Mechanical stress stimulates RhoA a

Mechanical stress stimulates RhoA activation and F‐actin filaments assembly in CTCsWe noticed that when the CTCs entering the host capillaries, they were greatly elongated (Fig. 2a and Supporting Information Fig. S4). Such slenderized cells were suffering from extremely high mechanical stress from vascular luminal walls when passaging through these narrow straits. In fact, many researchers have reasoned that mechanical stress was an important parameter controlling the cell function and behaviors, which include but not limited to cell shape, cell invasion ability, differentiation and even immunogenicity.22, 23 To test whether the mechanical stress from the capillaries was associating with F‐actin assembly in CTCs, we designed a blood capillary‐like micropore arrays (200 × 200 pores, pore diameter = 8 μm, thickness = 100 μm), which was printed using a DLP‐based bioprinter–DOPsL with photopolymerizable poly(ethylene glycol) diacrylate (PEGDA).24 B16 tumor cells were then pushed passing through the 3D printed strains at the same rate as they entered the zebrafish trunk capillaries (∼10 μm/min in our setting) (Figs. 4a and 4b). The squeezed tumor cells were floating cultured in ultra‐low attachment culture dish for 4 hr with or without the treatment of Rho kinase inhibitor (Y‐27632, 2 μM). Then the floating cells were spun down using cytospinTM on microscope slides and stained using Rhodamine‐phalloidin. To avoid the potential effect of cytospinning on the rounding of cells, cells were fixed immediately (