Fibrillar structure and elasticity of hydrating collagen: A quantitative multiscale approach

Abstract

It is well known that hydration of collagenous tissues leads to their swelling, as well as to softening of their elastic behavior. However, it is much less clear which microstructural and micromechanical "rules" are involved in this process. Here, we develop a theoretical approach cast in analytical mathematical formulations, which is experimentally validated by a wealth of independent tests on collagenous tissues, such as X-ray diffraction, vacuum drying, mass measurements, and Brillouin light scattering. The overall emerging picture is the following: air-drying leaves water only in the gap zones between the triple-helical collagen molecules; upon re-hydration, the extrafibrillar space is established at volumes directly proportional to the hydration-induced swelling of the (micro) fibrils, until the maximum equatorial distance between the long collagen molecules is reached. Thereafter, the volume of the fibrils stays constant, and only the extrafibrillar volume continues to grow. At all these hydration stages, the elastic behavior is governed by the same, hydration-invariant mechanical interaction pattern of only two, interpenetrating mechanical phases: transversely isotropic molecular collagen and isotropic water (or empty pores in the vacuum-dried case).

Matrix metalloproteinases modulate ameboid-like migration of neutrophils through inflamed interstitial tissue

“…Because hydration has been found to induce shape changes of collagen fibers in vitro, 28,29 leakage of the macromolecule fluorescein isothiocyanate (FITC) dextran and, concomitantly, interstitial collagen fiber density were analyzed in further experiments ( Figure 2B). Depletion of neutrophils (which disrupt endothelial junctions during their extravasation) almost completely inhibited the PAF-elicited microvascular leakage as well as the subsequent inflammatory changes in interstitial collagen density ( Figure 2C-D).…”

Average refractive index of tendon as a function of water content

“…In the alternative mode (H < H c ), changes in the total water content are accompanied by changes in water content both in collagen fibrils and extrafibrillar space [33][34][35][36]. For RTT, H c ≈ 0.82 [32,35], which corresponds to C w ≈ 0.52. Fig.…”

“…The significant deviation of the actual n g (C w ) curve from this approximating line in the region C w ≤ 0.52 may be attributed to a change of the mode of hydration. In the literature, two modes of collagenous tissue hydration are distinguished [33][34][35][36]. For relatively high values of H (H > H c , where H c is a critical value, the so-called fibrillar saturation point [35]), changes in the total water content in the tissue lead to changes of the water content in extrafibrillar space while the water content in collagen fibrils remains unchanged [7,[33][34][35][36].…”

“…In the literature, two modes of collagenous tissue hydration are distinguished [33][34][35][36]. For relatively high values of H (H > H c , where H c is a critical value, the so-called fibrillar saturation point [35]), changes in the total water content in the tissue lead to changes of the water content in extrafibrillar space while the water content in collagen fibrils remains unchanged [7,[33][34][35][36]. In the alternative mode (H < H c ), changes in the total water content are accompanied by changes in water content both in collagen fibrils and extrafibrillar space [33][34][35][36].…”

Multiscale approach including microfibril scale to assess elastic constants of cortical bone based on neural network computation and homogenization method

“…Morin et al, [69] consider that the collagen matrix anisotropic or approximately transversely isotropic.The elastic constant values employed for collagen and hydroxyapatite are taken from Gong et al [70] and Biltz and Pellegrino [71]. Hill bounds, which are tensorial forms of the classical Voigt (V) and Reuss (R) bounds, are estimated for the collagen-water and mineral-water composites using the following equations [18]:…”