Surface modification of poly-l-lactic acid fibrous scaffolds by a molecular-designed multi-walled carbon nanotube multilayer for enhancing cell interactions

We presented a molecular-designed multi-walled carbon nanotube (MWCNT) layer-by-layer (LbL) multilayer on poly-l-lactic acid (PLLA) electrospun fibers for engineering cell/CNT interfaces. A stable, positively charged monolayer was created on the fiber surface by the aminolysis reaction of poly(ethylene imine) (PEI) with PLLA, followed by alternate deposition in negatively charged MWCNT and positively charged chitosan (CS). Thermogravimetric analysis indicated a sustained growth of the MWCNT during the self-assembly process. The interactions between MWCNT and polycation crucially affected the specific structure and properties of the MWCNT multilayer. MWCNT/PEI electrostatic interactions reduced the gap between MWCNTs and improved the π → π¹ transitions. However, the CS chains tended to be more serpentine than the chains of PEI molecules, which might have hindered the π → π¹ transitions. On the other hand, the electrostatic interactions might have enhanced the disorder grade of the MWCNT structure, as indicated by Raman analysis. The scaffolds maintained their fibrous and porous structure after MWCNT multilayer modification and supported fibroblast growth. The MWCNT multilayer induced cell migration toward the interior of the scaffolds. Therefore, we created a simple yet efficient method of building a CNT multilayer on three-dimensional (3D) fibrous scaffolds for enhancing cell-matrix interactions.     

Surface modification and PEGylation of branched polyethyleneimine for improved biocompatibility

In this article, we report the surface modification of branched polyethyleneimine (PEI) for improved biocompatibility. PEIs with different surface functionalities were synthesized via covalent modification of the PEI amines, including neutralized PEI modified with acetic anhydride, negatively charged PEI modified with succinic anhydride, hydroxylated PEI modified with glycidol, and PEI–poly(ethylene glycol) (PEG) conjugates modified with both PEG and acetic anhydride. The modified PEI derivatives were characterized with ¹H‐NMR, Fourier transform infrared spectroscopy, and ζ‐potential measurements. An in vitro cytotoxicity assay of mouse fibroblasts revealed that the biocompatibility of PEI was significantly improved after these modifications. The neutral and negatively charged PEIs were nontoxic at concentrations up to 200 μg/mL, whereas the pristine PEI was toxic to cells at concentrations as low as 10 μg/mL. The successfully modified PEIs with different surface charges and functionalities may provide a range of opportunities for various biomedical applications. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Electrophoretic deposition of titania–carbon nanotubes nanocomposite coatings in different alcohols

The suspensions of titania nanoparticles in different alcohols (methanol, ethanol and butanol) were prepared using triethanolamine (TEA) as a dispersant. The optimum concentration of TEA was 16.67, 8 and 0.33 mL/L in methanol, ethanol and butanol, respectively. Two component suspensions of titania (20 g/L) and carbon nanotubes (CNTs) (0.1, 0.2, 0.5 and 1 g/L) were prepared in different alcohols without and with optimum concentration of TEA. The finer and positively charged titania nanoparticles were heterocoagulated on the surface of coarser and negatively charged CNTs and generated the titania–CNT composite particles with the net positive charge. In the presence of TEA, titania nanoparticles completely covered CNTs surface due to their higher positive surface charge. At same CNT concentration, the deposition rate was faster for suspensions with TEA additive due to the faster mobility of the composite particles. The photocatalysis efficiency of coatings for methylene blue degradation increased as CNTs were incorporated in their microstructure.     

Surface modification of polypiperazine-amide membrane by self-assembled method for dye wastewater treatment☆

Polypiperazine-amide membranes were modified with poly(ethyleneimine) (PEI) by self-assembled method, through which PEI molecules were fixed on the membrane surface by ionic interaction. In the experiments, the PEI concentration ranged from 50 to 2000 mg·L?1 while the depositing time was fixed at 20 min. The results showed that low PEI concentration resulted in a slight increase of pure water flux, which was attributed to the enhanced membrane surface hydrophilicity. The PEI adsorption on membrane surface had less effect on the re-jections to neutral PEG and sucrose, but improved the rejections to divalent cationic ions and methylene blue as the result of reversion of the membrane surface charge from negative to positive according to the XPS analysis and zeta potential measurements. The membrane modified at PEI=1500 mg·L?1 exhibited high rejection to methylene blue (MB) and is potential to be applied in the treatment of effluents containing positively charged dyes.     

