Exploring the Effects of Electrospinning Processing Protocols on Fiber Surface Morphology and Polymer Chain Conformation
Jean S Stephens, John F Rabolt*, D Bruce Chase+
Polymers (854), Materials Science and Engineering, University of Delaware*, and Dupont+
Electrospinning is a fiber formation technique that uses electrostatic forces to create continuous, nanometer diameter fibers. A wide variety of polymers have been electrospun from the solution and melt phase and are of interest for an assortment of application areas that require high surface area materials (filtration membranes and biomedical devices). The work presented here focuses on the continuing efforts to build a stronger fundamental understanding of electrospinning by exploring structure/property/process relationships. The investigations examined the effects of process protocols on fiber surface morphology and polymer chain conformation.
Raman spectroscopy has been used to investigate the effect of electrospinning on the chain conformation and crystalline structure of bioinspired polymers (nylon 6, nylon 12, and a dragline spider silk analog). Comparing the spectrum of the bulk material to that of the electrospun material effectively identified conformational changes in nylon 6 and the silk analog. The conformational change in nylon 6 (a -form to g -form) was a result of the stresses induced on the electrospinning jet during fiber formation, whereas the conformational change in the silk analog (b -sheet to a -helical) results from electric field assembling of the charged a -helical segments of the protein polymer in solution. These conformational changes have provided important insights into the nature of the electrospinning process.
By varying the processing parameters it has also been possible to produce fibers with unique surface features, microtextured/nanoporous fibers and nanowebs. In the microtextured/nanoporous fiber studies, changing the processing protocols (solution concentration, solvent volatility, relative humidity) was found to alter the size, shape, and distribution of the pores. Through a judicious choice of the electrospinning processing parameters we have also been able to create "spider web" like structures of nanofibers (5 nm to 25 nm).
The investigations described here have allowed us to build a virtual
database of the processing conditions needed to create materials with the
specific properties to meet application needs, such as tissue engineering
constructs. The properties that are applicable for tissue engineering devices
have been identified and electrospun membranes fit the criteria. Preliminary
cell attachment studies have revealed that the cells have migrated into
the electrospun membranes indicating that the membranes are suitable for
tissue engineering scaffolds.
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