pH‐sensitive polyelectrolyte films derived from submicron chitosan/Eudragit® L 100‐55 complexes: Physicochemical characterization and in vitro drug release

The objectives of this study were to prepare films from submicron chitosan/Eudragit^® L100‐55 polyelectrolyte complexes (CH/EL PEC) and to assess the influence of CH molecular weight and CH/EL mass ratio on their structure and drug‐release properties. The films were obtained by a simple, environmentally friendly, casting/solvent evaporation method and the verapamil hydrochloride (VH) was used as model drug. Submicron size, narrow size distribution, and acceptable stability of CH/EL PECs were confirmed by DLS and laser Doppler microelectrophoresis. SEM analysis revealed nonporous inner structure and flat surface of the films. Interactions between comprising polymers and formation of CH/EL PEC were established by DSC and FT‐IR spectroscopy. In vitro swelling and drug release studies revealed the pH sensitivity of the films, with burst drug release in acidic conditions (pH 1.2) and sustained release in phosphate buffers pH 5.8, 6.8, and 7.4. The slowest VH release was achieved from the films prepared from equal amounts of EL and CH of higher molecular weight, confirming the significance of the CH/EL ratio and CH molecular weight on their ability to sustain drug release. The obtained results suggested that presented, simple, and eco‐friendly preparation procedure can be used to obtain pH‐sensitive CH/EL PEC films with a promising potential as drug carriers. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42583.     

Adsorption mechanism of fulvic acid onto freeze dried poly(hydroxo aluminum) intercalated bentonites

Two poly(hydroxo aluminum) intercalated Wyoming bentonites were prepared starting from two different aluminum pillaring solutions. The sorption mechanism of Laurentian fulvic acid (FA) onto these poly(hydroxo aluminum) intercalated bentonites was investigated at different pH values and at different ionic strengths (NaCl or CaCl₂). Three mechanisms contribute to the FA adsorption, depending on the pH and the nature (NaCl or CaCl₂) and ionic strength of the background electrolyte. In the presence of NaCl the FA sorption onto poly(hydroxo aluminum) intercalated bentonites can be mainly ascribed to ligand exchange between the amphoteric poly(hydroxo aluminum) hydroxyl groups and the deprotonated carboxylic groups of the FA. The FA adsorption due to ligand exchange reactions decreases with increasing pH. In presence of Ca²⁺ ions the FA adsorption is enhanced, compared to the presence of Na⁺, due to Ca²⁺ bridging between negatively charged groups on the FA molecules and the poly(hydroxo aluminum) intercalated bentonite. The FA adsorption due to Ca²⁺ bridging increases with increasing pH. A third mechanism is enhanced FA adsorption ascribed to FA-Ca-FA bridging and was detected from the FA adsorption in presence of Ca²⁺ at the zero point of charge of the poly(hydroxo aluminum) bentonite (pH 5).     

Formation of a DNA/N‐dodecylated chitosan complex and salt‐induced gene delivery

An N‐dodecylated chitosan (CS‐12) was synthesized from dodecyl bromide and chitosan and was assembled with DNA to form a polyelectrolyte complex (DNA/CS‐12 PEC). UV was used to examine the thermal stability of DNA embedded in PEC. The results indicate that the incorporation of dodecylated chitosan can enhance the thermal stability of DNA. The analysis of AFM image shows that PEC develops a globule‐like structure composed of 40–115 DNA molecules. Dissociation of PEC was investigated by the addition of low molecular weight electrolytes. The added small molecular salts dissociate the PEC, inducing DNA to release. The ability of Mg²⁺ to dissociate PEC is greater compared to that of Na⁺ and K⁺. From AFM images, it can be visualized that DNA remains intact and undamaged due to the protection from DNase offered by alkylated chitosan. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3391–3395, 2001     

Inward Migration of Glass‐Modifier Cations During Heat Treatment Under an N2 Atmosphere