Gradient nanoporous phenolics as substrates for high-flux nanofiltration membranes by layer-by-layer assembly of polyelectrolytes

Thin film composite(TFC) membranes represent a highly promising platform for efficient nanofiltration(NF)processes. However, the improvement in permeance is impeded by the substrates with low permeances. Herein,highly permeable gradient phenolic membranes with tight selectivity are used as substrates to prepare TFC membranes with high permeances by the layer-by-layer assembly method. The negatively charged phenolic substrates are alternately assembled with polycation polyethylenimine(PEI) and polyanion poly(acrylic acid)(PAA)as a result of electrostatic interactions, forming thin and compact PEI/PAA layers tightly attached to the substrate surface. Benefiting from the high permeances and tight surface pores of the gradient nanoporous structures of the substrates, the produced PEI/PAA membranes exhibit a permeance up to 506 L? m~(-2)?h~(-1)?MPa~(-1), which is ～2–10 times higher than that of other membranes with similar rejections. The PEI/PAA membranes are capable of retaining N 96.1% of negatively charged dyes following the mechanism of electrostatic repulsion. We demonstrate that the membranes can also separate positively and neutrally charged dyes from water via other mechanisms.This work opens a new avenue for the design and preparation of high-flux NF membranes, which is also applicable to enhance the permeance of other TFC membranes.     

Ethoxy Carboxylate Extended Surfactant: Surface Charge of Surfactant-Modified Alumina, Adsolubilization and Solubilization of Phenylethanol and Styrene

Adsolubilization of contaminants by surfactant-modified material is an important phenomenon for surfactant-based environmental technologies. Recently, extended surfactants have been shown to enhance the adsolubilization capacity of organic solutes. In this study, two extended surfactants (ethoxy propoxylated carboxylate extended surfactant—C16PO4EO5C and propoxylate extended sulfate surfactant—C16PO4S) were selected for modifying positively charged alumina surfaces with the aim of enhancing adsolubilization of organic solutes with varying degrees of polarity (phenanthrene, styrene, and phenylethanol). The nature of the charged surface as a function of extended surfactant adsorption was evaluated through the zeta potential measurements. The results showed that at maximum bilayer coverage, the zeta potential of the alumina surface remained constant and was oppositely charged (negative) to the unmodified alumina (positive). Zeta potential measurements showed that the adsorbed bilayer of carboxylate-based extended surfactant produced more negatively charged surface. Surfactant desorption results showed that the surfactant-modified surface retained their negatively charge, albeit reduced, indicating that partial desorption occurred but not to the point that the positively charged alumina surface was realized. The adsolubilization results suggest a benefit of the ethoxy groups in adsolubilizing the polar phenylethanol in the palisade layer.     

A novel multilayer film with temperature dependent solubilization property

A PEO-PPO-PEO block copolymer, Pluronic P123, was reacted with phosphorus oxychloride for the synthesis of phosphorylation substitution of Pluronic P123 (PS-P123). A novel multilayer film composed of PS-P123 micelles was fabricated by alternating deposition of the negatively charged polymer micelles and positively charged polyethylenimine (PEI). Pyrene as a model hydrophobic organic molecule was loaded into the PS-P123 micelles. The PEI/PS-P123 multilayer films have temperature dependent solubilization property due to the formation of more hydrophobic microenvironment at higher immersed solution temperature. The reversible loading and release of pyrene by the multilayer films was also observed. The PEI/PS-P123 multilayer films have potential use in controlled drug release, extraction, and other technical use.     

