Title

Processing and Characterization of Biodegradable Polymer Composites

Date of Award

January 2015

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Biomedical and Chemical Engineering

Advisor(s)

Patrick T. Mather

Subject Categories

Engineering

Abstract

The purpose of this work was to determine processing parameters for the fabrication of biodegradable composites, and then to characterize these composites to determine their feasibility as stent materials. This was accomplished by using biodegradable polymers. The objective at first was to self-reinforce fibers melt spun using this polymer through hot compaction, which also required additional processing of the melt spun fibers. However, due to inadequate mechanical properties, improvements in the material were necessary. The next goal was to test the material with the inclusion of another, highly ductile polymer as a fiber binder. The results showed that this composite had promising mechanical properties for a coronary stent application.

In Chapter 1, motivation as to why a bioabsorbable stent would be beneficial and advantageous over other stent types is given, along with the reasoning behind using poly(lactic acid) (PLA) as the material. A brief description of the three projects is also provided. Chapter 2 introduces the issues with as-melt spun PLA fibers, which are amorphous due to the processing method used. This was solved by applying a strain to the fibers at a temperature above their glass transition temperature, and then annealing them while maintaining strain. It was observed that a strain was necessary to induce crystalline alignment, but strain beyond 10% had little effect on this alignment. In Chapter 3, compacted blow-spun PLA (Ingeo) fibers and the annealed melt spun fibers were reinforced using the hot compaction method, where heat and pressure are applied to the fibers for a specified amount of time. The temperature at which these fibers were compacted had a significant effect on the thermal, mechanical, and microstructural properties of the compacted material, and optimal compaction temperatures were found for the Ingeo and melt spun fibers. However, the strain-to-failure for the compacted material was less than 10% and was deemed inadequate for stent applications. As a result, in Chapter 4, an additional polymer, poly(xi-caprolactone) (PCL), was added to improve the ductility of the composite, and this incorporation was accomplished through dual electrospinning. The dual spun composites were then heated to a temperature above the melting point of PCL, but below the melting point of PLA, and characterized and compared to their neat material counterparts. It was found that increasing PCL content increased the mechanical properties, and made the resulting material more suiTable for a stent application. Finally, Chapter 5 gives a summary of work accomplished for each project, provides conclusions drawn from the results, and discusses potential future directions.

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