Increase In Crosslinking Time Research Articles

Dual-stimuli-responsive poly(vinyl alcohol) nanofibers for localized cancer treatment: Magnetic hyperthermia and drug release studies

Smart materials are a promising option for a more personalized cancer treatment approach. In particular, materials that can respond to an external stimulus may be manipulated to provide a tailored response when and where it is needed. This work confined thermoresponsive poly (N-isopropyl acrylamide) microgels and superparamagnetic iron oxide nanoparticles into poly (vinyl alcohol) nanofibrous membranes. Physical and chemical crosslinking methods were tested to obtain membranes stable in physiological environments for long-term applications, and their effect on the membranes' morphology, swelling, and mechanical properties was evaluated. The results demonstrated that thermal crosslinking for 10 min is enough to obtain a robust membrane for biomedical applications that retain their components' magnetic and thermal responses. The swelling degree decreases with the increase of crosslinking time and is even smaller for chemically crosslinked membranes. Similarly, a high crosslinking degree is associated with more brittle membranes than ductile membranes with thermal crosslinking. Drug delivery assays using doxorubicin as a model drug demonstrated that only membranes with a smaller crosslinking degree are suitable for drug delivery purposes, with about 10 % of doxorubicin released for 15 days. Additionally, magnetic hyperthermia assays showed that composite membranes can increase the surrounding temperature by 10 °C in only 10 min of applying an alternating magnetic field. This work demonstrates the potential of combining stimuli-responsive materials using a simple, low-cost, and easily scalable technique (electrospinning) to produce smart materials for biomedical applications.

Facile Synthesis of Polymer-Reinforced Silica Aerogel Microspheres as Robust, Hydrophobic and Recyclable Sorbents for Oil Removal from Water.

With the rapid development of industry and the acceleration of urbanization, oil pollution has caused serious damage to water, and its treatment has always been a research hotspot. Compared with traditional adsorption materials, aerogel has the advantages of light weight, large adsorption capacity and high selective adsorption, features that render it ideal as a high-performance sorbent for water treatment. The objective of this research was to develop novel hydrophobic polymer-reinforced silica aerogel microspheres (RSAMs) with water glass as the precursor, aminopropyltriethoxysilane as the modifier, and styrene as the crosslinker for oil removal from water. The effects of drying method and polymerization time on the structure and oil adsorption capacity were investigated. The drying method influenced the microstructure and pore structure in a noteworthy manner, and it also significantly depended on the polymerization time. More crosslinking time led to more volume shrinkage, thus resulting in a larger apparent density, lower pore volume, narrower pore size distribution and more compact network. Notably, the hydrophobicity increased with the increase in crosslinking time. After polymerization for 24 h, the RSAMs possessed the highest water contact angle of 126°. Owing to their excellent hydrophobicity, the RSAMs via supercritical CO2 drying exhibited significant oil and organic liquid adsorption capabilities ranging from 6.3 to 18.6 g/g, higher than their state-of-the-art counterparts. Moreover, their robust mechanical properties ensured excellent reusability and recyclability, allowing for multiple adsorption-desorption cycles without significant degradation in performance. The novel sorbent preparation method is facile and inspiring, and the resulting RSAMs are exceptional in capacity, efficiency, stability and regenerability.

Robustness 4, 4′-Diphenylmethane diisocyanate modified sponge-like porous AramidSeparators for boosting safety and electrochemical performance in lithium-ion batteries

The fabrication of novel separators with high safety and remarkable performance has always been a hot topic due to their effect on the safety and electrochemical performance of lithium-ion batteries (LIBs). In this study, the impregnation method is used to create the 4, 4′-diphenylmethane diisocyanate (MDI) modified poly (m-phenylene isophthalamide) (PMIA) separators (PMIA-M) with 3-D sponge-like porous network structure. With the increase of cross-linking time, the elongation at break of PMIA-M separators increases to 47.2%, and the mechanical strength decreases after increasing to 31.7 MPa. In addition, PMIA-M separators has excellent thermal stability, no dimensional shrinkage at 200 °C and self-extinguishing property. Moreover, the expansion of polar groups improves the surface polarity of the PMIA-M separators, promoting the electrolyte-philic property and leading to a significant increase in electrochemical performance. Transport channels of Li+ can be regulated, so that the growth of lithium dendrites can be inhibited and the cycle stability is significantly improved. The capacity retention of the LiCoO2/Li cell assembled by the PMIA-M-12 separator is 94.7% after 50 cycles at 0.2C and prior to that of the pristine PMIA separator (77.6%). Therefore, the PMIA-M separators are promising material for electronic products and new energy vehicles.

