Exploring the effects of electrospinning processing protocols on fiber surface morphology and polymer chain conformation

Electrospinning is a fiber formation technique that uses electrostatic forces to create continuous, nanometer diameter fibers. The work presented here focuses on the continuing efforts to build a stronger fundamental understanding of electrospinning by exploring structure/property/process relationships by investigating the effects of process protocols on fiber surface morphology and polymer chain conformation.; By varying the processing parameters it has been possible to produce fibers with unique surface features, microtextured/nanoporous fibers and nanowebs. In the microtextured/nanoporous fiber studies, changing the solution concentration, solvent volatility, and relative humidity was found to alter the size, shape, and distribution of pores on the fiber surface. The mechanisms that can explain the pore formation and texturing on the surface of the fibers are phase separation (aggregation into polymer rich and polymer lean regions) and breath figures (evaporative cooling and vapor condensation). Through a judicious choice of the electrospinning processing parameters we have also been able to create “web” like structures of nanofibers (5–25 nm) from collagen, dragline silk analog, nylon, and denatured collagen. Electrostatic repulsion and thin film dewetting are thought to be responsible for the formation of the nanowebs. These unique structures were characterized using FESEM, TEM, OM, and AFM. Raman spectroscopy, initially developed as a “real time” characterization technique to study electrospun fiber formation, has also been used to investigate the effect of electrospinning on the chain conformation of bioinspired polymers. Comparing the spectrum of the bulk material to that of the electrospun material identified conformational changes in nylon 6 and dragline silk analog. The conformational change in nylon 6 (α-form to γ-form) results from the stresses induced on the electrospinning jet during fiber formation, whereas the conformational change in the silk analog (β-sheet to α-helical) result from electric field assembling of the charged a-helical segments of the protein polymer in solution.; The investigations described here have allowed us to build a virtual database of the processing conditions needed to create materials for tissue engineering constructs. Electrospun collagen membranes have been used in preliminary cell attachment studies. From the trials it was observed that the cells migrated into the membranes indicating that the membranes are suitable for tissue engineering scaffolds.