Capillary-dominated electrified jets of a viscous leaky dielectric liquid.

The capillary-dominated regime of dynamics of electrified jets of a viscous leaky dielectric liquid is studied numerically. In this regime the effective force in the direction of an applied field due to tangential electric stresses is balanced by the gradient of liquid pressure governed by the surface-tension stresses. As is characteristic of this regime, the electric current and the characteristic jet radius are dependent on the surface-tension coefficient and not on viscosity. In the scope of this work, the conditions of the existence of this regime are determined. A qualitative order-of-magnitude analysis gives the power-law dependences of the jet radius and electric current on the parameters of the problem (conductivity, applied electric field, flow rate, and surface-tension coefficient). Numerical results are obtained for low conductive liquids for a large range of the dimensionless flow rate (capillary number, Ca). The order-of-magnitude estimations of electric current are in agreement with the numerical results given a small Ca. The corresponding numerically obtained jet shapes are discussed and explained.

Encapsulation of bacterial cells in electrospun microtubes.

Encapsulation of whole microbial cells in microtubes for use in bioremediation of pollutants in water systems was the main focus of this investigation. Coelectrospinning of a core polymeric solution with bacterial cells and a shell polymer solution using a spinneret with two coaxial capillaries resulted in microtubes with porous walls. The ability of the microtube's structure to support cell attachment and maintain enzymatic activity and proliferation of the encapsulated microbial cells was examined. The results obtained show that the encapsulated cells maintain some of their phosphatase, ß-galactosidase and denirification activity and are able to respond to conditions that induce these activities. This study demonstrates electrospun microtubes are a suitable platform for the immobilization of intact microbial cells.

3-D Nanofibrous electrospun multilayered construct is an alternative ECM mimicking scaffold.

UNLABELLED: Extra cellular matrix (ECM) is a natural cell environment, possesses complicated nano- and macro- architecture. Mimicking this three-dimensional (3-D) web is a challenge in the modern tissue engineering. This study examined the application of a novel 3-D construct, produced by multilayered organization of electrospun nanofiber membranes, for human bone marrow-derived mesenchymal stem cells (hMSCs) support. The hMSCs were seeded on an electrospun scaffold composed of poly epsilon-caproloactone (PCL) and collagen (COL) (1:1), and cultured in a dynamic flow bioreactor prior to in vivo implantation. Cell viability after seeding was analyzed by AlamarBlue Assay. At the various stages of experiment, cell morphology was examined by histology, scanning electron microscopy (SEM) and confocal microscopy. RESULTS: A porous 3-D network of randomly oriented nanofibers appeared to support cell attachment in a way similar to traditionally used tissue culture polysterene plate. The following 6 week culture process of the tested construct in the dynamic flow system led to massive cell proliferation with even distribution inside the scaffold. Subcutaneous implantation of the cultured construct into nude mice demonstrated good integration with the surrounding tissues and neovascularization. CONCLUSION: The combination of electrospinning technology with multilayer technique resulted in the novel 3-D nanofiber multilayered construct, able to contain efficient cell mass necessary for a successful in vivo grafting. The success of this approach with undifferentiated cells implies the possibility of its application as a platform for development of constructs with cells directed into various tissue types.

One-step production of polymeric microtubes by co-electrospinning.

Herein we demonstrate the ability to fabricate polymeric microtubes with an inner diameter of approximately 3 microm through co-electrospinning of core and shell polymeric solutions. The mechanism by which the core/shell structure is transformed into hollow fibers (microtubes) is primarily based on the evaporation of the core solution through the shell and is described here in detail. Additionally, we present the filling of these microtubes, thus demonstrating their possible use in microfluidics. We also report the incorporation of a protein (green fluorescent protein) within such fibers, which is of interest for sensorics.

Age- and flow-dependency of salivary viscoelasticity.

Measuring salivary viscoelasticity (by relaxation times) is of paramount importance, since salivary rheology behavior has been associated with the development of oral disease conditions (such as dental caries) in animal and human model studies. In addition, novel and improved methods to evaluate salivary distribution and lubrication are of clinical interest. We used a novel method for measuring the viscoelasticity of saliva secreted from the different glands, at rest or under stimulation and at different ages, all conditions where different viscoelastic properties might be clinically important. Submandibular/sublingual salivary viscoelasticity was significantly higher than that of parotid saliva, especially under stimulation. In addition, an age-related reduction in flow rate (by 62%) was demonstrated, accompanied by an increase in both relaxation time (by 54%) and protein (by 48%). Increased salivary viscoelasticity results in compromised salivary rheology and lubrication properties, which may render the oral cavities of the elderly and other xerostomic persons more vulnerable.

Postprocesses in tubular electrospun nanofibers.

The postprocesses that occur in coelectrospun polymer nanofibers are investigated. The high rate of solvent evaporation during the electrospinning of fibers results in such a rapid formation of the shell of the tubular nanofibers, that the polymer molecules composing the fibers are in a nonequilibrium state. This stretched state of macromolecules is assumed to be stabilized in a solid matrix, and can account for the anomalous properties of the nanofibers. During this processing stage a considerable amount of solvent remains inside the tubular nanofibers. The evaporation of the solvent continues for several minutes, and is accompanied by further evolution of the nanofibers in both their microstates and macrostates. In this paper, we examine possible macrostate modifications of the nanofibers, such as radial buckling. The theoretical model which describes the kinetics of the solvent evaporation is found to be in good agreement with experimental observations. Thus, the physical parameters of the system in question can be estimated, and the conditions of fiber shell instability that produce buckling of the tubular nanofibers can also be predicted.

Biohybrid nanosystems with polymer nanofibers and nanotubes.

Advanced techniques for the preparation of nanofibers, core shell fibers, hollow fibers, and rods and tubes from natural and synthetic polymers with diameters down to a few nanometers have recently been established. These techniques, among them electro- and co-electrospinning and specific template methods, allow the incorporation not only of semiconductor or catalytic nanoparticles or chromophores but also enzymes, proteins, microorganism, etc., directly during the preparation process into these nanostructures in a very gentle way. One particular advantage is that biological objects such as, for instance, proteins can be immobilized in a fluid environment within these polymer-based nano-objects in such a way that they keep their native conformation and the corresponding functions. The range of applications of such biohybrid nanosystems is extremely broad, for instance, in the areas of biosensorics, catalysis, drug delivery, or optoelectronics.

Encapsulation of bacteria and viruses in electrospun nanofibres.

Bacteria and viruses were encapsulated in electrospun polymer nanofibres. The bacteria and viruses were suspended in a solution of poly(vinyl alcohol) (PVA) in water and subjected to an electrostatic field of the order of 1 kV cm(-1). Encapsulated bacteria in this work, (Escherichia coli, Staphylococcus albus) and bacterial viruses (T7, T4, λ) managed to survive the electrospinning process while maintaining their viability at fairly high levels. Subsequently the bacteria and viruses remain viable during three months at -20 and -55 °C without a further decrease in number. The present results demonstrate the potential of the electrospinning process for the encapsulation and immobilization of living biological material.