Cross-linking Properties Research Articles

An effective salt-tolerant fluid loss additive-suitable for high temperature oil well cement

In this article, high temperature resistant and salt-tolerant fluid loss additive (FLA) is synthesized by aqueous free radical copolymerization of terpolymer comprising sodium p-styrene sulfonate (SSS), N-hydroxymethyl acrylamide (HAM), and itaconic acid (IA), and then evaluated as FLA (SSS/HAM/IA) in oil-well cement. Based on thermogravimetric analysis and fluid loss of experiments, it is found that the SSS/HAM/IA exhibits good temperature resistance and fluid loss performance, and can be used in temperatures ranging from 30 to 180 °C. Under the condition of 120 °C, using 6% SSS/HAM/IA ensures that the API fluid loss of saturated brine cement slurry systems is less than 50 mL, and strong salt resistance is retained. This is due to the cross-linking properties of the HAM molecule, which causes the terpolymer to exhibit a cross-linked structure, improving SSS/HAM/IA fluid loss ability.

Extracellular production of Streptomyces ladakanum transglutaminase in a food-grade strain, Bacillus subtilis

Background: Transglutaminase (TG) is an enzyme of the transferase family with cross-linking properties, which has been widely used in the food industry. Traditionally, TG is isolated from strains of Streptomyces sp. However, the development of a facile and efficient production of commercial TG is always desirable. Purpose: In the current study, we described an efficient route for TG production in a food-grade strain of bacteria, Bacillus subtilis. Method: Two strategies were employed for the extracellular production of S. ladakanum TG in B. subtilis. Sixteen signal peptides were optimized to secret TG into the extracelluar medium. Site-directed mutageneses in pro-peptide were further utilized to improve the enzymatic activity. The enzymatic characteristics of S. ladakanum TG expressed in B. subtilis were analyzed. Results: The N-terminal amino acids played important roles in enzymatic activity. Signal peptides of SacB (SPSacB) and AbnA (SPAbnA) showed good abilities to direct the secretion of TG into the medium. The enzyme was secreted into the medium and exhibited good Ca2+ stability and temperature stability, which were comparable to those produced by commercial strains. The enzymatic activity in the supernatant of culture reached 7.6 U/mg. Conclusion: Our study demonstrated that B. subtilis may be a good candidate for the efficient and stable production of TG and has a much easier purification process. Keywords: Transglutaminase (TG), Streptomyces TG, Bacillus subtilis, Food-grade strain.

Blue emissive dimethylmethylene-bridged triphenylamine derivatives appending cross-linkable groups.

Five new dimethylmethylene-bridged triphenylamine (DTPA) derivatives 4a-e bearing peripheral cross-linkable vinyl and trifluorovinyl groups were synthesized. The chemical structure of these compounds was characterized by 1H NMR, 13C NMR and HRMS. Their optical properties were studied by UV/Vis spectroscopy and fluorescence spectroscopy. Based on these studies, blue-coloured fluorescence and high fluorescence quantum yields were obtained for 4a-e. The electrochemical properties of these compounds were studied by cyclic voltammetry and the results were further elucidated by DFT calculations. Furthermore, the thermotropic properties of the new DTPAs were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). Compounds 4a-d exhibit high thermal stability and thermal cross-linkable properties. These results provide an effective strategy for the design and synthesis of thermally stable and cross-linkable DTPA derivatives with tunable optical and electrochemical properties.

Improved cell viability for large-scale biofabrication with photo-crosslinkable hydrogel systems through a dual-photoinitiator approach.

Biofabrication with various hydrogel systems allows the production of tissue or organ constructs in vitro to address various challenges in healthcare and medicine. In particular, photocrosslinkable hydrogels have great advantages such as excellent spatial and temporal selectivity and low processing cost and energy requirements. However, inefficient polymerization kinetics of commercialized photoinitiators upon exposure to UV-A radiation or visible light increase processing time, often compromising cell viability. In this study, we developed a hydrogel crosslinking system which exhibited efficient crosslinking properties and desired mechanical properties with high cell viability, through a dual-photoinitiator approach. Through the co-existence of Irgacure 2959 and VA-086, the overall crosslinking process was completed with a minimal UV dosage during a significantly reduced crosslinking time, producing mechanically robust hydrogel constructs, while most encapsulated cells within the hydrogel constructs remained viable. Moreover, we fabricated a large PEGDA hydrogel construct with a single microchannel as a proof of concept for hydrogels with vasculature to demonstrate the versatility of the system. Our dual-photoinitiator approach allowed the production of this photocrosslinkable hydrogel system with microchannels, significantly improving cell viability and processing efficiency, yet maintaining good mechanical stability. Taken together, we envision the concurrent use of photoinitiators, Irgacure 2959 and VA-086, opening potential avenues for the utilization of various photocrosslinkable hydrogel systems in perfusable large artificial tissue for in vivo and ex vivo applications with improved processing efficiency and cell viability.

