| In this project, a novel electrospinning collection system was developed to produce nanofibrous materials with improved organizational control. The system functions by rapidly oscillating the deposition signal (RODS) of multiple collectors, allowing significantly improved nanofiber deposition control by manipulating the electric field which drives the electrospinning process. Other modern electrospinning techniques designed to impart deposited fiber organizational control, such as rotating mandrels or parallel collector systems, are incapable of producing seamless constructs with high quality alignment in sizes large enough to be of interest in real-world applications. Although these two techniques represent the current state of the art in the alignment niche, rotating mandrels produce poor quality alignment and parallel collectors have extremely limited product size. In contrast, the RODS collection system produces deposited fiber networks with highly pure alignment in a variety of product forms and sizes.;High quality alignment was produced in sizes and in shapes of flat (3"x3"), tubular (0.5" dia), or rope-like microbundle (45microm dia) samples from 8% - 11% Fibroin:PEO (4:1) blended solutions. The RODS collection system produced 83+/-7% of its fibers aligned within 5°, nearly a three-fold improvement over the rotating mandrel technique which aligned 30+/-19% of fibers, and a twelve-fold increase over the standard collection system which only aligned 6+/-1% of fibers. Methanol treatment produced a general contraction of the fibrous mesh and a subsequent reduction of void area in standard meshes by 81% to 5.55+/-3%, while the void area of aligned fiber meshes reduced only by 45% to 6.03+/-2.41%. This was 8.6% more void area than was preserved by randomly oriented meshes. Profilometry revealed mesh sample composed of fibers aligned parallel to the axis were thinner than standard meshes. The thinnest aligned mesh measured 2.80 microm in thickness, while the mean thickness of six samples was 5.26+/-2.26 microm. The randomly aligned samples had one member with a thickness measurement of 13.03 microm, however, the mean thickness of six samples was 18.18+/-3.18 microm.;The meshes produced from 9% (w/v) Fibroin:PEO (4:1) using the RODS collectors demonstrated significant mechanical anisotropy, which resulted from high quality fiber alignment. In 37° C PBS, aligned samples produced an ultimate tensile strength (UTS) of 16.25 +/- 2.06 MPa, a Young's modulus of 13.17 MPa, and a yield strength of 1.73+/-1.22 MPa with zero offset. The material was found to be 81% stiffer, when extended in the direction of fiber alignment, and required more than double the amount of force to be deformed, compared to aligned meshes extended perpendicular to fiber orientation. Regardless of extension direction, Young's moduli reveal the aligned meshes were 60-fold more stiff when extended in 22° C ambient air conditions, compared to extension in 37° C PBS.;9% (w/v) Fibroin:PEO (4:1) solution, with a lower cutoff of 8.5% (w/v), produced from fibroin degummed for 40 minutes or less, and dissolved for longer than 90 minutes gave consistently good results. It was found that a switch rate of 30/min, combined with a collector to spinneret distance of 9.5 inches, with a 4.25 inch offset from the center of the collector plane angled at 45° most efficiently drove and collected nanofibers evenly between collectors.;In this thesis, the traditional and RODS electrospinning processes are described. Electrospun materials with improved nanofiber organizations are demonstrated. The RODS technique can theoretically be applied to any electrospinnable polymer, overcomes the limited uniformity and induced mechanical strain of mechanical wheel techniques, and greatly surpasses the limited length of the grounded bridge techniques. The RODS collection system has also been demonstrated to be capable of producing exceptional electrospun materials such as seamless, axially aligned, nanofibrous tubes and axially aligned-to-random fiber orientation gradient silk meshes. Such meshes can potentially accurately emulate the strength and elasticity of a variety of in vivo tissues including blood vessels and ligaments and provide topological cues to developing tissues. |
