Surface functionalization modulates collective cell behavior at integer topological defects

Living cells establish long-range orientational order through collective alignment, giving rise to topological defects whose functional relevance is increasingly recognized in tissue organization and morphogenesis. Engineered topographical patterns have been used to induce such defects in cell monolayers, mimicking natural biological phenomena. In this work, we investigate the effect of cell-surface adhesion on collective cell dynamics at a vortex integer topological defect imposed by a topographical ring pattern. Adhesion strength is controlled via surface functionalization with poly-D-lysine, fibronectin, or covalently bonded fibronectin, and quantified using atomic force microscopy. As surface chemistry is modified, cell morphology changes from irregular to spindle-like, and two distinct collective modes emerge: weakly adhered cells exhibit strong inward motion, while strongly attached cells move tangentially to the ring. Spindle-shaped cells exhibit higher nematic order and promote the emergence of two +1/2 topological defects in the monolayer. We further characterize collective cell dynamics by analyzing correlation lengths and demonstrate the scaling of number density fluctuations in cell systems.