Review transglutaminases: part II-industrial applications in food, biotechnology, textiles and leather products.

Because of their protein cross-linking properties, transglutaminases are widely used in several industrial processes, including the food and pharmaceutical industries. Transglutaminases obtained from animal tissues and organs, the first sources of this enzyme, are being replaced by microbial sources, which are cheaper and easier to produce and purify. Since the discovery of microbial transglutaminase (mTGase), the enzyme has been produced for industrial applications by traditional fermentation process using the bacterium Streptomyces mobaraensis. Several studies have been carried out in this field to increase the enzyme industrial productivity. Researches on gene expression encoding transglutaminase biosynthesis were performed in Streptomyces lividans, Escherichia coli, Corynebacterium glutamicum, Yarrowia lipolytica, and Pichia pastoris. In the first part of this review, we presented an overview of the literature on the origins, types, mediated reactions, and general characterizations of these important enzymes, as well as the studies on recombinant microbial transglutaminases. In this second part, we focus on the application versatility of mTGase in three broad areas: food, pharmacological, and biotechnological industries. The use of mTGase is presented for several food groups, showing possibilities of applications and challenges to further improve the quality of the end-products. Some applications in the textile and leather industries are also reviewed, as well as special applications in the PEGylation reaction, in the production of antibody drug conjugates, and in regenerative medicine.

Incorporation of dumbbell-shaped and Y-shaped cross-linkers in adjustable pullulan/polydopamine hydrogels for selective adsorption of cationic dyes

Hydrogel adsorbents have attracted considerable attention due to their sludge minimization, good water permeability and renewable performance. Here, a promising strategy for the one-step preparation of pullulan/polydopamine hybird hydrogels (PPGels) was presented. Dumbbell-shaped cross-linker neopentyl glycol diglycidyl ether (NGDE, 2 arms) and Y-shaped cross-linker trimethylolpropane triglycidyl ether (TTE, 3 arms) were selected to study the relationship between cross-linker structure and hydrogel performances. The NGDE possessing less molecular repulsive force and higher reactivity demonstrated more effective cross-linking with the pullulan, which leaded to a decrease in pore size of the hydrogel. Meanwhile, the introduction of polydopamine significantly enhanced the adsorption ability and gave the resulting hybrid gel the specific selectivity toward cationic dyes (96 mg/g for crystal violet, 25.8 mg/g for methylene blue and barely not adsorption for azophloxine). Our data suggested that the electrostatic interaction played a vital role in the dye adsorption process, and the adsorption data could be explained by pseudo-second-order model and Langmuir isotherm model. Furthermore, the obtained PPGel could be easily separated after adsorption. This study describes the relationship between cross-linker structure and properties of pullulan/polydopamine hybrid gels, which provides a new strategy to create polysaccharide-based adsorbents for wastewater remediation.

Genipin as An Emergent Tool in the Design of Biocatalysts: Mechanism of Reaction and Applications

Genipin is a reagent isolated from the Gardenia jasminoides fruit extract, and whose low toxicity and good crosslinking properties have converted it into a reactive whose popularity is increasing by the day. These properties have made it widely used in many medical applications, mainly in the production of chitosan materials (crosslinked by this reactive), biological scaffolds for tissue engineering, and nanoparticles of chitosan and nanogels of proteins for controlled drug delivery, the genipin crosslinking being a key point to strengthen the stability of these materials. This review is focused on the mechanism of reaction of this reagent and its use in the design of biocatalysts, where genipin plays a double role, as a support activating agent and as inter- or intramolecular crosslinker. Its low toxicity makes this compound an ideal alterative to glutaraldehyde in these processes. Moreover, in some cases the features of the biocatalysts prepared using genipin surpassed those of the biocatalysts prepared using other standard crosslinkers, even disregarding toxicity. In this way, genipin is a very promising reagent in the design of biocatalysts.

