[Spatial Constraints of Rectangular Hydrogel Microgrooves Regulate the Morphology and Arrangement of Human Umbilical Vein Endothelial Cells]

Objective

To construct microscale rectangular hydrogel grooves and to investigate the morphology and alignment of human umbilical vein endothelial cells (HUVECs) under spatial constraints. Vascular endothelial cell morphology and alignment are important factors in vascular development and the maintenance of homeostasis.

Methods

A 4-arm polyethylene glycol-acrylate (PEG-acrylate) hydrogel was used to fabricate rectangular microgrooves of the widths of 60 μm, 100 μm, and 140 μm. The sizes and the fibronectin (FN) adhesion of these hydrogel microgrooves were measured. HUVECs were seeded onto the FN-coated microgrooves, while the flat surface without micropatterns was used as the control. After 48 hours of incubation, the morphology and orientation of the cells were examined. The cytoskeleton was labelled with phalloidine and the orientation of the cytoskeleton in the hydrogel microgrooves was observed by laser confocal microscopy.

Results

The hydrogel microgrooves constructed exhibited uniform and well-defined morphology, a complete structure, and clear edges, with the width deviation being less than 3.5%. The depth differences between the hydrogel microgrooves of different widths were small and the FN adhesion is uniform, providing a micro-patterned growth interface for cells. In the control group, the cells were arranged haphazardly in random orientations and the cell orientation angle was (46.9±1.8)°. In contrast, the cell orientation angle in the hydrogel microgrooves was significantly reduced (P<0.001). However, the cell orientation angles increased with the increase in hydrogel microgroove width. For the 60 μm, 100 μm, and 140 μm hydrogel microgrooves, the cell orientation angles were (16.4±2.8)°, (24.5±3.2)°, and (30.3±3.5)°, respectively. Compared to that of the control group (35.7%), the number of cells with orientation angles <30° increased significantly in the hydrogel microgrooves of different widths (P<0.001). However, as the width of the hydrogel microgrooves increased, the number of cells with orientation angles <30° gradually decreased (79.9%, 62.3%, 54.7%, respectively), while the number of cells with orientation angles between 60°-90° increased (P<0.001). The cell bodies in the microgrooves were smaller and more rounded in shape. The cells were aligned along the direction of the microgrooves and corresponding changes occurred in the arrangement of the cell cytoskeleton. In the control group, cytoskeletal filaments were aligned in random directions, presenting an orientation angle of (45.5±3.7)°. Cytoskeletal filaments were distributed evenly within various orientation angles. However, in the 60 μm, 100 μm, and 140 μm hydrogel microgrooves, the orientation angles of the cytoskeletal filaments were significantly decreased, measuring (14.4±3.1)°, (24.7±3.5)°, and (31.9±3.3)°, respectively. The number of cytoskeletal filaments with orientation angles <30° significantly increased in hydrogel microgrooves of different widths (P<0.001). However, as the width of the hydrogel microgrooves increased, the number of cytoskeletal filaments with orientation angles <30° gradually decreased, while the number of cytoskeletal filaments with orientation angles between 60°-90° gradually increased (P<0.001).

Conclusion

Hydrogel microgrooves can regulate the morphology and orientation of HUVECs and mimic to a certain extent the in vivo microenvironment of vascular endothelial cells, providing an experimental model that bears better resemblance to human physiology for the study of the unique physiological functions of vascular endothelial cells. Nonetheless, the molecular mechanism of spatial constraints on the morphology and the assembly of vascular endothelial cell needs to be further investigated.

[Research progress on vascularization of organoids]

Organoids are three-dimensional structures formed by self-organizing growth of cells in vitro, which own many structures and functions similar with those of corresponding in vivo organs. Although the organoid culture technologies are rapidly developed and the original cells are abundant, the organoid cultured by current technologies are rather different with the real organs, which limits their application. The major challenges of organoid cultures are the immature tissue structure and restricted growth, both of which are caused by poor functional vasculature. Therefore, how to develop the vascularization of organoids has become an urgent problem. We presently reviewed the progresses on the original cells of organoids and the current methods to develop organoids vascularization, which provide clues to solve the above-mentioned problems.