A simple and efficient method to induce porosity both in the core and on the surface of electrospun submicrometer polymer fibers has been demonstrated by combining nonsolvent-induced phase separation with electrospinning. In this modified electrospinning process, fibers are collected in a bath filled with a nonsolvent for the polymer being electrospun. The presence of residual solvent in the nanofibers causes phase separation once the fibers reach the nonsolvent bath. Poly(acrylonitrile) (PAN) in dimethylformamide (DMF) is chosen as the model polymer/solvent system. The versatility of the approach is demonstrated by extending the technique to poly(styrene)/DMF, poly(styrene)/toluene, and poly(methyl methacrylate)/DMF systems. With a suitable solvent (ethanol) and optimized tip-to-collector distance, the specific surface area of the porous PAN fibers increased to an order of magnitude compared to that of the smooth fibers obtained by the conventional electrospinning. Further, this electrospinning technique is extended to coreÀshell electrospinning, enabling the fabrication directly in one step of PAN-based hollow fibers having porosity both in the surface and the bulk.
Diabetic wounds are susceptible to microbial infection. The treatment of these wounds requires a higher payload of growth factors. With this in mind, the strategy for this study was to utilize a novel payload comprising of Eudragit RL/RS 100 nanofibers carrying the bacterial inhibitor gentamicin sulfate (GS) in concert with recombinant human epidermal growth factor (rhEGF); an accelerator of wound healing. GS containing Eudragit was electrospun to yield nanofiber scaffolds, which were further modified by covalent immobilization of rhEGF to their surface. This novel fabricated nanoscaffold was characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The thermal behavior of the nanoscaffold was determined using thermogravimetric analysis and differential scanning calorimetry. In the in vitro antibacterial assays, the nanoscaffolds exhibited comparable antibacterial activity to pure gentemicin powder. In vivo work using female C57/BL6 mice, the nanoscaffolds induced faster wound healing activity in dorsal wounds compared to the control. The paradigm in this study presents a robust in vivo model to enhance the applicability of drug delivery systems in wound healing applications. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A: 641-651, 2018.
Modulation of initial burst and long term release from electrospun fibrous mats can be achieved by sandwiching the drug loaded mats between hydrophobic layers of fibrous polycaprolactone (PCL). Ibuprofen (IBU) loaded PCL fibrous mats (12% PCL-IBU) were sandwiched between fibrous polycaprolactone layers during the process of electrospinning, by varying the polymer concentrations (10% (w/v), 12% (w/v)) and volume of coat (1 ml, 2 ml) in flanking layers. Consequently, 12% PCL-IBU (without sandwich layer) showed burst release of 66.43% on day 1 and cumulative release (%) of 86.08% at the end of 62 days. Whereas, sandwich groups, especially 12% PCLSW-1 & 2 (sandwich layers—1 ml and 2 ml of 12% PCL) showed controlled initial burst and cumulative (%) release compared to 12% PCL-IBU. Moreover, crystallinity (%) and hydrophobicity of the sandwich models imparted control on ibuprofen release from fibrous mats. Further, assay for cytotoxicity and scanning electron microscopic images of cell seeded mats after 5 days showed the mats were not cytotoxic. Nuclear Magnetic Resonance spectroscopic analysis revealed weak interaction between ibuprofen and PCL in nanofibers which favors the release of ibuprofen. These data imply that concentration and volume of coat in flanking layer imparts tighter control on initial burst and long term release of ibuprofen.
Well-crystalline ultrathin GaS nanobelts have been successfully synthesized on silicon substrates by a simple thermal evaporation process. The GaS nanobelts were examined by X-ray diffraction (XRD), scanning electron microscope (SEM), high-resolution transmission electron microscope (HRTEM), and energy dispersive X-ray analysis (EDAX). The XRD pattern indicates formation of well-crystalline hexagonal phase GaS nanostructures. The SEM image shows uniformly distributed GaS nanostructures covering the entire substrate surface. The TEM results reveal that the GaS nanostructures are "nanobelts" of widths 20 to 50 nm and lengths up to several microns, and some of them are L-shaped. The growth mechanism and formation of GaS straight and L-shaped nanobelts has been explained. The field emission studies revealed that the threshold field required to draw an emission current of ∼1 nA is to be 2.9 V/µm, and a current density of ∼5.7 µA/cm 2 can be drawn at an applied field of 6.0 V/µm. The Fowler-Nordheim plot, derived from the observed current densityapplied field characteristics depicts nonlinear behavior over the entire range of applied field. The field enhancement factor is estimated to be ∼2.0 × 10 4 . The emission current stability investigated over a duration of more than 2 h at the preset value ∼4.0 µA shows initial increment followed by stabilization to a higher value ∼6.0 µA. The average emission current at the stabilized value is seen to be fairly constant with current fluctuations within (10%. The results suggest the use of GaS nanobelts as a promising electron source for applications in field emission based devices.
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