Development of Modified Electrospinning Hardware and Techniques to Enable Production of Novel Materials.
Jose, Rodrigo.
2011
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Abstract: 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 ... read moremodern 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 (45µm 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
µm in thickness, while the mean thickness of six samples was 5.26±2.26
µm. The randomly aligned samples had one member with a thickness measurement of
13.03 µm, however, the mean thickness of six samples was 18.18±3.18 µm.
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.
Thesis (M.S.)--Tufts University, 2011.
Submitted to the Dept. of Biomedical Engineering.
Advisor: Robert Peattie.
Committee: David Kaplan, and Robert White.
Keyword: Biomedical engineering.read less - ID:
- 1n79hg86c
- Component ID:
- tufts:20869
- To Cite:
- TARC Citation Guide EndNote