Cross-linker Length Research Articles

Impact of Cross-Linker Length on the Characteristics of Anion Exchange Membrane Water Electrolyzer

Water electrolysis, utilizing renewable energy to split water into oxygen and hydrogen, stands out as a promising avenue for generating and storing clean energy from sustainable sources. This study focuses on creating pore-filling anion exchange membranes (PFAEMs) employing an electrolyte monomer incorporating a quaternary ammonium group. Various cross-linker groups of different chain lengths were introduced, while porous polyethylene substrates were treated with surfactants to transition from hydrophobic to hydrophilic. Evaluation of the anion exchange membrane conductivity was conducted in both in-plane and through-plane configurations at room temperature and 60 ℃. Additionally, comprehensive characterizations of the anion exchange membranes encompassing water uptake, swelling ratio, mechanical strength, contact angle, FTIR, SAXs, WAXs, DSC, and TGA analyses were carried out. Consequently, the PFAEM demonstrated notably high ion conductivity with minimal areal swelling ratio and exceptional chemical stability in a KOH solution for 500 hours. As a crucial component of AEMWE, the catalyst layer was prepared using catalyst inks, namely XB-7 ionomer-based and Nafion ionomer-based inks for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) catalyst layers, to assess impedance and I-V polarization curves. Acknowledgment This research was supported in part by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20213030040520) and by 2021 Green Convergence Professional Manpower Training Program of the Korea Environmental Industry and Technology Institute funded by the Ministry of Environment.

How Do Active Chain Density and Cross-Link Length Influence the Mullins Softening in Filled and Unfilled Natural Rubbers?

How Do Active Chain Density and Cross-Link Length Influence the Mullins Softening in Filled and Unfilled Natural Rubbers?

Effect of the Protein Chain Conformation on the Collapse into Nanoparticles.

Protein single-chain nanoparticles can outperform synthetic nanoparticles in biomedical applications due to enhanced biocompatibility. Compared to synthetic (co)polymers, the chemical complexity of proteins challenges chain conformation control. Here, we investigate the impact of the precursor chain conformation of bovine serum albumin (BSA) on the nanoparticle structure after intramolecular cross-linking. We explore the urea concentration (denaturant), pH, salt, cross-linker length, and concentration. Small-angle neutron scattering and dynamic light scattering experiments reveal a shrinking chain conformation upon cross-linking. However, the ability to collapse depends on solvent conditions: more expanded chains collapse more, whereas proteins that are already compact barely change in size upon cross-linking. Static light scattering measurements demonstrate that binding is primarily intramolecular. The use of a shorter cross-linker does not lead to collapse of extended chains. Overall, BSA exhibits a similar behavior to that of polymer nanoparticles, which then allows to harness the precursor conformation for morphological control.

Restoration of the Ultrastructural Integrity of the Dermal Collagen Network by 12-Week Ingestion of Special Collagen Peptides.

This pilot study investigated the effects of a 12-week administration of a nutritional supplement containing special collagen peptides on the structural and molecular properties of the collagen fiber network in the human skin. For the assessments, the suction blister method and electron microscopical comparisons were used. Three suction blisters were generated on the inner forearm of each test subject before and after the 12-week administration of the nutritional supplement. High-resolution scanning electron microscopy (SEM) was employed to meticulously investigate the structural characteristics of the skin's collagen network, including the length and diameter of collagen fibers within the suction blister roof. Furthermore, the analysis included immunohistochemistry and fluorescence light microscopy to study hyaluronic acid within the extracellular matrix. Additional assessments encompassed changes in various epidermal parameters. Nine female participants within the age range of 43.7-61.8years (mean: 52.5 ± 5.9years) completed the study in accordance with the study protocol. Compared with baseline, the 12-week supplementation regimen led to a statistically significant average increase in the collagen fiber network size of 34.56% (p < 0.0001). Additionally, collagen fiber cross-linking and fiber length were substantially increased. The ingestion of the supplement also resulted in an 18.08% elevation in epidermal hyaluronic acid concentration (p < 0.0001). No adverse events were recorded during the study. Using an innovative approach, this study demonstrated the ability of a targeted nutritional supplement to effectively restore the ultrastructural integrity of the dermal collagen network, which is typically disrupted by the natural aging process of the skin. These findings not only corroborate existing data regarding the positive effects of oral collagen peptides on skin structure and function but also contribute to our understanding of ultrastructural morphological aspects of changes in the skin's collagen network. Supplementation can induce regeneration of the collagen fiber network in the human skin. German Clinical Trials Register, DRKS-ID DRKS00034161- Date of registration: 06.05.2024, retrospectively registered.

