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The Contribution of Interfibrillar Shear Load Transfer to Tendon Fascicle Multiscale Mechanics
Start Date: 9/28/2016Start Time: 4:00 PM
End Date: 9/28/2016End Time: 5:30 PM

Event Description
BIOMED Seminar

Title:
The Contribution of Interfibrillar Shear Load Transfer to Tendon Fascicle Multiscale Mechanics

Speaker:
Spencer E. Szczesny, PhD
NRSA Postdoctoral Fellow
McKay Orthopaedic Research Laboratory
University of Pennsylvania

Abstract:
While proper tendon function is critical for daily activity and a high quality of life, the specific micro-structural mechanisms underlying tendon mechanics and function are unclear. A central unresolved question is whether collagen fibrils in tendon bear load independently or if the applied load is transferred across fibrils through interfibrillar forces.

In this presentation, Dr. Spencer Szczesny will discuss his work aimed at determining the effects of interfibrillar sliding on tendon fascicle macroscale mechanics, quantifying the magnitude of the associated interfibrillar shear stresses, and identifying the possible physical structures that transmit load between fibrils. Multiscale experimental testing using confocal microscopy demonstrated that greater interfibrillar sliding correlated with a decrease in the macroscale tissue modulus and increased stress relaxation. This relationship between interfibrillar sliding and fascicle macroscale mechanics was further supported by shear lag modeling, which demonstrated that load transfer between discontinuous fibrils via shearing of a plastic interfibrillar matrix uniquely explains the observed experimental data. The magnitude of the interfibrillar shear stress produced with fibril sliding was estimated by performing notch tension testing of tendon fascicles and was found to be comparable to that predicted by the shear lag model. Ultrastructural analysis of tendon fascicles using serial block-face scanning electron microscopy showed that small diameter fibrils weave around and fuse with larger diameter fibrils, suggesting that these small diameter fibrils, and not extrafibrillar tissue components, may be the structural origin of interfibrillar shear forces in tendon. This hypothesis was supported by trypsin digestions, which successfully removed the extrafibrillar proteins, but did not change the fascicle mechanical behavior.

Collectively, these data strongly suggest that fibrils are discontinuous and that interfibrillar sliding and shear load transfer are the mechanisms underlying tendon fascicle multiscale mechanics. Current work is focused on understanding how tendon multiscale mechanics change with fatigue loading and how this alters cell phenotypes leading to tendon degeneration.

For more info, please visit drexel.edu/biomed.

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Biosketch:
Spencer Szczesny, PhD, is currently a postdoctoral researcher at the University of Pennsylvania in Philadelphia, PA. In July 2016, he received an NIH National Research Service Award (NRSA) Individual Postdoctoral Fellowship (F32) to investigate the role of stem cell mechanotransduction during fatigue loading in the development of tendon degeneration. In May 2015, he received a PhD in Bioengineering at the University of Pennsylvania for his work investigating the contribution of interfibrillar sliding and shear load transfer on tendon fascicle multiscale mechanics. Prior to his doctorate, Dr. Szczesny worked as a Design Engineer for Aesculap Implant Systems developing spinal implants and as a research assistant at the Helmholtz Institute for Biomedical Technology in Aachen, Germany. Dr. Szczesny obtained an MS in Mechanical Engineering at the Massachusetts Institute of Technology in 2005 and a BS in Mechanical Engineering at the University of Pennsylvania in 2003.

In recognition of his contribution to the field of soft tissue biomechanics, Dr. Szczesny has received several award, including a New Investigator Recognition Award (NIRA) Finalist at the 2016 ORS Annual Meeting, 1st Place in the PhD competition at the 2015 Summer Biomechanics, Bioengineering, and Biotransport Conference (SB3C), 1st Place in the PhD competition at the 2013 ASME Summer Bioengineering Conference, and the President Gutmann Leadership Award from the University of Pennsylvania. Dr. Szczesny is a member of the American Society of Mechanical Engineers (ASME) and Orthopaedic Research Society (ORS) and served on the 2013-2014 ASME Bioengineering Division Student Leadership Committee.
Contact Information:
Name: Ken Barbee
Phone: 215-895-1335
Email: barbee@drexel.edu
Spencer Szczesny
Location:
Papadakis Integrated Sciences Building (PISB), Room 120, located on the northeast corner of 33rd and Chestnut Streets.
Audience:
  • Undergraduate Students
  • Graduate Students
  • Faculty
  • Staff
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  • Online Access

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