Anti-inflammatory drug releasing absorbable surgical sutures using poly(lactic-co-glycolic acid) particle carriers

The goal of the current study was to develop an absorbable surgical suture incorporating poly(lactic-co-glycolic acid) (PLGA) particles loaded with dexamethasone (DEX) as an anti-inflammatory drug. DEX-loaded PLGA (DEX/PLGA) particles, prepared using a water-in-oil emulsion method, were electrostatically immobilized onto the surface of absorbable sutures. The surfaces of these DEX/PLGA particles were coated with positively charged polyethyleneimine (PEI) molecules, which imparted a net positive surface charge. These modified PEI-coated DEX/PLGA (PEI/DEX/PLGA) particles were then immobilized on negatively charged absorbable suture surfaces by electrostatic attraction. The results showed that DEX was efficiently loaded into PLGA particles and that the surfaces of DEX/PLGA particles were successfully coated with PEI. PEI/DEX/PLGA particles were well dispersed and immobilized onto suture surfaces. In addition, PEI/DEX/PLGA particles remained adherent to suture surfaces in vitro and demonstrated sustained DEX release in phosphate-buffered saline (pH 7.4) at 37 °C for up to 28 days under static conditions. The tensile strength and elongation at break of PEI/DEX/PLGA particle-treated sutures were almost the same as that of non-treated control sutures. Findings of this study show that various therapeutic drugs could be efficiently incorporated into absorbable sutures using biodegradable polymeric particles, and suggest that the devised absorbable, drug-eluting, sutures offer a promising basis for a novel absorbable surgical suture system.     

Polyethylenimine‐functionalized multiwalled carbon nanotube for the adsorption of hydrogen sulfide

Functionalized multiwalled carbon nanotubes (MWCNTs) were synthesized with ethane diamine and polyethylenimine (PEI) with molecular weights of 1800 [MWCNT‐PEI weight‐average molecular weight (M_w) = 1800] and 70,000 (MWCNT‐PEI M_w = 70,000), respectively. The structures and properties of the ethane diamine functionalized MWCNTs and PEI‐functionalized MWCNTs were characterized by Raman spectroscopy, thermogravimetric analysis, X‐ray powder diffraction, and scanning electron microscopy. An increase with the D/G (D, Disorder band; G, Graphite) ratio of the functionalized MWCNTs in the Raman spectra proved that the ethane diamine and PEI were successfully bonded to the surface of the pristine MWCNTs. The results of TGA also confirmed this. In addition, the structure of the functionalized MWCNTs showed no significant changes compared with the pristine MWCNTs; this was confirmed by X‐ray powder diffraction. Hydrogen sulfide (H₂S) sorption on the functionalized MWCNTs was studied by UV spectroscopy. As expected, the results of UV spectroscopy shows that the MWCNTs bonded with higher molecular weight PEI had a more excellent H₂S adsorption efficiency than those bonded with low‐molecular‐weight PEI and ethane diamine, a micromolecular amine. The effects of the pH and temperature on the adsorption of H₂S were also studied. Under the conditions investigated, the maximum first‐time H₂S adsorption efficiency of 1.94 mmol/g was observed for MWCNT‐PEI (M_w = 70,000) in the 60 mg/L sodium hydrosulfide (NaHS) aqueous solution. In addition, the H₂S reversible adsorption of the functionalized MWCNTs was conducted, and the second‐time H₂S adsorption efficiency of MWCNT‐PEI (M_w = 70,000) reached 1.83 mmol/g in the 60 mg/L NaHS aqueous solution. The results demonstrate that the MWCNTs decorated with high‐molecular‐weight PEI were potentially excellent and reversible H₂S adsorbents. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44742.     

Multi-walled carbon nanotube/polyimide composite film fabricated through electrophoretic deposition

Multi-walled carbon nanotube (MWCNT)/polyimide composite films were fabricated through electrophoretic deposition (EPD) of MWCNT-polyamic acid colloidal suspension which was derived from carboxylated-MWCNTs and poly(pyromellitic dianhydride-co-4,4′-oxydianiline) (PMDA-ODA). Under electric field, both negatively charged MWCNTs and PMDA-ODA colloid particles migrate onto a positively charged anode simultaneously, and are converted to a coherent MWCNT/polyimide composite film in the ensuing imidization reaction. Uniform dispersion of MWCNTs in the composite film was observed using transmission electron microscopy. The thickness of the prepared composite film can be tuned by varying processing conditions such as deposition time and anode conductivity. The electrical conductivity of the composite film increased with increasing the concentration of MWCNTs in EPD suspension. The mechanical reinforcement of polyimide using MWCNTs was evaluated by tensile testing and nanoindentation testing.     