An Na⁺/Ca²⁺‐deficient layer is observed to form on the glass surface region up to a depth of hundreds of nanometers when a soda‐lime‐silicate glass is heat treated under an N₂ atmosphere near its glass‐transition temperature. The measurements were performed using X‐ray photoelectron spectroscopy with C₆₀‐ion sputtering (C₆₀‐XPS) and dynamic secondary‐ion mass spectrometry (D‐SIMS) with consideration of the mass and charge balances. The increase in the amount of hydrogen is substantially less than the decrease in the total charge due to the loss of modifier cations in the Na⁺/Ca²⁺‐deficient layer; furthermore, the oxygen concentration in this layer is lower than the bulk value, suggesting that the silanol groups in the surface layer of the glass are dehydrated. A high‐concentration layer of Ca²⁺ is also confirmed in the dehydration layer of the glass heat treated under an N₂ atmosphere, suggesting that Na⁺ and Ca²⁺ ions migrate inward into the glass via an ion‐exchange reaction with protons, which migrate toward the surface from the bulk. We also confirmed that a thicker Na⁺/Ca²⁺‐deficient layer is formed on glass surfaces with higher water content. Our results suggest that the dehydration of the silanol groups is the driving force of the inward migration of Na⁺ and Ca²⁺ ions.     

Facile preparation and characterization of sodium alginate/graphite conductive composite hydrogel

Conductive composite hydrogels based on sodium alginate (SA) and graphite were fabricated by a facile method via dispersing homogeneously conductive graphite into SA hydrogel matrix. The hydrogel was formed by in situ release of Ca²⁺ from Ca–EDTA, thus eliminating the multistep reactions and tedious purification compared to the previous work. Raman spectra, scanning electron microscopy (SEM), X‐ray diffraction (XRD), and thermogravimetric analysis (TGA) were used to characterize the structure, crystalline nature, and thermostability of SA/graphite composite hydrogels. The SA/graphite composite hydrogels exhibited the improved network and layer‐type structure. The thermal stability of the hydrogel decreased slightly after the graphite was incorporated into the SA hydrogel matrix regardless of the content of graphite. The enhanced mechanical strength of SA/graphite composite hydrogel was achieved via increasing the f value (i.e., [Ca²⁺]/[COO^‐ in alginate]) and lowering graphite content. The conductivity of the composite hydrogels could be varied in a broad range, reaching up to 10⁻³ S/cm, mainly depending on the content of graphite and the f value. POLYM. COMPOS., 37:3050–3056, 2016. © 2015 Society of Plastics Engineers     

Poly[poly(oxypropylene) phosphate] macroionophores for transport and separation of cations in a hybrid: Cation‐exchange polymer and liquid membrane system

Poly[poly(oxypropylene) phosphate]s (PPOPP, M_n = 5800, 8100, 10,400), with different POP units (400, 1200, 2000), were synthesized and applied as cation‐selective macroionophores in a multimembrane hybrid system (MHS). The solution of PPOPP in dichloroethane formed the flowing liquid membrane (FLM) circulating between two polymer cation‐exchange membranes, and subsequently, between two polymer‐made pervaporation (PV) membranes. It was found that the PPOPP macroionophores activate the preferential transport of Zn²⁺ cations from aqueous solutions containing competing Cu²⁺, Ca²⁺, Mg²⁺, K⁺, and Na⁺ cations. The following separation orders were observed for PPOPPs with POP‐400 and POP‐1200: Zn²⁺ > Cu²⁺ ? Ca²⁺, Mg²⁺, K⁺, Na⁺, and for PPOPP with POP‐2000: Zn²⁺ > Cu²⁺,Ca²⁺ ? Mg²⁺, K⁺, Na⁺. Always, the particular cations are separated as: Zn²⁺ > Cu²⁺, Ca²⁺ > Mg²⁺, and K⁺ > Na⁺. The properties of PPOPPs were compared to respective transport and separation characteristics corresponding to those of respective poly(propylene glycol)s and poly(oxypropylene) bisphosphates. The results of investigation indicate that the bifunctional character of PPOPPs is caused by the presence of ionizable groups and probably pseudocyclic POP structures. By comparing the separation of cations in the simple MHS[FLM] system and the system supported by pervaporation unit [MHS[FLM‐PV] it was found that continuous dehydration of an organic FLM improves the system overall performance. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 1436–1445, 2004     

Infusion of Ag‐Ion from Aqueous Solution into Solid Calcium Phosphate of Hydroxyapatite (HA) Crystal Structure

