Charged Polymer Solutions Research Articles

Influence of salt addition on polymer-free electrospinning of cyclodextrin nanofibers

Solution conductivity is one of the critical parameters affecting the electrospinning of polymer solutions as the jet formation is directly related to the movement of an electrically charged polymer solution to a grounded target. Hence, the solution conductivity has been studied for the electrospinning of various polymeric systems, but not yet for the electrospinning of polymer-free systems. In this regard, this study investigates the influence of solution conductivity on the electrospinning of CD molecules (i.e., hydroxypropyl (HP) modified β and γ -CDs) at various concentrations in the presence of quaternary ammonium salt (i.e., tetraethylammonium bromide, TEAB) from aqueous solutions. The addition of TEAB significantly boosted the conductivity of the CD solutions. It could lead to smaller particles at low CD concentrations because of electrohydrodynamic spraying, while the transformation from beaded-fibers to bead-free fibers was observed with an increase in the CD concentration. The salt addition decreased the fiber diameter and resulted in thinner nanofibers. Likewise, the incorporation of NaCl –used as an alternative to TEAB- caused thinning of the fibers due to enhanced solution conductivity. On the other hand, at higher salt contents, the fiber morphology was worsened for both CDs, leadings to beads on the fibers. Overall, this paper, for the first time, investigates the effect of solution conductivity of the electrospinning of a polymer-free system (i.e., CD), and the experimental findings show that increasing the solution conductivity with salt addition causes significant changes on the electrospinnability and fiber properties.

Soil structuring using interpolyelectrolyte complexes of water‐soluble polysaccharides

Soil degradation is an important problem on a global scale. Suitable materials for its solution are interpolyelectrolyte complexes (IPEC) of biodegradable polymers. IPEC based on the oppositely charged pairs of biodegradable polymers—chitosan and sodium alginate (Ch‐SA), chitosan and sodium carboxymethylcellulose (Ch‐SC), and chitosan‐gellan gum (Ch‐GG) were prepared and studied using different physicochemical techniques (FTIR‐spectroscopy, dynamic light scattering, conductometric and turbidimetric titration, and rheoviscometric measurements). Thin films of IPECs were prepared by pouring polymer solutions on a flat surface and subsequent evaporation of water. These films were tested using mechanical analysis. Young modulus of IPEC films increases in the following order: Ch‐SC < Ch‐GG < Ch‐SA. Urban soil samples were sequentially treated with Ch solution and negatively charged polymer solution (SC, SA, GG). This technique of soil treatment leads to formation of IPEC within the soil surface layer. The soil structures and also soil treated with pure water and individual polymer solutions were also tested using mechanical analysis. It was found that the most durable structures are formed by IPEC based on Ch and SC. All the applied systems can be arranged in the following sequence in ascending order of the Young's modulus: GG < Ch < SA < Water < SC < Ch‐GG < Ch‐SA < Сh‐SC. The IPEC based on biodegradable and biocompatible polymers of polysaccharide nature can be successfully used for soil structuring. These polymers significantly increase the mechanical strength of the soil without harmful effects to the environment. Among the studied systems, the Ch‐SC system has the greatest structuring ability. These soil structuring agents can be applied for improving of the quality of urban and agricultural soils.

Electrospinning and emerging healthcare and medicine possibilities.

Electrospinning forms fibers from either an electrically charged polymer solution or polymer melt. Over the past decades, it has become a simple and versatile method for nanofiber production. Hence, it has been explored in many different applications. Commonly used electrospinning assembles fibers from polymer solutions in various solvents, known as solution electrospinning, while melt and near-field electrospinning techniques enhance the versatility of electrospinning. Adaption of additive manufacturing strategy to electrospinning permits precise fiber deposition and predefining pattern construction. This manuscript critically presents the potential of electrospun nanofibers in healthcare applications. Research community drew impetus from the similarity of electrospun nanofibers to the morphology and mechanical properties of fibrous extracellular matrices (ECM) of natural human tissues. Electrospun nanofibrous scaffolds act as ECM analogs for specific tissue cells, stem cells, and tumor cells to realize tissue regeneration, stem cell differentiation, and in vitro tumor model construction. The large surface-to-volume ratio of electrospun nanofibers offers a considerable number of bioactive agents binding sites, which makes it a promising candidate for a number of biomedical applications. The applications of electrospinning in regenerative medicine, tissue engineering, controlled drug delivery, biosensors, and cancer diagnosis are elaborated. Electrospun nanofiber incorporations in medical device coating, in vitro 3D cancer model, and filtration membrane are also discussed.

