Thermoresponsive Conductivity of Graphene-Based Fibers.

Smart materials are versatile material systems which exhibit a measurable response to external stimuli. Recently, smart material systems have been developed which incorporate graphene in order to share on its various advantageous properties, such as mechanical strength, electrical conductivity, and thermal conductivity as well as to achieve unique stimuli-dependent responses. Here, a graphene fiber-based smart material that exhibits reversible electrical conductivity switching at a relatively low temperature (60 °C), is reported. Using molecular dynamics (MD) simulation and density functional theory-based non-equilibrium Green's function (DFT-NEGF) approach, it is revealed that this thermo-response behavior is due to the change in configuration of amphiphilic triblock dispersant molecules occurring in the graphene fiber during heating or cooling. These conformational changes alter the total number of graphene-graphene contacts within the composite material system, and thus the electrical conductivity as well. Additionally, this graphene fiber fabrication approach uses a scalable, facile, water-based method, that makes it easy to modify material composition ratios. In all, this work represents an important step forward to enable complete functional tuning of graphene-based smart materials at the nanoscale while increasing commercialization viability.

A prospect of cost-effective handling and transportation of graphene oxides: folding and redispersion of graphene oxide microsheets.

Controlling the assembly of 2D materials such as graphene oxides (GO) has a significant impact on their properties and performance. One of the critical issues on the processing and handling of GO is that they need to be in dilution solution (0.5 to 2.5 wt%) to maintain their high degree of exfoliation and dispersion. As a result, the shipment of GO in large quantity involves a huge volume of solvent (water) and thus the transportation costs for large sales volume would become extremely high. Through cross-sectional scanning electron microscopy and polarized optical microscopy together with x-ray diffraction and small-angle x-ray scattering studies, we demonstrated that the assembly and structure of GO microsheets can be preserved without restacking, when assembled GO via water-based wet spinning are re-dispersed into solution. A couple of alkyl ammonium bromides, CTAB and TBAB, as well as NaOH, were examined as coagulants and the resulting fibers were redispersed in an aqueous solution. The redispersed solution of fibers that were wet-spun into the commonly used CTAB and TBAB coagulation baths, maintained their physico-chemical properties (similar to the original GO dispersion) however, did not reveal preservation of liquid crystallinity. Meanwhile, the redispersed fibers that were initially spun into NaOH coagulation bath were able to maintain their liquid crystallinity if the lateral size of the GO sheets was large. Based on these findings, a cost-effective solid handling approach is devised which involves (i) processing GO microsheets in solution into folded layers in solid-state, (ii) transporting assembled GO to the customers, and (iii) redispersion of folded GO into a solution for their use. The proposed solid handling of GO followed by redispersion into solution can greatly reduce the transportation costs of graphene oxide materials by reducing the transportation volume by more than 90%.

Exploring the Role of an Electrolyte Additive in Suppressing Surface Reconstruction of a Ni-Rich NMC Cathode at Ultrahigh Voltage via Enhanced In Situ and Operando Characterization Methods.

Vinylene carbonate (VC) is a widely used electrolyte additive in lithium-ion batteries for enhanced solid electrolyte interphase formation on the anode side. However, the cathode electrolyte interphase (CEI) formation with VC has received a lot less attention. This study presents a comprehensive investigation employing advanced in situ/operando-based Raman and X-ray absorption spectroscopy (XAS) to explore the effect of electrolyte composition on the CEI formation and suppression of surface reconstruction of LixNiyMnzCo1-y-zO2 (NMC) cathodes. A novel chemical pathway via VC polymerization is proposed based on experimental results. In situ Raman spectra revealed a new peak at 995 cm-1, indicating the presence of C-O semi-carbonates resulting from the radical polymerization of VC. Operando Raman analysis unveiled the formation of NiO at 490 cm-1 in the baseline system under ultrahigh voltage (up to 5.2 V). However, this peak was conspicuously absent in the VC electrolyte, signifying the effectiveness of VC in suppressing surface reconstruction. Further investigation was carried out utilizing in situ XAS compared X-ray absorption near edge structure spectra from cells of 3 and 20 cycles in both electrolytes at different operating voltages. The observed shift at the Ni K-edge confirmed a more substantial reduction of Ni in the baseline electrolyte compared to that in the VC electrolyte, thus indicating less CEI protection in the former. A sophisticated extended X-ray absorption fine structure analysis quantitatively confirmed the effective suppression of rock-salt formation with the VC electrolyte during the charging process, consistent with the operando Raman results. The in situ XAS results thus provided additional support for the key findings of this study, establishing the crucial role of VC polymerization in enhancing CEI stability and mitigating surface reconstruction on NMC cathodes. This work clarifies the relationship between the enhanced CEI layer and NMC degradation and inspires rational electrolyte design for long-cycling NMC cathodes.

