydrogels with multifunctional performance (a combination of adhesive, mechanical, and electrical properties) in biological, tissue engineering, robotics, and smart device applications. However, a majority of existing hydrogels are relatively rigid and brittle, with limited stretchability; this hinders their application in the emerging field of flexible devices. In this study, cheap and abundant potato residues were used with polyacrylamide (PAM) to fabricate a multifunctional hydrogel, and chitosan was used for the design of a three-dimentional (3D) network-structured hydrogel. The as-prepared hydrogels exhibited excellent stretchability, with an extension exceeding 900% and a recovery degree of over 99%. Due to the combination of physical and chemical cross-linking properties and the introduction of dopamine, the designed hydrogel exhibits a remarkable self-healing ability (80% mechanical recovery in 2 h), high tensile strength (0.75 MPa), and ultra-stretchability (900%). The resultant products offer superior properties compared to those of previously reported tough and self-healing hydrogels for wound adhesion. Chitosan and potato residues were used as scaffold materials for the hydrogels with excellent mechanical properties. In addition, in vitro experiments show that these hydrogels feature excellent antibacterial properties, effectively hindering the reproduction of bacteria. Moreover, the ternary hydrogel can act as a strain sensor with high sensitivity and a gauge factor of 1.6. The proposed strategy is expected to serve as a reference for the development of green and recyclable conductive polymers to fabricate hydrogels. The proposed hydrogel can also act as a suitable strain sensor for bio-friendly devices such as smart wearable electronic devices and/or for health monitoring.

Prospective in vivo evaluation of three different hyaluronic acid gels to varying doses of hyaluronidase with long-term follow-up

Several injectable hyaluronic acid dermal fillers exist in the market, each with different rheologic and cross-linking properties. Their reversibility is useful for managing complications. We sought to determine the response of three different hyaluronic acid gels to varying doses of hyaluronidase. Each of 18 arms of nine subjects were prospectively randomized to receive intradermal injections of hyaluronic acid gel (Restylane-L, Juvéderm Ultra, Juvéderm Voluma). Seven sites on each arm were randomized to receive 0.2 mL of hyaluronic acid gel in anticipation of dissolution 1 week later with varying doses of hyaluronidase (Hylenex), 2.5, 5, 10, or 20 units or to be a control site. The outcome measures of diameter, elevation, and firmness were measured pre-injection and at varying time points to beyond 4 years. Subjects, graders, and injectors were masked. The most dramatic changes for all fillers occurred starting at the 30-min time point through 3 h time point, with continued gradual degradation through week 2. A mild dose response was found for Juvéderm and Restylane; however, a clear dose response was seen from 2.5 to 10 units for Voluma, with 2.5 units showing features more like those of saline only or no hyaluronidase control. One Restylane arm had controls lasting four years. All fillers had a dose response, with Voluma exhibiting it most clearly. Voluma required higher doses of hyaluronidase for dissolution, i.e., more than 20 units per 0.2 mL of filler. Restylane appeared to respond most readily to hyaluronidase, at the dose of even 2.5 units, but it also was fastest to dissolve on its own.

Optimization of hyaluronic acid-tyramine/silk-fibroin composite hydrogels for cartilage tissue engineering and delivery of anti-inflammatory and anabolic drugs

Injury of articular cartilage leads to an imbalance in tissue homeostasis, and due to the poor self-healing capacity of cartilage the affected tissue often exhibits osteoarthritic changes. In recent years, injectable and highly tunable composite hydrogels for cartilage tissue engineering and drug delivery have been introduced as a desirable alternative to invasive treatments. In this study, we aimed to formulate injectable hydrogels for drug delivery and cartilage tissue engineering by combining different concentrations of hyaluronic acid-tyramine (HA-Tyr) with regenerated silk-fibroin (SF) solutions. Upon enzymatic crosslinking, the gelation and mechanical properties were characterized over time. To evaluate the effect of the hydrogel compositions and properties on extracellular matrix (ECM) deposition, bovine chondrocytes were embedded in enzymatically crosslinked HA-Tyr/SF composites (in further work abbreviated as HA/SF) or HA-Tyr hydrogels. We demonstrated that all hydrogel formulations were cytocompatible and could promote the expression of cartilage matrix proteins allowing chondrocytes to produce ECM, while the most prominent chondrogenic effects were observed in hydrogels with HA20/SF80 polymeric ratios. Unconfined mechanical testing showed that the compressive modulus for HA20/SF80 chondrocyte-laden constructs was increased almost 10-fold over 28 days of culture in chondrogenic medium which confirmed the superior production of ECM in this hydrogel compared to other hydrogels in this study. Furthermore, in hydrogels loaded with anabolic and anti-inflammatory drugs, HA20/SF80 hydrogel showed the longest and the most sustained release profile over time which is desirable for the long treatment duration typically necessary for osteoarthritic joints. In conclusion, HA20/SF80 hydrogel was successfully established as a suitable injectable biomaterial for cartilage tissue engineering and drug delivery applications.

