Rate Of Crosslinking Research Articles

The effect of NaY‐zeolite on mechanical, thermal, and spectroscopic behavior of crosslinked polyvinyl alcohol films

AbstractThe effects of sodium y zeolite (NaY‐zeolite) on crosslinked Polyvinyl alcohol (CrPVA) composite films were investigated. The spectroscopic analysis showed that crosslinks were formed between PVA, Tartaric acid (TA), and NaY‐zeolite particles. The thermal stability of the CrPVA film was improved with the addition of zeolite. Optimum thermal stability was observed for 5 wt % zeolite content. It can be seen that the mechanical properties also improved for 5 wt % zeolite‐doped CrPVA composite films when compared with CrPVA. It was observed that Young's modulus increased 54.14 to 74.49 MPa. While the degree of crystallinity of the composite film decreased from 20.42 to 14.77% due to zeolite content. This is thought to be due to the increase in the structure's crosslinking rate. The utilization of TA and NaY zeolite in membrane applications may be considered an advantage for improving the mechanical characteristics and the recyclability of membrane technology.

The effect of crosslinking rate on the thermal and mechanical properties of liquid crystal elastomer: A molecular dynamics study

Crosslinking rate is an important factor affecting thermo-mechanical properties of liquid crystal elastomers (LCEs). In this paper, molecular models for LCEs with different crosslinking rates are firstly established, and then the thermo-phase transition process is simulated. The variation of volume fraction and energy in each molecular component during the phase transition are given, and the relationship between phase transition temperature and crosslinking rate is formulated. Modulus contour map for LCEs with different crosslinking rates are plotted to see the influence of crosslinking rate on their mechanical properties. The results indicate that the inflection point on the free volume-temperature curve corresponds to the glass transition temperature at which the rotation and twisting of mesogen and PMHS is strengthened. Crosslinking enhances molecular bonds between mesogen and PMHS which results in longer glassy plateau, and moderate crosslinking benefits the improvement of elastic moduli of LCEs. The results obtained in the paper provide a guidance for the molecular design of liquid crystal elastomers.

Self-Neutralizing Melamine-Urea-Formaldehyde-Citric Acid Resins for Wood Panel Adhesives.

In this study, we used a self-neutralizing system to counteract too acidic a pH, unsuitable for wood adhesives, and tested it on MUF resins augmented by the addition of citric acid or other organic acids, based on the addition of small percentages of hexamine or another suitable organic base to form an acid-base buffer. In this manner, the pH of the adhesive was maintained above the minimum allowed value of 4, and the strength results of wood particleboard and plywood bonded with this adhesive system increased due to the additional cross-linking imparted by the citric acid. Thus, the wood constituents at the wood/adhesive interface were not damaged/degraded by too low a pH, thus avoiding longer-term service failure of the bonded joints. The addition of the buffering system increased the strength of the bondline in both the plywood and particleboard, both when dry and after hot water and boiling water tests. The IB strength of the particleboard was then increased by 15-17% when dry but by 82% after boiling. For the plywood, the shear strengths when dry and after 3 h in hot water at 63 °C were, respectively, 37% and 90% higher than for the control. The improvement in the bonded panel strength is ascribed to multiple reasons: (i) the slower, more regular cross-linking rate due to the action of the buffer; (ii) the shift in the polycondensation-degradation equilibrium to the left induced by the higher pH and the long-term stability of the organic buffer; (iii) the additional cross-linking by citric acid of some of the MUF resin amine groups; (iv) the already known direct linking of citric acid with the carbohydrates and lignin constituents at the interface of the wood substrate; and (v) the likely covalent linking to the interfacial wood constituents of the prelinked MUF-citric acid resin by some of the unreacted citric acid carboxyl groups.

