Fibrous materials may undergo an internal reorganization, which turns out in the emergence of preferential directions. This is a peculiar behavior of many biological tissues, which drive reorientation by external stimuli at chemo-mechanical levels. In particular, it is detected that contractile cells can reorganize fibrous extracellular matrices and form dense tracts of aligned fibers (tethers), that guide the development of tubular tissue structures and may provide paths for the invasion of cancer cells. Tether formation is caused by buckling instability of network fibres under cell-induced compression. We present a simple mechanical model within a variational framework that captures the essential aspects of these phenomena. The model qualitatively describes: (i) the emergence, induced by local compressive strain, of anisotropy, where fibrous materials exhibit directional preferences; (ii) the occurrence of micro-buckling, which leaves a lasting plastic deformation in the material; and (iii) the formation of localized field patterns, which contribute to the overall behavior of the material. By considering these fundamental aspects, our model provides insights into the mechanical response of fibrous materials and sheds light on the underlying mechanisms driving their behavior.

纤维材料可能会经历内部重组，从而出现优先方向。这是许多生物组织的特殊行为，它们在化学机械水平上通过外部刺激驱动重新定向。特别是，我们发现收缩细胞可以重组纤维细胞外基质并形成密集的排列纤维束（系绳），引导管状组织结构的发育，并可能为癌细胞的侵袭提供路径。系绳的形成是由细胞诱导的压缩下网络纤维的屈曲不稳定性引起的。我们在变分框架内提出了一个简单的力学模型，捕捉了这些现象的基本方面。该模型定性地描述了：（i）由局部压缩应变引起的各向异性的出现，其中纤维材料表现出方向偏好；(ii) 发生微屈曲，从而在材料中留下持久的塑性变形；(iii) 局部场模式的形成，这有助于材料的整体行为。通过考虑这些基本方面，我们的模型提供了对纤维材料机械响应的见解，并揭示了驱动其行为的潜在机制。