Crosslinking Conditions Research Articles

Prediction of Viscoelastic Properties of Enzymatically Crosslinkable Tyramine-Modified Hyaluronic Acid Solutions Using a Dynamic Monte Carlo Kinetic Approach.

The present study deals with the mathematical modeling of crosslinking kinetics of polymer–phenol conjugates mediated by the Horseradish Peroxidase (HRP)-hydrogen peroxide (H2O2) initiation system. More specifically, a dynamic Monte Carlo (MC) kinetic model is developed to quantify the effects of crosslinking conditions (i.e., polymer concentration, degree of phenol substitution and HRP and H2O2 concentrations) on the gelation onset time; evolution of molecular weight distribution and number and weight average molecular weights of the crosslinkable polymer chains and gel fraction. It is shown that the MC kinetic model can faithfully describe the crosslinking kinetics of a finite sample of crosslinkable polymer chains with time, providing detailed molecular information for the crosslinkable system before and after the gelation point. The MC model is validated using experimental measurements on the crosslinking of a tyramine modified Hyaluronic Acid (HA-Tyr) polymer solution reported in the literature. Based on the rubber elasticity theory and the MC results, the dynamic evolution of hydrogel viscoelastic and molecular properties (i.e., number average molecular weight between crosslinks, Mc, and hydrogel mesh size, ξ) are calculated.

How solvent-free crosslinking conditions alter the chemistry and topology of hemiketal based polymer networks

A solvent free reaction of PCL based polyester polyols with a crosslinking molecule based on a vicinal tricarbonyl results covalent adaptable polymer networks that differ in their thermal behavior, swelling, and solubility properties. Mild processing results polymer networks based on hemiketal/ketone equilibrium with properties typical for dissociative networks including dissolution in presence of water or elevated temperature and self-healing properties. Further thermal treatment of the polymer entails changes in swelling, and solubility properties. Constant glass transition temperatures of the differently treated polymers indicate a steady overall network density, but changes in the nature of the network structure. By varying the number of OH-groups, molar mass and stoichiometric ratio of the polyester polyol and the crosslinking molecule, respectively, material properties can be adjusted. This approach gives access to reversibly crosslinked polymers varying in their responsivness and overall mechanical properties.

Influence of Rhamnolipids and Ionic Cross-Linking Conditions on the Mechanical Properties of Alginate Hydrogels as a Model Bacterial Biofilm.

The literature indicates the existence of a relationship between rhamnolipids and bacterial biofilm, as well as the ability of selected bacteria to produce rhamnolipids and alginate. However, the influence of biosurfactant molecules on the mechanical properties of biofilms are still not fully understood. The aim of this research is to determine the effect of rhamnolipids concentration, CaCl2 concentration, and ionic cross-linking time on the mechanical properties of alginate hydrogels using a Box–Behnken design. The mechanical properties of cross-linked alginate hydrogels were characterized using a universal testing machine. It was assumed that the addition of rhamnolipids mainly affects the compression load, and the value of this parameter is lower for hydrogels produced with biosurfactant concentration below CMC than for hydrogels obtained in pure water. In contrast, the addition of rhamnolipids in an amount exceeding CMC causes an increase in compression load. In bacterial biofilms, the presence of rhamnolipid molecules does not exceed the CMC value, which may confirm the influence of this biosurfactant on the formation of the biofilm structure. Moreover, rhamnolipids interact with the hydrophobic part of the alginate copolymer chains, and then the hydrophilic groups of adsorbed biosurfactant molecules create additional calcium ion trapping sites.

Effects of preparation parameters on the properties of the crosslinked pectin nanofiber mats

Pectin nanofiber mats prepared with periodate oxidation–electrospinning–adipic acid dihydrazide crosslinking strategy are promising for biomedical applications. In this study, we systematically examined the effects of electrospinning and crosslinking conditions on the properties of pectin nanofiber mats. The properties of mats were tunable in the range of 200–400 nm fiber size, 11–21% ADH residue content, 13–28 times absorbency, 13°–21° contact angle, 2 weeks or longer degradation time, 1.5–2.2 MPa tensile strength, 40–70% elongation, and 0.25–0.27 g/(cm2·24 h) permeability. Increasing polymer concentration, adipic acid dihydrazide amount, time or temperature could increase fiber size and its tensile strength, and decrease the absorbency, hydrophilicity, degradation rate, and elongation. These results indicate that controlling the process parameters can effectively regulate the properties of pectin nanofiber mats and meet the requirements of various biomedical applications.

