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The effect of fiber spacing on the mechanical properties of fiber reinforced composites for meniscus replacements
Thesis   Open access

The effect of fiber spacing on the mechanical properties of fiber reinforced composites for meniscus replacements

Mary Katharine Ziegler
Master of Science (M.S.), Drexel University
Jun 2014
DOI:
https://doi.org/10.17918/etd-4511
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Abstract

Fibrous composites--Mechanical properties Meniscus (Anatomy)--Surgery Colloids Materials Science
The majority of orthopedic surgeries are related to meniscus repair with approximately one million surgeries performed in the United States annually. Typically, tears to the meniscus are treated with a partial meniscectomy; however, this increases peak load pressure on the knee leading to osteoarthritis. The prevalence of meniscus damage, and the limited treatment options, has driven research to develop suitable materials to restore stress-distribution across the knee while preventing joint deterioration. Research at Drexel University has shown the viability of physically cross-linked poly-vinyl alcohol (PVA) hydrogels reinforced with ultrahigh molecular weight polyethylene (UHMWPE) fibers as a meniscus replacement, which is the foundation for this thesis. UHMWPE-PVA hydrogel composites offer the innate ability to tailor properties for specific applications. Work at Drexel University demonstrates the advantages of UHMWPE reinforced PVA hydrogels while highlighting that improvements can still be made since. The mechanical properties of the composites were less than predicted. Poor stress transfer from the matrix to the fibers could explain the lower mechanical properties. Stress transfer is improved by increasing the contact area amongst the fibers and hydrogel. UHMWPE fiber was separated from braids, with an average diameter of 507 ± 43[mu]m, to individual fibers, with an average diameter of 20± 3.6[mu]m. Separating the braids to fibers allows the investigation of increased contact area while maintaining a constant surface area. The tensile and tear properties of these composites were also investigated. The incorporation of fiber reinforcements decreased the hydrogel rich regions among the composite, which lead to an increase in mechanical properties compared to braided samples. The tensile modulus increased with fiber concentration. Samples with increased surface area outperformed braided samples at each concentration, ranging from 0.1 to 40 MPa and 0.1 to 13.1 MPa, respectfully. A similar trend was noted in tear properties, with tear force ranging from 0.04 to 0.06N and 0.07 to 6.6 N for braided and fiber samples, respectfully. The UHMWPE-PVA interface was a significant weakness, requiring the use of a PVA-glutaraldehyde grafting technique to increase adhesion. Samples that were surface treated led to improved tear properties to the extent that the force recorded was equivalent to the force required to pull samples from testing grips. This is important, as the primary failure for previous in vivo studies was delamination of reinforcements. This study enhances future applications for an UHMWPE-PVA composite for meniscus replacements and other soft tissue applications.

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