Crosslinking Conditions Research Articles

Exploring the Segregating and Mineralization-Inducing Capacities of Cationic Hydrophilic Polymers for Preparation of Robust, Multifunctional Mesoporous Hybrid Microcapsules

A facile approach to preparing mesoporous hybrid microcapsules is developed by exploring the segregating and mineralization-inducing capacities of cationic hydrophilic polymer. The preparation process contains four steps: segregation of cationic hydrophilic polymer during template formation, cross-linking of the segregated polymer, biomimetic mineralization within cross-linked polymer network, and removal of template to simultaneously generate capsule lumen and mesopores on the capsule wall. Poly(allylamine hydrochloride) (PAH) is chosen as the model polymer, its hydrophilicity renders the segregating capacity and spontaneous enrichment in the near-surface region of CaCO3 microspheres; its biopolyamine-mimic structure renders the mineralization-inducing capacity to produce titania from the water-soluble titanium(IV) precursor. Meanwhile, CaCO3 microspheres serve the dual templating functions in the formation of hollow lumen and mesoporous wall. The thickness of capsule wall can be controlled by changing the polymer segregating and cross-linking conditions, while the pore size on the capsule wall can be tuned by changing the template synthesizing conditions. The robust hybrid microcapsules exhibit desirable efficiency in enzymatic catalysis, wastewater treatment and drug delivery. This approach may open facile, generic, and efficient pathway to designing and preparing a variety of hybrid microcapsules with high and tunable permeability, good stability and multiple functionalities for a broad range of applications.

Effect of softeners and crosslinking conditions on the performance of easy-care cotton fabrics with different weave constructions

This study reports an experimental investigation on the effect of softeners, crosslinking conditions, and laundering on the comfort related and low stress mechanical properties of cotton fabrics with different weave constructions. Softeners with different chemical natures, in conjunction with the crosslinking agent and catalyst, were padded onto the cotton fabrics of three types of weave constructions, viz. plain, twill, and a newly developed plant-structured weave design. Two crosslinking conditions, namely dry and moist curing conditions, were compared. Scanning electron microscope (SEM) and Fourier transform infrared (FTIR) spectroscope were used to visualize and quantify the morphological and chemical changes on fabrics. The experimental results showed that the dry-crosslinking condition is preferable to achieve better comfort and easy-care properties, while moist-crosslinking condition is a better choice when strength-related properties are the main requirement. The study further showed that silicone elastomer softener can be applied to improve fabric strength whereas micro-emulsion of functional amino-polysiloxane plus emulsion containing polyalkylene is beneficial for comfort characteristic. The plant-structured cotton fabric finished in the dry-crosslinking condition with softener in nano-emulsion form can result in superb water absorption, excellent air permeability, good handle, acceptable strength, and improved easycare property.

Regulation of IgE-Dependent Zinc Release from Human Mast Cells

Background: Zinc (Zn) affects many aspects of immune function, including thymic development and the activities of immune cells. Zn is also involved in many steps of high-affinity IgE receptor (FcεRI)-induced mast cell (MC) activation, which is required for degranulation and cytokine production. Intracellular Zn levels increase in mouse MCs after FcεRI stimulation. We previously reported that Zn distribution in a human MC line, LAD2, changed dramatically following FcεRI aggregation with synchrotron radiation microbeams. However, the kinetics of Zn distribution and the underlying mechanisms following FcεRI cross-linking remain unknown. Methods: We used cord-blood-derived MCs and LAD2 cells. Degranulation was assessed by β-hexosaminidase (β-hex) release. Extracellular Zn levels were determined by inductively coupled plasma atomic emission spectrometry or based on the fluorescence intensity of a Zn indicator. We also used RNAi to knockdown ZnT1 expression. mRNA expression levels were determined by real-time RT-PCR. Results: Zn was rapidly released from human MCs after FcεRI aggregation. The kinetics and optimal conditions for FcεRI cross-linking for Zn release were different from those for degranulation. Treating LAD2 cells with an intracellular Ca²⁺ chelator significantly inhibited IgE-mediated β-hex release but not Zn release. We investigated IgE-mediated β-hex and Zn release with specific inhibitors of signaling pathways. Zn and β-hex release were partly correlated with but also partly independent of IgE. Knockdown of the Zn efflux transporter, ZnT1, significantly inhibited Zn release from human MCs. Conclusions: Our results indicate that IgE-dependent Zn release from human MCs involves signaling cascades that are distinct from those of degranulation. Thus, Zn may have a unique function as a mediator of allergic inflammation.