Preparation and properties of unsaturated zinc carboxylate/EPDM composites

ABSTRACT The unsaturated zinc carboxylate/Ethylene-Propylene-Diene Monomer (EPDM) composites were prepared by mechanical blending. The effects of hydroxy (2-methylprop-2-enoato-O)zinc (ZMMA) and zinc dimethacrylate (ZDMA) on the hydrophobicity, mechanical properties, ageing resistance, and electrical properties of the composites were studied. The results show that the mechanical properties, crosslinking rate, crosslinking density, and oil resistance of the composite are significantly improved with the increase of ZMMA and ZDMA content. The crosslinking density of EPDM filled with 15 phr of ZDMA composite material is 3.22 × 10−3 mol/cm3, compared with the samples without ZDMA filling, the improvement was 175.2%, and the tensile strength reaches 16.9 MPa, which increases by 33.6%. The addition of a small amount of unsaturated carboxylate has a positive effect on the electrical properties of EPDM matrix composites. The volume resistivity of the EPDM filled with 5 phr of ZDMA is 16.2 × 1013 Ω·m, an increase of 36.1%.

Effect of Chemical Composition of Metal-Organic Crosslinker on the Properties of Fracturing Fluid in High-Temperature Reservoir.

To investigate the effect of the chemical composition of a metal-organic crosslinker on the performances of fracturing fluid in high-temperature conditions, four zirconium (Zr) crosslinkers and one aluminum-zirconium (Al-Zr) crosslinker with a polyacrylamide were used. The crosslinkers possessed the same Zr concentration, but they differed in component amounts and the order of the addition of the crosslinker components, leading to different chemical compositions in the crosslinkers. The fracturing fluids prepared by different tested crosslinkers were compared in terms of properties of rheological behavior, sand-carrying ability, microstructure, and gel breaking characteristics. The results showed that the fracturing fluids prepared by zirconium lactic acid, ethanediamine, and sorbitol crosslinkers offered the slowest viscosity development and highest final viscosity compared to the zirconium lactic acid crosslinker and the zirconium lactic acid and ethanediamine crosslinker. The zirconium sorbitol, lactic acid, and ethanediamine crosslinker exhibited a faster crosslinking rate and a higher final viscosity than the zirconium lactic acid, ethanediamine, and sorbitol crosslinker; the crosslinker showed crosslinking density and crosslinking reactivity, resulting in more crosslinking sites and a higher strength in the fracturing fluid. The Al-Zr-based crosslinker possessed better properties in temperature and shear resistance, viscoelasticity, shear recovery, and sand-carrying ability than the Zr-based crosslinker due to the synergistic crosslinking effect of aluminum and zirconium ions. The tertiary release gelation mechanism of the Al-Zr-based fracturing fluid achieved a temperature resistance performance in the form of continuous crosslinking, avoiding the excessive crosslinking dehydration and reducing viscosity loss caused by early shear damage. These results indicated that the chemical compositions of metal-organic crosslinkers were important factors in determining the properties of fracturing fluids. Therefore, the appropriate type of crosslinker could save costs without adding the additional components required for high-temperature reservoirs.

Design and experimental study on rheological behavior and sealing performance of shear sensitive fluids to control lost circulation during drilling

Loss circulation is considered as a time-consuming, costly, and challenging issue while drilling or cementing jobs, which ought to be treated and resolved promptly. The choice of a treatment that quickly plugs the loss zone and helps to restore the circulation is critical. Cross-linkable polymer gels play a significant role in mitigating drilling fluid loss, but controlling the gelation time and pumpability are the main challenges of these gels. This research aims to evaluate a novel smart fluid that has high flexibility in design. The shear sensitive fluid (SSF) is an oil-based fluid containing a polymer, gelation agents, and multi-crosslinkers. After passing through the drilling bit, the SSF is crosslinked with time to produce a high strength gel. The designed shear sensitive fluid is one of the possible solutions for severe loss circulation.The overall purpose of this research was to scrutinize the gelation behavior and SSF performance as a smart lost circulation treatment, which was followed in two sections including experimental analysis and empirical modeling. The effect of various factors including the type of crosslinker, shear rate, emulsifier concentration, temperature, shear history, salinity, etc. on the performance of the formed gels was studied. Furthermore, the maximum sealing pressure of formed gels in the highly permeable porous medium and fractured core as well as the probability of formation damage was evaluated.In order to determine the correlations required to predict the ultimate gelation time of SSF, the response surface methodology was utilized according to the central composite design. The considerable values of correlation coefficients (R2 = 0.91) prove the validity of estimated models for the fit enough responses with the experimental data. For the designed SSFs, depending on the operating conditions, the appropriate gelation time can be adjusted by emulsifier concentration and shear rate values. Also, the minimum gelation time and the highest crosslinking rate occur approximately at the shear rate of 45,000 1/s. At high shear rates, the effect of temperature on the functionality of the formed gels decreases, which is due to the high rate of crosslinking. Based on dynamic sealing pressure tests, the SSFs have a high potential in mitigation of lost circulation during drilling. The maximum sealing pressure was measured above 1000 psi in highly permeable porous medium and up to 600 psi in fractured core, which indicate the high strength of the formed gels against drilling fluid pressure. The designed SSFs could be easily removed from reservoir by 15 vol% hydrochloric acid, indicating the non-damaging properties of the formed gels.

