Bimodal collagen fibril diameter distributions direct age-related variations in tendon resilience and resistance to rupture

• Published in: Journal of applied physiology (1985) Vol. 113; no. 6; pp. 878 - 888
• Main Authors: Goh, K L, Holmes, D F, Lu, Y, Purslow, P P, Kadler, K E, Bechet, D, Wess, T J
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 15-09-2012
• Subjects: Age Factors; Aging - metabolism; Aging - pathology; Analysis of Variance; Animals; Biomechanical Phenomena; Collagen; Fibrillar Collagens - metabolism; Fibrillar Collagens - ultrastructure; Life Sciences; Linear Models; Male; Mice; Mice, Inbred C57BL; Microscopy, Electron, Transmission; Models, Biological; Models, Statistical; Regression analysis; Strain; Stress, Mechanical; Tendon Injuries - metabolism; Tendon Injuries - pathology; Tendon Injuries - prevention & control; Tendons; Tendons - metabolism; Tendons - ultrastructure; Tensile Strength; Transmission electron microscopy; finite mixture model; stress transfer; CROSS-LINKING; work of fracture; MODEL; MECHANICAL-PROPERTIES; CONNECTIVE TISSUES; I-COLLAGEN; PATELLAR TENDON; strain energy density; BIOMECHANICAL PROPERTIES; FORCE; MORPHOLOGY
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/japplphysiol.00258.2012

Scaling relationships have been formulated to investigate the influence of collagen fibril diameter (D) on age-related variations in the strain energy density of tendon. Transmission electron microscopy was used to quantify D in tail tendon from 1.7- to 35.3-mo-old (C57BL/6) male mice. Frequency histograms of D for all age groups were modeled as two normally distributed subpopulations with smaller (D(D1)) and larger (D(D2)) mean Ds, respectively. Both D(D1) and D(D2) increase from 1.6 to 4.0 mo but decrease thereafter. From tensile tests to rupture, two strain energy densities were calculated: 1) u(E) [from initial loading until the yield stress (σ(Y))], which contributes primarily to tendon resilience, and 2) u(F) [from σ(Y) through the maximum stress (σ(U)) until rupture], which relates primarily to resistance of the tendons to rupture. As measured by the normalized strain energy densities u(E)/σ(Y) and u(F)/σ(U), both the resilience and resistance to rupture increase with increasing age and peak at 23.0 and 4.0 mo, respectively, before decreasing thereafter. Multiple regression analysis reveals that increases in u(E)/σ(Y) (resilience energy) are associated with decreases in D(D1) and increases in D(D2), whereas u(F)/σ(U) (rupture energy) is associated with increases in D(D1) alone. These findings support a model where age-related variations in tendon resilience and resistance to rupture can be directed by subtle changes in the bimodal distribution of Ds.