Effects of Cross-linker Chemistry on Bioelectrocatalytic Reactions in a Redox Cross-linked Network of Glucose Dehydrogenase and Thionine.

Enzyme-mediator bioconjugation is emerging as a building block for designing electrode platforms for the construction of biosensors and biofuel cells. Here, we report a one-pot bioconjugation technique for flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) and thionine (TH) using a series of cross-linkers, including epoxy, N-hydroxysuccinimide (NHS), and aldehydes. In this technique, FAD-GDH and thionine are conjugated through an amine cross-linking reaction to generate a redox network, which has been successfully employed for the oxidation of glucose. The bioconjugation chemistry of cross-linkers with the amino groups on FAD-GDH and thionine plays a vital role in generating distinct network structures. The epoxy-type cross-linker reacts with the primary and secondary amines of thionine at room temperature, thereby producing an FAD-GDH-TH-FAD-GDH hyperbranched bioconjugate network, the aldehyde undergoes a rapid cross-linking reaction to produce a network of FAD-GDH-FAD-GDH, while the NHS-based cross-linker can react with the primary amines of both FAD-GDH and thionine, forming an FAD-GDH-cross-linker-TH polymeric network. This reaction has the potential to enable the conjugation of a redox mediator with a FAD-GDH network, which is particularly essential when designing an enzyme electrode platform. The data demonstrated that the polymeric cross-linked network based on the NHS cross-linker exhibited a considerable increase in electron transport while producing a catalytic current of 830 μA cm-2. The cross-linker spacer arm length also affects the overall electrochemical function of the network and its performance; an adequate spacer length containing a cross-linker is required, resulting in a faster electron transfer. Finally, a leaching test confirmed that the stability of the enzyme electrode was improved when the electrode was tested using the redox probe. This study elucidates the relationship between cross-linking chemistry and redox network structure and enhances the high performance of enzyme electrode platforms for the oxidation of glucose.

Digital Light Processing to Afford High Resolution and Degradable CO2-Derived Copolymer Elastomers.

Vat photopolymerization 3D printing has proven very successful for the rapid additive manufacturing (AM) of polymeric parts at high resolution. However, the range of materials that can be printed and their resulting properties remains narrow. Herein, we report the successful AM of a series of poly(carbonate-b-ester-b-carbonate) elastomers, derived from carbon dioxide and bio-derived ϵ-decalactone. By employing a highly active and selective Co(II)Mg(II) polymerization catalyst, an ABA triblock copolymer (Mn=6.3 kg mol-1, ÐM=1.26) was synthesized, formulated into resins which were 3D printed using digital light processing (DLP) and a thiol-ene-based crosslinking system. A series of elastomeric and degradable thermosets were produced, with varying thiol cross-linker length and poly(ethylene glycol) content, to produce complex triply periodic geometries at high resolution. Thermomechanical characterization of the materials reveals printing-induced microphase separation and tunable hydrophilicity. These findings highlight how utilizing DLP can produce sustainable materials from low molar mass polyols quickly and at high resolution. The 3D printing of these functional materials may help to expedite the production of sustainable plastics and elastomers with potential to replace conventional petrochemical-based options.

Partial fluorinated silica incorporated with tuneable alkyl cross-linker based multi-cationic alkaline membrane for vanadium redox flow battery

