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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). Powered by TCPDF (www.tcpdf.org)
