Vascularization by endothelial cells (ECs) is an essential element in tissue-engineering of organoids. Morphogenesis of these cells is regulated not only by the biochemical properties of the extracellular matrix (ECM) but also by its mechanical properties. Here, we investigated the effect of substrate mechanical properties on the formation of capillary-like networks by ECs; in particular, we examined the three-dimensional (3D) configurations of the resulting networks. Bovine pulmonary microvascular ECs (BPMECs) were cultured on a series of collagen gels of different stiffness but the same collagen concentration. Imaging techniques revealed that cells cultured in rigid and flexible gels formed 3D networks via different processes; cells formed dense, thin networks in the flexible gel, whereas thicker and deeper networks were formed in the rigid gel. Cross-sections of the networks revealed that those formed within the rigid gel had large lumens composed of multiple cells, whereas those formed within the flexible gel had small, intracellular vacuoles. The expression of vinculin, a focal adhesion protein, appeared to change with the mechanical properties of collagen gel. Our results indicate that the mechanical properties of adhesion substrates play an important role in regulating 3D network formation.

Background and Purpose-Little attention has been focused on the role of fluid-induced wall shear stress in fully developed cerebral aneurysms. The purpose of this study is to evaluate the alternation and distribution of wall shear stress over 1 cardiac cycle in patients' aneurysms. Methods-A middle cerebral artery aneurysm and a basilar tip aneurysm with localized outpouching (blebs) in their domes were selected for this study. With the use of a stereo lithography machine, geometrically realistic aneurysm models were created on the basis of 3-dimensional CT angiograms. In vitro shearing velocity measurement was conducted with the use of laser-Doppler velocimetry at multiple points on the aneurysmal wall to calculate the value of wall shear stress. The wall shear stress was documented at multiple points in the aneurysm inflow zone, dome, and outflow zone. Results-Distribution of wall shear stress was not uniform in the aneurysm walls, and particular regions were exposed to relatively high wall shear stress. The wall shear stress changed dynamically throughout 1 cardiac cycle at the point where a high value of wall shear stress was noted. The blebs of both aneurysms were exposed to high wall shear stress. Unlike previous reports in which an ideal spherical aneurysm model was used, the aneurysm inflow zone was not exposed to high shear stress. Conclusions-In

Hemodynamic and biochemical factors play important roles in critical steps of angiogenesis. In particular, interstitial flow has attracted attention as an important hemodynamic factor controlling the angiogenic process. Here, we applied a wide range of interstitial flow magnitudes to an in vitro three-dimensional (3D) angiogenesis model in a microfluidic device. This study aimed to investigate the effect of interstitial flow magnitude in combination with the vascular endothelial growth factor (VEGF) concentration on 3D microvascular network formation. Human umbilical vein endothelial cells (HUVECs) were cultured in a series of interstitial flow generated by 2, 8, and 25 mmH 2 O. Our findings indicated that interstitial flow significantly enhanced vascular sprout formation, network extension, and the development of branching networks in a magnitude-dependent manner. Furthermore, we demonstrated that the proangiogenic effect of interstitial flow application could not be substituted by the increased VEGF concentration. In addition, we found that HUVECs near vascular sprouts significantly elongated in >8 mmH 2 O conditions, while activation of Src was detected even in 2 mmH 2 O conditions. Our results suggest that the balance between the interstitial flow magnitude and the VEGF concentration plays an important role in the regulation of 3D microvascular network formation in vitro .

This clear acrylic model of a BA tip aneurysm manufactured using a CT angiogram allowed qualitative and quantitative analysis of its flow during a cardiac cycle. Accumulated knowledge from this type of study may reveal pertinent information about aneurysmal flow dynamics that will help practitioners understand the relationship among anatomy, flow dynamics, and the natural history of aneurysms.