Herein, we report partial fluorinated polymer (poly(vinylidene fluoride-co-hexafluoropropylene); PVDF-co-HFP)-based multi-cationic (quaternary ammonium, and imidazolium groups) cross-linked (tuneable carbon chain cross-linker) anion exchange membrane (AEM) incorporated with functionalized silica to avoid any structural deformations under harassed environment. Prepared membranes are cross-linked using different cross-linking agents, to study the effect of cross-linker chain length on the membrane performance. Incorporation of functionalized silica by acid-catalyzed sol-gel process improves membrane properties and stabilities. Reported PVIm-C10-APS AEM shows high conductivity (7.20 × 10−2 S/cm), and ion exchange capacity (1.48 meq/g). Well optimized positively charged PVIm-C10-APS AEM exhibits extremely low permeability of vanadium cations because of “Donnan exclusion” (9.80 × 10−7 cm2/s). During VRFB operation, PVIm-C10-APS AEM exhibits 98.10% coulombic efficiency (CE) and 77.60% voltage efficiency at 100 mA/cm2 without any significant deterioration up to 300 charge-discharge cycles. Further, PVIm-C10-APS membrane also shows >1.50 V OCV and 345 mW/cm2 peak power density at 400 mA/cm2. Reported AEM has been bench-marked with other membranes reported in the literature, and assessed as a promising material for VRFB or membrane separator for energy devices.

Responsive Microgels through RAFT-HDA Dynamic Covalent Bonding Chemistry.

This paper developed a method for preparing ultrasound-responsive microgels based on reversible addition fragmentation chain transfer-hetero Diels-Alder (RAFT-HAD) dynamic covalent bonding. First, a styrene cross-linked network was successfully prepared by a Diels-Alder (DA) reaction between phosphoryl dithioester and furan using double-ended diethoxyphosphoryl dithiocarbonate (BDEPDF) for RAFT reagent-mediated styrene (St) polymerization, with a double-ended dienophile linker and copolymer of furfuryl methacrylate (FMA) and St as the dienophile. Subsequently, the microgel system was constructed by the HDA reaction between phosphoryl disulfide and furan groups using the copolymer of polyethylene glycol monomethyl ether acrylate (OEGMA) and FMA as the dienophore building block and hydrophilic segment and the polystyrene pro-dienophile linker as the cross-linker and hydrophobic segment. The number of furans in the dienophile chain and the length of the dienophile linker were regulated by RAFT polymerization to investigate the effects of the single-molecule chain functional group degree, furan/dithioester ratio, and hydrophobic cross-linker length on the microgel system. The prepared microgels can achieve the reversible transformation of materials under force responsiveness, and their preparation steps are simple and adaptive to various potential applications in biomedical materials and adaptive electrical materials.

Length effect of crosslinkers on the mechanical properties and dimensional stability of vitrimer elastomers with inhomogeneous networks

Inhomogeneous network construction is a useful strategy to solve the trade-off between mechanical strength and creep in vitrimer rubbers. But it is still lack of tools to tune the mechanical properties and network dynamics of this new system. In this paper, uneven distribution of functional groups was realized by sequential coordination polymerization of myrcene and isoprene and epoxidation. The following epoxidation and curing generated VMI-x samples with inhomogeneous network. Polyisoprene was used to prepare control samples called VPI-x with homogeneous network. Different lengths of dicarboxylic acid crosslinkers (SA = succinic acid, HA = heptanedioic acid, DA = decanedioic acid) were used to probe their effects on dynamic behaviors, mechanical properties and recyclability. Morphological test and nanomechanical mapping confirmed the inhomogeneous feature of VMI-x samples. For both inhomogeneous and homogeneous samples, SA and DA crosslinkers brought higher tensile strength and modulus, earlier SIC phenomenon and higher orientation percentage of amorphous molecular chains than those of HA, which are ascribed to extra permanent cross-linking existing in SA samples and transition entanglements existing in DA samples. However, the constrain effect of SA crosslinker is too strong in inhomogeneous network to sacrifice the extensibility, which is much smaller than those of HA and DA. SA and DA samples also present restricted segmental motion and superior creep resistant properties compared to HA samples according to the results of broadband dielectric spectroscopy and DMA test. Differently, at high temperature above 130 °C, the stress relaxation, topology freezing transition temperature (Tv) and recycling efficiency of strength are dominated by the crosslinker length monotonically, probably due to the disentanglement of DA crosslinkers. Compared to homogeneous network, inhomogeneous ones showed obvious enhanced mechanical properties, lower hysteresis, quicker segmental relaxation, lower creep and quicker network relaxation. This work demonstrates that crosslinker lengths could tune the vast aspects of vitrimer elastomers and is a non-negligible factor to determine their properties, especially for those with inhomogeneous networks.