Molecular dynamics simulation of cross-linking processes and material properties for epoxy resins using first-principle calculation combined with global reaction route mapping algorithms

Herein, epoxy resin is cured by coupling quantum chemical calculations with molecular dynamics simulations that enable the prediction of material characteristics with fewer artificial parameters. A polymer network is formed by the reaction between base resin and curing agent. The reaction uses activation energy and heat of formation data obtained by first-principle calculations coupled with global reaction route mapping algorithms. Density, glass-transition temperature, Young’s modulus, and curing conversion are used to validate the procedure. Experimental and simulation results indicate that base resin with multi-functional reaction groups increase glass-transition temperature and Young’s modulus because of cross-linking at the molecular scale.

Using facile one-pot thiol-ene reaction to prepare elastomers filled with silica

Novel elastomers filled with different contents of silica through a two-step one-pot thiol-ene reaction were reported. Two monomers of poly (ethylene glycol) dimethacrylate and 1,6-hexanedithiol were used in the first step to synthesize a vinyl-terminated prepolymer at room temperature. In the second step, silica and chemical cross-linker trimethylolpropane tris(3-mercaptopropionate) were directly added to the prepolymer in sequence and transparent elastomers were obtained in 30 min at room temperature. The cross-linking kinetics and mechanical properties in the presence of different contents of silica were investigated in detail by rheological, tensile and cyclic loading measurements. It was found that silica had a significant reinforcing effect on the mechanical properties of the elastomers. Our synthetic method is simple, solvent-free and energy- and cost-efficient. Our findings pave a new way to fabricate novel sulfur-containing elastomers using thiol-ene chemistry.

The current chemical biology tool box for studying ion channels.

Ion channels play important roles in human physiology and their dysfunction is linked to a variety of diseases. This has sparked considerable interest in their molecular function and pharmacology and generated a need to manipulate them with great precision. The use of high-sensitivity electrophysiological methods allows for the implementation of chemical biology manipulations, as even minute protein amounts can be studied. For example, modification of solvent-accessible cysteines is a powerful tool to site-selectively modify proteins through the introduction of charged moieties or those with fluorescent properties. This has been harnessed to study ion conduction pathways and monitor conformational dynamics. In ligand-directed chemistry, a high-affinity ligand is used to modify an ion channel with a chemical probe via a reactive linker. While these approaches are typically limited to extracellular positions, genetic code expansion provides a means to introduce non-canonical amino acids in any position of the protein. This enables the insertion of subtle analogues of naturally occurring side chains or the protein backbone, as well as amino acids with fluorescent, cross-linking or photo-switchable properties. Finally, protein semi-synthesis enables the simultaneous insertion of multiple modifications, including those that would not be tolerated by the ribosomal translation machinery. Collectively, these chemical biology tools have overcome various shortcomings of conventional mutagenesis and vastly expanded the scope of possible modifications and the type of ion channels they can be applied to. Their application in both heterologous and native cell systems will no doubt play an increasingly important role in ion channel research.

New gellan gum-graft-poly(d,l-lactide-co-glycolide) copolymers as promising bioinks: Synthesis and characterization

This research focused on the aim of tackling the urgent demand of printable biomaterials, hence we synthetized and characterized three gellan gum-graft-poly(d,l-lactide-co-glycolide) copolymers (GGm-PLGA a, b and c) which differed in the graft substitution degree. We investigated the effect of the polyester chain grafted onto hydrophilic backbone of gellan gum in terms of physicochemical properties and the ability of the system to print 3D cell laden constructs. In particular, we evaluated thermo-rheological, ionotropic crosslinking, shear thinning, swelling and stability properties of these copolymers and their derived biomaterials and findings related to the degree of functionalization. Moreover, the optimization of the 3D process parameters and the effect of different water/DPBS mixtures was investigated, demonstrating the feasibility of the system to print 3D constructs. Finally, biological tests revealed that fibroblasts and chondrocytes remained viable after printing and over a culture period of seven days into scaffolds.

Degradation Urushiol Coating Composition Crosslinked by Diallyl Trisulfide

Urushiol (UR) was a kind of natural paint with a long history and excellent performance. Its high price restricts its development. For the sake of the sustainable development of UR, we prepared a new urushiol based coating composition which is of degradation. To be more specific, we develop a blend by diallyl trisulfide (TS) and urushiol, in which a free radical copolymerization process would take place to form a coating composition under UV irradiation. In this work, FT-IR was used to prove the reaction proces; the reversibly cross-linking properties and the rheological properties were also been proved; the basic mechanisms active in microstructure and the associated surface energy was elucidated; mechanical analysis and showed the mechanical property of coating composition. It was found that a copolymer formed by copolymerization of diallyl trisulfide and urushiol. The introduction of trisulfide bonds assists in achieving the reversibly cross-linking under extreme alkalinity (pH > 8). various trisulfide densities brought about different microstructures on the modified urushiol. The surface energy of coating composition had been enhanced after UV-curing and its increase was related to the phase inversion (represented by microstructure). What was more, the existence of flexible segments offered the coating composition with excellent flexibility (2 mm) and rheological properties (15 MPa.S), while the hardness of coating dropped to 2H.