Enhanced Energy Storage in Lithium-Metal Batteries via Polymer Electrolyte Polysulfide-Polyoxide Conetworks.

The present article entails a novel concept of storing extra energy in a multifunctional polymer electrolyte membrane (PEM) beyond the storage capacity of a cathode, which is achieved by so-called "prelithiation" upon simply deep discharging to a low potential range of a lithium-metal electrode (i.e., -0.5 to 0.5 V). This unique extra energy-storage capacity has been realized recently in the PEM consisting of polysulfide-co-polyoxide conetworks in conjunction with succinonitrile and LiTFSI salt that facilitate complexation via ion-dipole interaction of dissociated lithium ions with thiols, disulfide, or ether oxygen of the conetwork. Although ion-dipole complexation may increase the cell resistance, the prelithiated PEM provides excess lithium ions during oxidation (or Li+ stripping) at the Li-metal electrode. Once the PEM network is fully saturated with Li ions, the remaining excess ions can move through the complexation sites at ease, thereby affording not only facile ion transport but also extra ion-storage capacity within the PEM conetwork. Of particular interest is that the lithiated polysulfide-co-polyoxide polymer network-based PEM exhibits a high conductivity of 1.18 × 10-3 S/cm at ambient, which can also store extra energy with a specific capacity of about 150 mAh/g at a 0.1C rate in the PEM voltage range of 0.01-3.5 V in addition to 165 mAh/g at 0.2C of an NMC622 (nickel manganese cobalt oxide) cathode (i.e., 2.5-4.6 V) with a Coulombic efficiency of approximate unity. Moreover, its Li-metal battery assembly with an NMC622 cathode exhibits a very high specific capacity of ∼260 mAh/g at 0.2C in the full battery range of 0.01-5 V, having a higher Li+ transference number of 0.74, suggestive of domination by the lithium cation transport relative to those (0.22-0.35) of organic liquid electrolyte lithium-ion batteries.

Overview of Tissue Engineering and Drug Delivery Applications of Reactive Electrospinning and Crosslinking Techniques of Polymeric Nanofibers with Highlights on Their Biocompatibility Testing and Regulatory Aspects.

Traditional electrospinning is a promising technique for fabricating nanofibers for tissue engineering and drug delivery applications. The method is highly efficient in producing nanofibers with morphology and porosity similar to the extracellular matrix. Nonetheless, and in many instances, the process has faced several limitations, including weak mechanical strength, large diameter distributions, and scaling-up difficulties of its fabricated electrospun nanofibers. The constraints of the polymer solution's intrinsic properties are primarily responsible for these limitations. Reactive electrospinning constitutes a novel and modified electrospinning techniques developed to overcome those challenges and improve the properties of the fabricated fibers intended for various biomedical applications. This review mainly addresses reactive electrospinning techniques, a relatively new approach for making in situ or post-crosslinked nanofibers. It provides an overview of and discusses the recent literature about chemical and photoreactive electrospinning, their various techniques, their biomedical applications, and FDA regulatory aspects related to their approval and marketing. Another aspect highlighted in this review is the use of crosslinking and reactive electrospinning techniques to enhance the fabricated nanofibers' physicochemical and mechanical properties and make them more biocompatible and tailored for advanced intelligent drug delivery and tissue engineering applications.

Exceptional colloidal stability of acidified whey protein beverages stabilized by soybean soluble polysaccharide.

