Crowding tunes 3D collagen fibrils and reveals matrix regulation of cancer cell morphogenesis

It is well established that the collagenous extracellular matrix surrounding solid tumors significantly influences the dissemination of cancer cells. However, the underlying mechanisms remain poorly understood, in part because of a lack of methods to modulate collagen fibril topology in the presence of embedded cells. In this work, we develop a technique to tune the fibril architecture of cell-laden 3D collagen matrices using PEG as an inert molecular crowding agent. With this approach, we demonstrate that fibril length and pore size can be modulated independently of bulk collagen density and stiffness. Using live cell imaging and quantitative analysis, we show that matrices with long fibrils induce cell elongation and single cell migration, while shorter fibrils induce cell rounding, collective migration, and morphogenesis. We conclude that fibril architecture is an independent regulator of cancer cell phenotype and that cell shape and invasion strategy are functions of collagen fibril length.