Many biological tissues throughout the body are fiber-reinforced composites, built primarily of water, collagen fibers, and a soft extrafibrillar matrix. Failure or tearing of these tissues causes pain and disability. Tissue composition and molecular architecture are important to the tissue mechanical properties both during physiological loading and during failure. To date, there has been insufficient research focused on molecular level failure mechanics of fiber-reinforced tissues such as the intervertebral discs of the spine. Determining tissue failure properties and the roles that the various molecules of the tissue play in failure behavior is important for preventing disc disease and to designing new medical approaches for repairing the disc. The goal of this project is to determine how the fiber-reinforced tissue structure controls damage mechanics. For this work the PI will focus on the annulus fibrosus of the intervertebral disc because of its cross-ply fiber architecture and medical relevance. The educational outreach effort in this project is an expansion of the Girls in Engineering (GiE) Summer Program coordinated by the College of Engineering at Berkeley. The PI also will train graduate and undergraduate students from diverse backgrounds in her laboratory during performance of the research project.

In this project, the PI will evaluate the role of the extrafibrillar matrix composition and fiber composition and network on time-dependent and -independent failure behavior. She will combine computational and experimental techniques to study failure mechanisms of fiber-reinforced materials, such as stress distributions between fibers and the extrafibrillar matrix. Her research team will leverage its previous work that developed an experimental method for robust failure testing of the annulus fibrosus. Data from tissue-level experiments will be incorporated into the existing finite element model of the disc joint to elucidate the role of fiber-matrix interactions during joint-level failure. In broader terms, the unique computational model developed from this research, where the extrafibrillar matrix and collagen fibers are described as separate and distinct materials will be beneficial for material scientists outside of biomechanics research (e.g., carbon fiber reinforced polymers) and for scientists investigating the contribution of fibers and extrafibrillar matrix on tissue mechanics (sub-failure and failure mechanics) with injury, aging, or repair.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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University of California Berkeley
United States
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