In contrast to extensive literature concerning Ag incorporation in hydroxyapatite, HA, while the phosphate approximated to stoichiometry of Ca₁₀(PO₄)₆(OH)₂, with added Ag has been precipitating from an aqueous solution, the paper presents Ag incorporation through Ag ion infusion from AgNO₃ solution into solid HA pressed in pellet and ignited at 800°C. After Ag ions infused into the HA‐solid (crossed the interfacial solution‐solid boundary), they diffused across the crystal structure to a depth of time‐dependent several mm. The path of Ag diffusion in the solid HA was recorded using SEM‐EDS point analyses of Ag, Ca, P, EDS‐linear analyses of those elements, and elemental mapping. Time‐dependent concentrations of Ag⁺, Ca²⁺, and PO₄^3? in AgNO₃ solutions were also analyzed. The appearance of Ag in the crystalline HA with simultaneous local depletion in Ca and phosphate recorded as P, observed by EDS with simultaneous appearance of Ca²⁺ and PO₄^3? ions and a decrease in Ag⁺ concentration in AgNO₃ solution led the authors to a conclusion that Ag⁺ for Ca²⁺ substitution supported by PO₄^3? charge balancing in the crystalline HA was in process. The HA particles in the section of the pellet without Ag had a uniform shape and size approximated to 300–400 nm. SEM image of the HA solid section, where Ag ions appeared was characterized by irregular aggregates of smaller crystals with sporadically present large, shaped in prism blocks identified by the XRD as Ag₃PO₄.     

Antiarrhythmic and Inotropic Effects of Selective Na+/Ca2+ Exchanger Inhibition: What Can We Learn from the Pharmacological Studies?

Life-long stable heart function requires a critical balance of intracellular Ca²⁺. Several ion channels and pumps cooperate in a complex machinery that controls the influx, release, and efflux of Ca²⁺. Probably one of the most interesting and most complex players of this crosstalk is the Na⁺/Ca²⁺ exchanger, which represents the main Ca²⁺ efflux mechanism; however, under some circumstances, it can also bring Ca²⁺ into the cell. Therefore, the inhibition of the Na⁺/Ca²⁺ exchanger has emerged as one of the most promising possible pharmacological targets to increase Ca²⁺ levels, to decrease arrhythmogenic depolarizations, and to reduce excessive Ca²⁺ influx. In line with this, as a response to increasing demand, several more or less selective Na⁺/Ca²⁺ exchanger inhibitor compounds have been developed. In the past 20 years, several results have been published regarding the effect of Na⁺/Ca²⁺ exchanger inhibition under various circumstances, e.g., species, inhibitor compounds, and experimental conditions; however, the results are often controversial. Does selective Na⁺/Ca²⁺ exchanger inhibition have any future in clinical pharmacological practice? In this review, the experimental results of Na⁺/Ca²⁺ exchanger inhibition are summarized focusing on the data obtained by novel highly selective inhibitors.     

Transfer of Monovalent and Divalent Cations in Salt Solutions by Electrodialysis

Abstract

The selectivity mechanism of transport of Na⁺, Ca²⁺ and Mg²⁺ through commercial monovalent‐cation permselective membranes is investigated in batch electrodialysis experiments with synthetic salt solutions containing monovalent and divalent cations. The role of hydration energy, steric effect, kinetic effect as well as effects of permselectivity of cation exchange membrane has been elucidated with electrodialysis of single solutions (NaCl, CaCl₂, MgCl₂). The mechanism of interferences is investigated in (Na⁺/Ca²⁺, Na⁺/Mg²⁺, Ca²⁺/Mg²⁺ and Na⁺/Ca²⁺/Mg²⁺) mixtures.     

Tunable Color of Eu2+/Mn2+ Coactivated Na5Ca2Al(PO4)4 via Energy Transfer

Eu²⁺ and Eu²⁺/Mn²⁺‐activated Na₅Ca₂Al(PO₄)₄ phosphors have been synthesized by the combustion method. X‐ray powder diffraction profiles, luminescence spectra, chromaticity variation, and energy transfer of Na₅Ca₂Al(PO₄)₄:Eu²⁺, Mn²⁺ were investigated as a function of the Eu²⁺ and Mn²⁺ concentrations in Na₅Ca₂Al(PO₄)₄. The Na₅Ca₂Al(PO₄)₄:Eu²⁺,Mn²⁺ phosphors can be effectively excited at wavelength ranging from 300 to 430 nm, which matches well with that for near‐ultraviolet (UV) light‐emitting diode (LED) chips. Under excitation at 354 nm, Na₅Ca₂Al(PO₄)₄:Eu²⁺,Mn²⁺ not only exhibits blue‐green emission band attributed to 4f⁶5d¹→4f⁷ of Eu²⁺ but also gives an orange emission band attributed to ⁴T₁→⁶A₁ of Mn²⁺. The emission color of the phosphor can be systematically tuned from blue‐green through white and eventually to orange by adjusting the relative content of Eu²⁺ and Mn²⁺ through the principle of energy transfer. The results indicated that Na₅Ca₂Al(PO₄)₄:Eu²⁺, Mn²⁺ may serve as a potential color‐tunable phosphor for near UV white‐light LED.     