Abstract 3167: Impact of gemcitabine modification on redox-driven responses in pancreatic cancer organoids cultured in distinct 3D microenvironments

Abstract Pancreatic ductal adenocarcinoma (PDAC) poses a formidable challenge in oncology, characterized by its high lethality and limited treatment options. The advanced stage at diagnosis, aggressive metastasis, and the constrained efficacy of conventional therapeutic drugs collectively contribute to the grim prognosis associated with PDAC. Gemcitabine, a nucleoside analog and the longstanding standard chemotherapy for pancreatic cancer, encounters a significant hurdle in its efficacy due to the development of resistance. To establish a cancer-acquired resistance model applicable to Gem-modified drugs, it is crucial to account for the dense extracellular matrix (ECM) composition characteristic of PDAC. In this investigation, we employ three-dimensional (3D) cell culture models, specifically utilizing pancreatic cancer patient-derived organoids (PDOs) within a 3D matrix with tunable density and stiffness by incorporating variations in transglutaminase crosslinking rates. PDAC cells from different patients exhibit diverse adaptations within these altered gel matrix environments, manifesting differences in morphology, doubling time, and responses to drugs. Notably, PDAC cells display pronounced stemness characteristics in the dense matrix, featuring a more rounded and compact appearance and an increase in ABC transporters.Addressing the challenge of gemcitabine resistance, modifications such as gemcitabine conjugates with stearate (Gem-S) have shown promise in preclinical studies. Exploring the effects of both Gem and Gem-S in a viscoelastic-specific ECM model derived from PDAC patient-derived organoids, distinct responses based on matrix stiffness come to light. The physical properties of the matrix exert a significant influence on cellular function, thereby impacting the effectiveness of therapeutic agents. Intriguingly, within a stiffer environment, Gem-S demonstrates higher sensitivity compared to Gem, suggesting the potential application of Gem-S in the dense pathological PDAC environment. Further investigation reveals that Gem-S treatment induces a noteworthy increase in reactive oxygen species (ROS) and HIF-1 expression compared to Gem. Surprisingly, the role of multidrug transporters in Gem-S sensitivity is limited, while the downregulation of NRF (Nrf2) after Gem-S treatment hints at distinct mechanisms underlying the development of drug resistance. This study provides valuable insights into the intricate interplay between gemcitabine resistance and the PDAC microenvironment. Understanding the matrix-specific responses opens avenues for tailored therapeutic interventions, offering the potential for improved outcomes in PDAC patients. Citation Format: Bo Han, Shuqing Zhao, Edward Agyare, Xueyou Zhu, Jose Trevino, Sherise Rogers, Enrique Velazquez, Jason Brant, Payam Eliahoo, Jonathan Barajas, Ba Xuan Hoang. Impact of gemcitabine modification on redox-driven responses in pancreatic cancer organoids cultured in distinct 3D microenvironments [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3167.

Evaluating protein cross-linking as a therapeutic strategy to stabilize SOD1 variants in a mouse model of familial ALS.