Fabrication of Bacterial Cellulose Membrane-Based Alkaline-Exchange Membrane for Application in Electrochemical Reduction of CO2

As the core component of the electrochemical reduction of CO2 (ERC), alkaline anion-exchange membranes (AEMs) in a CO2 electrolyzer can not only transport hydroxide ions as conductors, but also prevent fuel crossover between two electrodes and reduce fuel loss. However, the membrane is threatened by low conductivity and poor stability. In this paper, AEMs based on polymer composites of bacterial cellulose (BC)/poly (diallyldimethyl ammonium chloride) (PQ-6, PDDA) are developed for use in ERC, via a proposed impregnation, chemical cross-linking and ion-exchange process. The effects of crosslinking conditions and different BC:PDDA mass ratio on the hydroxide-ion conductivity, water content, microscopic and macroscopic morphological structure, and stability of BC-PDDA-OH- membrane are thoroughly evaluated. The hydroxide-ion conductivity, incorporating BC:PDDA = 1:0.5 mass ratio, remained at 28.5mS cm-1 and 17.89mS cm-1 after the membrane soaking in 0.5M KHCO3 and 0.5M KOH solution for 720h, respectively. At an applied potential of -0.96VRHE, the BC-PDDA-OH- membrane exhibits the highest Faradaic efficiency of 50.84% for formate (FEHCOO-) in 0.5M KHCO3 electrolyte, and the FEHCOO - only attenuates by 8.85% after 20 h of continuous electrolysis. In comparison, the BC-PDDA-OH- membrane in 0.5M KOH electrolyte produced the FEHCOO - of 50.92% at an applied potential of -1.006VRHE. The electrochemical performances of both systems are superior to that of commercial acidic Nafion117 and commercial alkaline A901 membranes, which prove the feasibility of BC membrane fabricated AEMs application in high performance of ECR.

High Adhesive Polyimide Binder for Silicon Anodes of Lithium Ion Batteries

Silicon has been extensively studied as an anode material in lithium-ion batteries due to its extremely high theoretical specific capacity of 3578 mAh/g (assuming Li15Si4 as intermediate product). However, silicon undergoes huge volume variations during repeated discharge and charge, leading to poor electrode mechanical integrity, continual electrolyte decomposition and fast capacity decay. Developing high strength binders in silicon anodes have been considered as an efficient pathway to alleviate various capacity decay pathways.Currently, lithiated poly acrylic acid (LiPAA) is mostly used as the binder for silicon electrodes due to its strong binding capability and (electro)chemical compatibility with Si and electrolyte. However, cracks at the electrode level can still be observed for the cycled electrodes, which suggests that a stronger binder is required to mitigate volume expansion of Si electrode and hold the particles together. Herein we study the polyimide (PI) materials as the binders for Si anode in an attempt to achieve stable cycling performance. With PI binder, the silicon electrode exhibits a higher tensile strength than that of conventional PAA binder. The strong adhesion of the PI binder suppresses the structural collapse of the Si negative electrode during lithiation/delithiation, enabling high capacity retention and stable cycle life. However, the PI crosslinking process requires high temperature and inert atmosphere, which is a challenge for its practical application. In this work, we explore various PI crosslinking conditions and their effects on electrochemical performance. This work offers us an alternative binder material with high tensile strength for the Si electrode.AcknowledgementWe gratefully acknowledge the support from the U.S. Department of Energy's Vehicle Technologies Office. This work is conducted under the Cell Analysis, Modeling, and Prototyping (CAMP) Facility at Argonne National Laboratory. Argonne National Laboratory is operated for DOE office of Science by UChicago Argonne, LLC, under contract number DE-AC02-06CH11357.