Separation of proteins by charged ultrafiltration membranes

The separation of a protein mixture by charged ultrafiltration membranes was studied. A negatively charged polymer was obtained by sulfonation of polysulfone, and a positively charged polymer was synthesized by chloromethylation of polysulfone and then by quaternization of the amino group. Then, the negatively and positively charged ultrafiltration membranes were cast from solutions of charged polymer/NMP(or DMF)/lithium nitrate. The molecular weight cut-off of the membranes were controlled by the changing casting conditions.

Single protein solutions were ultrafiltrated at the isoelectric point and at another pH level by the use of charged membranes. At the isoelectric point, rejection of the protein was low, while it was high at the pH level which gave the protein the same sign of charge as that of the membrane.

A protein mixture of myoglobin and cytochrome C was separated by the charged ultrafiltration membranes at the isoelectric point of one of the proteins. At the isoelectric point of cytochrome C, myoglobin has a negative charge. Thus myoglobin was rejected with a rejection of about 80% by the negatively charged membrane. At the same time, cytochrome C permeated completely through the membrane. Conversely, at the isoelectric point of myoglobin, cytochrome C has a positive charge and thus it was rejected with a rejection of about 20% by the positively charged membrane. The rejection of myoglobin here was almost zero.     

Novel polyethyleneimine/TMC-based nanofiltration membrane prepared on a polydopamine coated substrate

Most commercial NF membranes are negatively charged at the pH range of a typical feed solution. In order to enhance the removal of cations (such as Mg²⁺ or Ca²⁺), we utilized polyethyleneimine (PEI) and trimesoyl chloride (TMC) to perform interfacial polymerization reaction on a polydopamine coated hydrolyzed polyacrylonitrile substrate to obtain a positively charged nanofiltration membrane. Effects of polydopamine coating time, PEI concentration, TMC reaction time and concentration on the membrane physicochemical properties and separation performance were systematically investigated using scanning electron microscopy, streaming potential and water contact angle measurements. The optimal NF membrane showed high rejection for divalent ions (93.6±2.6% for MgSO₄, 92.4±1.3% for MgCl₂, and 90.4±2.1% for Na₂SO₄), accompanied with NaCl rejection of 27.8±2.5% with a permeation flux of 17.2±2.8 L·m⁻²·h⁻¹ at an applied pressure of 8 bar (salt concentrations were all 1000 mg·L⁻¹). The synthesized membranes showed promising potentials for the applications of water softening.     

Effect of Dispersants on the Electrophoretic Deposition of Hydroxyapatite‐Carbon Nanotubes Nanocomposite Coatings

Isopropanolic Suspensions of HA nanoparticles (20 g/L) plus various concentrations of carbon nanotubes (CNTs) were prepared using Tris and triethanolamine as dispersant. The positively charged HA nanoparticles were heterocoagulated on the negatively charged CNTs and generated the HA‐CNT composite particles with net positive surface charge. The heterocoagulation was more intensive in dispersant‐containing suspensions (DCS) due to the higher zeta potential of HA nanoparticles in them. HA‐CNTs particles can be rotated and aligned parallel to electric field as a result of torque exerted on them due to the generation of a dipole moment in CNTs during electrophoretic deposition (EPD). The mobility of HA‐CNTs particles aligned parallel to electric field is ≈50% higher than that of HA nanoparticles leading to the faster EPD from DCS when CNTs are added into them. CNTs more efficiently reinforced the coatings deposited from DCS due to the stronger electrostatic bonding between CNTs and HA nanoparticles in them.     

