Metastatic cancer cells differ from their non-metastatic counterparts not only in terms of molecular composition and genetics, but also by the very strategy they employ for locomotion. Here, we analyzed large-scale statistics for cells migrating on linear microtracks to show that metastatic cancer cells follow a qualitatively different movement strategy than their non-invasive counterparts. The trajectories of metastatic cells display clusters of small steps that are interspersed with long “flights”. Such movements are characterized by heavy-tailed, truncated power law distributions of persistence times and are consistent with the Lévy walks that are also often employed by animal predators searching for scarce prey or food sources. In contrast, non-metastatic cancerous cells perform simple diffusive movements. These findings are supported by preliminary experiments with cancer cells migrating away from primary tumors in vivo. The use of chemical inhibitors targeting actin-binding proteins allows for “reprogramming” the Lévy walks into either diffusive or ballistic movements.
Preliminary results on the influence of periodically distributed cylindrical nanoinclusions introduced into the f.c.c. hard sphere crystal on its elastic properties and the Poisson's ratio are presented. The nanoinclusions are oriented along the [001]-direction and filled with hard spheres of diameter different from the spheres forming the matrix crystal. The Monte Carlo simulations show that symmetry of the crystal changes from the cubic to tetragonal one. In the case when spheres inside the inclusion are smaller than spheres forming the crystal, the changes of Poisson's ratio are qualitatively similar to the changes observed earlier in the Yukawa sphere crystal, that is, the introduction of nanochannels causes simultaneous decrease of the Poisson's ratio in the [110][1 10]-direction, and its increase in [110][001]-direction. Filling the nanochannel with spheres having diameters greater than that of the spheres in the crystalline matrix, causes a decrease of the Poisson's ratio value from 0.065 down to À0.365 in [111][11 2]-direction. The dependence of the minimal Poisson's ratio on the direction of the applied load is shown in a form of surfaces in spherical coordinates, for selected values of nanochannel particle diameters. The most negative value of the Poisson's ratio found amongst all systems studied was as low as À0.873.
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