Protein-rich beverages have gained significant attention in recent years. It is a challenge to produce whey protein beverages with high stability, good transparency, and a smooth mouthfeel. The polysaccharide (PS)-protein complex might help the food industry overcome these obstacles. In this study, soybean soluble polysaccharide (SSPS) and high methoxylated pectin (HMP, a traditional PS) are used, at different ratios to the protein, to improve the colloidal stability of the acidified whey protein solution. Both heated and unheated complexes were studied. SSPS-whey protein complexes have shown exceptional stabilities in all ratios while HMP-whey protein complexes revealed coacervation after 72 hr of storage. The prepared complexes exhibited comparable sizes and ζ-potentials. The SSPS-whey protein complexes were less turbid than HMP-whey protein complexes at similar PS to protein ratios. Results also show that greater repulsive interactions occurred in SSPS-whey protein complexes when compared to HMP-whey protein complexes, as examined by free thiol content and intrinsic fluorescence intensity measurements. PRACTICAL APPLICATION: It is a challenge to produce whey protein isolate (WPI) beverages with high stability, good transparency, and smooth mouthfeel. The polysaccharide (PS)-protein complex might help the food industry overcome these obstacles. We have demonstrated that soybean soluble polysaccharide (SSPS), at [SSPS]:[acWPI] ratios of 1:2 to 1:30, can significantly improve the colloidal stability of the acidified whey protein beverages. This SSPS-whey protein system could be used as a stable beverage base for a variety of beverages.

Facile Production of Graphenic Microsheets and Their Assembly via Water-Based, Surfactant-Aided Mechanical Deformations.

Expandable graphite (EG) and few-layer graphene (FLG) have proven to be instrumental materials for various applications. The production of EG and FLG has been limited to batch processes using numerous intercalating agents, especially organic acids. In this study, a Taylor-Couette reactor (TCR) setup is used to expand and exfoliate natural graphite and produce a mixture of EG and FLG in aqueous solutions using an amphiphilic dispersant and a semiflexible stabilizer. Laminar Couette flow structure and high shear rates are achieved via the rotation of the outer cylinder while the inner cylinder is still, which circumvents vortex formation because of the suppression of centrifugal forces. Our results reveal that the level of expansion and exfoliation using an aqueous solution and a TCR is comparable to that using commercial EG (CEG) synthesized by intercalating sulfuric acid. More importantly, the resultant EG and FLG flakes are more structurally homogeneous than CEG, the ratio of FLG to EG increases with increasing shearing time, and the produced FLG sheets exhibit large lateral dimensions (>10 µm). The aqueous solutions of EG and FLG are wet-spun to produce ultralight fibers with a bulk density of 0.35 g/cm3. These graphene fibers exhibit a mechanical strength of 0.5 GPa without any modification or thermal treatment, which offers great potential in light-weight composite applications.

An investigation into the role of polarity of diamines in controlling the electron migration mechanism of photoluminescent poly(amide-imide)s.

Several diamines with remarkable different polarities were used to produce photoactive poly(amide-imide)s (PAI)s in a quantitative yield. The absorption, fluorescence and photophysical properties of series of poly(amide-imide)s containing fused aromatic systems as energy donor and energy acceptor with different diamines cores are described. Poly(amide-imide)s exhibit broad fluorescent characteristic, and its fluorescent intensity is related to the intermolecular chain-chain or chain-solvent interaction. The fluorescence spectra confirmed an efficient singlet-singlet energy transfer between fused aromatic systems. The self-quenching mechanism was studied according to the specific behavior of these polymers in different solvents. The self-quenching rate constant for the association reaction in the excited state (Kq) could be measured from the Stern-Volmer equation. The kind of fused system and diamines show different electron migration mechanisms and photoluminescent properties in the singlet-excited states. By using the exothermic energy transfer as a function of diamine polarity, the electron transfer mechanism was evaluated for aromatic poly(amide-imide)s. In principle, the fluorescence energy is absorbed by different (PAI)s and raises the molecules to one of its excited states. Afterwards this excitation energy transfers through the different relaxation channels, i.e. columbic or exchange energy transfer.