Assessing monocyte phenotype in poly(γ-glutamic acid) hydrogels formed by orthogonal thiol–norbornene chemistry

Hydrogels with tunable properties are highly desirable in tissue engineering applications as they can serve as artificial extracellular matrix to control cellular fate processes, including adhesion, migration, differentiation, and other phenotypic changes via matrix induced mechanotransduction. Poly(γ-glutamic acid) (PGA) is an natural anionic polypeptide that has excellent biocompatibility, biodegradability, and water solubility. Moreover, the abundant carboxylic acids on PGA can be readily modified to introduce additional functionality or facilitate chemical crosslinking. PGA and its derivatives have been widely used in tissue engineering applications. However, no prior work has explored orthogonal crosslinking of PGA hydrogels by thiol–norbornene (NB) chemistry. In this study, we report the synthesis and orthogonal crosslinking of PGA-norbornene (PGANB) hydrogels. PGANB was synthesized by standard carbodiimide chemistry and crosslinked into hydrogels via either photopolymerization or enzymatic reaction. Moduli of PGA hydrogels were readily tuned by controlling thiol–NB crosslinking conditions or stoichiometric ratio of functional groups. Orthogonally crosslinked PGA hydrogels were used to evaluate the influence of mechanical cues of hydrogel substrate on the phenotype of naïve human monocytes and M0 macrophages in 3D culture.

Crosslinked Silk Fibroin/Gelatin/Hyaluronan Blends as Scaffolds for Cell-Based Tissue Engineering.

3D porous scaffolds fabricated from binary and ternary blends of silk fibroin (SF), gelatin (G), and hyaluronan (HA) and crosslinked by the carbodiimide coupling reaction were developed. Water-stable scaffolds can be obtained after crosslinking, and the SFG and SFGHA samples were stable in cell culture medium up to 10 days. The presence of HA in the scaffolds with appropriate crosslinking conditions greatly enhanced the swellability. The microarchitecture of the freeze-dried scaffolds showed high porosity and interconnectivity. In particular, the pore size was significantly larger with an addition of HA. Biological activities of NIH/3T3 fibroblasts seeded on SFG and SFGHA scaffolds revealed that both scaffolds were able to support cell adhesion and proliferation of a 7-day culture. Furthermore, cell penetration into the scaffolds can be observed due to the interconnected porous structure of the scaffolds and the presence of bioactive materials which could attract the cells and support cell functions. The higher cell number was noticed in the SFGHA samples, possibly due to the HA component and the larger pore size which could improve the microenvironment for fibroblast adhesion, proliferation, and motility. The developed scaffolds from ternary blends showed potential in their application as 3D cell culture substrates in fibroblast-based tissue engineering.

Fabrication of bacterial cellulose membrane-based alkaline-exchange membrane for application in electrochemical reduction of CO2

As the core component of the electrochemical reduction of CO2 (ERC), alkaline anion-exchange membranes (AEMs) in a CO2 electrolyzer can not only transport hydroxide ions as conductors, but also prevent fuel crossover between two electrodes and reduce fuel loss. However, the membrane is threatened by low conductivity and poor stability. In this paper, AEMs based on polymer composites of bacterial cellulose (BC)/poly (diallyl dimethyl ammonium chloride) (PDDA) are developed for use in ERC, via a proposed impregnation, chemical cross-linking and ion-exchange process. The effects of crosslinking conditions and different BC:PDDA mass ratio on the hydroxide-ion conductivity, water content, microscopic and macroscopic morphological structure, and stability of BC-PDDA-OH- membrane are thoroughly evaluated. The hydroxide-ion conductivity, incorporating BC:PDDA = 1:0.5 mass ratio, remains at 28.5mS cm−1 and 17.89 mS cm−1 after the membrane soaking in 0.5 M KHCO3 and 0.5 M KOH solution for 720 h, respectively. At an applied potential of −0.96VRHE, the BC-PDDA-OH- membrane exhibits the highest Faradaic efficiency of 50.84% for formate (FEHCOO-) in 0.5 M KHCO3 electrolyte, and the FEHCOO- only attenuates by 8.85% after 20 h of continuous electrolysis. In comparison, the BC-PDDA-OH- membrane in 0.5 M KOH electrolyte produced the FEHCOO- of 50.92% at an applied potential of −1.006VRHE. The electrochemical performances of both systems are superior to that of commercial acidic Nafion117 and commercial alkaline A901 membranes, which prove the feasibility of BC membrane fabricated AEMs application in high performance of ERC.

