Shape that matters: Yolk geometry spatially modulates developing vascular networks within chick chorioallantoic membrane

Controlling the multiscale organization of vasculature within diverse geometries is essential for shaping tissue-specific and organ-specific architectures. Nevertheless, how geometrical characteristics of surrounding tissues influence vessel morphology and blood flow remains unclear. Where the regulation of vascular organization by mechanical signals associated with fluid flow is well known, this study postulates that the organization of developing vasculature can also be regulated by mechanical signals connected to the confinement and thus the deformation of surrounding tissues. To test the Shape-Induced Vascular Adaptation (SIVA) concept, fertilized chicken egg contents containing developing vasculature were cultured within engineered eggshell platforms of different shapes. Our findings demonstrate that the vascularized chick chorioallantoic membrane (CAM) adapts to the shape of engineered eggshell, long before reaching its boundaries. This adaptation affects the organization of the vascular network within the CAM, affecting parameters such as vessel area, branching, orientation, length, diameter and endpoints. Specifically, we observed that sharp corners in the engineered eggshell led to more elongated vascular structures. To further explore the dynamic nature of this phenomenon, a proof-of-concept experiment was performed using a shape-shifting engineered eggshell that deforms the egg content from circle to square shape. Using this shape-shifting prototype, we observed a direct effect of eggshell deformation on the vessel morphology and flow dynamics in a time-dependent manner. Overall, our exovo experimental platform provides a unique opportunity to study how mechanical stimuli such as shape influence the spatial and temporal organization of developing vascularized tissues. By subjecting these tissues to various static and dynamic conditions, we induced both local and global changes in their organization. This class of perturbation provides us with an additional tool which can be used for shaping vascular organization within developing tissues and to engineer tissues with geometrically tunable vessel structures.