Abstract - Hydrogels are widely used in cell cultures and microfluidic organ-on-chip devices as a mimic for an extracellular matrix. Soft and porous, they provide a gentle scaffold for the cell colonies to develop into properly structured tissues and organoids. A key factor in this process is the transmission of forces through the hydrogel, originating from the flowing perfusate and propagating toward and among the cells. Such forces serve as mechanical cues in the proliferation and differentiation of cells and in their aggregation into functional organoids. In this work, we use a poroelastic model to study the mechanical interaction among cells that is mediated by the hydrogel. The model predicts that closely spaced cells induce the formation of prominent "tension ribbons" within the hydrogel, actively pulling neighboring cells together and prompting the development of mutual protrusions. In larger cellular arrays, the deformation patterns become highly heterogeneous, strongly dependent on the relative positions of individual cells. These insights provide valuable guidance for optimizing the design and operational parameters of organ-on-chip devices.