Cells communicate through the extracellular matrix (ECM) in many physiological and pathological processes. This is particularly important during cell migration, where cell communication can alter both the speed and the direction of migration. However, most cell culture systems operate with large volumes relative to cell numbers, creating low cell densities and diluting factors that mediate cell communication. Furthermore, they lack the ability to isolate single cells or small groups of cells. Droplet forming devices allow for an ability to embed single or small groups of cells into small volume segregated 3D environments, increasing the cell density to physiological levels. In this paper we show a microfluidic droplet device for fabricating 3D collagen-based microtissues to study breast cancer cell motility. MDA-MB-231 cells fail to spread and divide in small, thin chambers. Cell migration is also stunted as compared to thick 3D gels. However, larger chambers formed by a thicker devices promote cell spreading, cell division and faster migration. In the large devices, both cell-ECM and cell-cell interactions affect cell motility. Increasing collagen density decreases cell migration and increasing the number of cells per chamber increases cell migration speed. Furthermore, cells appear to sense both the ECM-chamber wall interface as well as other cells. Cells migrate towards the ECM-chamber interface if within roughly 150 μm, whereas cells further than 150 μm tend to move towards the center of the chamber. Finally, while cells do not show enhanced movement towards the center of mass of a cell cluster, their migration speed is more variable when further away from the cell cluster center of mass. These results show that microfluidic droplet devices can array 3D collagen gels and promote cell spreading, division and migration similar to what is seen in thick 3D collagen gels. Furthermore, they can provide a new avenue to study cell migration and cell-cell communication at physiologically relevant cell densities.

This paper reports, for the first time, an optimized microfluidic droplet device for fabricating 3D microtissues and studying the cell behaviors in 3D microtissues. It has been found by properly selecting the size of the microchambers on the microfluidic device and choosing an optimal concentration of collagen (2 mg/ml) to fabricate microtissues, the behaviors of cells in the microtissues can be essentially the same as those of cells in a conventional cell culture system. The normal cell spreading and division in the microtissue have been observed, and the cell migration speed is ~14.1 μm/hr, close to that of 17.3 μm/hr in a macroscale tissue. All these experimental results suggest the microfluidic droplet device might provide a new avenue to replace other approaches to fabricate 3D microtissues and study cell behaviors.

The original version of this article unfortunately contained a mistake. One line indicating statistical significance was improperly placed in Fig. 5.