Preparation, Characterization, and Performance of Sulfated Chitosan/Polyacrylonitrile Composite Nanofiltration Membranes

Sulfated chitosan composite nanofiltration (NF) membranes having polyacrylonitrile (PAN) ultrafiltration (UF) membrane as the base material are prepared by coating and cross-linking, in which epichlorohydrin (ECH) aqueous solution is used as the cross-linking agent. Newly prepared membranes are characterized by FTIR-ATR, XRD, NMR, TGA, and SEM. Effects of various factors like concentration of cross-linking agent, casting solutions, and membrane preparation conditions on the performance of newly prepared composite NF membranes are studied. The results showed that the NF membrane with excellent rejection performance has 1.0 wt% of sulfated chitosan concentration, 0.4 wt% ECH concentrations, 1 hour cross-linking at 60°C. With this composite NF membrane, the solutes rejection from electrolyte solutions is observed to be in the order: R ZnSO4 > R CuSO4 > R ZnCl2 > R CuCl2. Due to adsorption of anions from electrolyte solution, the active layer of the membrane develops a negative surface charge.

Dynamic chromatin remodelling of ciliate macronuclear DNA as determined by an optimized chromatin immunoprecipitation (ChIP) method for Paramecium tetraurelia

We report the detailed evaluation of crucial parameters for chromatin immunoprecipitation (ChIP) of macronuclear DNA in the unicellular eukaryote Paramecium tetraurelia. Optimized parameters include crosslinking conditions, chromatin sonication and antibody titration thus providing a detailed protocol for successful ChIP in P. tetraurelia. As this ciliate is bacterivorous and RNAi by feeding represents a powerful tool for analysis of gene function, we moreover determined the effects of ingested nucleic acids by food bacteria. Feasibility of our protocol is demonstrated by characterisation of chromatin remodelling at promoters of cytosolic HSP70 isoforms during transcriptional activation under heat shock conditions by analyzing RNA abundance, nucleosome occupancy and levels of H3 lysine 9 acetylation.

Preparation and Characterization of Alveolar Bone and Periodontal Ligament Interface Scaffolds

To mimic the alveolar bone and periodontal ligament interface, a chitosan(CS for short) composite polysaccharide scaffold was fabricated which was cross-linked with sodium alginate(SA for short). The conditions of physical crosslinking in the scaffolds were discussed. By characterization after biomineralization, it turns out that pH=5.0 and 40min crosslinking time can make for crosslinking. Better crosslinking makes the material more antiswelling and give more compressive strength. In the other hand, the biomineralization can improve the physical properties of the material. We hope that after further research it can come to a scaffold material with good properties.

Influence of the range of particle sizes of the filler on the adhesion strength and residual stresses in epoxy composites

We study the influence of the contents and physical nature of coarse-grained (60–65 μm) and finegrained (3–10 μm) particles on the adhesion strength and residual stresses in epoxy composites for functionally gradient coatings. The temperature-and-time conditions of cross-linking of the epoxy matrix are optimized. The maximum adhesion strength (49.2–50.0 МРа) is attained as a result of the addition of copper-oxide filler (60–65 μm) to the epoxy oligomer in the following amounts: q = 60–80 m.p. per 100 m.p. of the epoxy matrix. The residual stresses vary from 4.5 to 4.8 МРа.

