Orientation and morphology development in electrospun nanofibers.

This thesis presents the morphology and orientation development of electrospun fibers from polymer solutions with volatile solvents. Polymer solution concentration had a strong effect on the morphology of both Nylon 6,6 and poly(lactic acid) (PLLA) fibers. Successful electrospinning occurred above the overlap concentration, c* (∼0.1 wt% for Nylon 6,6 and 0.13 to 0.16 wt% for PLLA). Beaded fiber to smooth fiber transitions (5.4 to 8.3 wt% for Nylon 6,6 and 3.0 wt% for PLLA) were observed around the entanglement concentrations, ce, corresponding to entanglement characteristic values, [eta]C, of 5.4 to 8.5 (Nylon 6,6) and 20 to 24 (PLLA). Processing parameters, including DC voltage (VD), AC voltage (VA), frequency of VA, and tip-to-target distance, did not significantly affect the morphology of electrospun Nylon 6,6 fibers, but increasing VA or frequency resulted in more uniform fibers. Fully-aligned, defect-free PLLA scaffolds with diameters between 200 and 800 nm were electrospun by decreasing the solution feed rate, increasing the voltage and tip-to-target distance, and using concentrations near the beaded to smooth fiber transition. Neurites from dorsal root ganglion (DRG) explants that were seeded on these scaffolds were shown to follow the direction of these fibers upon contact. After 12 days, these neurites still adhered to the fibers and extended ∼1.5 to 2 cm from their original contact position. Neuroblastoma (SH-EP and SH-SY5Y) and Schwann cells were found to elongate and align parallel to the direction of the fibers. Orientation of electrospun fibers was found to be a function of fiber diameters. Polarized light optical microscopy was used to characterize banded structures in electrospun poly(hexyl isocyanate) (PHIC) fibers. The orientational order observed in fibers with diameters between 2 mum and 13 mum increased linearly with decreasing diameters. The structure of electrospun PLLA fibers was determined to be the beta structure. Using the intensity profile of the (110) reflection from the electron diffraction (ED) pattern, the orientational order of electrospun PLLA fibers was found to increase with decreasing fiber diameters. The effective crystallite size, D, for electrospun PLLA fibers was calculated to range from 2 to 20 nm and decreased with increasing fiber diameter.Ph.D.Applied SciencesBiomedical engineeringMaterials sciencePolymer chemistryPure SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/125422/2/3192704.pd