Hierarchically aligned fibrous hydrogel films through microfluidic self-assembly of graphene and polysaccharides.

Despite significant interest in developing extracellular matrix (ECM)-inspired biomaterials to recreate native cell-instructive microenvironments, the major challenge in the biomaterial field is to recapitulate the complex structural and biophysical features of native ECM. These biophysical features include multiscale hierarchy, electrical conductivity, optimum wettability, and mechanical properties. These features are critical to the design of cell-instructive biomaterials for bioengineering applications such as skeletal muscle tissue engineering. In this study, we used a custom-designed film fabrication assembly, which consists of a microfluidic chamber to allow electrostatic charge-based self-assembly of oppositely charged polymer solutions forming a hydrogel fiber and eventually, a nanocomposite fibrous hydrogel film. The film recapitulates unidirectional hierarchical fibrous structure along with the conductive properties to guide initial alignment and myotube formation from cultured myoblasts. We combined high conductivity, and charge carrier mobility of graphene with biocompatibility of polysaccharides to develop graphene-polysaccharide nanocomposite fibrous hydrogel films. The incorporation of graphene in fibrous hydrogel films enhanced their wettability, electrical conductivity, tensile strength, and toughness without significantly altering their elastic properties (Young's modulus). In a proof-of-concept study, the mouse myoblast cells (C2C12) seeded on these nanocomposite fibrous hydrogel films showed improved spreading and enhanced myogenesis as evident by the formation of multinucleated myotubes, an early indicator of myogenesis. Overall, graphene-polysaccharide nanocomposite fibrous hydrogel films provide a potential biomaterial to promote skeletal muscle tissue regeneration.

Metabolic Profiling of Urine by Capillary Electrophoresis-Mass Spectrometry Using Non-covalently Coated Capillaries.

In the field of metabolomics, capillary electrophoresis-mass spectrometry (CE-MS) can be considered a very useful analytical tool for the profiling of polar and charged metabolites. However, variability of migration time is an important issue in CE. An elegant way to minimize this problem is the use of non-covalently coated capillaries that is dynamic coating of the bare fused-silica capillary with solutions of charged polymers. In this protocol, an improved strategy for the profiling of cationic metabolites in urine by CE-MS using multilayered non-covalent capillary coatings is presented. Capillaries are coated with a bilayer of polybrene (PB) and poly(vinyl sulfonate) (PVS) or with a triple layer of PB, dextran sulfate (DS), and PB. The bilayer- and triple-layer-coated capillaries have a negative and positive outside layer, respectively. It is shown that the use of such capillaries provides very repeatable migration times.

Influence of solution properties and pH on the fabrication of electrospun lentil flour/HPMC blend nanofibers

Electrospinning is a method used in fiber production in which an electric force is applied to create jets of charged polymer solutions. The objective of this study was to obtain homogeneous nanofibers from lentil flour and hydroxypropyl methylcellulose (HPMC) blend by using electrospinning method. Distilled water was used as solvent. The effects of pH (7, 10 and 12), lentil flour concentration (1% and 2% (w/v)) and HPMC concentration (0.25%, 0.5% and 1% (w/v)) on solution properties and fiber morphology were investigated. When the pH was increased, the viscosity of the solutions containing 1% and 2% lentil flour decreased. Increasing the pH values caused an increase in the electrical conductivity. At pH value of 7, homogeneous nanofibers could not be obtained whereas fibers were perfectly homogeneous at alkaline pH values. Nanofiber diameter decreased with increase in pH when 2% lentil flour was used. On the other hand, diameter of fibers did not show any significant change with pH for 1% lentil flour. When the lentil flour concentration was increased, viscosity and fiber diameter increased at pH10. When HPMC concentration was increased, both viscosity and fiber diameter increased but electrical conductivity did not show any significant change. Average fiber diameters ranged between 198±4 and 254±5nm for solutions prepared with different lentil flour and HPMC concentrations at different pH values.

