We investigate the steady state of an ellipsoidal active nematic shell using experiments and numerical simulations. We create the shells by coating microsized ellipsoidal droplets with a protein-based active cytoskeletal gel, thus obtaining ellipsoidal core-shell structures. This system provides the appropriate conditions of confinement and geometry to investigate the impact of nonuniform curvature on an orderly active nematic fluid that features the minimum number of defects required by topology. We identify new time-dependent states where topological defects periodically oscillate between translational and rotational regimes, resulting in the spontaneous emergence of chirality. Our simulations of active nematohydrodynamics demonstrate that, beyond topology and activity, the dynamics of the active material are profoundly influenced by the local curvature and viscous anisotropy of the underlying droplet, as well as by external hydrodynamic forces stemming from the self-sustained rotational motion of defects. These results illustrate how the incorporation of curvature gradients into active nematic shells orchestrates remarkable spatiotemporal patterns, offering new insights into biological processes and providing compelling prospects for designing bioinspired micromachines.

中文翻译：

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椭球液滴各向异性表面上有源缺陷的动力学


我们使用实验和数值模拟研究了椭球体主动向列壳的稳态。我们通过用基于蛋白质的活性细胞骨架凝胶包被微小的椭球体液滴来制造壳，从而获得椭球核壳结构。该系统提供了适当的约束和几何条件，以研究非均匀曲率对有序活性向列流体的影响，该流体具有拓扑所需的最少缺陷数。我们确定了新的时间依赖性状态，其中拓扑缺陷在平移和旋转状态之间周期性地振荡，导致手性的自发出现。我们对活性线虫流体动力学的模拟表明，除了拓扑和活动之外，活性材料的动力学还受到底层液滴的局部曲率和粘性各向异性以及缺陷自持旋转运动产生的外部流体动力的深刻影响。这些结果说明了曲率梯度如何整合到活性向列壳中协调非凡的时空模式，为生物过程提供了新的见解，并为设计仿生微机器提供了令人信服的前景。