David Lukas

Self-organization of jets in electrospinning from free liquid surface: A generalized approach

Electrospinning has enabled creation of excellent materials for a great number of applications. Previously, it was based on less productive capillary spinners. The present study is based on recent efforts to elevate electrospinning technology to an industrial level by simultaneously provoking innumerable polymeric jets from a sufficiently large liquid surface to increase productivity. Particularly, it deals with electrospinning from free surface of conductive liquids and validates a formulated hypothesis that explains self-organization of jets on one-dimensional free liquid surfaces in terms of electrohydrodynamic instability of surface waves. Here, it is shown how the hypothesis, based on a profound analysis of a dispersion law, explains that above a certain critical value of applied electric field intensity∕field strength the system starts to be self-organized in mesocopic scale due to the mechanism of the “fastest forming instability.” The mechanism plays a key role in selecting a particular wave with a characteristic wavelength whose amplitude boundlessly grows faster than the others. The fastest growing stationary wave, according to the hypothesis, marks the onset of electrospinning from a free liquid surface with its jets originating from the wave crests. Singularity of this approach lies in predicting critical values of the phenomenon, viz., critical field strength and corresponding critical interjet distance. The critical field strength, will, thereafter, be used in defining a unique dimensionless electrospinning number. It will, subsequently, be shown how the critical interjet distance, i.e., the maximal distance between the neighboring jets, simply depends on the capillary length. The capillary length represents a latent characteristic spatial scale of the system. The theory also predicts interjet distance for field strengths above the critical value. The said prediction is universally applicable for all conductive liquids if it is expressed in terms of the dimensionless parameters of the interjet distance and the electrospinning number. The theory also predicts relaxation time, necessary for spontaneous jetting after a high voltage is applied. The theoretical considerations are eventually compared to that of Zeleny’s, obtained for capillary electrospinner to demonstrate universality of the approach. Eventually, jetting from free liquid surface on specially designed linear cleft electrospinner are observed, analyzed, and compared to the theoretical predictions obtaining satisfactory results.Electrospinning has enabled creation of excellent materials for a great number of applications. Previously, it was based on less productive capillary spinners. The present study is based on recent efforts to elevate electrospinning technology to an industrial level by simultaneously provoking innumerable polymeric jets from a sufficiently large liquid surface to increase productivity. Particularly, it deals with electrospinning from free surface of conductive liquids and validates a formulated hypothesis that explains self-organization of jets on one-dimensional free liquid surfaces in terms of electrohydrodynamic instability of surface waves. Here, it is shown how the hypothesis, based on a profound analysis of a dispersion law, explains that above a certain critical value of applied electric field intensity∕field strength the system starts to be self-organized in mesocopic scale due to the mechanism of the “fastest forming instability.” The mechanism plays a key role in selecting a particular wave with ...

Core/Shell Nanofibers with Embedded Liposomes as a Drug Delivery System

The broader application of liposomes in regenerative medicine is hampered by their short half-life and inefficient retention at the site of application. These disadvantages could be significantly reduced by their combination with nanofibers. We produced 2 different nanofiber-liposome systems in the present study, that is, liposomes blended within nanofibers and core/shell nanofibers with embedded liposomes. Herein, we demonstrate that blend electrospinning does not conserve intact liposomes. In contrast, coaxial electrospinning enables the incorporation of liposomes into nanofibers. We report polyvinyl alcohol-core/poly-ε-caprolactone-shell nanofibers with embedded liposomes and show that they preserve the enzymatic activity of encapsulated horseradish peroxidase. The potential of this system was also demonstrated by the enhancement of mesenchymal stem cell proliferation. In conclusion, intact liposomes incorporated into nanofibers by coaxial electrospinning are very promising as a drug delivery system.

Physical principles of electrospinning (Electrospinning as a nano-scale technology of the twenty-first century)

The history of electrospinning is briefly introduced at the beginning of the article. The fundaments of the process are then analysed physically to be translated into a successful technology. Self-organisation of fluid in electrospinning is perceived as a consequence of various instabilities, based on electrohydrodynamics and, thus, highlighted as a key factor, theorising the subject successfully to elevate it to a highly productive technology to manufacture nano-scale materials. The main physical principle of the self-organisation is appearance of unstable tiny capillary waves on liquid surfaces, either on a free liquid surface or on that confined in a capillary, which is influenced by external fields. The jet path is described, as well as its possible control, by special collectors and spinning electrodes. Two electrospinning variants, i.e. melt and core–shell electrospinning, are discussed in detail. Two scarcely referred exceptional features of electrospinning, electric wind and accompanying irradiations, are introduced in in-depth detail. Lastly, care is taken over the quality of polymeric solutions for electrospinning from the standpoint of Hansen solubility parameters and entanglements among polymeric chains.

