Visual Characterization of Aponeurosis Microstructure
Author:Olivia Dyer ’22
Co-Authors:Dr. Mark Seeley, Benjamin B. Wheatley
Faculty Mentor(s):Benjamin B. Wheatley, Mechanical Engineering
Funding Source:Schotz Family Fund
Aponeurosis is a tendinous sheath-like tissue found in many muscle-tendon units that covers the muscle belly and transitions into tendon. Little research has been done to understand how collagen fiber microstructure contributes to aponeurosis stiffness and mechanical function. The goal of this study was to use scanning electron microscopy (SEM) to characterize the microstructure of aponeurosis tissue be comparing waviness values measured in unstretched and stretched tissue. It is hypothesized that the waviness of the collagen fibers will decrease after tissue has been stretched. Porcine shoulder tissue was dissected to obtain 40×10 mm specimens. Unstretched samples (n=10) were fixed in 10% formaldehyde, while stretched samples (n=10) were fixed at five percent strain. Images were taken at 50, 100, 1k, and 3.5k magnification. Waviness of the stretched and unstretched aponeurosis was quantified as the ratio of the true length of the collagen fiber to the tangent of two endpoints of that same collagen fiber. Aponeurosis exhibited a hierarchical structure, similar to that of tendon or ligament, with collagen-rich fascicles, fibers, and fibrils. Waviness in the collagen fibers was observed at lower magnifications (100 μm), while at higher magnifications the sheet-like structure of the collagen fibrils was seen (1,000 μm). Unstretched tissue exhibits a high degree of waviness or collagen crimp (1.17 ± 0.21) compared to tissue that has been fixed under a five percent stretch (1.05 ± 0.06, p = 6.615e-08). Future work will include using computational modeling to study the effect of collagen structure on aponeurosis mechanics.