Pullulan/poly(N‐vinylimidazole) cryogel: An efficient adsorbent for methyl orange

AbstractPullulan/poly(N‐vinylimidazole) (PNVI) hybrid cryogels were synthesized under free radical polymerization and chemical crosslinking conditions in an alkaline, aqueous solution of pullulan (PUL), N‐vinylimidazole (NVI), ammonium persulfate and epicholorohydrin (ECH) at −18°C. PUL and PNVI cryogels alone were also synthesized under similar conditions. Optimum cryogel formation conditions were determined by considering product yields and gel fractions of the samples. The products were characterized by elemental analysis, FTIR‐ATR spectrometry, Thermal gravimetric analysis, and scanning electron microscopy (SEM) analyses. It has been found that PUL/PNVI hybrid samples bear improved physicochemical properties compared to ECH crosslinked PUL and PNVI samples alone. They act as hydrogels in aqueous medium reaching equilibrium swelling capacity values of the order of 600%. Dried PUL/PNVI cryogels show higher thermal stability than the dried cryogels of the parent polymers and maintain their physical integrity over a prolonged time period. Macroporous morphology was revealed by SEM analysis. Having 54.2 mg/g maximum equilibrium adsorption capacity in 200 ppm methyl orange solution and maintaining 95% of its adsorption capacity at the end of seven consecutive adsorption/desorption cycles, PUL/PNVI cryogel proved to be an efficient and durable dye adsorbent using methyl orange as the model compound in aqueous solution.

Analysis of the swelling kinetic in hydrogels gelled by radiation and by thermal cycling

Hydrogels are cross-linked polymer networks, which are of interest in biomedical applications such as drug delivery system. To achieve successful results in this kind of application it is essential to understand the diffusion mechanisms which are generated in the hydrogel during the swelling process. For this reason, this work consists in carrying out an analysis of the swelling kinetics in hydrogels elaborated through gamma radiation and the combination of gamma radiation with thermal cycling processes. The hydrogels were synthesized using biocompatible polymers irradiating their solution at different doses. A swelling test was performed and the diffusion coefficient and the diffusional exponent were calculated, making an analysis of the kind of diffusion mechanism in the hydrogel matrix. This test showed that the higher radiation absorbed used to get the gels, the lower the swelling percentage, as well as the diffusion coefficient of the water molecules in the hydrogel. The results of the kinetic analysis showed an anomalous diffusion mechanism for the gels obtained at 25 kGy. For those gels of 30 kGy, the diffusion was Fickian. Finally since those gels of 35 kGy was not possible to classify it according to the Fick's law of diffusion. Furthermore, we could observe that the hydrogels that had been obtained by thermal cycling and by irradiation had higher swelling percentages compared to those that were only cross-linked by irradiation. This analysis allowed us to understand the intrinsic behavior of the polymer / solvent mesh system at different doses and under two different crosslinking conditions.

Silane crosslinkable polyethylene waste as bitumen modifier: A new fortunate destiny by in time recycling of thermoplastic waste before conversion to thermoset end-of-life unrecyclable polymer