Design and Development of a Series-configuration Mazzilli Zero Voltage Switching Flyback Converter as a High-voltage Power Supply for Needleless Electrospinning

Nanofiber is one-dimensional material that has broad application. It can be formed by applying a high-voltage source to a polymer solution so that the polymer solution becomes charged. Usingthe high electric field, the charged polymer solution is formed as a Taylor cone and then drawn to the collector to form long, nanoscale fibers. This method is known as electrospinning. There are two types of electrospinning method; they are needle and needleless electrospinning. The latter is intended for mass production nanofibers because it can make tens to hundreds ofjets at a time. Therefore, the high-voltage source required for the needleless electrospinning process must have a higher voltage and current compared to those for the needle one. Accordingly, the high voltage power supply using a series-configuration Mazzilli ZVS flyback converter was designed and developed. The Mazzilli flyback converter was able to generate a high voltage with relatively high power. Two converters were connected in series to achieve more output voltage. The output voltage was adjusted by changing the input voltage. The single converter could generate a high voltage up to 34kV whereas the series-configuration converter could increase the voltage by 98.41% to be 67kV. The output voltage of converter was relatively stable and good enough to perform nanofibers synthesis using the needleless electrospinning. Visual observation confirmed that the nanofibers were formed well on the collector.

Hybrid windshield-glass heater for commercial vehicles fabricated via enhanced electrostatic interactions among a substrate, silver nanowires, and an over-coating layer

We introduce a transparent windshield-glass heater produced via transparent electrodes using silver nanowire (AgNW) networks for conventional use in the automobile industry. A high-quality conducting hybrid film is deposited on a plasma-treated glass substrate by spraying AgNWs, immersing the sprayed product in positively charged adhesive polymer solution, and then spraying negatively charged graphene oxide (GO) and a silane layer as an over-coating layer (OCL).The results of heating tests conducted after adhesion tests show that the sheet resistance changes with the application of polymer glue. Surprisingly, the transmittance of the film with the GO OCL is higher than that of the film without the GO OCL. Heating and defrosting tests are carefully conducted via infrared (IR) monitoring. Adhesive-polymer-treated and GO-protected AgNW transparent glass heaters exhibit the best performance with low sheet resistance; thus, through strong electrostatic interaction among the substrate, adhesive layer, and OCL, our AgNW hybrid glass heater can reach the target temperature with a standard vehicle voltage of 12 V in a short period of time.

Phase diagram of mixtures of colloids and polymers in the thermal crossover from good to θ solvent.

We determine the phase diagram of mixtures of spherical colloids and neutral nonadsorbing polymers in the thermal crossover region between the θ point and the good-solvent regime. We use the generalized free-volume theory, which takes into account the polymer-concentration dependence of the depletion thickness and of the polymer compressibility. This approach turns out to be quite accurate as long as q = Rg/Rc ≲ 1 (Rg is the radius of gyration of the polymer and Rc is the colloid radius). We find that, close to the θ point, the phase diagram is not very sensitive to solvent quality, while, close to the good-solvent region, changes of the solvent quality modify significantly the position of the critical point and of the binodals. We also analyze the phase behavior of aqueous solutions of charged colloids and polymers, using the approach proposed by Fortini et al. [J. Phys.: Condens. Matter 17, 7783 (2005)].

Mass Production of Nanofibers from a Spiral Coil

In this study, we have demonstrated that a rotating metal wire coil can be used as a nozzle to electrospin nanofibers on a large-scale. Without using any needles, the rotating wire coil, partially immersed in a polymer solution reservoir, can pick up a thin layer of charged polymer solution and generate a large number of nanofibers from the wire surface simultaneously. This arrangement significantly increases the nanofiber productivity. The fiber productivity was found to be determined by the coil dimensions, applied voltage and polymer concentration. The dependency of fiber diameter on the polymer concentration showed a similar trend to that for a conventional electrospinning system using a syringe needle nozzle, but the coil electrospun fibers were thinner with narrower diameter distribution. The profiles of electric field strength in the coil electrospinning was calculated and showed concentrated electric field intensity on the top wire surface.

Fabrication of protein micropatterns using a functional substrate with convertible protein-adsorption surface properties

A functional substrate capable of regulating protein adsorption was prepared using a crosslinked albumin (cl-albumin) film for use in the fabrication of protein micropatterns. The adsorption of proteins with different characteristics onto cl-albumin film, including serum proteins, serum albumin, and lysozyme, was investigated using a quartz crystal microbalance. The results showed that surfaces coated with cl-albumin film are highly resistant to protein adsorption, regardless of protein charge and rigidity. In addition, this adsorption-resistance property can be easily converted to promote protein adsorption by exposing the cl-albumin film to a charged polymer solution. By combining the convertible surface property of cl-albumin film and inkjet printing techniques, a precise protein micropattern was successfully fabricated on the substrate. Protein adsorption onto the wall surface of microchannels could also be suppressed or promoted by coating the surface with cl-albumin film. This approach will aid in the development of biomaterials carrying protein micropatterns, such as biosensors, biochips, and cellular scaffolds.