Characterization of CR/BR/nZnO blends filled with silica mineral fillers

This paper discusses the effect of the silica mineral fillers: chalcedony, Sillitin, aerosil on the cross-linking, mechanical and thermal properties of chloroprene and butadiene rubber (CR/BR) blends. A novelty is also the use of nano-zinc oxide (nZnO) as a cross-linking agent. The results revealed that chalcedony, Sillitin and aerosil can be used to the reinforcement of the CR/BR/nZnO vulcanizates. All filled composites were characterized by satisfying tensile strength and tear resistance investigated by means of a Zwick testing machine. Additionally, the tests of mechanical properties also included Shore hardness measurement. The dumping properties were determined for vulcanizates subjected to compressive stresses. The filler dispersion in the elastomer matrix was carried out by using scanning electron microscopy (SEM). Based on the hysteresis losses measurement and the Payne effect, it was found that these fillers in the elastomer matrix (CR/BR) formed the specific extra-network by the filler-filler interactions. Thermal stability studies were performed using Differential Scanning Calorimetry (DSC). Very high resistance to flame of filled CR/BR/nZnO vulcanizates was confirmed by measuring the oxygen index (OI).

Prevention of dental caries by grape seed extract supplementation: A systematic review.

Dental caries are the most prominent chronic disease of children and adults worldwide, and facilitating evidence-based, preventative care for their prevention is critical. Caries are traditionally and successfully prevented by regular fluoride use, but there are opportunities to halt and restore caries with alternative agents in addition to fluoride use. Grape seed extract (GSE) is a readily available plant-based supplement that, due to its concentrated levels of proanthocyanidins, has promising characteristics that may assist in dental caries prevention. The goal of this review was to investigate whether current research supports use of grape seed extract to prevent dental caries formation. A systematic review of articles related to grape seed extract, prevention of dental caries, inhibition of Streptococcus mutans, and remineralization was conducted. Articles were first chosen by inclusion of dental models that used grape seed extract as an intervention, and then by strength of study design. Twenty articles were reviewed. Studies overall supported three unique grape seed extract properties facilitating dental caries prevention. In the first articles reviewed, grape seed extract inhibited proliferation of bacterial biofilms on tooth surfaces. In addition, studies reviewed indicated that grape seed extract promoted dental remineralization. Caries prevention by grape seed extract may be unique compared with fluoride, and is linked to grape seed extract's bacteriostatic and collagen crosslinking properties. Future research should investigate potential delivery methods, and benefits of combined grape seed extract use with known caries preventative agents, in human participants.

Hydroxypropylation of cross-linked sesbania gum, characterization and properties

Sesbania gum (SG) was successfully modified by combining cross-linking with hydroxypropylation in solvent of ethanol. The hydroxypropylation technology parameters were optimized by the orthogonal test. The results indicated that both cross-linking and hydroxypropylation could improve the freeze-thaw stability, acid and alkali resistance of SG. After the cross-linking and hydroxypropylation of SG, the retrogradation was evidently strengthened. The surfaces of SG derivatives such as cross-linked sesbania gum (CLSG) and hydroxypropyl cross-linked sesbania gum (HCLSG) particles also became very rough, compared with SG. The sequence combination of first cross-linking and then hydroxypropylation was helpful to the follow-up hydroxypropylation of SG. The cross-linking and hydroxypropylation resulted in an obvious reduction in the melting enthalpy of SG, which belonged to a semicrystalline polymer. The cross-linking and hydroxypropylation influenced the thermal properties, and destroyed the crystalline regions of SG. According to SEM, the hydroxypropylation has greater contribution to the destruction than cross-linking. Both cross-linking and hydroxypropylation gave rise to the expansion of SG grains, but the swelling manner was different each other.

Ligand modified cellulose fabrics as support of zinc oxide nanoparticles for UV protection and antimicrobial activities

This work is a critical preventive study for providing a healthy life and enhancing people's safety at work in which introduces of highly efficient and durable UV-protection and antibacterial textiles. With this aim, ZnO nanoparticles are in situ synthesized on the modified cotton fabric to produce the multifunctional fabrics. Herein, the cotton fabric is oxidized by periodate and then treated by 4-aminobenzoic acid ligand (PABA). The modified cotton fabrics are characterized via X-ray powder diffraction, Fourier-transform infrared spectroscopy-attenuated total reflectance, scanning electron microscope, X-ray photoelectron spectroscopy, and thermogravimetric analysis. Moreover, the anti-bacterial, UV-protection, hydrophilicity, and mechanical properties of samples are investigated. The results show that pre-oxidization cotton fabric provides better active sites for the treatment with PABA. Then, PABA treatment provides significant sites for the growth of the ZnO nanoparticles and maintains cross-linking property between oxidized cellulosic fibers and the ZnO nanoparticles which improves the formation and durability of ZnO nanoparticles. The simultaneous sample treatment with ZnO and PABA had synergistic effects on UV protection, stability, and mechanical properties. Moreover, the ZnO PABA oxidized cotton fabrics show excellent UV-protection and significant antibacterial efficacy after 20 washing cycles and 100 abrasion cycles, which can be used in advanced protective textiles.