Influence of Type of Cross-Linking Agent on Structure and Transport Properties of Polydecylmethylsiloxane.

The development of membrane materials with high transport and separation properties for the removal of higher hydrocarbons from gas mixtures is an important and complex task. This work examines the effect of a cross-linking agent on the structure and transport properties of polydecylmethylsiloxane (C10), a material characterized by high selectivity towards C3+ hydrocarbons. C10 was cross-linked with various diene hydrocarbons, such as 1,7-octadiene (C10-OD), 1,9-decadiene (C10-DD), 1,11-dodecadiene (C10-DdD), and vinyl-terminated polysiloxanes, of different molecular weights: 500 g/mol (C10-Sil500) and 25,000 g/mol (C10-Sil25-OD). Using a number of characterization methods (IR-spectroscopy, WAXS, DSC, toluene sorption, and gas permeability), it was revealed that a change in the type and length of the cross-linking agent (at the same mole concentration of cross-linking agent) led to a significant change in the structure of the polymer material. The nature of cross-linking agent affected the arrangement of the decyl side-groups of the polymer, resulting in noticeable differences in the solubility, diffusivity, permeability, and selectivity of tested gases (N2, CH4, C2H6, and C4H10). For instance, an increase in the length of the hydrocarbon cross-linker was associated with a drop of n-butane permeability from 5510 (C10-OD) to 3000 Barrer (C10-DdD); however, the transition to a polysiloxane cross-linker led to an increase in corresponded permeability up to 8200 Barrer (C10-Sil25-OD). The n-butane/nitrogen selectivity was significantly higher for diene-type cross-linkers, and the maximum value was achieved for 1,7-octadiene (α(C4H10/N2) = 104).

High-performance di-piperidinium-crosslinked poly(p-terphenyl piperidinium) anion exchange membranes

Anion exchange membranes (AEMs) are the core component of anion exchange membrane fuel cells (AEMFCs), among which poly(aryl piperidinium) (PAP) based AEMs have been studied. Herein, we report some scalable di-piperidinium cationic crosslinkers to enhance the mechanical properties, ionic conductivity and alkaline stability of PAP-based AEMs. The results show that the morphology of AEMs can be affected by adjusting the length of crosslinker. PTP-DPC/C6-50% shows a high OH− conductivity (80 °C, 131.2 mS cm−1) due to its microphase separation. It also has excellent elongation at break (20.8%) and tensile strength (36.5 MPa). The peak power density of the PTP-DPC/C6-50% based cell can reach 616.2 mW cm−2 under H2–O2 conditions. The crosslinked network formed by long alkyl spacer chains is helpful to improve the alkaline stability of the AEM. After alkaline stability test, the conductivity of the PTP-DPC/C10-50% membrane maintained at 92.2%.

Microstructurally and mechanically tunable acellular hydrogel scaffold using carboxymethyl cellulose for potential osteochondral tissue engineering

In tissue engineering, scaffold microstructures and mechanical cues play a significant role in regulating stem cell differentiation, proliferation, and infiltration, offering a promising strategy for osteochondral tissue repair. In this present study, we aimed to develop a facile method to fabricate an acellular hydrogel scaffold (AHS) with tunable mechanical stiffness and microstructures using carboxymethyl cellulose (CMC). The impacts of the degree of crosslinking, crosslinker length, and matrix density on the AHS were investigated using different characterization methods, and the in vitro biocompatible of AHS was also examined. Our CMC-based AHS showed tunable mechanical stiffness ranging from 50 kPa to 300 kPa and adjustable microporous size between 50 μm and 200 μm. In addition, the AHS was also proven biocompatible and did not negatively affect rabbit bone marrow stem cells' dual-linage differentiation into osteoblasts and chondrocytes. In conclusion, our approach may present a promising method in osteochondral tissue engineering.