Characterization of ionically crosslinked alginate films: Effect of different anion-based metal cations on the improvement of water-resistant properties

In general, calcium ions are widely used to crosslink alginate films for improved mechanical properties. But for the poor water resistance of the alginate films due to their hydrophilicity, various ion-crosslinking agents (CaCl 2 , FeCl 2 , FeCl 3 , and FeSO 4 ) were used to prepare alginate films, with an emphasis on cations (Ca 2+ , Fe 2+ , and Fe 3+ ) and anions (Cl − and SO 4 2− ) with different valences. Chemical, morphological, optical, and mechanical properties were evaluated to demonstrate their influences on ion-crosslinking. All crosslinked films exhibited higher tensile strength and lower elongation at break than the control alginate film. Optically, the films crosslinked with Fe ions showed a yellow appearance, while the CaCl 2 -crosslinked film showed no significant color difference from the alginate film. As for the water-resistant properties [moisture content, water solubility, water vapor permeability (WVP), and swelling index (SI)], the FeSO 4 -crosslinked film presented the lowest WVP value with the highest SI value than others, suggesting the possibility to WVP increase depending on the reaction time. Thus, we studied the effect of crosslinking time on the water resistance of films using CaCl 2 and FeSO 4 . The FeSO 4 -crosslinked film exhibited a significant decrease in WVP value with increased crosslinking time, an opposite trend from that of the CaCl 2 -crosslinked one. Because water vapor permeability is an important property of food packaging materials, FeSO 4 , which is generally recognized as safe (GRAS) but has rarely been studied as an ionic crosslinking agent for alginate, has a high potential to be used as such in alginate films. • Alginate was used as a polymer to produce biodegradable food packaging materials. • Three types of iron compounds (FeCl 2 , FeCl 3 , and FeSO 4 ) were used to crosslink alginate films. • FeSO 4 -crosslinked film indicated the lowest water vapor permeability compared to other films. • An increase in crosslinking time enhanced the water barrier properties of the FeSO 4 -crosslinked film. • FeSO 4 showed the greatest potential to replace CaCl 2 as a crosslinking agent of alginate film.

Effect of Polymer Concentration and Crosslinking Time On Drug Release from Microspheres of Mucuna Gum

The study investigated the feasibility of delivering diclofenac sodium in microspheres of mucuna gum and whether polymer concentration and crosslinking time would affect drug release. Diclofenac sodium microspheres were successfully prepared using the chemical and thermal crosslinking method. Gluteraldehyde was used as the crosslinking agent. Thereafter, invitro release of diclofenac sodium from the microspheres was evaluated using simulated intestinal fluid as the medium. Increase in mucuna gum concentration did not delay rate of drug release but increased total cumulative drug released. Increase in crosslinking time slowed down release of the drug from the microspheres, an indication that modification of crosslinking time is important for sustained release. This could contribute towards producing sustained release diclofenac sodium which will improve patient compliance as a result of subsequent reduction in dosing frequency. None of the batches gave 100% drug release. This being the case, drug loading can be modified for optimum therapeutic effect.

Effects of Thermal Crosslinking on the Properties and Release Profiles of Three-Dimensional (3D)-Printed Poly Vinyl Alcohol (PVA) Tablets

The objective of this study was to investigate the effects of thermal crosslinking on the properties of 3D-printed poly-vinyl alcohol (PVA) tablets loaded with fluorescein sodium (NaFl). The PVA filaments were selected for the fabrication of 3D-printed tablets. Different infill densities (80% and 100%) of the tablets were applied. The tablets were crosslinked at different temperatures and times. The physiochemical properties of the tablets and the release profiles of fluorescein from the 3D-tablets were investigated. The 3D-printed PVA tablets were successfully produced with favorable physical and mechanical properties. A smooth surface with a mesh pattern was obtained with a yellow color of NaFl. The 100% infilled tablets provided slightly greater loading efficiency and loading capacity in comparison with the 80% infilled tablets. The release of NaFl increased with an increase in crosslinking time and temperature. However, crosslinking at 140 °C for 4 h (80% CFT4 and 100%CFT4) showed similar release characteristic compared to the non-crosslink one. The release kinetics of 3D-printed tablets were observed to be Quasi-Fickian diffusion mechanism.