Selective cross-linking of oligosilazanes to tailored meltable polysilazanes for the processing of ceramic SiCN fibres

An interesting alternative for the processing of non-oxide ceramic fibres at lower costs than that for the current commercially available fibre types was developed by modifying different commercially available liquid oligosilazanes (ML33 and HTT1800) into polysilazanes by selective cross-linking via the N–H and Si–H groups with tetra-n-butylammoniumfluoride (TBAF) as a catalyst. Termination of the reaction with calcium borohydride allows the processing of meltable solid polysilazanes (ML33S and HTTS) with tailored chemical and thermal properties, to fulfil the requirements for the melt spinning of mechanically stable and homogeneous polymeric fibres. The chemical and thermal stability of the polysilazanes ML33S and HTTS were investigated by using GPC, DSC and rheological measurements. These techniques indicate the dependency of the molecular weight and glass temperature on the catalytical cross-linking conditions. Polymers with up to ∼10 000 g mol−1 show glass–liquid transition (Tg) between 65 and 81 °C and viscoelasticity, which are essential properties for the melt-spinning process. The thermal stability of ML33S is ensured up to 220 °C. In contrast the thermal stability of HTTS is limited to 170 °C due to the presence of vinyl-groups. The viscoelastic behaviour of the polymer melts, measured by oscillatory rheometry, and the sufficient thermal stability allowed the continuous processing of stable green fibres by melt spinning in the temperature range of 110 to 130 °C. After fast electron beam irradiation curing of the green fibres and pyrolysis of continuous amorphous ceramic SiCN fibres from both ML33S and HTTS polysilazanes were successfully synthesized, while a defined Tg point influences the shape and the smoothness positively.

Rigid-Rod Poly(phenylenesulfonic acid) Proton Exchange Membranes with Cross-Linkable Biphenyl Groups for Fuel Cell Applications

Biphenyl was grafted on rigid-rod aromatic poly(p-phenylenesulfonic acids) (IEC ∼ 8 mequiv g–1) to generate cross-linkable polyelectrolytes. Cross-linking conditions and film properties before and after cross-linking were studied. Films equilibrated between 20 and 30% relative humidity (RH) had tensile moduli of 2 to 1 GPa and broke at 5 to 9% elongation. The moduli decreased as RH increased and dropped drastically at high humidity if the films were not cross-linked. Grafted films had conductivities at 80 °C 4–5 times that of Nafion NR-212 over the whole relative humidity range even after cross-linking. The sample reported in detail here had a conductivity of 0.10 S cm–1 at 120 °C and 30% RH. As is usual for this class of materials, even after the loss of 24% of starting sulfonic acid groups by grafting and cross-linking, ionic conductivity was high at low humidity. A membrane electrode assembly (MEA) prepared with this rigid-rod poly(phenylenesulfonic acid) proton exchange membrane and tested in a fuel cell exhibited performance and properties similar to those of Nafion NR-212 films. The power density was ∼95% of that of the Nafion MEA over the operating range in spite of relatively high hydrogen crossover due to the presence of nanocracks in the membrane.

Strengthening soy protein hydrogels filled with protein-coated montmorillonite nanoclay by glutaraldehyde crosslinking

To strengthen interactions in bio-nanocomposite systems, montmorillonite (MMT) was intercalated by surface-coating with soy protein before being incorporated within soy protein dispersions for cross-linking by glutaraldehyde (GA). Dynamic small strain tests were utilized as a non-destructive method to reveal the improvement of network structure in the bio-nanocomposite system. The storage modulus (G′) and loss modulus (G″) gradually increased with increasing GA concentration during isothermal treatment at 23, 60 and 90 °C. The incorporation of intercalated MMT resulted in an order of magnitude increase in the moduli. The moduli were higher at pH 5.5 than those at pH 6.5 and 10.0. At a GA concentration equal to 10 g/100 g mass of soy protein, G′ and G″ in the absence of MMT increased with an increase in temperature, while those in the presence of intercalated MMT showed the opposite trend due to restructuring of aggregated MMT. The present results confirmed that the mechanical strength of bio-nanocomposite systems can be significantly improved by first intercalating MMT with protein and subsequently cross-linking with the continuous phase protein molecules. The established chemical cross-linking method and conditions can be beneficial for preparing bio-nanocomposite materials with enhanced mechanical properties.