Rubber Magnetic Composites Cross-Linked with Peroxide Curing Systems

Styrene–butadiene rubber and acrylonitrile–butadiene rubber as elastomer matrices were filled with barium ferrite in order to prepare rubber magnetic composites. For cross-linking of rubber compounds, peroxide curing systems consisting of dicumyl peroxide as curing agent and four types of low molecular weight organic compounds as co-agents were used. The work was focused on the investigation of different types of co-agents on the cross-linking, physical-mechanical and magnetic properties of the prepared composites. The results revealed that the type and amount of co-agent has no influence on magnetic characteristics of composites. On the other hand, cross-link density and physical-mechanical properties were significantly dependent on the composition of curing system. Co-agents contribute to the improvement of adhesion on the interphase filler-rubber. Considering the type of rubber matrix, higher values of tensile strength exhibited composites based on acrylonitrile–butadiene rubber. As magnetic filler and co-agents are polar materials, their compatibility with polar elastomers like acrylonitrile-butadiene rubber is much higher when compared to no-polar elastomers like styrene–butadiene rubber.

Synthesis and characterisation of smart poly vinyl ester / Pb2O3 nanocomposite for gamma radiation shielding

Different ratios of Pb2O3 nanoparticles were mixed with poly vinyl ester to apply the same in gamma radiation shielding. Moreover, exposing the accelerated electron beam to the mixture proved to be an efficient tool to achieve the final cross-linking and optimum physical properties. Proper composition (PVE with 50% of Pb2O3 by weight) and irradiation dose (50 kGy) of the prepared nanocomposite (PVPbNC) led to a lesser amount of lead leachate. The PVPbNC was characterised in the following ways: chemically by using Fourier transformer infrared (FTIR) spectroscopy, thermally by performing thermogravimetric analysis (TGA) and morphologically by employing scanning electron microscopy (SEM). Different physical properties such as hardness, gel fraction (%), as well as water and toluene uptake (WR) were investigated. Additionally, gamma shielding properties and their impacts on PVPbNC such as attenuation% (att%) (at different thicknesses), which reached 86%, was measured. The half-value layer (HVL), tenth-value layer (TVL), mean free path (MFP), linear attenuation coefficient (μ) and mass attenuation coefficient (μm) (at different irradiation sources) were also evaluated. Furthermore, composite heaviness was studied in comparison to different traditional gamma radiation absorbers. The PVPbNC applicability in gamma shielding properties exceeded all previously performed glass systems, the majority of polymeric materials, as well as steel and metal alloys, and can be applied successfully in different fields. PVPbNC durability confirmed their applicability to being exposed to 662 keV up to 5000 kGy in comparison to different radiation absorbers that have been previously analysed.

Synthesis and Properties of Polycarbosilanes Having Lactose‐Derived Structures

ABSTRACTA polycarbosilane having lactose‐derived structures was synthesized, and its thermal property, cytotoxicity, chemical crosslinking, and protein adsorption properties were investigated. The polycarbosilane (PSB‐Lac) was prepared by a thiol‐ene reaction between precursor poly(1‐(3‐butenyl)‐1‐methylsilacyclubane) (PSB) and heptaacetyl lactose that carried a thiol group at the anomeric position, and the successive deprotection of the acetyl groups. The lactose introduction efficiency determined by 1H NMR measurement was 75%. TGA and DSC revealed that the polymer had a 5 wt% decomposition temperature of 260 °C and glass transition temperature (Tg) of 84 °C, which indicated that PSB‐Lac was a thermally stable polymer. PSB‐Lac had no significant cytotoxicity, which was evaluated by human liver cancer cell line HepG2 cultivation on the polystyrene dishes coated with the polymer. Urethane‐crosslinked PSB‐Lac films were prepared by casting solutions of PSB‐Lac and hexamethylene diisocyanate and heating at 120 °C after evaporation of the solvent. The crosslinked PSB‐Lac showed higher adsorption of bovine serum albumin than the similarly crosslinked polycarbosilane that had a glucose structure (PSB‐Glc). © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2420–2425