Effect of acupressure on constipation in patients undergoing hemodialysis: A randomized double-blind controlled clinical trial.

OBJECTIVE: Constipation is one of the most common digestive problems in patients undergoing hemodialysis. It has a negative effect on quality of life in these patients. As routine treatments are not effective in this regard, complementary therapies may help to overcome this condition. This study aimed to investigate the effect of acupressure on constipation in patients undergoing hemodialysis. MATERIALS AND METHODS: This was a randomized double- blind placebo- controlled clinical trial conducted in 2014. A convenience sample of 70 patients undergoing hemodialysis was selected from hemodialysis units of three hospitals affiliated to Mazandaran University of Medical Sciences, Mazandaran, Iran. Patients were randomly assigned to intervention or control group. Intervention group received acupressure in acupressure points three times a week for four weeks during hemodialysis. In control group, acupressure was delivered in false points. We assessed the frequency of defecation in the two groups before and after the study. The study instruments consisted of a demographic questionnaire, and a data sheet for documenting constipation frequency. RESULTS: The results indicated a significant difference between intervention group (13.73±3.63) and control group (10.06±3.77) in frequency of defecation during the fourth week of intervention (p<0.001). Regarding quality of stool, there was a meaningful difference between the groups in the fourth week in a way that the stool in the intervention group was more natural and in the control group, it was thicker and more adhesive. CONCLUSION: Acupressure seems to be an effective complementary treatment for constipation in patients undergoing hemodialysis.

Formation of shelf stable Pickering high internal phase emulsions (HIPE) through the inclusion of whey protein microgels.

High internal phase emulsions (HIPE) prepared using whey protein microgels (WPMs) as a surfactant were demonstrated to have substantially higher stability than HIPEs prepared using similar loadings of non-gelled whey protein isolate (WPI) or Tween 20. Microgel colloids were prepared from WPI solutions by heat treatment at 85 °C in a narrow pH range (5.8-6.0) to particle sizes of approximately 90, 160 and 350 nm in diameter. ζ-potentials of the WPM increased in negativity with decreasing particle size from -7.4 ± 2.5 down to -21.1 ± 0.9 at 90 nm. All WPMs conferred high stability to corn oil based HIPE when used as an emulsifier. Light microscopy and cryo-scanning electron microscopy showed that both increasing WPM concentration and decreasing WPM particle size produced increasingly smaller and more hexagonally shaped corn oil emulsion droplets; WPI and Tween 20 based HIPE droplets were generally smaller and spherical in shape. The HIPE (75% w/w corn oil) produced with 1% (w/w) WPM as an emulsifier showed stability through 6 months storage at 4 °C at all WPM sizes tested, while the HIPE prepared with 1% (w/w) WPI or Tween 20 exhibited significant creaming. WPM and WPI based HIPE both showed thermal stability at 70 °C and 95 °C while the heating of Tween 20 based HIPE resulted in droplet coalescence and oil-phase separation. HIPE production with WPMs significantly improved the viscoelastic properties of the HIPE, imparting drastic increases in yield stress, critical stress, complex modulus and elastic modulus over HIPE prepared with WPI or Tween 20. The more rigid rheology of the WPM HIPE indicated by these data is likely the primary mechanism driving the improved stability of these emulsions.

New Three-Dimensional Poly(decanediol-co-tricarballylate) Elastomeric Fibrous Mesh Fabricated by Photoreactive Electrospinning for Cardiac Tissue Engineering Applications.

Reactive electrospinning is capable of efficiently producing in situ crosslinked scaffolds resembling the natural extracellular matrix with tunable characteristics. In this study, we aimed to synthesize, characterize, and investigate the in vitro cytocompatibility of electrospun fibers of acrylated poly(1,10-decanediol-co-tricarballylate) copolymer prepared utilizing the photoreactive electrospinning process with ultraviolet radiation for crosslinking, to be used for cardiac tissue engineering applications. Chemical, thermal, and morphological characterization confirmed the successful synthesis of the polymer used for production of the electrospun fibrous scaffolds with more than 70% porosity. Mechanical testing confirmed the elastomeric nature of the fibers required to withstand cardiac contraction and relaxation. The cell viability assay showed no significant cytotoxicity of the fibers on cultured cardiomyoblasts and the cell-scaffolds interaction study showed a significant increase in cell attachment and growth on the electrospun fibers compared to the reference. This data suggests that the newly synthesized fibrous scaffold constitutes a promising candidate for cardiac tissue engineering applications.