Effect of cross-linker chain length on biophysical property of hyaluronic acid hydrogel dermal filler

Effect of cross-linker chain length on biophysical property of hyaluronic acid hydrogel dermal filler

A non-cationic crosslinking strategy to improve the performance of anion exchange membranes based on poly(aryl piperidinium) for fuel cells

As a backbone with ether-free for anion exchange membranes (AEMs) with good alkali stability, poly(aryl-co-aryl piperidine) (c-PAP) has received much attention in the development of polyelectrolytes. More importantly, the trade-off between high conductivity and stability has been a thorny issue for researchers in the study of AEMs. Typically, non-cationic crosslinked membranes have lower water absorption and swelling rates compared to multi-cationic crosslinked membranes, resulting in better dimensional stability of the membrane. Here, we designed a non-cationic crosslinked AEMs based on poly(p-terphenyl-co-1,2-diphenylethane piperidinium) (PDTP). The experimental results show that the combination of hydrophobic crosslinking and side chain induction results in excellent conductivity and alkali resistance of the membranes. The crosslinked membranes reached an OH- conductivity of 104.61 mS cm−1 and a swelling rate of less than 15 % at 80 °C. In addition, the length of the hydrophobic crosslinker was varied to explore its effect on the membrane properties. The PDTP-BMP-6 C membrane (C=6 in crosslinker) shows the most excellent overall performance among them. The conductivity was retained at 86.5 % after immersion in 2 M NaOH at 80 °C for 720 h, and the peak power density reached 214 mW cm−2.

Biodegradation Behavior Control for Shape Memory Polyester Poly(Glycerol-Dodecanoate): An In Vivo and In Vitro Study.

Poly(glycerol-dodecanoate) (PGD) has garnered increasing attention in biomedical engineering for its degradability, shape memory, and rubber-like mechanical properties. Adjustable degradation is important for biodegradable implants and is affected by various aspects, including material properties, mechanical environments, temperature, pH, and enzyme catalysis. The crosslinking and chain length characteristics of poly(lactic acid) and poly(caprolactone) have been widely used to adjust the in vivo degradation rate. The PGD degradation rate is affected by its crosslink density in in vitro hydrolysis; however, there is no difference in vivo. We believe that this phenomenon is caused by the differences in enzymatic conditions in vitro and in vivo. In this study, it is found that the degradation products of PGD with different molar ratios of hydroxyl and carboxyl (MRH/C) exhibit varied pH values, affecting the enzyme activity and thus achieving different degradation rates. The in vivo degradation of PGD is characterized by surface erosion, and its mass decreases linearly with degradation duration. The degradation duration of PGD is linearly extrapolated from 9-18 weeks when MRH/C is in the range of 2.00-0.75, providing a protocol for adjusting the degradation durations of subsequent implants made by PGD.

Degradation of oligo[poly(ethylene glycol) fumarate] hydrogels through stimulus-mediated pendent group cyclization

Hydrogels are of interest for a wide range of applications including drug delivery, regenerative medicine, agriculture, and personal care products. Among the water-soluble synthetic polymers that can be processed to form hydrogels, oligo[poly(ethylene glycol) fumarate] (OPF) has attracted significant attention. The degradation of OPF can be tuned to some extent based on the poly(ethylene glycol) chain length and amount of cross-linker incorporated, but the degradation is generally quite slow, occurring over several months. Here we introduce a new approach to tune and trigger the degradation of OPF. Fumarate alkenes were functionalized to introduce protected pendent amines, that after deprotection could cyclize to 6-membered lactams, thereby cleaving the polymer backbone. Using light as a model stimulus, we demonstrated that the cleavage of an o-nitrobenzyl carbamate protecting group led to more rapid polymer degradation. Remaining unfunctionalized fumarates allowed the functionalized OPF to be cross-linked, forming a hydrogel. Treatment with light led to breakdown of the hydrogels, as indicated by a substantial reduction in the compressive modulus. The functionalization and stimulus-responsive cleavage mechanism should be applicable to other stimuli, providing a versatile approach to control OPF degradation for various applications.

Does AlphaFold2 model proteins’ intracellular conformations? An experimental test using cross-linking mass spectrometry of endogenous ciliary proteins

A major goal in structural biology is to understand protein assemblies in their biologically relevant states. Here, we investigate whether AlphaFold2 structure predictions match native protein conformations. We chemically cross-linked proteins in situ within intact Tetrahymena thermophila cilia and native ciliary extracts, identifying 1,225 intramolecular cross-links within the 100 best-sampled proteins, providing a benchmark of distance restraints obeyed by proteins in their native assemblies. The corresponding structure predictions were highly concordant, positioning 86.2% of cross-linked residues within Cɑ-to-Cɑ distances of 30 Å, consistent with the cross-linker length. 43% of proteins showed no violations. Most inconsistencies occurred in low-confidence regions or between domains. Overall, AlphaFold2 predictions with lower predicted aligned error corresponded to more correct native structures. However, we observe cases where rigid body domains are oriented incorrectly, as for ciliary protein BBC118, suggesting that combining structure prediction with experimental information will better reveal biologically relevant conformations.