Mutations in the gene encoding Cu-Zn superoxide dismutase 1 (SOD1) cause a subset of familial amyotrophic lateral sclerosis (fALS) cases. A shared effect of these mutations is that SOD1, which is normally a stable dimer, dissociates into toxic monomers that seed toxic aggregates. Considerable research effort has been devoted to developing compounds that stabilize the dimer of fALS SOD1 variants, but unfortunately, this has not yet resulted in a treatment. We hypothesized that cyclic thiosulfinate cross-linkers, which selectively target a rare, 2 cysteine-containing motif, can stabilize fALS-causing SOD1 variants in vivo. We created a library of chemically diverse cyclic thiosulfinates and determined structure-cross-linking-activity relationships. A pre-lead compound, "S-XL6," was selected based upon its cross-linking rate and drug-like properties. Co-crystallographic structure clearly establishes the binding of S-XL6 at Cys 111 bridging the monomers and stabilizing the SOD1 dimer. Biophysical studies reveal that the degree of stabilization afforded by S-XL6 (up to 24°C) is unprecedented for fALS, and to our knowledge, for any protein target of any kinetic stabilizer. Gene silencing and protein degrading therapeutic approaches require careful dose titration to balance the benefit of diminished fALS SOD1 expression with the toxic loss-of-enzymatic function. We show that S-XL6 does not share this liability because it rescues the activity of fALS SOD1 variants. No pharmacological agent has been proven to bind to SOD1 in vivo. Here, using a fALS mouse model, we demonstrate oral bioavailability; rapid engagement of SOD1G93A by S-XL6 that increases SOD1G93A's in vivo half-life; and that S-XL6 crosses the blood-brain barrier. S-XL6 demonstrated a degree of selectivity by avoiding off-target binding to plasma proteins. Taken together, our results indicate that cyclic thiosulfinate-mediated SOD1 stabilization should receive further attention as a potential therapeutic approach for fALS.

Evaluation of Microbiological Susceptibility and Long-term Adhesive Properties to Dentin of Primers with Terminalia catappa Linn.

To investigate the antibacterial effects of Terminalia catappa Linn (TCL) leaf extracts at different concentrations and the effects of these extracts used as primers on the long-term adhesive properties of two universal adhesives. After extract preparation, the antimicrobial and antibacterial activities of TCL against Streptococcus mutans (UA 159) were assessed in microdilution assays to provide the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). Additionally, to provide quantitative data on the ability of TCL extract to reduce cell viability, colony forming units (CFU) were counted. To examine adhesive properties, 288 human molars were randomly assigned to 32 experimental conditions (n = 9) according to the following variables: (1) treatment agent: negative control (untreated surface), and primers at concentrations of 1xMIC, 5xMIC, and 10xMIC; (2) adhesives: Scotchbond Universal (SBU) and Futurabond Universal (FBU); (3) adhesive strategy: etch-and-rinse (ER) or self-etch (SE); and (4) storage time: 24 h or after 2 years. Primers were applied for 60 s, upon which the teeth were incrementally restored and sectioned into adhesive-dentin bonded sticks. These were tested for microtensile bond strength (μTBS) and nanoleakage (NL) after 24-h and 2-year water storage, as well as in-situ degree of conversion (DC) at 24 h. The chemical profile of the hybrid layer was determined via micro-Raman spectroscopy. Biofilm assay data were analyzed using the Kruskal-Wallis test; the pH of culture media and the chemical profile were analyzed by one-way ANOVA. The adhesive properties (µTBS, NL, DC) were evaluated using a four-way ANOVA and Tukey's test. Significance was set at 5%. Similar values of MIC and MBC were observed (2 mg/ml), showing bactericidal potential. CFU analysis demonstrated that concentrations of 5xMIC and 10xMIC significantly inhibited biofilm formation (p < 0.001). The application of the TCL primer at all concentrations significantly increased the immediate μTBS and DC, and decreased the immediate NL values when compared to the control group (p < 0.05), regardless of the adhesive and adhesive strategies. Despite an increase in the NL values for all groups after 2 years (p > 0.05), in groups where the TCL primer was applied, the μTBS remained constant after 2 years for both adhesives, while a decrease in the μTBS was observed in the control groups (p < 0.05). Usually, 10xMIC showed better results than 1xMIC and 5xMIC (p < 0.05). The application of TCL promoted cross-linking; cross-linking rates increased proportionally to the concentration of TCL (p < 0.05). Primers containing TCL promoted bactericidal and bacteriostatic action, as well as cross-linking with dentin, while maintaining the adhesive properties of the adhesive-dentin interface after 2 years of water storage.

