Mechanical Analysis of Multi-Component Tissues

Abstract

Collagen is the major structural fiber found in mammalian tissues. It is a protein in the form of a triple-helix which is found in several subfamilies, the most abundant of which is the fiber forming group containing Types I, II and III. Type I collagen is found in tendons, skin, cornea, bone, lung and vessel walls. This collagen is thought to give rise to the high tensile strengths of collagen fibers in tissues; in addition, it is actively involved in other physiologic processes such mechanotransduction. However, the non-linear mechanical behavior and viscoelasticity of collagen fibers make analysis of the mechanical properties of tissues complicated. Mechanistically, during mechanical loading, a tensional increase in the D period is observed with increasing strain that is associated with: 1) molecular elongation at the triple-helical level of structure; 2) increases in the gap distance between the end of one triple-helix and the start of the next one in the microfibril; and 3) molecular slippage. In this paper, we discuss the relationship between collagen hierarchical structure and its non-linear mechanical properties. Using vibrational analysis and optical coherence tomography, it is hoped that the mechanical properties of collagenous tissues can be studied in vivo in order to better understand tissue mechanics and to be better able to offer early diagnosis and differentiation of different disease states.

Energy Storage and Dissipation in the Eye: The Importance of the Biomechanical Connections between the Cornea-Limbus-Scleral Series Biomechanical Element and the Scleral-Optic Nerve-Posterior Segment Tissues in Protecting Sensitive Visual Components from Mechanical Damage

“…Equation ( 1) was used to calculate the modulus values and is an empirical equation based on calibration studies using decellularized human skin (dermal collagen), animal tissues, and synthetic polymers tested in uniaxial tension and simultaneously using VOCT [1,[20][21][22][23]. The elastic modulus measured using VOCT is a materials property at the resonant frequency at low strains since the viscous component of the behavior is only 5% to 7% at frequencies above 110 Hz of the total modulus [18,19] and the modulus is unchanged at strains less than about 7% for collagenous materials [18,19].…”

“…Energy storage, transmission and dissipation by mammalian tissues has been elucidated by x-ray diffraction and biomechanical studies on both tendon, skin and cartilage [14][15][16][17][18]. These properties are a consequence of the viscoelasticity of the macromolecular components found in extracellular matrices [19].…”

“…These properties are a consequence of the viscoelasticity of the macromolecular components found in extracellular matrices [19]. They are related to the ability of extracellular matrices to undergo reversible stretching of the collagen triple helix (energy storage), reversible stretching of collagen molecules and crosslinks, and sliding of the quarter-staggered collagen molecules [14][15][16][17][18]. These deformation mechanisms increase the D period (energy storage and transmission), and result in energy dissipation through sliding and rearrangement of both water and proteoglycans surrounding collagen fibrils [14][15][16][17][18][19][20].…”