Seminar - New Insights into Collagen Structure, Material Properties, and Failure Behavior
Date: May 17, 2005
Time: 11:00 AM
Location: Baiada Center, Room: Wedge Room
Todd C. Doehring, Ph.D.
Department of Biomedical Engineering
Lerner Research Institute
Cleveland Clinic Foundation
The primary load-bearing constituent of soft connective tissues is collagen. In ligaments and tendons, the collagen has been described (Kastelic, 1978) as a nested hierarchy of cross-linked micro-fibrils, fibrils, fibers, and fiber bundles (or fascicles). Since Kastelicís original diagram, however, there have been few new descriptions of collagen structure, particularly at scales larger than the single fascicle (e.g. fiber bundle groups, fiber-membrane connectivity). This is because collagen fibers are difficult to visualize. Staining or other contrast enhancing methods tend to affect all of the collagen, regardless of its orientation or bundle structure. This lack of topological data has limited the development of accurate and predictive computational models of tissue behavior. To address this problem, we have applied a new imaging technique that uses elliptically polarized light to reveal previously invisible collagen structure in fresh, non-embedded tissues.
Based on this system, we have developed a mesostructural testing system (MSTS) that combines controlled loading with marker-less video strain tracking to measure the nonuniform deformations of tissue structures under controlled loads-to-failure. Local material and structural properties can then be estimated using inverse finite element analysis. In this presentation, I will describe the system and present some new results from human Achillesí tendon, porcine aortic valve, bovine pericardium and canine knee meniscus.
Dr. Doehring obtained his Ph.D. in 2001 from the University of Pittsburgh under the mentorship of Lars Gilbertson, Ph.D. (primary advisor) and Savio L-Y Woo, Ph.D. (co-advisor), where his focus was on developing a robotic testing system for measuring spine kinetics and load-sharing between structures. After finishing his degree, he moved to the Lerner Research Center to pursue post-doctoral research in soft-tissue mechanobiology and constitutive modeling, primarily on the structure-function behavior of the aortic valve under the mentorship of Dr. Ivan Vesely. Currently he is working on the staff of the Lerner Research Center, focusing on foot and knee related soft tissue mechanics research with Drs. Peter Cavanagh and Cahir McDevitt.
The Baiada Center is located at 3225 Arch Street. Enter on Arch Street, between 32st and 33nd Streets.