Role of Jet Path on Uniformity of Electrospun Nanofibers

This paper reports on the role of jet path in obtaining uniform and bead free nanofibers during electrospinning process. Polyethylene oxide (PEO) nanofibers were electrospun by varying the molecular weight of PEO and concentration of poly allylamine hydrochloride (PAH) in the spinning solution. Different modes of fiber formation were captured by a camera and analyzed further by image processing technique in order to assess their influence in the formation of uniform and bead free nanofibers. Two different jet paths during fiber formation, namely straight and whipping were assessed. The length of the straight jet path during the fiber formation played a major role in the formation of uniform nanofibers in comparison to the length of the whipping path. The diameter and surface morphology of the nanofibers were characterized by SEM. Nanofibers spun using higher concentration of PAH exhibited longer straight jet path and therefore more uniform nanofibers in comparison to that spun at lower concentration of PAH. Flow simulations of the electrically charged polymer solutions were carried out to observe the changes in the solution flow rate and Taylor cone shape. Increased flow rate and changes in the Taylor cone shape with the increasing PAH concentration in low molecular weight polymer were observed.

Preliminary Investigation of Airgap Electrospun Silk-Fibroin-Based Structures for Ligament Analogue Engineering

The process of electrospinning has proven to be highly beneficial for use in a number of tissue-engineering applications due to its ease of use, flexibility and tailorable properties. There have been many publications on the creation of aligned fibrous structures created through various forms of electrospinning, most involving the use of a metal target rotating at high speeds. This work focuses on the use of a variation known as airgap electrospinning, which does not use a metal collecting target but rather a pair of grounded electrodes equidistant from the charged polymer solution to create highly aligned 3D structures. This study involved a preliminary investigation and comparison of traditionally and airgap electrospun silk-fibroin-based ligament constructs. Structures were characterized with SEM and alignment FFT, and underwent porosity, permeability, and mechanical anisotropy evaluation. Preliminary cell culture with human dermal fibroblasts was performed to determine the degree of cellular orientation and penetration. Results showed airgap electrospun structures to be anisotropic with significantly increased porosity and cellular penetration compared to their traditionally electrospun counterparts.

Structural observation of nanofibre surface by AFM

Electrospinning, a process which allows the production of nanofibres, was recently rediscovered. Electrospinning uses the electrostatic attraction between an electrically charged polymer solution and a collector related to the ground. Polyamid-6 (PA-6) was electrospun in different spinning conditions such as the distance between needle tip and collector, the voltage and the needle tip geometry. Using scanning electron microscopy (SEM) and atomic force microscopy (AFM), the nanoweb longitudinal and cross-sectional morphologies were evidenced. Different morphologies, exhibiting various nanoroughnesses, were observed, which could be related to the experimental electrospinning parameters. These structural differences could be attributed to instability of the polymer jet and to the intrinsic behaviour of the electrospinning solution.

Silica Nanoparticles at Interfaces Modulated by Amphiphilic Polymer and Surfactant

The interfacial behavior of silica nanoparticles in the presence of an amphiphilic polymer poly( N-isopropylacrylamide) (PNIPAM) and an anionic surfactant sodium dodecyl sulfate (SDS) is studied using neutron reflectivity. While the nanoparticles do not show any attraction to hydrophilic and hydrophobic surfaces in pure water, presence of the amphiphilic polymer induces significant adsorption of the nanoparticles at the hydrophobic surface. This interfacial behavior is activated due to interaction of the nanoparticles with PNIPAM, the amphiphilic nature of which leads to strong adsorption at a hydrophobic surface but only weak interaction with a hydrophilic surface. The presence of SDS competes with nanoparticle-PNIPAM interaction and in turn modulates the interfacial properties of the nanoparticles. These adsorption results are discussed in relation to nanoparticle organization templated by dewetting of charged polymer solutions on a solid substrate. Our previous studies showed that nanoparticle assembly can be induced to form complex morphologies produced by dewetting of the polymer solutions, such as a polygonal network and long-chain structures. This approach, however, works on a hydrophilic substrate but not on a hydrophobic substrate. These observations can be explained in part by particle-substrate interactions revealed in the present study.

