On the Mechanics of Microtubule Filaments

Quantitative understanding of cell mechanics has challenged biological scientists during the past couple of decades. one of the promising attempts towards mechanical modeling of the cytoskeleton has been the “tensegrity” cytoskeletal model, which simplifies the complex network of cytoskeletal filaments as a structure merely composed of compression-bearing elements (hinge-ended struts) and tensile members (cables). This discrete model can interestingly explain many experimental observations in cell mechanics. However, evidence suggests that the simplicity of this model may undermine the accuracy of its predictions [1–2]. Continuum mechanics predicts that a free, simply-supported beam tends to buckle in the first mode of buckling and that is the case for an in vitro loading of a single microtubule. However, in vivo imaging of microtubules indicates that the buckling mostly occurs in higher modes. This buckling mode switch takes place mostly because of lateral support of microtubules via their connections to actin and intermediate filaments, which themselves are tensile members of the tensegrity cytoskeleton model. Since these loads are exerted throughout the microtubule length, they introduce a considerable amount of microtubule bending behavior. The objective of this paper is to explore the influence of this flexural behavior on the accuracy of the tensegrity model, given the model’s underlying assumption that “every single member bears solely either tensile or compressive behavior”.