Nonlinear mechanics of soft fibrous networks

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Original entry: Tom Kodger, APPHY 226, Spring 2009


A Kabla, L. Mahadevan. J.R. Soc. Interface 4, 99 (2007);


Nonlinear mechanics, macroscopic fiber, network, biopolymer


Mechanical networks of fibres arise on a range of scales in nature and technology, from the cytoskeleton of a cell to blood clots, from textiles and felts to skin and collageneous tissues. Their collective response is dependent on the individual response of the constituent filaments as well as density, topology and order in the network. Here, we use the example of a lowdensity synthetic felt of athermal filaments to study the generic features of the mechanical response of such networks including strain stiffening and large effective Poisson ratios. A simple microscopic model allows us to explain these features of our observations, and provides us with a baseline framework to understand active biomechanical networks.

Capillarity In Action

This article contains virtually no capillarity phenomena, but is a very good example of making relatively simple macroscopic measurement that directly relate to the microscopic phenomena of interest.

The authors deform synthetic felt in a macroscopic strain device and relate the various non-linear mechanical responses to microscopic semi-flexible biopolymers such as actin, vimentin, etc. Two independent causes of the non-linear response of these networks are the response of individual single fibers and the non-affine collective deformation of the network. By using a macroscopic model system (felt) the authors conclude that the single fiber response is sufficient to explain the main non-linear mechanics response in both a qualitative and quantitative fashion. While macroscopic felt lack two key feature of biopolymers (i.e. active polymerization and thermal fluctuations) this conclusion could have large implication on the overall mechanical response of such network. Additionally, it is known that the response of actin network for example is dominated by the mechanics of the cross-linking proteins. The authors do not discuss the possibility of cross-linkers in their macroscopic model system.

This article is a very good treatise on network verses individual fiber mechanics. Interesting in its simplicity, this possibly oversimplified model system does not have all the features of a biopolymer network but has many of the same mechanical response; which begs the question as to whether cross-linkers are the major mechanical 'players' in a biopolymer network??