Description:

Living tissues are mechanically supported by elastic networks, which need to be soft enough to allow for cell migration and proliferation, yet stiff at high deformation to prevent tissue rupture.
The physical origin of this exceptional strain-stiffening response has been widely studied using single-component networks of collagen fibers [1]. However, real tissues are more complex. In particular, collagen networks are often embedded in a softer and charged elastic matrix, like hyaluronic acid (HA). In this talk, I will first present our study on such composite networks [2]. By combining mechanical experiments and computer simulations, we demonstrate that composite networks exhibit a synergistic mechanics characterized by an enhanced stiffness in the linear regime and a delayed strain-stiffening, strongly dependent on HA concentration. We rationalize these effects on the basis of the internal stress generated by the HA matrix. Our findings not only elucidate how biology combines polymers with complementary properties to finely-tune the mechanics of living tissues; but also provide a new avenue for the design of synthetic materials where internal stress can be used as a powerful knob to tune their mechanical response.
In the second part of the talk, I will focus on the fracture behavior of (single-component) elastic networks. Recent studies [3,4] suggest that material rigidity, that can be for example controlled by varying network connectivity, plays a key role in material failure. Even to the point that stress concentration (and therefore crack nucleation) might be suppressed at all length-scales when the networks are sub-isostatic [4]. Here, I will show results from extensive off-lattice simulations of spring networks with different topologies, connectivity, thresholds, and unprecedentedly large system sizes. We observe that fracture in large networks occurs unavoidably via crack-nucleation, even when sub-isostatic. However, the main descriptors of fracture (e.g. amount of damage, maximum load sustainable) do strongly depend on rigidity-related properties. Finally, I will conclude the talk by showing novel fracture experiments of networks formed by collagen molecules extracted from different sources and self-assembled at different conditions. By highlighting how the experimental results can be interpreted in terms of connectivity, system size and fiber properties, we clearly assess the role of rigidity on material failure.

[1] Sharma et al. Nat. Phys. (2016).
[2] F. Burla, J. Tauber, S. Dussi, J. van der Gucht, G. Koenderink, Nature Physics 15, 549 (2019).
[3] Driscoll et al. PNAS (2015).
[4] Zhang et al. Phys. Rev. Materials (2017).

Dr. Simone Dussi, Wageningen University, Netherlands

Host: Michelle Driscoll

Keywords: Physics, Astronomy, Complex Systems