Small-angle neutron scattering from typical synthetic and biopolymer solutions

Small-angle neutron scattering (SANS) has been used to investigate the solution properties of four model polymers, two poly-amino acids (poly(lysine) and poly (proline)), and two water-soluble synthetic polymers (poly (acrylic acid) and poly(ethylene oxide)). In each case, one of the two polymers is charged, while the other is neutral. SANS measurements were made in the semi-dilute con- centration regime in two different solvents (d-water and d- ethylene glycol). The scattering signals were decomposed into low-Q clustering and high-Q solvation contributions. The temperature dependence of the scattering parameters was determined for poly(lysine) and poly(ethylene oxide) solutions over the temperature range of 13 to 82 °C. Analysis of the SANS spectra revealed that with increasing temper- ature, the solvation intensity increased in both solvents, while the clustering intensity increased in d-water and decreased in d-ethylene glycol. Significant differences were observed between the SANS spectra of charged and neutral polymer solutions. However, biopolymers and synthetic polymers exhibited qualitatively similar behavior.

Shapes of Polyelectrolyte Titration Curves. 1. Well-Behaved Strong Polyelectrolytes

The charge content of aqueous polymers is measured routinely by polyelectrolyte titrations in which an unknown polymer is titrated with an oppositely charged standard polymer solution, usually poly(diallyldimethyl ammonium chloride) or potassium poly(vinyl sulfate). Polyelectrolyte titration end points are frequently determined with a streaming current detector (SCD). The shapes of polyelectrolyte titration curves from polyelectrolytes with fixed electrical charges were simulated by a diffuse electrical double layer model. Well-behaved titration curves obtained with fixed charged polyelectrolytes were fit by the modeling, giving support for the basic hypothesis that the net charge of material adsorbed on the SCD wall is a linear function of the volume of added titrant. The shapes of titration curves from deviant systems such as poly(vinyl alcohol)-borate cannot be predicted by the model.

Liquid Templating for Nanoparticle Organization into Complex Patterns

Dewetting of thin films of charged polymer solutions produces complex patterns that can be applied to direct nanoparticle organization on solid substrates. The morphology produced by dewetting can be controlled by the solution properties, temperature, and substrate wetting. In this work, new results on this liquid-template self-assembly system are presented, with special emphasis on producing large arrays of organized nanoparticles. On a hydrophilic substrate with complete wetting, the patterns include polygonal networks and parallel-track arrays that extend over several hundreds of microns. These large structures are formed under well-controlled drying conditions and characterized by scanning electron microscopy, which is better suited for the examination of large as well as small areas than atomic force microscopy. On partial wetting substrates, new patterns are observed, including a complex set of parallel curved bands with variable particle number densities.

Self-consistent mode-coupling theory for the viscosity of rodlike polyelectrolyte solutions.

A self-consistent mode-coupling theory is presented for the viscosity of solutions of charged rodlike polymers. The static structure factor used in the theory is obtained from polymer integral equation theory; the Debye-Huckel approximation is inadequate even at low concentrations. The theory predicts a nonmonotonic dependence of the reduced excess viscosity eta(R) on concentration from the behavior of the static structure factor in polyelectrolyte solutions. The theory predicts that the peak in eta(R) occurs at concentrations slightly lower than the overlap threshold concentration, c*. The peak height increases dramatically with increasing molecular weight and decreases with increased concentrations of added salt. The position of the peak, as a function of concentration divided by c*, is independent of salt concentration or molecular weight. The predictions can be tested experimentally.

Controlled Nanoparticle Assembly by Dewetting of Charged Polymer Solutions

In this paper, we present an alternative approach for controlled nanoparticle organization on a solid substrate by applying dewetting patterns of charged polymer solutions as a templating system. Thin films of charged polymer solutions dewet a solid substrate to form complex dewetting patterns that depend on the polymer charge density. These patterns, ranging from polygonal networks to elongated structures that are stabilized by viscous forces during dewetting, serve as potential templates for two-dimensional nanoparticle organization on a solid substrate. Thus, while nanoparticles dried in pure water undergo self-assembly to form close-packed arrays, addition of charged polymer in the dispersion leads to the formation of open structures that are directed by the dewetting patterns of the polymer solution. In this study, we focus on the application of elongated structures resulting from dewetting of high-charge-density polymer solutions to align nanoparticles of silica and gold into long chains that are several micrometers in length. The particle ordering process is a two-step mechanism: an initial confinement of the nanoparticles in the dewetting structures and self-assembly of the particles within these structures upon further drying by lateral capillary attractions.