Dithiolane-Crosslinked Poly(ε-caprolactone)-Based Micelles: Impact of Monomer Sequence, Nature of Monomer, and Reducing Agent on the Dynamic Crosslinking Properties.

Dithiolanes are used to obtain dynamic and reversible crosslinks between polymer chains. Copolymers of two different dithiolane-containing cyclic carbonate monomers and ε-caprolactone (CL) were synthesized by ring-opening polymerization using a methoxy-poly(ethylene glycol) (mPEG) initiator and different catalysts (diphenyl phosphate (DPP), methanesulfonic acid (MSA), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), or Sn(Oct)2). Each catalyst required a different temperature, which had a pronounced influence on the reactivity ratio of the monomers and occurrence of transesterification reactions and, therefore, the monomer sequence. Self-crosslinkable copolymers were obtained when the dithiolane units were connected closely to the polymer backbone, whereas the presence of a linker unit between the dithiolane and the backbone prevented self-crosslinking. The former amphiphilic PEGylated block copolymers formed micelles by nanoprecipitation in the aqueous environment and crosslinked spontaneously by disulfide exchange during subsequent dialysis. These dithiolane-crosslinked micelles showed reduction-responsive dissociation in the presence of 10 mM glutathione, making them promising drug delivery systems for the intracellularly triggered cargo release.

Crosslinking Strategies for 3D Bioprinting of Polymeric Hydrogels.

Three-dimensional (3D) bioprinting has recently advanced as an important tool to produce viable constructs that can be used for regenerative purposes or as tissue models. To develop biomimetic and sustainable 3D constructs, several important processing aspects need to be considered, among which crosslinking is most important for achieving desirable biomechanical stability of printed structures, which is reflected in subsequent behavior and use of these constructs. In this work, crosslinking methods used in 3D bioprinting studies are reviewed, parameters that affect bioink chemistry are discussed, and the potential toward improving crosslinking outcomes and construct performance is highlighted. Furthermore, current challenges and future prospects are discussed. Due to the direct connection between crosslinking methods and properties of 3D bioprinted structures, this Review can provide a basis for developing necessary modifications to the design and manufacturing process of advanced tissue-like constructs in future.

Effects of microencapsulated abamectin on the mechanical, cross-linking, and release properties of PBS

Herein, nanocomposite microencapsulated abamectin (A-G-G) have been prepared by composite coacervation method with gelatin and gum arabic as the wall materials and abamectin (A–W) as core material. The formation mechanism of A-G-G was determined by fourier-transform infrared spectroscopy, scanning electron microscopy, and other characterization methods. Then, polybutylene succinate (PBS)/A-G-G composite films with different contents of A-G-G microcapsules were prepared. The effects of adding A-G-G microcapsules on the mechanical and sustained-release properties of the composite films were studied. Results show that there is a strong interaction between the CO groups in PBS and free OH of the A-G-G microcapsules. With an increase in the A-G-G microcapsule content, the elongation at the break of composite films increases significantly. When the A-G-G content is 15 %, the elongation at break of the composite films reaches 178.6 ± 6.26 %. The maximum water absorption is 329 ± 5.84 %. Overall, the PBS/A-G-G composite films exhibit good slow-release performance.

Influence of selected hydrocolloids on the rheological, functional, and textural properties of wheat‐pumpkin flour bread

Three hydrocolloids (carboxymethyl cellulose, guar gum, and xanthan gum) were used to improve rheological, functional, and textural properties of wheat-pumpkin flour. First, different supplementation levels of pumpkin flour (5, 10, 15, 20% wt/wt) were incorporated in wheat flour to investigate textural and sensorial parameters. Second, different hydrocolloids were substituted (0.50% wt/wt) to explore their behavior on supplemented flour. The pasting properties like peak, final, breakdown back, and setback viscosity were: 931–1,479 cP, 1,123–1,517 cP, 464–632 cP, and 656–670 cP, respectively. Dough density ranged from 1.02 to 1.19 g/cm3, whereas foaming properties like foaming capacity and foaming stability exhibited variations from 22.8% to 30.8% and 8.69% to 20.0%. Scanning electron microscope (SEM) showed that guar gum improved the microstructure and cross-linking properties of bread. It can be concluded, that mixing of pumpkin flour and guar gum improves different properties of baked products and playing positive role in baking industry. Practical applications The focus of this research is on the quality parameters of supplemented flour dough and breads under the effect of different hydrocolloids. Hydrocolloids, due to their hydrophilic nature, impart positive rheological properties to dough having better viscoelastic behavior then control treatments by strengthening gluten network and improved functional properties. The bread samples exhibit smooth texture and better heat stability which is quite beneficial in baking and for food products that require high-temperature processing. In the end, images of scanning electron microscope demonstrated that hydrocolloids improved porosity and microstructure of bread significantly, hence, it is concluded that guar gum have positive impact on quality parameters of bread containing wheat and pumpkin flours.