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ECCOMAS Congress 2016
Sources of viscoelasticity and damage in soft connective tissues: molecular and
intermolecular mechanisms in collagen fibrils
1*
2
3
1
Michele Marino , René B. Svensson , Giuseppe Vairo , Peter Wriggers
1
Institute of Continuum Mechanics, Leibniz Universität Hannover
Appelstr. 11, 30167 Hannover, Germany
[email protected], [email protected]
2
Institute of Sports Medicine Copenhagen, Bispebjerg Hospital, University of Copenhagen
Bispebjerg Bakke 23, 2400 Copenhagen NV, Denmark
[email protected]
3
Department of Civil Engineering and Computer Science, University of Rome "Tor Vergata"
Via del Politecnico 1, 00133 Rome, Italy
[email protected]
ABSTRACT
Viscoelastic effects and damage in soft connective tissues are related to inelastic mechanical behaviour of
collagen fibrils, one of the main tissue constituent. In turn, collagen fibril mechanics highly depend on
biochemical and biophysical features such as, for instance, cross-link density, water content and protein
sequence. The aim of this work is to provide an insight on the viscoelastic and damage behavior of collagen
fibrils by highlighting the relationship between their biochemistry and mechanics. Accordingly, an
experimental-modeling joint-work is presented and going towards a better comprehension of the physiopathological behavior of tissues in living and remodeling organs. Experimental tests, addressing the uniaxial
traction of collagen fibrils and based on the procedure employed in [1], have been conducted and analyzed
by means of an analytical model, firstly developed in [2] and refined in [3]. In its original formulation [3],
the model is based on a multiscale approach that incorporates and couples: thermal fluctuations in collagen
molecules; the uncoiling of collagen triple helix; the stretching of molecular backbone; slip-pulse
mechanisms due to the rupture of intermolecular weak bonds; molecular damage due to interstrand
delamination or covalent bonds rupture. Moreover, the model is enriched by accounting for intra-microfibril
sliding mechanisms, as well as unbound and bound water molecules.
Experimental data, conducted on human patellar and rat tail tendons, reveal the three-region shape of fibrils
mechanics, highlighting the role of cross-link density in tuning the mechanical behavior and, in particular, in
the transition from a yielding-like to a brittle-like behavior. Moreover, performing loading-unloading
traction tests, obtained data show that collagen fibril mechanics is characterized by significant strain-rate
effects, as well as residual strains. The effectiveness of the proposed modeling approach is verified by
comparison with obtained experimental data, as well as available atomistic results. The afore-described
peculiar features of collagen fibril mechanics are recovered with a special insight on the underlying
nanoscale mechanisms. The model is based on parameters with a clear biophysical and biochemical meaning,
resulting in a promising tool for analyzing the effect of pathological or pharmacological-induced
histochemical alterations on the functional mechanical response of collagenous tissues.
References
[1] Svensson, R.B., Mulder, H., Kovanen, V. and Magnusson SP “Fracture Mechanics of Collagen Fibrils:
Influence of Natural Cross-Links”, Biophysical J. 104, 2476-2484 (2013).
[2] Marino, M. and Vairo, G “Influence of inter-molecular interactions on the elasto-damage mechanics of
collagen fibrils: a bottom-up approach towards macroscopic tissue modelling”, J Mech Physics Solids 73,
38-54 (2014).
[3] Marino, M. “Molecular and intermolecular effects in collagen fibril mechanics: a multiscale analytical
model compared with atomistic and experimental studies”, Biomech. Model. Mechanobiol.,
doi:10.1007/s10237-015-0707-8 (2015).
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