Polymer modification of bitumen is a popular method to enhance its performance. Over the years, researchers have suggested and developed various polymeric bitumen modifiers, and this trend in research is in progress to introduce new polymers with higher modification efficacies. Silane crosslinkable polyethylene is a widely used polymer as cable insulation, and its waste was used as bitumen modifier in this study. After shaping this polymer around the metal conductors and providing the crosslinking condition, silane-crosslinked polyethylene (Si-XLPE) insulation is obtained. When compared to ordinary polyethylene, Si-XLPE exhibits superlative performance, such as enhanced thermal, mechanical, elasticity, and stress cracking properties. Herein, the cable production wastes of this polymer were utilized for bitumen modification before crosslinking. Comprehensive analyses were carried out for characterizing the fabricated samples, including conventional physical (softening point, penetration, and storage stability), morphological (optical and fluorescence microscopies), chemical (FTIR), thermal (DSC), and performance grade (PG) assessments. For PG determination, rolling thin film oven (RTFO) and pressure aging vessel (PAV) tests, along with rotational viscometer (RV), dynamic shear rheometer (DSR), and bending-beam rheometer (BBR) tools were employed. Findings indicated the formation of a polymeric phase network in the bitumen matrix with altering shapes depending on the polymer content. This was identified to be the origin of appeared structural enhancements in the Si-XLPE modified bitumen samples. Moreover, it was revealed that Si-XLPE contents in 2% and more led to phase separations in the unaged or aged states due to high swelling ratio of Si-XLPE. Strikingly, it was seen that only 1% of Si-XLPE could change the PG 58-22 of base bitumen to PG 70-22, which confirmed promising efficiency of recycled Si-XLPE in low contents for significant improvements in the bitumen's high temperature performance without adverse effects on its low temperature performance. Eventually, recycled silane crosslinkable polyethylene can be an advantageous potential bitumen-modifier that is favorable from technical, environmental, and economical perspectives.

Optimal method for preparing sulfonated polyaryletherketones with high ion exchange capacity by acid‐catalyzed crosslinking for proton exchange membrane fuel cells

AbstractSulfonated polyaryletherketones (SPAEK) bearing four sulfonic acid groups on the phenyl side groups were synthesized. The benzophenone moiety of polymer backbone was further reduced to benzydrol group with sodium borohydride. The membranes were crosslinked by acid‐catalyzed Friedel‐Crafts reaction without sacrifice of sulfonic acid groups and ion exchange capacity (IEC) values. Crosslinked membranes with the same IEC value but different water uptake could be prepared. The optimal crosslinking condition was investigated to achieve lower water uptake, better chemical stability (Fenton's test), and higher proton conductivity. In addition, the hydrophilic ionic channels from originally course and disordered could be modified to be narrow and continuous by this crosslinking method. The crosslinked membranes, CS4PH‐40‐PEKOH (IEC = 2.4 meq./g), reduced water uptake from 200 to 88% and the weight loss was reduced from 11 to 5% during the Fenton test compared to uncrosslinked one (S4PH‐40‐PEK). The membrane showed comparable proton conductivity (0.01–0.19 S/cm) to Nafion 212 at 80°C from low to high relative humidity (RH). Single H2/O2 fuel cell based on the crosslinked SPAEK with catalyst loading of 0.25 mg/cm2 (Pd/C) exhibited a peak power density of 220.3 mW/cm2, which was close to that of Nafion 212 (214.0 mW/cm2) at 80°C under 53% RH. These membranes provide a good option as proton exchange membrane with high ion exchange capacity for fuel cells.

Multifunctional materials for lean processing of waferscale optics

AbstractThe continuous miniaturization of components and devices along with the increasing need of sustainability in production requires materials which can fulfill the manifold requests concerning their functionality. From an industrial point of view emphasis is on cost reduction either for the materials, the processes, or for both, along with a facilitation of processing and a general reduction of resource consumption in manufacturing. Multifunctional nanoscale materials have been widely investigated due to their tunable material properties and their ability to fulfill the increasingly growing demands in miniaturization, ease of processes, low-cost manufacturing, scalability, reliability, and finally sustainability. A material class which fulfills these requirements and is suited for integrated or waferscale optics are inorganic–organic hybrid polymers such as ORMOCER®s [ORMOCER®is registered by the Fraunhofer Gesellschaft für Angewandte Forschung e.V. and commercialized by microresist technology GmbH under license since 2003]. The combination of chemically designed multifunctional low-cost materials with tunable optical properties is very attractive for (integrated) optical and waferscale applications via a variety of different nano- and microstructuring techniques to fabricate micro- and nano-optical components, typically within less than a handful of process steps. The influence of photoinitiator and cross-linking conditions onto the optical properties of an acrylate-based inorganic–organic hybrid polymer will be discussed, and its suitability for being applied in waferscale optics is demonstrated and discussed for miniaturized multi- and single channel imaging optics.