Mechanistic elucidation and evaluation of biosorption of metal ions by grapefruit peel using FTIR spectroscopy,kinetics and isotherms modeling,cations displacement and EDX analysis

BACKGROUND: The performance and mechanism of the biosorptive removal of Ni²⁺ and Zn²⁺ from aqueous solution using grapefruit peel (GFP) as a new biosorbent was investigated by using different experimental approaches, such as potentiometric titration, Fourier transform infrared (FTIR) and energy‐dispersive X‐ray spectroscopy (EDX) analysis, chemical blocking of functional groups and concomitant release of cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) from GFP with metal (Ni²⁺, Zn²⁺) uptake. RESULTS: GFP removed Ni²⁺ and Zn²⁺ rapidly, with 84.73% and 92.46% of the equilibrium sorption being reached in 30 min for Ni²⁺ and Zn²⁺, respectively. The equilibrium process was described well by the Langmuir isotherm model, with maximum sorption capacity of 1.33 and 1.51 meq g^?1 for Ni²⁺ and Zn²⁺, respectively. Release of cations (Ca²⁺, Mg²⁺, Na⁺, K⁺) and protons H⁺ from GFP during uptake of Ni²⁺ and Zn²⁺ and EDX analysis of GFP before and after metal sorption revealed that the main mechanism of sorption was ion exchange. FTIR spectroscopy showed that carboxyl and hydroxyl groups were involved in the sorption of Ni²⁺ and Zn²⁺. Blocking of these groups revealed that carboxylic group was responsible for 78.57% and 73.31% of Ni²⁺ and Zn²⁺ removal, respectively whereas 22.63% and 28.54% was due to the hydroxyl group. The GFP could be regenerated using 0.1 mol L^?1 HCl, with more than 98% metal recovery and reused for five cycles without any significant loss in its initial sorption capacity. CONCLUSIONS: The study suggests that GFP has promising potential for use as an efficient and cost‐effective biosorbent for the removal and recovery of Ni²⁺ and Zn²⁺ from aqueous solution. Copyright © 2009 Society of Chemical Industry     

Preparation of tricalcium phosphate–calcium alginate composite flat sheet membranes and their application for protein release

Tricalcium phosphate–calcium alginate (TCP–CA) composite flat sheet membranes with the thickness of 150–200 μm were prepared by Ca²⁺ crosslinking of TCP and sodium alginate (SA) aqueous solution. The composite flat sheet membranes were characterized by SEM, FTIR, DSC and BET method. The mechanical properties of the membranes were tested with a tensile testing machine in wet form. Hemoglobin (HB) was immobilized in the following four matrices (1) HB was adsorbed onto the TCP powders directly, (2) HB and SA dissolved together, and then crosslinked by CaCl₂, (3) HB was pre‐adsorbed onto TCP powders, and then mixed with SA aqueous solution, finally crosslinked by CaCl₂, (4) HB and TCP powders were individually dispersed in the SA aqueous solution and then crosslinked by CaCl₂. The release behaviors of the four materials were investigated in phosphate buffer (pH = 6.86), Tris‐HCl solution (pH = 7.4) and NaCl solution (0.9 wt%). SEM observation showed that the TCP particles were well embedded and homogeneously distributed in the alginate matrix. DSC and FTIR indicated that there were additional interactions between the TCP and the polymer. TCP can improve the mechanical properties of CA membranes and the swelling ratio of TCP–CA membrane in NaCl solution decreased with the increase of TCP content. The sustained release behaviors of matrix 3 were shown in PBS, Tris‐HCl and NaCl solutions. POLYM. COMPOS., 36:1899–1906, 2015. © 2014 Society of Plastics Engineers     

Effects of monovalent and multivalent ions on the stability of a polyelectrolyte complex with entrapped surfactants