PH-induced Crosslinking of Rice Starch via Schiff Base Formation

Rice starch is an abundant, inexpensive, and biocompatible biopolymer with a wide range of potential applications, particularly in the biomedical field. However, the use of rice starch is limited because of its water-solubility. One way of addressing this is to modify the crosslinking properties. If the degree of crosslinking is sufficiently high, the starch becomes insoluble in water, but it remains swellable. In this study, the first synthesis of pH-induced crosslinking of rice starch without the use of any external chemical crosslinking agent was demonstrated. The crosslinked rice starch was prepared by forming a Schiff base reaction (imine) between the two modified starches: oxidized rice starch (ORS) and amino rice starch (ARS). Here, the ORS and ARS were successfully synthesized, with the content of the glucose units being 32.01 and 27.80 mol%, respectively. Imine bonds were shown to be formed from the aldehyde and amine groups. The relationships between the pH and the degree of crosslinking were also investigated. The chemical structures of the synthesized ORS and ARS and their crosslinked products at different pH levels were determined by 1H NMR, 13C NMR, and FTIR Furthermore, the effect of pH on swelling behavior was explored. The relationships between the pH and the chemical structure agreed well with the swelling behavior. The swelling ratio was the highest at pH 5 and decreased with increased pH. Under basic conditions, hydrolysis was initiated, reducing the crosslink density and the efficiency of water uptake. The present study suggests that the pH-induced crosslinked rice starch can be a promising biomaterial for controlled release applications.

Dynamic Mechanical Analysis and Creep-recovery behaviour of Polyvinyl Alcohol based cross-linked Biocomposite reinforced with Basalt fiber

Polyvinyl alcohol (PVA) is a synthetic, semi-crystalline, biodegradable and water soluble polymer having moderate mechanical properties. In the present investigation, restriction in water absorption of PVA is achieved by cross-linking with hydrochloric acid (HCl) which is confirmed by Fourier transform infrared spectroscopy (FTIR) and water uptake test. Results suggest that due to the formation of cross-linked bonds thermal and mechanical properties of PVA based cross-linked composite are improved as compared to pristine PVA. Further improvement in physical, mechanical and thermal properties is achieved by reinforcing basalt fibers. Tensile test results show that ultimate tensile strength (UTS) of basalt fiber reinforced composites increased by 79.4% as compared to the cross-linked PVA. Dynamic mechanical analysis of fabricated composites has been carried out to determine the storage modulus, glass transition temperature and activation energy. Effect of stress and temperature on creep and recovery behavior of cross-linked PVA and basalt fiber reinforced composite are studied and burger model is used to study the creep data.

Crystal structure, DNA crosslinking and photo-induced cytotoxicity of oxovanadium(IV) conjugates of boron-dipyrromethene

Cis-dichloro-oxovanadium(IV) complexes [VO(L1/L2)Cl2], where L1 is N-(4-(5,5-difluoro-1,3,7,9-tetramethyl-5H-4ʎ4,5ʎ4-dipyrrolo[1,2-c:2′,1′-f][1,3,2]diazaborinin-10-yl)benzyl)-1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine in 1 and L2 is N-(4-(5,5-difluoro-2,8-diiodo-1,3,7,9-tetramethyl-5H-4ʎ4,5ʎ4-dipyrrolo[1,2-c:2′,1′-f][1,3,2]diazaborinin-10-yl)benzyl)-1-(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine in 2) having 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene as boron-dipyrromethene (BODIPY) appended dipicolylamine bases were prepared, characterized and their photocytotoxicity studied. X-ray crystal structure of 1 showed distorted octahedral geometry with a VIVON3Cl2 core having Cl-V-Cl angle of 91.93(4)°. The complexes showed variable solution conductivity properties. They were non-electrolytes in dry DMF at 25 °C but showed 1:1 electrolytic behavior in an aqueous medium due to dissociation of one chloride ligand as evidenced from the mass spectral study. Complexes 1 and 2 showed absorption bands at 500 and 535 nm, respectively. The calf thymus DNA melting study revealed their interaction through DNA crosslinking on exposure to light which was further confirmed from the alkaline agarose gel electrophoresis using plasmid supercoiled pUC19 DNA. Complex 2 showed disruption of the mitochondrial membrane potential in the JC-1 (1,1′,3,3′-tetraethyl-5,5′,6,6′-tetrachloroimidacarbocyanine iodide) assay. The complexes were photocytotoxic in visible light (400–700 nm, power: 10 J cm−2) in cervical cancer HeLa and breast cancer MCF-7 cells. Complex 2 having a photoactive diiodo‑boron-dipyrromethene moiety gave a singlet oxygen quantum yield (ΦΔ) value of ~0.6. It showed singlet oxygen mediated apoptotic photodynamic therapy activity with remarkably low IC50 (half maximal inhibitory concentration) value of ~0.15 μM. The cis-disposition of chlorides gave a cis-divacant 4-coordinate intermediate structure from the density functional theory (DFT) study thus mimicking the DNA crosslinking property of cisplatin.