Morphological study of cellulosic hydrogel nanofiber for biomedical application

In this work, water-insoluble and biocompatible hydrogel nanoweb was prepared via electrospinning. Sodium carboxymethyl cellulose (CMCNa), the cellulose derivative with water solubility and biocompatibility, was electrospun with help of building polymer, poly(ethylene oxide) (PEO). After removal of PEO, the CMCNa in the nanoweb was ionically crosslinked by FeCl3. The viscosity of the mixed solution was decreased with the increase of PEO content mainly due to the smaller molecular size of PEO comparing to CMCNa. The reduced interaction resulted from small molecular size decreased the viscosity with the increase of PEO content. The PEO also improved the spinnability of the solution by screening repulsive force between the CMCNa molecules. As a result, the increase of PEO content resulted in the decreases of the viscosity and the fiber diameter simultaneously. After extraction of PEO, the diameter was significantly reduced. The surface of the nanowebs became bumpy after crosslinking and fiber diameter increased with the increase of crosslinking time. The chemical structure changes of the nanowebs during the process were analyzed by FT-IR spectra. The cytotoxicity of the nanoweb was also assessed using MTT assay. Furthermore, the drug release behaviors of the nanowebs were evaluated using UV–Vis spectrometer. The nanoweb with increased fiber diameter showed more sustained release behavior because of its low specific surface area.

Mechanical anisotropy in compressed collagen produced by localised photodynamic cross-linking

Orientated focal cross-linking can be used to generate surface anisotropy, improve material stiffness and layer integration for the production of a stable 3D construct. Riboflavin (0.25mM) diffusion into plastically compressed (PC) collagen gel was assessed by measuring the diffusion depth of riboflavin with time. The dynamic force analyser was used for peel force testing for interlayer cross-linking and material stiffness in perpendicular axis after orientated/topical cross-linking. One minute riboflavin diffusion time on either surface will saturate >12% of the collagen gel. Bonding strength doubled between PC collagen gel layers with a 5min increase in cross-linking time (between 4 and 9min) and break stress was increased significantly after cross-linking. Importantly, mechanical anisotropy was introduced in the break stress using orientated stripes of riboflavin in cross-linking, almost doubling the break stress parallel to the stripes. Limited riboflavin penetration in 1min means that surface photo-dynamic cross-linking will enhance deep cell survival within the gel. Riboflavin mediated focal/orientated cross-linking generated new predictable anisotropy at the construct. The increase in bonding strength between layers after cross-linking enhances layer integration and graded surface stiffness will impact on cellular/mechanical properties of compressed gels.

Polyelectrolyte microcapsules for sustained delivery of water-soluble drugs

Polyelectrolyte capsules composed of weak polyelectrolytes are introduced as a simple and efficient system for spontaneous encapsulation of low molecular weight water-soluble drugs. Polyelectrolyte capsules were prepared by layer-by-layer (LbL) assembling of weak polyelectrolytes, poly(allylamine hydrochloride) (PAH) and poly(methacrylic acid) (PMA) on polystyrene sulfonate (PSS) doped CaCO3 particles followed by core removal with ethylene-diaminetetraacetic acid (EDTA). The loading process was observed by confocal laser scanning microscopy (CLSM) using tetramethylrhodamineisothiocyanate labeled dextran (TRITC-dextran) as a fluorescent probe. The intensity of fluorescent probe inside the capsule decreased with increase in cross-linking time. Ciprofloxacin hydrochloride (a model water-soluble drug) was spontaneously deposited into PAH/PMA capsules and their morphological changes were investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The quantitative study of drug loading was also elucidated which showed that drug loading increased with initial drug concentration, but decreased with increase in pH. The loaded drug was released in a sustained manner for 6h, which could be further extended by cross-linking the capsule wall. The released drug showed significant antibacterial activity against E. coli. These findings indicate that such capsules can be potential carriers for water-soluble drugs in sustained/controlled drug delivery applications.