Improving the extraction performance of polymer inclusion membranes by cross-linking their polymeric backbone

This study aims at comprehensively investigating the possibility of fabricating cross-linked polymer inclusion membranes (PIMs) using the most common base polymers (i.e., poly(vinyl chloride), cellulose triacetate and poly(vinylidene fluoride-co-hexafluoropropylene)), cross-linking polymers or monomers (i.e., poly(ethylene glycol) dimethylacrylate, poly(ethylene glycol) divinylether and N-ethylmaleimide) and photo-initiators (i.e., 2,2-dimethoxy-2-phenyl acetophenone, triarylsulfonium hexafluorophosphate and triphenylphosphine oxide). The suitability of the photo-initiators for the different cross-linking polymers/monomers in poly(vinyl chloride)-based membranes (without extractants) was assessed for the first time, which was followed by optimizing the cross-linking conditions (i.e., membrane composition and duration of UV-irradiation) for all three base polymers studied. The optimum concentrations of photo-initiator and UV-treatment times were different for the different base polymers used, thus highlighting the importance of this study. Aliquat 336 and di-(2-ethylhexyl)phosphoric acid, as the most frequently used PIM extractants, were added to the compositions of the homogeneous cross-linked membranes produced under optimal conditions and the extraction performance of the newly developed cross-linked PIMs was compared with that of their non-cross-linked counterparts in the extraction of SCN− and Zn2+, respectively. The results showed that all but one of the 13 homogeneous cross-linked PIMs obtained in this study could extract up to 45% more of the corresponding target species than their non-cross-linked counterparts and the remaining one performed similarly to the relevant non-cross-linked PIM. The initial fluxes for the cross-linked PIMs were up to 10 times higher than those of the relevant non-cross-linked membranes and in two cases the fluxes were similar in value. These results demonstrate the potential of cross-linking for enhancing the extraction performance of PIMs.

Phototunable interpenetrating polymer network hydrogels to stimulate the vasculogenesis of stem cell-derived endothelial progenitors

Vascularization of engineered scaffolds remains a critical obstacle hindering the translation of tissue engineering from the bench to the clinic. We previously demonstrated the robust micro-vascularization of collagen hydrogels with induced pluripotent stem cell (iPSC)-derived endothelial progenitors; however, physically cross-linked collagen hydrogels compact rapidly and exhibit limited strength. We have synthesized an interpenetrating polymer network (IPN) hydrogel comprised of collagen and norbornene-modified hyaluronic acid (NorHA) to address these challenges. This dual-network hydrogel combines the natural cues presented by collagen's binding sites and extracellular matrix (ECM)-mimicking fibrous architecture with the in situ modularity and chemical cross-linking of NorHA. We modulated the IPN hydrogel's stiffness and degradability by varying the concentration and sequence, respectively, of the NorHA peptide cross-linker. Rheological characterization of the photo-mediated gelation process revealed that the IPN hydrogel's stiffness increased with cross-linker concentration and was decoupled from the bulk NorHA content. Conversely, the swelling of the IPN hydrogel decreased linearly with increasing cross-linker concentration. Collagen microarchitecture remained relatively unchanged across cross-linking conditions, although the addition of NorHA delayed collagen fibrillogenesis. Upon iPSC-derived endothelial progenitor encapsulation, robust, lumenized microvascular networks developed in IPN hydrogels over two weeks. Subsequent computational analysis showed that an initial rise in stiffness increased the number of branch points and vessels, but vascular growth was suppressed in high stiffness IPN hydrogels. These results suggest that an IPN hydrogel consisting of collagen and NorHA is highly tunable, compaction resistant, and capable of supporting vasculogenesis.