In this article, we report the effects of nine different monovalent and multivalent salts on the particle size and stability of refined, positively charged polyelectrolyte complexes (PECs) with entrapped surfactant. Dynamic light scattering and ζ potential measurements of these polymeric particles as a function of various salt concentrations showed that both counter ions and co‐ions induced a concentration‐dependent increase in the particle size and a decrease in the ζ potential. We found that the anion concentration where the particle size doubled and the maximum anion concentration beyond which particle precipitation occurred (C_a,max) demonstrated a power law dependence on the anion valence. Moreover, for anions of the same valence but different hydration radio, C_a,max decreased in the following order: NO₃ → Cl → HPO₄^2? > SO₄^2? > PO₄^3?. However, unlike the case of hard colloids where co‐ions have relatively little effect on particle interactions, the co‐ions also increased the hydrodynamic radii of our PECs in the following order: K⁺ ≈ Na⁺ > Ca²⁺ > Mg²⁺ > Al³⁺. Furthermore, we found that the entrapped surfactants were shielded from the adverse effect of multivalent ions; this established that the monovalent and multivalent ions interacted with the polyelectrolyte shells of the PEC. This behavior was in contrast with the effect of salts on mixtures containing the polyelectrolyte and surfactant components, where the addition of salts typically causes an interaction with the individual components. Because several biomedical and technological applications involving PECs require saline environments, our studies provide insight into how small ions influence the PEC stability in applications involving varying salinities. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42099.     

Preparation of composites of liquid‐crystalline matrix of poly(p‐phenylene‐sulfoterephthalamide) and CaCO3 by In situ mineralization

Liquid‐crystalline (LC) hydrogels were obtained from an aqueous solution of poly(p‐phenylene‐sulfoterephthalamide) (PPST) by the addition of calcium ions (Ca²⁺). The critical hydrogel formation ratio of Ca²⁺ to the sulfonic acid group in PPST (^crtR_Ca = [Ca²⁺]/[ ]) depended on the concentration of PPST, and was independent of the molecular weight of PPST. When the LC hydrogel was prepared at a concentration of 0.5 wt % and ^crtR_Ca = 0.6, and was exposed to ammonium carbonate vapor for 96 h, all Ca²⁺ in the LC hydrogel were converted into calcite crystals. The alternate soaking process for the LC hydrogel induced the formation of two mesocrystal morphologies on and in the Ca²⁺ cross‐linked LC hydrogel. Plate‐like calcite mesocrystals grew at the hydrogel/solution interface and cubic mesocrystals were present in the inner space of the hydrogel, thus composites with some ordered structures of LC matrix and CaCO₃ have been prepared through in situ mineralization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41455.     

The design of cyclic fixed-bed ion-exchange operations—III. Softening solutions containing Na+, Mg2+, Ca2+

The method presented in parts 1 and 2 for the design of simple cyclic ion-exchange processes in foxed beds is extended to the case where Na⁺, Mg²⁺ and Ca²⁺ are all present in the saturation solution. Two properties are established: firstly that the breakthrough curves corresponding to Ca²⁺ and Na⁺ mixtures in different proportions can be reduced to a single curve by using generalised coordinates, and secondly that Ca²⁺ and Mg²⁺ can be considered as a single ion of “hardness”. This means that the ternary mixture can be treated as a binary possessing the first property. These effects are incorporated into the cyclic material balances allowing the treatment given in parts 1 and 2 to be used.     

Use of the empirical Hill equation for characterization of the effect of added cations on the viscosity of aqueous solutions of partially hydrolyzed polyacrylamide

Summary An empirical method based on the Hill equation has been developed to characterize the effects of added cations (Na⁺, K⁺, Mg²⁺, and Ca²⁺) on the viscosities of aqueous solutions of partially hydrolyzed polyacryl-amide.     

Selective and Efficient Liquid Membrane Transport of Thallium (III) Ion by Potassium‐dicyclohexyl‐18‐crown‐6 as Specific Carrier

Abstract

Potassium‐dicyclohexyl‐18‐crown‐6 was used as a selective and efficient carrier for the uphill transport of thallium (III) ion as [TlCl₄]^? complex ion through a chloroform bulk liquid membrane. By using oxalate anion as a metal ion acceptor in the receiving phase, the amount of thallium (III) transported across the liquid membrane after 120 min was 96±2%. The selectivity and efficiencies of thallium transport from aqueous solutions containing Cu²⁺, Zn²⁺, Ni²⁺, Cd²⁺, Pb²⁺, Co³⁺, Mn²⁺ _, Cr³⁺, Mg²⁺, Ca²⁺, K⁺, Na⁺, and Fe³⁺ ions were investigated. In the presence of Na₃PO₄ (0.01 M) at pH=3 as a suitable precipitation agent in the source phase, the interfering effect of Pb²⁺ ion were diminished drastically.     

