Chain entanglements are one of many parameters that can significantly influence fiber formation during polymer electrospinning. While the importance of chain entanglements has been acknowledged, ...there is no clear understanding of how many entanglements are required to affect/stabilize fiber formation. In this paper, polymer solution rheology arguments have been extrapolated to formulate a semi-empirical analysis to explain the transition from electrospraying to electrospinning in the good solvent, non-specific polymer–polymer interaction limit. Utilizing entanglement and weight average molecular weights (
M
e,
M
w), the requisite polymer concentration for fiber formation may be determined a priori, eliminating the laborious trial-and-error methodology typically employed to produce electrospun fibers. Incipient, incomplete fiber formation is correctly predicted for a variety of polymer/solvent systems at one entanglement per chain. Complete, stable fiber formation occurs at ≥2.5 entanglements per chain.
Intumescent coatings expand upon exposure to a flame to create a protective char layer between the flame and underlying substrate. Widely used commercially, these coatings are applied notably to ...steel load-bearing beams, significantly extending their time to failure. Boric acid has proved to be a particularly effective additive in the formulation in these coatings, although regulatory concerns are driving an urgent need for more environmentally friendly additives. We report here the characterization of poly(acrylic acid) (PAA) for its use as a novel material in flame-retardant and intumescent coatings. Thermogravimetric analysis (TGA) and microscale combustion calorimetry (MCC) were performed on the novel flame-retardant additives to evaluate individual degradation mechanisms and heat release rates. Promising compositions were immobilized in an epoxy binder and formulated with other intumescent additives such as ammonium polyphosphate (APP) and melamine (MEL) to evaluate performance in a coating system. These formulations were then evaluated via quantitative cone calorimetry. Particular PAA-containing formulations show peak heat release rates (PHRR) and total heat release (THR) of 283 kW/m2 and 50.5 MJ/m2, respectively, which compare favorably to data for BA-containing systems, specifically PHRR = 229 kW/m2 and THR = 43.1 MJ/m2. Results showed promise and need for further investigation into PAA as a multifunctional additive for use in flame-retardant and intumescent coatings.
Electrospun fiber mats are explored as drug delivery vehicles using tetracycline hydrochloride as a model drug. The mats were made either from poly(lactic acid) (PLA), poly(ethylene-co-vinyl acetate) ...(PEVA), or from a 50:50 blend of the two. The fibers were electrospun from chloroform solutions containing a small amount of methanol to solubilize the drug. The release of the tetracycline hydrochloride from these new drug delivery systems was followed by UV–VIS spectroscopy. Release profiles from the electrospun mats were compared to a commercially available drug delivery system, Actisite
® (Alza Corporation, Palo Alto, CA), as well as to cast films of the various formulations.
Nanofiber scaffolds of collagen have been fabricated via electrospinning using benign solvent systems as a replacement for 1,1,1,3,3,3 hexafluoro‐2‐propanol. Simple binary mixtures of ...phosphate‐buffered saline and ethanol have been found to be highly effective for electrospinning. FTIR spectra suggest that the triple helical structure of collagen was conserved after dissolution and electrospinning. Crosslinking of the electrospun collagen scaffolds was achieved with standard methods.
We employed aqueous solutions of highly-hydrolyzed (>99+%) poly(vinyl alcohol), PVA, to coat plastic dishes as a method to efficiently induce three-dimensional (3D) culturing of cells. The coatings ...were prepared by simple evaporation of 3 wt/vol% solutions of PVA in water and require no additional processing steps after air drying under sterile conditions. The coating allows spheroids to form in solution. Spheroid formation is usually preferable to two-dimensional (2D) culturing as it creates a more realistic ex vivo model of some human tissues and tumors. Using PVA-coated cell culture plates, we demonstrated that we can grow reproducibly sized spheroids using several human glioma cell lines, including LN229, U87 MG, and Gli36, and the embryonic kidney cell line, 293T. Spheroids formed on PVA-coated plates grow as well as on other commercially-available, low-attachment plates, and have excellent optical imaging properties. As spheroids, LN229 cells express markers of cancer stem cells. Finally, we confirmed that spheroids generated on PVA-coated plates are sensitive to molecular perturbations, as increased expression of the cell adhesion molecule PTPμ significantly increased the size of spheroids. The PVA hydrogel layer is an effective tool for creating a more realistic ex vivo culture system than traditional 2D culture and can be used to generate cell spheroids for potential application in drug screening and personalized medicine for diseases such as cancer.
The first results of electrospinning fibrinogen nanofibers for use as a tissue-engineering scaffold, wound dressing, or hemostatic bandage are reported. Structures composed of fibrinogen fibers with ...an average diameter of 80−700 nm were electrospun from solutions composed of human or bovine fibrinogen fraction I dissolved in 1,1,1,3,3,3-hexafluoro-2-propanol and minimal essential medium (Earle's salts). In summary, the electrospinning process is a simple and efficient technique for the fabrication of 3D structures composed of fibrinogen fibers, as would be present in the physiologic environment.
Small organic molecules offer a rich opportunity to discuss the interplay of chemical structure with properties such as the melting point and phenomena such as glass formation and can form the basis ...of fundamental considerations of structure–property relationships in macromolecules. Of particular importance are thermal transitions, specifically melting points and glass transition temperatures, and each is discussed in the context of structure–property correlations. Connections are made to a few commercially important polymers and their thermal transitions.
Electrospun DOXY-h loaded-poly(acrylic acid) (PAA) nanofiber mats (PAA/DOXY-h nanofiber mats) were prepared by the electrospinning technique and post-spinning sorption method at various doses: ...PAA/DOXY-h125, PAA/DOXY-h250, PAA/DOXY-h500, and PAA/DOXY-h1000. The morphology, drug content, release characteristics, and antibacterial activities of the PAA/DOXY-h nanofiber mats were investigated with scanning electron microscopy, UV-vis spectrophotometry, and disc diffusion methodology. The PAA/DOXY-h nanofiber mats had a diameter range of 285-340 nm, and a smooth surface without beads. Adsorption isotherms of DOXY-h could be described well with the Freundlich model. The amounts of DOXY-h, after the post-spinning sorption process, in the PAA/DOXY-h nanofiber mats ranged between 27.57 and 101.71 mg/g. All of the PAA/DOXY-h nanofiber mats exhibited an initial burst release characteristic with cumulative releasing percentages between 37.14 and 45.97%, which followed the Fickian diffusion mechanism. Based on the antibacterial investigation, the tested gram-positive bacteria, Staphylococcus aureus and Streptococcus agalactiae, seemed to be more sensitive to PAA/DOXY-h nanofiber mats than the tested gram-negative bacteria, Pseudomonas aeruginosa. These PAA/DOXY-h nanofiber mats could be used as an antibacterial wound dressing.
Solutions of poly(ethylene-co-vinyl alcohol) or EVOH, ranging in composition from 56 to 71
wt% vinyl alcohol, can be readily electrospun at room temperature from solutions in 70% 2-propanol/water ...(rubbing alcohol). The solutions are prepared at 80°C and allowed to cool to room temperature. Interestingly, the solutions are not stable at room temperature and eventually the polymer precipitates after several hours. However, prior to precipitation, electrospinning is extensive and rapid, allowing coverage of fibers on various substrates, including a grounded metal plate, dielectrics interposed between the charged jet and the metal ground, and on the human body. Fiber diameters of ca. 0.2–8.0
μm were obtained depending upon the solution concentration, an attractive range for tissue engineering, wound healing, and related applications. Electrospun EVOH mats have been shown to support the culturing of smooth muscle cells and fibroblasts.