Effect of solvent on crosslinking of a polyimide membrane using the liquid-phase crosslinking process for CO2/CH4 separation

The crosslinking within a polyimide membrane was investigated by means of a liquid-phase crosslinking process (L-PCP) in which a polymer and crosslinker are mixed in a solvent to prepare crosslinked membranes in a single step. To prepare crosslinked membranes, the polyimide polymer was dissolved in various solvents including tetrahydrofuran (THF), chloroform, dimethylsulfoxide (DMSO), dimethylformamide (DMF), and N-methylpyrrolidone (NMP) with p-phenylenediamine as a crosslinker, and the crosslinked membranes were then obtained by casting the polymer solution. The crosslinked membranes showed different degrees of crosslinking according to the solvent (NMP > DMF > DMSO > THF > chloroform). The highest degree of crosslinking was obtained with the membrane crosslinked in NMP, which also presented the best chemical stability and plasticization resistance against condensable CO2 gas. On the other hand, the membranes crosslinked in THF and chloroform exhibited poor chemical stability and plasticization resistance. This difference in crosslinking degrees arising from the use of various solvents can be correlated with solubility parameters of the polymer and solvent. A good solvent can swell the polymer chains and provide higher crosslinker diffusivity and more effective crosslinking conditions, and vice versa. For CO2/CH4 separation, the highest CO2 permeability was obtained from the crosslinked membrane in THF and chloroform (~8.2 barrer) with a modest CO2/CH4 selectivity of 35 at high pressure (30 barg) despite plasticization. Moreover, the highest CO2/CH4 selectivity (~39) could be obtained with the membranes crosslinked in DMSO and DMF with CO2 permeability of 5 barrer. The membrane crosslinked in NMP exhibited the lowest CO2 permeability of 2.8 barrer at 30 barg due to the highly inter-crosslinked polymer structure, which hinders gas diffusion.

Pore-Filled Ion-Exchange Membranes with Optimal Cross-Linking Degrees for Efficient Membrane Capacitive Deionization

In this work, we investigated the optimal design parameters of pore-filled ion-exchange membranes (PFIEMs) for the successful to a membrane capacitive deionization (MCDI) process. The PFIEMs were fabricated by employing a cheap and thin polyethylene-based porous substrate and filling ionomers based on the cross-linked polystyrene. In particular, the cross-linking degrees of the PFIEMs were controlled by adjusting the cross-linker (i.e., divinylbenzene) contents in the monomer mixture. The PFIEMs exhibited much lower electrical resistance compared to those of commercial membranes because of the largely reduced film thickness and the high ion-exchange capacities. The results also revealed that the cross-linking degree significantly affected the membrane characteristics by influencing the free volume and the density of fixed charge groups. In addition, the membrane permselectivity dominated by the cross-linking degree was shown to be the most significant parameter in determining the salt removal efficiency (η) of MCDI. Consequently, the PFIEMs with the optimal cross-linking conditions were able to the achieve excellent desalting efficiency (η = 88.5%) of the MCDI, which was superior to that of expensive commercial membranes (η = 78.7%).

Influence of the stiffness of three-dimensionally bioprinted extracellular matrix analogue on the differentiation of bone mesenchymal stem cells into skin appendage cells

Influence of the stiffness of three-dimensionally bioprinted extracellular matrix analogue on the differentiation of bone mesenchymal stem cells into skin appendage cells

Citrate Crosslinked Poly(Glycerol Sebacate) with Tunable Elastomeric Properties.

Poly(glycerol-sebacate) (PGS) is a biodegradable elastomer known for its mechanical properties and biocompatibility for soft tissue engineering. However, harsh thermal crosslinking conditions are needed to make PGS devices. To facilitate the thermal crosslinking, citric acid is explored as a crosslinker to form poly(glycerol sebacate citrate) (PGSC) elastomers. The effects of varying citrate contents and curing times are investigated on the mechanical properties, elasticity, degradation, and hydrophilicity. To examine the potential presence of unreacted citric acid, material acidity is monitored in relation to the citrate content and curing times. It is discovered that a low citrate content and a short curing time produce PGSC with tunable mechanical characteristics similar to PGS with enhanced elasticity. The materials demonstrate good cytocompatibility with human umbilical vein endothelial cells similar to the PGS control. The research study suggests that PGSC is a potential candidate for large-scale biomedical applications because of the quick thermal crosslink and tunable elastomeric properties.