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Paul Kouwer1

1, Radboud University Nijmegen, Nijmegen, , Netherlands

The stiffness of cells and the extracellular matrix is governed by fibrillar hydrogels. Already at low concentrations, these soft gels form porous network that become rapidly stiffer as soon as they are strained.
Some years ago, we found a unique hydrogel that closely mimics the architecture and the linear and nonlinear mechanical properties of cytoskeletal and extracellular matrix materials.1 The synthetic nature of the material allowed us to tune the (mechanical) properties by changing straightforward parameters, like polymer length, concentration and environmental conditions.2 Despite their broadly distributed nanoscale architecture, the mechanical properties of the gels are well described by models for semi-flexible networks,3 even in the limits of network formation.4
The mechanics of the cytoskeleton and the extracellular matrix, however, are not determined by a single component, but are the result of the composite of various fibrous proteins. Here, we will discuss how the presence of flexible, semi-flexible and stiff components change the mechanical properties of a semi-flexible hydrogel5 and how we can use these hybrids to make extremely responsive materials, for instance a material that increases its stiffness 5000% when heated only 1 °C.

References:
1. P.H.J. Kouwer, et al. Nature 493, 651 (2013).
2. (a) M. Jaspers, M. Dennison, M.F.J. Mabesoone, F.C. Mackintosh, A.E. Rowan, P.H.J. Kouwer, Nat. Commun. 5, 5808 (2014); (b) M. Jaspers, A.E. Rowan, P.H.J. Kouwer, Adv. Funct. Mater. 25, 6503 (2015); (c) M. Jaspers, A.C.H. Pape, I.K. Voets, A.E. Rowan, G. Portale, P.H.J. Kouwer, Biomacromolecules 17, 2642 (2016).
3. (a) F.C. Mackintosh, J. Kas, P.A. Janmey, Phys. Rev. Lett. 75, 4425 (1995); (b) M.L. Gardel, J.H. Shin, F.C. Mackintosh, L. Mahadevan, N. Matsuda, D.A. Weitz, Science 304, 1301 (2004); (c) C. Storm, J.J. Pastore, F.C. Mackintosh, T.C. Lubensky, P.A. Janmey, Nature 435, 191 (2005).
4. M. Dennison, M. Jaspers, P.H.J. Kouwer, C. Storm, A.E. Rowan, F.C. Mackintosh, Soft Matter 12, 6995 (2016).
5. M. Jaspers, S.L. Vaessen, P. Van Schayik, D. Voerman, A.E. Rowan, P.H.J. Kouwer, Nat. Commun. 8, 15478 (2017).

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