Masters Theses

Date of Award

12-2006

Degree Type

Thesis

Degree Name

Master of Science

Major

Polymer Engineering

Major Professor

Larry Wadsworth

Committee Members

Roberto Benson, Randy Bresee

Abstract

Nonwoven fiber webs were formed through the processes of melt blowing and electro-spinning with the use of polyester thermoplastic polyurethane (TPU), aromatic polyether TPU, and aliphatic polycarbonate TPU. Each polyurethane was used to form fiber webs into sheets and onto stainless steel springs. Three types of fiber sheets were made: (1) melt blown, (2) electro-spun, and (3) melt blown coated with electro-spun fibers to form a composite structure. The melt blown sheets consisted of polyether TPU or aliphatic polycarbonate (PC) TPU. The electro-spun sheets were made from a 15wt% polymer solution of polyester TPU or aliphatic PC TPU. There were two composite sheets made: (1) melt blown polyether TPU covered with electro-spun polyester TPU and (2) melt blown aliphatic PC TPU with electro-spun aliphatic PC TPU. The electro-spun coatings were made from polymer solutions having concentrations ranging from 5wt% to 20wt%. The stainless steel springs were coated with the same material as the sheet samples.

Both sheets and coated springs were samples characterized in terms of their morphology and mechanical properties. The web sheets were subjected to tensile testing, porosity testing, and fiber diameter measurement. In addition, the sheets and coated springs were subjected to tests that would determine blood cell permeability and the effectiveness of the coated springs and sheets to inhibit vascular smooth muscle cell (VSMC) migration and to create new platelet activation.

Subsequent to the mechanical and morphological testing, the web sheets were evaluated for their ability to impair vascular smooth muscle cell (VSMC) migration and activate platelets growth. The melt blown polyether TPU coated with 15wt% concentration of electro-spun polyester TPU was determined to have the best performance. This composite material was determined to be the best material due to its pore diameters (3.7 to 5.6 μm) and tensile strength (0.4 to 0.6 psi). The second best material was the composite of melt blown aliphatic PC TPU with 10wt% concentration electro-spun aliphatic PC TPU. This material had a porosity of 2 to 6.5 μm and tensile strength of 0.05 to 0.08 psi.

The composites of melt blown and electro-spun TPU are a more suitable barrier for impairing vascular smooth muscle cell (VSMC) migration. The melt blown TPU sheets contained mean pore diameters of 19 to 35 μm, which are believed to be too large to prevent the migration of VSMC. Thus, in order to reduce the pore diameters, the melt blown webs were covered by electro-spun TPU nano-fibers, which formed the composites. Although the electro-spun sheets had mean pore diameters of 0.1 to 0.2 μm, the materials were too weak and fragile to be removed from the supporting paper for tensile testing and its potential strength could not be assessed prior to actual implantation.

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