Elastic three-dimensional poly (ε-caprolactone) nanofibre scaffold enhances migration, proliferation and osteogenic differentiation of mesenchymal stem cells

We prepared 3D poly (ε‐caprolactone) (PCL) nanofibre scaffolds and tested their use for seeding, proliferation, differentiation and migration of mesenchymal stem cell (MSCs).

Stochastic modelling of tear behaviour of coated fabrics

A stochastic approach, using the Ising model combined with the Monte Carlo simulation, is employed to study the phenomenon of tongue tear failure in coated fabrics. The complicated mechanisms involved can be realistically simulated with a relatively simple algorithm. The important factors, especially the effects of the interphase between the coating and the fabric, and the stretched part of the material at the crack front (the del-zone) can be represented by corresponding coefficients in the Hamiltonian expression of the system. The minimization of the system Hamiltonian yields the most likely new steps for crack propagation, while the Monte Carlo method is used to select the one that will actually occur, reflecting the stochastic nature in the behaviour of real systems, indicating the usefulness of this approach in studies of similar interfacial phenomena. However, this model like many others needs to be calibrated based on data from a real system for quantitative and accurate predictions.

Computer Simulation of Liquid Wetting Dynamics in Fiber Structures Using the Ising Model

We present in this paper a method which applies the so-called Ising model and Kawasaki thermodynamics, combined with the Monte Carlo computer simulation technique to study the liquid-fiber interaction and the wetting behavior of fiber networks. The various types of interactions occurring during a wetting process in a fiber mass are analyzed, and their individual contributions towards the Hamiltonian system are derived. The criterion for energy state exchange between the Ising spin variables is given as the critical step for the wetting simulation. The procedures of the simulation algorithm are provided. Various predictions of the wetting process including wetting of a fiber network, the spreading of a liquid drop on a single fiber as well as a brief parametric study are included in this paper.

Thin-Layer Hydroxyapatite Deposition on a Nanofiber Surface Stimulates Mesenchymal Stem Cell Proliferation and Their Differentiation into Osteoblasts

Pulsed laser deposition was proved as a suitable method for hydroxyapatite (HA) coating of coaxial poly-ɛ-caprolactone/polyvinylalcohol (PCL/PVA) nanofibers. The fibrous morphology of PCL/PVA nanofibers was preserved, if the nanofiber scaffold was coated with thin layers of HA (200 nm and 400 nm). Increasing thickness of HA, however, resulted in a gradual loss of fibrous character. In addition, biomechanical properties were improved after HA deposition on PCL/PVA nanofibers as the value of Youngs moduli of elasticity significantly increased. Clearly, thin-layer hydroxyapatite deposition on a nanofiber surface stimulated mesenchymal stem cell viability and their differentiation into osteoblasts. The optimal depth of HA was 800 nm.

A Two-dimensional Model of the Mechanical Properties of Textiles

A two-dimensional model of the mechanical properties of textiles is constructed, and the relations between model parameters and model behaviour are studied. The influence of the number of bonding sites in the model on stress-strain curves, on the CPU time consumption, and on the stability of model outputs is described. The methodology of computer-simulation methods in the study of textile mechanics is discussed.

Time-regulated drug delivery system based on coaxially incorporated platelet α-granules for biomedical use

AIM Platelet derivatives serve as an efficient source of natural growth factors. In the current study, α-granules were incorporated into coaxial nanofibers. MATERIALS & METHODS A nanofiber scaffold containing α-granules was prepared by coaxial electrospinning. The biological potential of the nanofiber scaffold was evaluated in chondrocyte and mesenchymal stem cell cultivation studies. Additionally, the concentration of TGF-β1 was determined. RESULTS Microscopy studies showed that intact α-granules were incorporated into the coaxial nanofibers. The cultivation tests showed that the novel scaffold stimulated viability and extracellular matrix production of chondrocytes and mesenchymal stem cells. In addition, the concentration of growth factors necessary for the induction of cell proliferation significantly decreased. CONCLUSION The system preserved α-granule bioactivity and stimulated cell viability and chondrogenic differentiation of mesenchymal stem cells. Core/shell nanofibers incorporating α-granules are a promising system for tissue engineering, particularly cartilage engineering.

A simple drug anchoring microfiber scaffold for chondrocyte seeding and proliferation

The structural properties of microfiber meshes made from poly(2-hydroxyethyl methacrylate) (PHEMA) were found to significantly depend on the chemical composition and subsequent cross-linking and nebulization processes. PHEMA microfibres showed promise as scaffolds for chondrocyte seeding and proliferation. Moreover, the peak liposome adhesion to PHEMA microfiber scaffolds observed in our study resulted in the development of a simple drug anchoring system. Attached foetal bovine serum-loaded liposomes significantly improved both chondrocyte adhesion and proliferation. In conclusion, fibrous scaffolds from PHEMA are promising materials for tissue engineering and, in combination with liposomes, can serve as a simple drug delivery tool.