Enhancing the Properties of Nanoscale Electrospun Polymer Fibers Through Chemical Architecture, Surface Texturing and Optimization of Processing Protocols (2003)

Adding submicron texture while simultaneously shaping a polymer saves energy, reduces manufacturing costs and adds “value” to a material. The University of Delaware’s NIRT is using a simple method to induce a nanoporous texture on polymer fibers as they are formed using an electrostatic spinning technique (electrospinning). Towards this goal, an integrative system that utilizes electroactive polymer/biopolymer synthesis to produce advanced materials for investigation has been developed. The integrative system then uses a unique processing protocol that involves the electrospinning of fibers, a technique that requires a small amount of sample, and a characterization protocol including mechanical/electrical analysis (via MEMS), vibrational spectroscopy, small angle neutron scattering, electron microscopy and x-ray diffraction. The goal of this NIRT is to use materials chemistry to place reactive groups at selective locations (1.0-3.0 nm) along an alpha-helical polypeptide backbone, then optimize the electrospinning process using rheological, spectroscopic, diffraction and electron microscopic characterization techniques to insure placement of these reactive groups on the fiber surface. Determination of the electrical and mechanical properties of these fibers will then be carried out on an automated MEMS test chip (“process-on-a-chip”), which can be used to simultaneously conduct multiple measurements on many fibers of differing chemical architecture and processing history. Initially, a helical protein with the sequence (AAAFAAFAAAF) x is being explored for its potential to display non-natural amino acids that can be modified with electroactive groups. Energy minimization of hybrid proteins of the above sequence, in which phenylalanine (F) residues have been modified with paraphenylenevinylene (PPV) pentamers, demonstrates that the PPV oligomers can be aligned on one face of the helical protein, with interchain distances of approximately 4A. No such alignment is observed in the energy-minimized structures of random coil proteins with pendant PPV groups. Short peptides of the above sequences, in which F is replaced with an aryl-bromide functionalized amino acid, have been produced and will be chemically modified in model reactions. Expression plasmids encoding the helical protein (AAAFAAFAAAF) x , where x = 2, 4, 6, 8, 10, 12, and 14, have been produced and their DNA sequence confirmed. Expression and purification of protein from bacterial hosts equipped with these plasmids is underway. Simultaneously, electrospinning studies of a commodity polymer, poly(styrene) (PS), have also been undertaken in order to determine the effect of various processing variables (surrounding atmosphere, solution concentration, molecular weight, field strength (spinning voltage), syringe-to-target distance, etc.) on fiber diameter and surface morphology. Initial results 1 indicated that increasing the spinning voltage decreases the average diameter of the fibers produced. On the other hand, an increase in solution viscosity was shown to increase the diameter of the resulting electrospun fiber. An interesting result was obtained when PS fibers were electrospun from a volatile solvent (e.g., tetrahydrofuran (THF)) in higher than 35%