Charge mosaic membranes with semi-interpenetrating network structures prepared from a polymer blend of poly(vinyl alcohol) and polyelectrolytes

Charge mosaic (CM) membranes with semi-interpenetrating network structures were prepared by blending poly(vinyl alcohol) as a membrane matrix, poly(allyl amine) as a polycation and poly(vinyl alcohol-co-2-acrylamido-2-methyl propane sulfonic acid) as a polyanion with varying polyelectrolyte contents under different cross-linking conditions. Our method can prepare CM membranes of a large area easily at low manufacture cost. Although the flux of electrolytes through the membrane is less than that through a typical charge mosaic membrane such as Desalton® (Tosoh Co., Ltd.), which was prepared using micro-phase separation, the permselectivity for electrolytes through the CM membrane was more than 4 times higher than Desalton®. These CM membranes have enough mechanical strength to form thin layer on a porous support membrane, thereby increasing the flux of electrolytes.

Effects of different crosslinking conditions on the chemical–physical properties of a novel bio-inspired composite scaffold stabilised with 1,4-butanediol diglycidyl ether (BDDGE)

Serious cartilage lesions (Outerbridge III, IV) may be successfully treated with a three-layered gradient scaffold made by magnesium-doped hydroxyapatite and type I collagen, manufactured through a bio-inspired process and stabilised by a reactive bis-epoxy (1,4-butanediol diglycidyl ether, BDDGE). Each layer was analysed to elucidate the effects of crosslinking variables (concentration, temperature and pH). The chemical stabilisation led to an homogeneous and aligned collagenous matrix: the fibrous structures switched to a laminar foils-based arrangement and organic phases acquired an highly coordinated 3D-organization. These morphological features were strongly evident when crosslinking occurred in alkaline solution, with BDDGE concentration of at least 1 wt%. The optimised crosslinking conditions did not affect the apatite nano-crystals nucleated into self-assembling collagen fibres. The present work allowed to demonstrate that acting on BDDGE reaction parameters might be an useful tool to control the chemical-physical properties of bio-inspired scaffold suitable to heal wide osteochondral defects, even through arthroscopic procedure.

Core–shell designed scaffolds of alginate/alpha‐tricalcium phosphate for the loading and delivery of biological proteins

Development of scaffolds to load and deliver therapeutic molecules like growth factors greatly enhances tissue regenerative capacity. Here, we report the core-shell design of fibrous scaffolds made of alginate and α-tricalcium phosphate (Alg/α-TCP) for in situ protein loading and controllable delivery. Direct deposition of Alg/α-TCP solution through designed coconcentric nozzle in CaCl(2) bath allowed the generation of fibrous scaffolds. Through the process, in situ protein loading was possible and the core and shell composition was controlled. Feasibility of the designed scaffolds in loading and release of biological model protein cytochrome C (cyt C) was investigated. Scaffolding formed in CaCl(2) led to a considerable loss of cyt C in a crosslinking time-dependent manner, and the change in hardening conditions (Alg concentration, CaCl(2) concentration, and Alg/α-TCP ratio) was not as effective in reducing the protein loss. Subsequent release of cyt C from Alg scaffolds displayed a marked initial burst depending on crosslinking conditions, and shortening crosslinking time and decreasing CaCl(2) concentration lowered the initial burst. The α-TCP addition (up to 75%) resulted in more continual and sustainable release patterns. Composition change (α-TCP content) in core or shell significantly altered the release profiles, suggesting the possible designing core-shell configuration for target release patterns, such as dual-protein delivery. Additionally, the α-TCP incorporation significantly increased the mechanical stiffness to values much closer to those of hard tissues. Results indicate that coaxial deposited α-TCP/Alg fibrous scaffolds may be useful for designing proper growth factor delivery systems in hard tissue engineering.

Photocurable O-carboxymethyl chitosan derivatives for biomedical applications: Synthesis, in vitro biocompatibility, and their wound healing effects

