Date of Award

5-2015

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Bioengineering

Committee Member

Dr. Karen J.L. Burg

Committee Member

Dr. M. Scott Taylor

Committee Member

Dr. Melinda Harman

Abstract

Traditionally, orthopedic repairs best served by encirclement or binding, such as sternotomy, have employed metallic implants. The permanence and rigidity of this type of implant is not ideal, leading to irritation, wound dehiscence, or other complications. As innovators look to polymeric solutions to support damaged tissue by encirclement in novel ways, long-lasting absorbable polymers present a unique opportunity for use in a cable tie device. While readily available absorbable materials fail to meet the combined requirements of long strength retention, tensile strength, and flexibility, a solution may be achieved by incorporating the strength of poly(lactide) (PLLA) and the flexibility of poly(ε-caprolactone) without reducing the strength retention profile of the construct. To respond to this need, the present study was conducted to assess combinations of l-lactide and ε-caprolactone through melt blending and copolymerization in ratios of 75:25 weight percent in injection molded tensile bar parts. These articles were analyzed for structural, chemical, and mechanical properties, both as-molded and throughout the course of a 12-week in vitro study. This data was used to assess the effects of 1) blending, resulting in modulation at the micro level, and 2) copolymerization, resulting in modulation at the molecular level, through a clinically relevant time period. While all materials exhibited changes from the homopolymer controls, copolymerization resulted in the largest reduction in tensile and bending moduli from that of PLLA. The diblock formulation exhibited the most similar strength and structural properties to the blended materials, with a more rapid reduction in tensile strength in vitro. The triblock copolymer, which exhibited lower initial tensile strength than the diblock copolymer, demonstrated a strength retention profile equal to that of the homopolymers and blends over the 12-week study, as well as a lower bending modulus. These results indicate the triblock formulation is the most likely candidate of the test materials to meet the anticipated combined requirements for use in an absorbable cable tie.

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