Modeling calcium diffusion and crosslinking dynamics in a thermogelling Alginate-Gelatin-Hyaluronic acid ink: 3D bioprinting applications

Alginate-based inks are widely used in 3D bioprinting. Its crosslinking by Ca2+ ions is extremely important to achieve scaffolds with optimal mechanical properties. Notably, despite previous studies on calcium diffusion in alginate systems, there have been no reported data regarding the effect of temperature on the diffusion and crosslinking dynamics of thermogelling alginate-based hydrogels. This study focuses on investigating the kinetics of the crosslinking front and Ca2+ diffusion within a matrix of Alginate-Gelatin-Hyaluronic acid ink, exploring the impact of temperature and Ca2+ concentration. The Ca2+ diffusion rate or ink crosslinking rate increase as the crosslinker concentration and ink temperature increase. Additionally, the mechanical properties of the scaffolds, assessed through compression, tension, and dynamic tests, were correlated with the crosslinking time.The innovative aspect of this study lies in the development of a code that simulates the diffusion of Ca2+ ions from the exterior to the interior of a hydrogel structure. Specifically, the code facilitates the calculation of the crosslinking time for a cylindrical structure up to a specified thickness, providing valuable insights for the production of airways or blood vessels. Furthermore, the Python script, incorporating the numerical model, manages to simulate the crosslinking dynamics of scaffolds of any shape, and properly fits the rheological measurements of dynamic moduli during the crosslinking process. This represents a significant advance for the precise and controlled scaffold fabrication process using 3D bioprinting.

Model Simulation and Rheological Research on Crosslinking Behavior of Polyethylene Resin.

The crosslinking behavior of polyethylene (PE) determines its exceptional performance and application. In this study, we investigated the crosslinking behaviors of different PE resins through model simulation and rheological methods. Specifically, the mathematical equation of "S" model was established for PE resin. According to this equation, the optimal maximum gel content for high-density polyethylene (HDPE) was found to be around 85%. Moreover, the maximum crosslinking degrees for different PE resins depended largely on their density and molecular weight. The melt viscosities before crosslinking in PE resins were highly influenced by their melt index. The higher melt indexes resulted in the lower storage moduli, improving melt processability during processing. In addition, the crosslinking rates of PE resins were strongly influenced by peroxide concentration, independent of PE resin structures. For high molecular weight and low-density PE resins, they exhibited decreased ti values, increased A0 values, and decreased k6 values. However, there were no noticeable variations in the values of k2 and phi among different PE resins. All simulated modeling outcomes showed remarkable consistency with the experimental rheological data. These findings are of strong significance in the industrial manufacture of PE resin.

Green Physical Modification of Polypropylene Fabrics by Cross-Linking Chitosan with Tannic Acid and Postmodification by Quaternary Ammonium Grafting to Improve Antibacterial Activity.

A green cross-linking and straightforward method to physically trap inert fibers in a network of chitosan was implemented. The cross-linking reaction involved a biosourced and biocompatible cross-linker [tannic acid (TA)] and mild conditions in water (pH = 8.5, O2 bubbling, 60 °C, 3 h). The steric hindrance of TA led to a low but effective cross-linking rate leaving parts of primary amines of chitosan available for postmodification such as the grafting of quaternary ammoniums for antibacterial purposes. Fabric's coatings were characterized by scanning electron microscopy coupled with energy-dispersive X-ray, infrared spectroscopy, and weight gain measurements. This allowed the optimization of process conditions. No significant antioxidant activity was observed on fabrics coated with chitosan cross-linked with TA, confirming the low cross-linking rate. This low cross-linking rate allowed grafting of quaternary ammoniums for antibacterial purposes, but it is possible to consider grafting other active molecules. Biological assays were conducted on this coating to assess its antibacterial properties. Reduction of bacterial colonization on both Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative), two of the major strains responsible for nosocomial infections, confirmed the potential of the coating for antibacterial purposes. This study displays a simple and ecofriendly process to coat inert fabrics with a chitosan network containing reactive functions (primary amines) available for grafting active molecules for various purposes.