In situ nanofibrillar composite fiber: A model system for understanding the structural evolution of crosslinked nanofibrils

AbstractIn situ formed nanofibrils, which are formed from the deformation of dispersed phase polymer during the shearing/stretching process, offer exciting opportunities for large scale manufacture of materials with high strength and toughness. However, how the topological structure, especially crosslinking network structure of dispersed phase polymer, affects the structural evolution of nano/microfibrils is remaining unclear. Here, the nanofibrillar morphology of nanofibrillar composite fibers is manipulated via controlling the crosslinking network structure of dispersed phase. By changing the length of crosslinker and mol ratio of crosslinkers, the diameter of nanofibrils can be controlled. The rheological property of the crosslinked microspheres and corresponding morphology of in situ formed nanofibrils confirm that the inhomogeneous crosslinking network shows lower storage modulus and consistency coefficient, leading to higher deformation adaptability of crosslinking network and smaller diameter of the nanofibrils. The distribution of nanofibrils along the axial direction of composite fiber greatly improved the tensile strength and toughness of composite fiber to 74 MPa and 719 MJ/m3, which are 45% and 180% increasement compared with the counterpart pure PMMA fiber. The findings in current study provide a new strategy to control the nanofibrillar morphology by increasing the heterogeneity of crosslinking network structure of the dispersed phase polymer.

Chemically Crosslinked Amphiphilic Degradable Shape Memory Polymer Nanocomposites with Readily Tuned Physical, Mechanical, and Biological Properties.

Facile surgical delivery and stable fixation of synthetic scaffolds play roles just as critically as degradability and bioactivity in ensuring successful scaffold-guided tissue regeneration. Properly engineered shape memory polymers (SMPs) may meet these challenges. Polyhedral oligomeric silsesquioxanes (POSSs) can be covalently integrated with urethane-crosslinked polylactide (PLA) to give high-strength, degradable SMPs around physiological temperatures. To explore their potential for guided bone regeneration, here we tune their hydrophilicity, degradability, cytocompatibility, and osteoconductivity/osteoinductivity by crosslinking star-branched POSS-PLA with hydrophilic polyethylene glycol diisocyanates of different lengths and up to 60 wt % hydroxyapatite (HA). The composites exhibit high compliance, toughness, up to gigapascal storage moduli, and excellent shape recovery (>95%) at safe triggering temperatures. Water swelling ratios and hydrolytic degradation rates positively correlated with the hydrophilic crosslinker lengths, while the negative impact of degradation on the proliferation and osteogenesis of bone marrow stromal cells was mitigated with HA incorporation. Macroporous composites tailored for a rat femoral segmental defect were fabricated, and their ability to stably retain and sustainedly release recombinant osteogenic bone morphogenetic protein-2 and support cell attachment and osteogenesis was demonstrated. These properties combined make these amphiphilic osteoconductive degradable SMPs promising candidates as next-generation synthetic bone grafts.

Highly Elastic hyperbranched polymer binder for silicon anodes in lithium-ion batteries

With extremely high theoretical capacity, silicon (Si) has been considered as one of the most promising anode materials for next-generation lithium ion batteries (LIBs). However, Si electrodes undergo huge volume changes and pulverization during the actual charge-discharge processes. In response, polymer binders can bind Si particles together, preventing the electrodes from decomposition during operation. On this basis, a novel Si-anodic elastic polymer binder system based on cross-linked hyperbranched polyethyleneimine (HPEI) with optimized cross-linker length was developed, which could achieve a good balance between the mechanical elasticity and bonding reversibility of the network. The as-prepared Si anode exhibits a high discharge capacity of 2630 mAh g−1 at a current density of 500 mA g−1, and maintains excellent cycling stability with a high capacity retention of 78.7% after 200 cycles at a high current rate of 2000 mA g−1.