UV-crosslinked acrylic pressure-sensitive adhesive systems containing unsaturated ethers

A new class of acrylic pressure-sensitive adhesives (PSA), containing oxirane groups [formula (VII)], were developed. PSA systems obtained from butyl acrylate, glycidyl methacrylate and acrylic acid were modified with selected unsaturated allyl, vinyl or 1-propenyl ethers [formulas (I)-(VI)] in amounts of 1.0 to 5.0 wt. %. Then they were cured (using UV lamp) in the presence of 1.0 wt. % of cationic photoinitiator Irganocure 261 at room temperature and air atmosphere for 3 min. The tack, adhesion to glass and cohesion values of the cured PSA samples were measured. The effects of the type and concentration of unsaturated ether monomers used on these properties were evaluated. It was found that vinyl and 1-propenyl ethers were the most UV reactive crosslinking monomers while allyl ethers deteriorated PSA properties. The most advantageous values of adhesion, cohesion and tack were obtained for the samples containing 2 wt. % of vinyl or 1-propenyl ether. The results of investigations showed also that increase in crosslinking time, under UV radiation, caused faster increase in cohesion of the samples modified with vinyl ethers in comparison with those modified with 1-propenyl ones.

Comparison of techniques for determining crosslinking in silane-water crosslinked materials

Degree of crosslinking in silane-water crosslinked ethylene–octene copolymer and its blends with low-density polyethylene was investigated, using three different techniques: the conventional gel content determination, solvent uptake factor method and infrared analysis. The results from those techniques show a similar trend in which the degree of crosslinking increases with increase of crosslinking time, and decreases with increase of crystalline portion in the materials. The measurement of gel content, although it is a direct way to yield results on degree of crosslinking, is time consuming and uses a large amount of solvent for extraction. Also, good care must be taken when analysing the gel content of samples with low degree of crosslinking. Analysis of FTIR data has shown potential for the determination of crosslink variations in the silane crosslinked materials and gives meaningful information on the progress of the silane-water crosslinking reaction.

The effects of chemical modifications on morphology and performance of 6FDA-ODA/NDA hollow fiber membranes for CO 2/CH 4 separation

We have studied the rheological characteristics, membrane formation and CO 2-induced plasticization phenomenon of almost defect-free copoly(4,4′-diphenylene oxide/1,5-naphthalene-2,2′-bis(3,4-dicarboxylphenyl) hexafluoropropane diimide) (6FDA-ODA/NDA) hollow fiber membranes. Experimental results indicate that the dope rheology changes from a Newtonian to non-Newtonian fluid with elasticity when increasing shear rate. The asymmetric 6FDA-ODA/NDA hollow fiber membranes exhibit plasticization if the feed pressure is greater than 75 psi. Chemical cross-linking modifications with p-xylenediamine were conducted at ambient temperature in order to enhance anti-plasticization characteristics of 6FDA-ODA/NDA hollow fiber membranes. Chemical modified membranes show a significant reduction in CO 2-induced plasticization at least up 550 psi (37.4 atm or 37.9 × 10 6 Pa) if the immersion time is great 1.5 min. However, deteriorations in permeance and permselectivity are clearly observed if the immerse time is greater than 5 min. FTIR spectra confirm that the 6FDA-ODA/NDA polyimide can be chemically cross-linked with p-xylenediamine, while wide-angle X-ray diffraction (WAXD) spectra imply the d-space of 6FDA-ODA/NDA membranes slightly decreases with an increase in cross-linking time. SEM pictures show that the outer selective skin as well as substructure becomes denser and thicker after chemical modification. The slight decrease in d-space may account for the permselectivity increase for the cross-linked membranes if the immersion time is short. However, the benefit of d-space reduction is offset by a denser and more compact selective skin and substructure when the immersion is prolonged.