In this work, photocurable water-soluble chitosan derivatives were prepared for biomedical applications by modifying water-soluble O-carboxymethyl chitosan (O-CMC) derivatives with furfuryl glycidyl ether (O-CMC/FGE). Successful derivatization of chitosan to the final product (O-CMC/FGE) was verified by UV and 1H NMR spectral analysis. The degree of photo-crosslinking was measured by a flow distance experiment after exposure to visible light for a certain period of time. The degree of crosslinking increased linearly in proportion to exposure time. The in vitro cell viability test revealed a lack of cytotoxicity of O-CMC/FGE against mouse 3T3 fibroblasts. However, poor cell attachment was observed for the cells seeded onto the photocured O-CMC/FGE; this is likely due to the anionic nature of this material. O-CMC/FGE displayed wound healing effects in an in vivo animal experiment using a burn wound model. Due to its good biocompatibility, wound healing effect, and mild cross-linking condition, together with an inhibitory effect on cell attachment, O-CMC/FGE would be a promising candidate as an anti-adhesion material for biomedical applications. Open image in new window

Syndrome hépatorénal dans une population de cirrhotiques : fréquence, facteurs prédictifs et pronostic

The impact of fabrication conditions on the chitosan (CS) membrane structure and its pervaporation (PV) performance are studied in this paper. Chitosan homogenous membranes were fabricated by casting a chitosan/acetic acid solution, then heating it at various temperatures and for different periods of post-heating time, followed by chemically cross-linking with H2SO4. The PV separation tests using the resulting membranes demonstrate that the chitosan membranes are capable of separating water–ethanol mixtures. The optimized conditions for chemical cross-linking of membranes were found to be 0.5 M of the cross-linking reagent (H2SO4) and 10 min reaction time at ambient temperature. The preparation temperature of chitosan membranes is the key factor to PV performance of separating water–ethanol. It was observed in orthogonal tests that the effect of membrane preparation temperature on the separation factor was significant. Further studies show that the separation factor is the highest when the heating temperature is 343 K. The results of differential scanning calorimetric (DSC) and X–ray diffraction analyses suggest that the chitosan membranes contain two major different types of crystals. It has been observed that the crystal degree of the chitosan membrane changes with varying heating membrane preparation temperature, i.e. the fractions of two types of crystal change as temperature changes. The present work clearly correlates the PV separation performance of water-ethanol by using the chitosan membrane with the crystal property resulting from the preparation temperature.

Oligo(∊-caprolactone)-Based Polymer Networks Prepared by Photocrosslinking in Solution

Polymer networks with adjustable properties prepared from endgroup-functionalized oligoesters by UV-crosslinking in melt have evolved into versatile multifunctional biomaterials. In addition to the molecular weight or architecture of precursors, the reaction conditions for crosslinking are pivotal for the polymer network properties. Crosslinking of precursors in solution may facilitate low-temperature processes and are compared here to networks synthesized in melt. Oligo(epsilon-caprolactone)-(z)methacrylate (oCL-(z)IEMA) precursors with a linear (z = di) or a four-armed star-shaped (z = tetra) architecture were crosslinked by radical polymerization in melt or in solution with UV irradiation. The thermal, mechanical, and swelling properties of the polymer networks obtained were characterized. Crosslinking in solution resulted in materials with lower Young's moduli (E), lower maximum stress (σmax), and higher elongation at break (epsilonB) as determined at 70 °C. Polymer networks from 8 kDa star-shaped precursors exhibited poor elasticity when synthesized in the melt, but can be established as stretchable materials with a semi-crystalline morphology, a high gel- content, and a high elongation at break when prepared in solution. The crosslinking condition of methacrylate functionalized precursors significantly affected network properties. For some types of precursors such as star-shaped telechelics, synthesis in solution provided semi-crystalline elastic materials that were not accessible from crosslinking in melt.

Encapsulation and release of cladribine from chitosan nanoparticles

AbstractThis study shows the potential of chitosan (CH) nanoparticles as both an oral and IV drug delivery system using the anticancer drug cladribine as a model drug. Smooth, spherical nanoparticles were prepared by the ionotropic gelation of CH with sodium tripolyphosphate. Nanoparticle size depended on degree of hydration, drug loading, and crosslinking conditions, with the smallest nanoparticles in the size range of 212 ± 51 nm. Cladribine was entrapped in the CH matrix with an entrapment efficiency of up to 62%, depending on the initial loading. The release of cladribine followed a near‐Fickian diffusion rate over the first several hours and then reached a plateau. A second release phase began after 30–40 h of incubation in the release medium, and proceeded until ∼100 h. Loaded CH nanoparticles that were crosslinked with genipin showed a delayed release profile, with only 40% of loaded drug being released after 100 h. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Poly(2‐oxazoline) Hydrogel Monoliths via Thiol‐ene Coupling