Optimization of silk fibroin membranes for retinal implantation.

Silk fibroin membrane displays potential for ocular tissue reconstruction as demonstrated by its ability to support a functioning retinal pigment epithelium (RPE) in vitro. Nevertheless, translation of these findings to the clinic will require the use of membranes that can be readily handled and implanted into diseased retinas, with minimal impact on the surrounding healthy tissue. To this end, we optimized the physical properties of fibroin membranes to enable surgical handling during implantation into the retina, without compromising biocompatibility or permeability. Our central hypothesis is that optimal strength and permeability can be achieved by combining the porogenic properties of poly(ethylene glycol) (PEG) with the crosslinking properties of horseradish peroxidase (HRP). Our study reveals that PEG used in conjunction with HRP enables the production of fibroin membranes with superior handling properties to conventional fibroin membranes. More specifically, the modified membranes could be more easily implanted into the retinas of rats and displayed good evidence of biocompatibility. Moreover, the modified membranes retained the ability to support construction of functional RPE derived from pluripotent stem cells. These findings pave the way for preclinical studies of RPE-implantation using the optimized fibroin membranes.

Effects of ex vivo ionizing radiation on collagen structure and whole-bone mechanical properties of mouse vertebrae.

Bone can become brittle when exposed to ionizing radiation across a wide range of clinically relevant doses that span from radiotherapy (accumulative 50 Gy) to sterilization (~35,000 Gy). While irradiation-induced embrittlement has been attributed to changes in the collagen molecular structure, the relative role of collagen fragmentation versus non-enzymatic collagen crosslinking remains unclear. To better understand the effects of radiation on the bone material without cellular activity, we conducted an ex vivo x-ray radiation experiment on excised mouse lumbar vertebrae. Spinal tissue from twenty-week old, female, C57BL/6J mice were randomly assigned to a single x-ray radiation dose of either 0 (control), 50, 1000, 17,000, or 35,000 Gy. Measurements were made for collagen fragmentation, non-enzymatic collagen crosslinking, and both monotonic and cyclic-loading compressive mechanical properties. We found that the group differences for mechanical properties were more consistent with those for collagen fragmentation than for non-enzymatic collagen crosslinking. Monotonic strength at 17,000 and 35,000 Gy was lower than that of the control by 50% and 73% respectively, (p < 0.001) but at 50 and 1000 Gy was not different than the control. Consistent with those trends, collagen fragmentation only occurred at 17,000 and 35,000 Gy. By contrast, non-enzymatic collagen crosslinking was greater than control for all radiation doses (p < 0.001). All results were consistent both for monotonic and cyclic loading conditions. We conclude that the reductions in bone compressive monotonic strength and fatigue life due to ex vivo ionizing radiation are more likely caused by fragmentation of the collagen backbone than any increases in non-enzymatic collagen crosslinks.

Carboxylic modification of welan gum

ABSTRACTWelan gum has disadvantages such as poor solubility, low viscosity, and poor crosslinking property, when it is applied in petroleum industry, comparing to guar gum. Two methods for the carboxylic modification of welan gum were developed, carboxyethyl modification and citric acid modification, to improve the solubility in water, viscosity, and crosslinking ability of welan gum in the borax crosslinking system. The solubility time of carboxyethyl modified and citric acid modified welan gum were shortened to 30 and 90 min, respectively. The highest viscosity of citric acid modified product was 49.4 mPa s, the viscosity after crosslinking was raised at least 1.2 times to the highest four times than that before crosslinking. The results indicated three factors affecting the properties of modified products: (1) how many function groups in the modifying agent; (2) the way to connect the function group; and (3) the whole structure of the modifying agent. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48301.