Synthesis, characterization & cytocompatibility of poly (diol-co-tricarballylate) based thermally crosslinked elastomers for drug delivery & tissue engineering applications.

The aim of this study was to investigate the synthesis and in vitro characterization of thermoset biodegradable poly (diol-co-tricarballylate) (PDT) elastomeric polymers for the purpose of their use in implantable drug delivery and tissue engineering applications. The synthesis was based on thermal crosslinking technique via a polycondensation reaction of tricarballylic acid with aliphatic diols of varying chain lengths (C6-C12). PDT prepolymers were synthesized at 140 °C for 20 min. After purification, the prepolymers were molded and kept at 120 °C for 18 h under vacuum to complete the crosslinking process. PDT prepolymers were characterized by DSC, FT-IR, 1H NMR and GPC. The PDT elastomers were also subjected to thermal and structural analysis, as well as sol content, mechanical testing, in vitro degradation and cytocompatibility studies. The mechanical properties and sol content were found to be dependent on synthesis conditions and can be controlled by manipulating the crosslinking density and number of methylene groups in the chain of precursor aliphatic diol. The family of thermally crosslinked PDT biodegradable polyesters were successfully prepared and characterized; besides they have promising use in drug delivery and other biomedical tissue engineering applications.

Fabrication & Characterization of 3D Electrospun Biodegradable Nanofibers for Wound Dressing, Drug Delivery and Other Tissue Engineering Applications.

BACKGROUND: The use of electrospinning technology (ET) in fabrication of threedimensional biodegradable electrospun nanofibers scaffolds (BENS) has recently gained considerable attention in tissue engineering. BENS are superior to other existing scaffolds in tissue regeneration as they provide high surface area-to-volume ratio, possess high porosity, and offer a biomimetic environment in a nanometer scale. OBJECTIVES: To fabricate & characterize BENS using Poly (ethylene glycol) (PEG35000) as a biodegradable polymer loaded with Amoxicillin Trihydrate (AMX) for use as a wound dressing. METHOD: Solutions of PEG35000 in chloroform of varying concentrations were used to fabricate BENS using ET. Blank & 1% w/v AMX-loaded BENS were fabricated & characterized. Morphology of BENS were assessed using Scanning Electron Microscopy (SEM). Fourier Transform Infrared (FT-IR) Spectroscopy was used to identify the interaction between PEG35000 and AMX. Differential Scanning Calorimetry (DSC) was used to assess the crystallinity and thermal behavior of the prepared BENS. The X-Ray Diffraction (XRD) analysis for the blank and drug loaded electrospun fibers was carried out to identify the changes in their crystalline pattern. The in vitro antibacterial activity against common skin Gram-negative and Gram-positive pathogens was also tested. RESULTS: Blank & AMX loaded 35% w/v PEG35000 solutions produced the most homogenous and intact nanofibers. Major bands of AMX in FTIR were clearly observed in the spectrum of AMX with PEG35000 post electrospinning. Moreover, DSC thermograms indicated that AMX existed in its amorphous dispersed state within PEG fibers supported by the disappearance of its melting peak at 190°C and confirmed by the complete absence of AMX crystals under SEM. Finally, the results of DSC were confirmed by XRD patterns. Characterizing XRD peaks of AMX loaded with PEG3500 post electrospinning disappeared as an indication of the complete dispersion of AMX in the loaded fibers and its complete conversion to the amorphous form. The in vitro antibacterial assay confirmed the efficiency of the drug loaded fibers against the common skin pathogens. CONCLUSION: BENS using PEG35000 loaded with AMX were successfully fabricated and characterized. Our findings show that PEG BENS has features that make it a promising candidate for wound healing applications.