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The Fu Foundation School of Engineering & Applied Science
Thesis Advisor: Michael G. Dunn, Ph.D.
Graduate Program: Biomedical Engineering
Clinical Academic Building
New Brunswick, NJ
Thursday, February 11, 2010
The anterior cruciate ligament (ACL) plays a primary role in knee stabilization. Due to its limited healing potential, injury of the ACL typically requires surgery. Current treatment options implement the use of autografts and allografts, both of which have significant drawbacks. Tissue-engineered resorbable scaffolds offer an alternative to current treatment options by initially serving to stabilize the knee and host tissue infiltration. As resorption occurs, the load is transferred from the degrading scaffold to the developing neoligament tissue.
This dissertation describes the development of a resorbable fiber scaffold composed of Bombyx mori silk and 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) crosslinked collagen for ACL reconstruction. It was hypothesized that this scaffold could be tailored to mechanically bear the loads of the knee, promote neoligament formation, and predictably degrade over time.
To test this hypothesis, preliminary mechanical characterization of varying silk-collagen fiber ratios was established. A nonfunctional in vivo model was used to determine the mechanical degradation and volume resorption rates of silk. Varying fiber ratios were also subjected to a biochemical assay in order to verify their ability to promote cellular attachment and proliferation. Based on these experiments, a 75% silk/ 25% collagen fiber count scaffold was selected for functional implantation in subsequent animal models.
ACL reconstruction surgeries were performed in rabbits using hybrid scaffolds enhanced with platelet-rich fibrin matrix (PRFM), and implant postoperative strength retention and neoligament formation were assessed. The short-term results demonstrated that silk-collagen scaffolds retained adequate strength and promoted tissue incorporation. PRFM was not found to enhance mechanical or biological outcomes, and therefore did not advance to experimentation in a large animal model.
The final stage of this study tested the device in a sheep ACL reconstruction model and the hypothesis was supported. The fabricated scaffold functioned as a load-bearing device and retained strength equivalent to projected values. It promoted increased tissue infiltration and vascularization over time, indicative of developing neoligament tissue. These encouraging outcomes suggest that a silk-collagen hybrid scaffold can potentially provide an alternative solution to the current ACL reconstruction therapies. However, further design modifications are necessary before it can become clinically relevant.