Dispersion of SiC coated MWCNTs in PEI/silicone rubber blend and its effect on the thermal and mechanical properties

Multi‐walled carbon nanotubes (MWCNTs) are modified by polycarbosilane derived SiC to improve the dispersion of MWCNTs in the polymer matrix. Unmodified and modified MWCNTs are dispersed in PEI/hydroxyl terminated PDMS(HTSR) blend by melt mixing. TEM and FESEM images shows better dispersion of SiC coated MWCNTs in the blend matrix when compared with pure MWCNTs. Thermal stability of the SiC coated MWCNTs added nanocomposite improved drastically than that of the pure MWCNTs. Compared with pure PEI/HTSR binary blend and unmodified MWCNTs/PEI/HTSR ternary blend, the storage modulus, tensile modulus, and tensile strength of SiC coated MWCNTs/PEI/HTSR blend increased, due to the better dispersion of the modified MWCNTs in polymer matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Interaction between Dipolar Lipid Headgroups and Charged Nanoparticles Mediated by Water Dipoles and Ions

In this work, a theoretical model describing the interaction between a positively or negatively charged nanoparticle and neutral zwitterionic lipid bilayers is presented. It is shown that in the close vicinity of the positively charged nanoparticle, the zwitterionic lipid headgroups are less extended in the direction perpendicular to the membrane surface, while in the vicinity of the negatively charged nanoparticle, the headgroups are more extended. This result coincides with the calculated increase in the osmotic pressure between the zwitterionic lipid surface and positively charged nanoparticle and the decrease of osmotic pressure between the zwitterionic lipid surface and the negatively charged nanoparticle. Our theoretical predictions agree well with the experimentally determined fluidity of a lipid bilayer membrane in contact with positively or negatively charged nanoparticles. The prospective significance of the present work is mainly to contribute to better understanding of the interactions of charged nanoparticles with a zwitterionic lipid bilayer, which may be important in the efficient design of the lipid/nanoparticle nanostructures (like liposomes with encapsulated nanoparticles), which have diverse biomedical applications, including targeted therapy (drug delivery) and imaging of cancer cells.     

Synthesis of Pt and Pd nanosheaths on multi-walled carbon nanotubes as potential electrocatalysts of low temperature fuel cells

Pt and Pd nanosheaths are successfully synthesized on multi-walled carbon nanotubes (MWCNTs) using the non-covalent poly(diallyldimethylammonium chloride) (PDDA) functionalization and seed-mediated growth methods. In this method, negatively charged Pt or Pd metal precursors are self-assembled with positively charged PDDA-functionalized MWCNTs, forming uniformly distributed Pt or Pd nanoseeds on MWCNTs supports. The contiguous and highly porous Pt and Pd nanosheath structured catalysts are then formed by the seed-mediated growth in corresponding metal precursors using ascorbic acid as the reducing agent. The essential role of uniformly dispersed Pt and Pd nanoseeds on PDDA-MWCNTs is demonstrated. The results indicate that both Pt and Pd nanosheaths show an enhanced catalytic activity for the methanol and formic acid oxidation reaction in acid solution, respectively, as compared with conventional Pt/C and Pd/C catalysts. The enhanced activities are most likely due to the reduced oxophilicity, which results in a weakened chemisorption energy with oxygen-containing species such as CO_ad, and the increased reactive sites due to the large number of grain boundaries of the Pt and Pd nanosheath structured electrocatalysts.     

Surface charge of gold nanoparticles mediates mechanism of toxicity

Recently gold nanoparticles (Au NPs) have shown promising biological and military applications due to their unique electronic and optical properties. However, little is known about their biocompatibility in the event that they come into contact with a biological system. In the present study, we have investigated whether modulating the surface charge of 1.5 nm Au NPs induced changes in cellular morphology, mitochondrial function, mitochondrial membrane potential (MMP), intracellular calcium levels, DNA damage-related gene expression, and of p53 and caspase-3 expression levels after exposure in a human keratinocyte cell line (HaCaT). The evaluation of three different Au NPs (positively charged, neutral, and negatively charged) showed that cell morphology was disrupted by all three NPs and that they demonstrated a dose-dependent toxicity; the charged Au NPs displayed toxicity as low as 10 μg ml(-1) and the neutral at 25 μg ml(-1). Furthermore, there was significant mitochondrial stress (decreases in MMP and intracellular Ca2+ levels) following exposure to the charged Au NPs, but not the neutral Au NPs. In addition to the differences observed in the MMP and Ca2+ levels, up or down regulation of DNA damage related gene expression suggested a differential cell death mechanism based on whether or not the Au NPs were charged or neutral. Additionally, increased nuclear localization of p53 and caspase-3 expression was observed in cells exposed to the charged Au NPs, while the neutral Au NPs caused an increase in both nuclear and cytoplasmic p53 expression. In conclusion, these results indicate that surface charge is a major determinant of how Au NPs impact cellular processes, with the charged NPs inducing cell death through apoptosis and neutral NPs leading to necrosis.     