Engineering alginate/carboxymethylcellulose scaffolds to establish liver cancer spheroids: Evaluation of molecular variances between 2D and 3D models

Natural polymeric hydrogels represent an optimal framework for 3D culture development. This study demonstrates a freeze-thaw-based ionic crosslinking technique for fabricating alginate/carboxymethylcellulose scaffold for culturing human hepatocellular carcinoma, Huh-7 cells to generate 3D spheroids. Consolidating morphological and biomechanical characterization of Alg/CMC scaffolds shows the formation of uniform hydrogels with significant crosslinking (ATR-FTIR), multiscale pores (FE-SEM), swelling/water absorbance, softer texture, viscoelasticity (rheology), spreading nature (contact angle), and degradation rate optimal for 3D culture establishment. The influence of cell seeding density and time with spheroid formation reveals a maximal size of 250–300 μm on day 7. Calcein AM and Propidium iodide staining confirm that a culmination of viable and dead cells generates spheroidal heterogeneity. RT-qPCR in 3D culture against RPL-13 and 2D culture controls indicate an upregulation of E-cadherin, N-cadherin, fibronectin, and integrin α9/β6. Further, western blotting and immunofluorescence confirm the collective display of cellular interactions in 3D spheroids. Thus, the expression profile signifies the role of key genes during the assembly and formation of 3D spheroids in 1%Alg/1%CMC scaffolds with a profound epithelial characteristic. In the future, this study will bring a 3D spheroid model in a platter for elucidating epithelial to mesenchymal transition of cells during in vitro disease modeling.

Optimization of chitosan adhesive properties by means of genipin crosslinking

ABSTRACT Chitosan is a polysaccharide resulting from chitin deacetylation. It has demonstrated interesting characteristics in the field of adhesion but loses most of its adhesive resistance in moist environment. A chemical crosslinking of chitosan with genipin has been implemented to improve its adhesive properties in the presence of water. The study of crosslinking kinetics using rheology revealed its dependency on crosslinking rate and chitosan concentration. The capacity of the chitosan-genipin systems for water absorption has been quantified as their Free Swelling Capacity. The cross-linkage of chitosan by genipin (1% w/w) decreased significantly its ability for water absorption. Finally, the adhesive strength of several chitosans be they supplemented or not with genipin and/or glycerol used as plasticizer have been performed on Thick Adherent Shear Test samples of beech wood according to standard EN 204:2016 and EN 205:2016. The chitosan adhesive formulation containing genipin and glycerol exhibits the better adhesive properties on wood and presents higher water resistance compared to the native chitosan formulation.

Effect of crosslinking on EVA-based encapsulant properties during photovoltaic module fabrication process

The key objective of this work is to create a comprehensive comparison between experimental analysis methods for detecting crosslinking reaction in EVA encapsulant material during PV module fabrication process. Several analytical methods, spanning from classical gel content extraction measurements over different thermo-analytic and mechanical approaches to spectroscopic analysis as Thermally Stimulated Current (TSC), have been investigated as to their ability to reveal the crosslinking state of ethylene vinyl acetate (EVA). The basic results show that TSC complements perfectly other thermal analysis methods like as Differential Scanning Calorimetry (DSC), Dynamic Mechanical Thermal Analysis (DMTA) to determine fundamental properties of EVA such as molecular mobility characteristics and also to monitor the crosslinking reaction. Exothermic peak as revealed by DSC analysis can be used to estimate the crosslinking rate of EVA during PV module encapsulation process as fast quality control test.

Gelation of Hydrophilic Polymer Bearing Metal-coordination Unit with Various Metal Ions

Abstract Gelation of a hydrophilic polymer bearing a metal-coordination unit with various metal ions was examined. Gels with different morphologies were formed depending on the metal ion species. The formation mechanism for these gels could be explained based on their cross-linking rates. Gelation in two-component solutions containing different ratios of PdII to other metal ions (AuIII and PtIV) was also investigated.