Calcium‐carboxymethyl chitosan hydrogel beads for protein drug delivery system

In this study, carboxymethyl chitosan (CMC) hydrogel beads were prepared by crosslinking with Ca²⁺. The pH‐sensitive characteristics of the beads were investigated by simulating gastrointestinal pH conditions. As a potential protein drug delivery system, the beads were loaded with a model protein (bovine serum albumin, BSA). To improve the entrapment efficiency of BSA, the beads were further coated with a chitosan/CMC polyelectrolyte complex (PEC) membrane by extruding a CMC/BSA solution into a CaCl₂/chitosan gelation medium. Finally, the release studies of BSA‐loaded beads were conducted. We found that, the maximum swelling ratios of the beads at pH 7.4 (17–21) were much higher than those at pH 1.2 (2–2.5). Higher entrapment efficiency (73.2%) was achieved in the chitosan‐coated calcium‐CMC beads, compared with that (44.4%) in the bare calcium‐CMC beads. The PEC membrane limited the BSA release, while the final disintegration of beads at pH 7.4 still leaded to a full BSA release. Therefore, the chitosan‐coated calcium‐CMC hydrogel beads with higher entrapment efficiency and proper protein release properties were a promising protein drug carrier for the site‐specific release in the intestine. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3164–3168, 2007     

Integrins Increase Sarcoplasmic Reticulum Activity for Excitation—Contraction Coupling in Human Stem Cell-Derived Cardiomyocytes

Engagement of the sarcoplasmic reticulum (SR) Ca²⁺ stores for excitation–contraction (EC)-coupling is a fundamental feature of cardiac muscle cells. Extracellular matrix (ECM) proteins that form the extracellular scaffolding supporting cardiac contractile activity are thought to play an integral role in the modulation of EC-coupling. At baseline, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) show poor utilisation of SR Ca²⁺ stores, leading to inefficient EC-coupling, like developing or human CMs in cardiac diseases such as heart failure. We hypothesised that integrin ligand–receptor interactions between ECM proteins and CMs recruit the SR to Ca²⁺ cycling during EC-coupling. hiPSC-CM monolayers were cultured on fibronectin-coated glass before 24 h treatment with fibril-forming peptides containing the integrin-binding tripeptide sequence arginine–glycine–aspartic acid (2 mM). Micropipette application of 40 mM caffeine in standard or Na⁺/Ca²⁺-free Tyrode’s solutions was used to assess the Ca²⁺ removal mechanisms. Microelectrode recordings were conducted to analyse action potentials in current-clamp. Confocal images of labelled hiPSC-CMs were analysed to investigate hiPSC-CM morphology and ultrastructural arrangements in Ca²⁺ release units. This study demonstrates that peptides containing the integrin-binding sequence arginine–glycine–aspartic acid (1) abbreviate hiPSC-CM Ca²⁺ transient and action potential duration, (2) increase co-localisation between L-type Ca²⁺ channels and ryanodine receptors involved in EC-coupling, and (3) increase the rate of SR-mediated Ca²⁺ cycling. We conclude that integrin-binding peptides induce recruitment of the SR for Ca²⁺ cycling in EC-coupling through functional and structural improvements and demonstrate the importance of the ECM in modulating cardiomyocyte function in physiology.     

Preparation of novel biomass humate flame retardants and their flame retardancy in epoxy resin

Humic acid (HA), a biomass material with plentiful oxygen-containing functional groups, showed huge potential to be considered as a promising charring agent in flame retardancy. In this study, this HA was modified with four different metal ions like Fe²⁺, Mn²⁺, Al³⁺, and Cu²⁺ and finally, introduced into the epoxy resin (EP) to enhance the flame retardancy of the EP and the dispersion of these flame retardants into the EP matrix. When 10 wt% of HA-Fe and HA-Mn were incorporated into EP matrix, the limiting oxygen index (LOI) was increased from 21.2% for EP to 26.6 and 25.3% for the EP composites and the peak heat release rate (pHRR) was reduced by 36 and 35.5%, respectively. Such a significant improvement in flame retardancy was attributed to the catalytic charring of HA in the presence of metal ions, which ultimately increased the residual char formation and produced compact char layers during the combustion process to retard the transfer of heat and combustible gases between the EP composites and the flame zone. Finally, this kind of application provided a feasible way for the development of an environmentally friendly flame retardant with high efficiency, which improved the fire safety of EP matrix.