Generation of charged nanoparticles during the synthesis of carbon nanotubes by chemical vapor deposition

Generation of charged nanoparticles in the gas phase has been frequently reported during the synthesis of thin films and nanostructures, such as nanowires, using chemical vapor deposition (CVD). In an effort to confirm whether charged carbon nanoparticles were also generated during the synthesis of carbon nanotubes (CNTs) by CVD, a differential mobility analyzer combined with a Faraday cup electrometer was connected to an atmospheric-pressure CVD reactor under typical conditions for CNT growth. The size distribution of positively and negatively charged nanoparticles abundantly generated in the gas phase could be measured. Under conditions in which charged nanoparticles were not generated, no nanotubes could be grown.     

Bipolar Diffusion Charging of Aggregates

In this paper, the effect of particle morphology on bipolar diffusion charging is studied. A modified tandem differential mobility analyzer (TDMA) method used to measure the charge distribution of submicron particles in the range of 70–300 nm is described in detail. The method requires an independent measurement of the neutral fraction, followed by the measurement of the size-dependent charge distribution, which requires the knowledge of the neutral fraction. The method was validated experimentally using dioctyl sebacate and ammonium sulfate spherical particles and compared with Fuchs’ theory. Diesel particles and silver aggregates were used to evaluate the impact of morphology on charging. The results show that aggregates have a slightly lower (about 7%) neutral fraction than spheres. These results are in agreement with the predictions of Lall and Friedlander's theory and previous studies. However, results from charge distribution indicate that more (about 46%) particles are negatively charged than predicted by Lall and Friedlander's theory, while 32% fewer particles are positively charged. This relatively large asymmetry between the negative and the positive charge fraction is not fully predicted by either Fuchs' or aggregate charging theories. Our results suggest that the current inversion method of scanning mobility particle sizer (SMPS) data, based on Fuchs’ or Lall and Friedlander's distribution, would underestimate the total number concentration by about 15% or 27% if applied to diesel aggregates.

Copyright 2012 American Association for Aerosol Research     

Study on charge transfer reactions at multilayers of polyoxometalates clusters and poly(allylamine hydrochloride) (Grotthuss-018)

Multilayers of anionic phosphotungstic acid (PTA) clusters and positively charged protonated poly(allylamine hydrochloride) (PAH) were assembled by layer-by-layer self-assembled method on Au electrode modified by 3-mercaptopropionic acid (3-MPA). The effect of the charge of the surface of the multilayer assembly on the kinetics of the charge transfer reaction was studied by using the redox probes [Fe(CN)₆]^3−/4− and [Ru(NH₃)₆]^2+/3+. The cyclic voltammetry experiments showed that the peak currents and peak-to-peak potential differences changed after assembling different layers on the electrode surface indicating that the charge of the surface has a significant effect on the kinetics of the studied charge transfer reactions. These reactions were studied in more detail by electrochemical impedance spectroscopy. When [Fe(CN)₆]^3−/4− was used as the redox label, multilayers that terminated with negatively charged PTA showed a high charge transfer resistance but multilayers that terminated with positively charged PAH showed lower charge transfer resistance. With [Ru(NH₃)₆]^2+/3+ as the redox label, the charge transfer resistance at multilayers that terminated with positively charged PAH was much higher than at the multilayer terminated by the negatively charged PTA. The charge transfer resistances also increased with the addition of number of layers indicating that the entire thickness of the multilayer assembly has also an effect on the kinetics of the studied charge transfer reactions and not only the electrostatic attraction or repulsion between the surface and the redox probes. The ohmic resistance of the multilayer assembly increased non-linearly with the number of layers. Assembling a layer of PAH increased the resistance more than assembling a layer of PTA.