Effect of Crosslinking on the Stretch‐Induced Polymorphic Transition of Trans‐1,4‐Polyisoprene

AbstractTrans‐1,4‐polyisoprene (TPI) is a typical polymorphic polymer with two crystal modifications. The transition between two crystal modifications (α to β) occurs during stretching. The underlying mechanism is still under debate. In this work, the effects of crosslinking and strain rates on the crystal transition are studied. The TPI, which mainly contains α crystal (α−TPI), is crosslinked by γ‐ray radiation. The results show that crystalline morphology does not change after radiation. The melting temperature and yield stress of crosslinked α−TPI decrease with the irradiation dose. The structural evolution is studied by in situ wide‐angle X‐ray diffraction and small‐angle X‐ray scattering. During stretching, the content of β crystal (Xβ) of crosslinked α−TPI increases in the strain‐hardening region. The Xβ is lower in the sample with a higher radiation dose under the same strain. On the other hand, with increasing strain rate, the Xβ of the crosslinked sample exhibits a non‐monotonic variation. A parallel mechanical model consisting of amorphous and crystal fibrils is proposed to explain the experimental observations.

Rates of infectious keratitis and other ocular surface adverse events in corneal cross-linking for keratoconus and corneal ectasias performed in an office-based setting: a retrospective cohort study

BackgroundThis study aimed to compare the complication rates of epithelium-off corneal cross-linking (epi-off CXL) performed in an office-based setting with those of epi-off CXL performed in an operating room.MethodsA retrospective cohort study, comprising 501 consecutive epi-off CXL procedures, performed in a non-sterile procedure room without laminar flow ventilation at the ELZA Institute in Zurich, Switzerland, between November 2015 and October 2021, was conducted.ResultsNo cases of postoperative infectious keratitis were observed, while sterile infiltrates occurred in 10 out of 501 (2.00%) patients, all of whom responded well to topical steroid therapy. Delayed epithelialization (> 7 days) occurred in 14 out of 501 (2.79%) patients. No other adverse events were noted.ConclusionsOffice-based epi-off CXL does not appear to be associated with an increased risk of complications when compared to operating room settings.

Chemical Structure and Side Reactions in Polyurea Synthesized via the Water-Diisocyanate Synthesis Pathway.

Industrial polyureas are typically synthesized using diisocyanates via two possible alternative pathways: the extremely quick and highly exothermal diamine-diisocyanate pathway and the relatively slow and mild water-diisocyanate pathway. Although polyurea synthesis via the water-diisocyanate pathway is known and has been industrially applied for many decades, there is surprisingly very little analytical information in the literature in relation to the type and extent of the occurring side reactions and the resulting chemical structures following this synthesis pathway. The synthesis of polyureas exhibiting very high concentrations of carbonyl-containing groups resulted in strong and accurate diagnostic analytical signals of combined FTIR and solid-state 13C NMR analysis. Despite the strictly linear theoretical chemical structure designed, the syntheses resulted in highly nonlinear and crosslinked polymers. It was analytically found that the water-diisocyanate pathway preferentially produced highly dominant and almost equal contents of both biuret structures and tertiary oligo-uret structures, with a very small occurrence of urea groups. This is in strong contrast with the chemical structures previously obtained via the diamine-diisocyanate polyurea synthesis pathway, which almost exclusively resulted in biuret structures. The much slower reaction and crosslinking rate of the water-diisocyanate synthesis pathway enabled the further access of isocyanate groups to the already-formed secondary nitrogens, thus facilitating the formation of complex hierarchical tertiary oligo-uret structures.

Development of foam-based support material for coaxial bioprinting of ionically crosslinking bioinks

In this study, a foam-based method is developed for three-dimensional coaxial bioprinting of ionically crosslinking bioinks. This method introduces the crosslinker to the bioink in calcium chloride-albumin foam which eliminates the need for multiple crosslinking steps and offers an excellent control over the crosslinking rate and the diameter of the hollow fibers. The effects of the foam and alginate flow rates were investigated on the outer diameter and the wall thickness of the hollow fibers. Various structures were 3D printed and characterized by printability number and the method showed an excellent layer adhesion among printed layers. The effects of foam composition and the alginate concentration on the mechanical properties were assessed through breaking strain and filament collapse tests to determine the optimum composition for hollow fiber fabrication. The hollow fiber composed of 2% (w/v) sodium alginate that is crosslinked with a foam made of 1.07% (w/v) albumin and 1.07% (w/v) calcium chloride showed superior mechanical properties. Furthermore, the viability of co-incubation with Neuro-2a cells over seven days was investigated and no significant negative effect of the used concentrations of albumin and calcium chloride was observed on the viability of the cells.