Copoly(2-oxazoline)s, prepared by the cationic ring-opening polymerization of 2-(dec-9-enyl)-2-oxazoline with either 2-methyl-2-oxazoline or 2-ethyl-2-oxazoline, are crosslinked with small dithiol molecules under UV irradiation to form homogeneous networks. In situ monitoring of the crosslinking reaction by photo-rheology reveals the formation of soft gels within minutes. The degree of swelling in water is tunable based on the hydrophilicity of the starting macromers and the proportion of alkene side arms present. Furthermore, degradable hydrogels are prepared based on incorporation of a hydrolytically cleavable dithiol crosslinker. The rapid synthesis of the macromers and mild crosslinking conditions make these materials ideal for future biomaterial applications.

Crosslinking strategies facilitate tunable structural properties of fibrin microthreads

A significant challenge in the design of biomimetic scaffolds is combining morphologic, mechanical, and biochemical cues into a single construct to promote tissue regeneration. In this study, we analyzed the effects of different crosslinking conditions on fibrin biopolymer microthreads to create morphologic scaffolds with tunable mechanical properties that are designed for directional cell guidance. Fibrin microthreads were crosslinked using carbodiimides in either acidic or neutral buffer, and the mechanical, structural, and biochemical responses of the microthreads were investigated. Crosslinking in the presence of acidic buffer (EDCa) created microthreads that had significantly higher tensile strengths and moduli than all other microthreads, and failed at lower strains than all other microthreads. Microthreads crosslinked in neutral buffer (EDCn) were also significantly stronger and stiffer than uncrosslinked threads and were comparable to contracting muscle in stiffness. Swelling ratios of crosslinked microthreads were significantly different from each other and uncrosslinked controls, suggesting a difference in the internal organization and compaction of the microthreads. Using an in vitro degradation assay, we observed that EDCn microthreads degraded within 24h, six times slower than uncrosslinked control threads, but EDCa microthreads did not show any significant indication of degradation within the 7-day assay period. Microthreads with higher stiffnesses supported significantly increased attachment of C2C12 cells, as well as increases in cell proliferation without a decrease in cell viability. Taken together, these data demonstrate the ability to create microthreads with tunable mechanical and structural properties that differentially direct cellular functions. Ultimately, we anticipate that we can strategically exploit these properties to promote site-specific tissue regeneration.

Fluxgate magnetorelaxometry: A new approach to study the release properties of hydrogel cylinders and microspheres

Hydrogels are under investigation as long term delivery systems for biomacromolecules as active pharmaceutical ingredients. The release behavior of hydrogels can be tailored during the fabrication process. This study investigates the applicability of fluxgate magnetorelaxometry (MRX) as a tool to characterize the release properties of such long term drug delivery depots. MRX is based on the use of superparamagnetic core-shell nanoparticles as model substances. The feasibility of using superparamagnetic nanoparticles to study the degradation of and the associated release from hydrogel cylinders and hydrogel microspheres was a major point of interest. Gels prepared from two types of photo crosslinkable polymers based on modified hydroxyethylstarch, specifically hydroxyethyl starch-hydroxyethyl methacrylate (HES-HEMA) and hydroxyethyl starch-polyethylene glycol methacrylate (HES-P(EG)(6)MA), were analyzed. MRX analysis of the incorporated nanoparticles allowed to evaluate the influence of different crosslinking conditions during hydrogel production as well as to follow the increase in nanoparticle mobility as a result of hydrogel degradation during release studies. Conventional release studies with fluorescent markers (half-change method) were performed for comparison. MRX with superparamagnetic nanoparticles as model substances is a promising method to analyze pharmaceutically relevant processes such as the degradation of hydrogel drug carrier systems. In contrast to conventional release experiments MRX allows measurements in closed vials (reducing loss of sample and sampling errors), in opaque media and at low magnetic nanoparticle concentrations. Magnetic markers possess a better long-term stability than fluorescent ones and are thus also promising for the use in in vivo studies.