Micro-mold Design Controls the 3D Morphological Evolution of Self-assembling Multicellular Microtissues

When seeded into nonadhesive micro-molds, cells self-assemble three-dimensional (3D) multicellular microtissues via the action of cytoskeletal-mediated contraction and cell-cell adhesion. The size and shape of the tissue is a function of the cell type and the size, shape, and obstacles of the micro-mold. In this article, we used human fibroblasts to investigate some of the elements of mold design and how they can be used to guide the morphological changes that occur as a 3D tissue self-organizes. In a loop-ended dogbone mold with two nonadhesive posts, fibroblasts formed a self-constrained tissue whose tension induced morphological changes that ultimately caused the tissue to thin and rupture. Increasing the width of the dogbone's connecting rod increased the stability, whereas increasing its length decreased the stability. Mapping the rupture points showed that the balance of cell volume between the toroid and connecting rod regions of the dogbone tissue controlled the point of rupture. When cells were treated with transforming growth factor-β1, dogbones ruptured sooner due to increased cell contraction. In mold designs to form tissues with more complex shapes such as three interconnected toroids or a honeycomb, obstacle design controlled tension and tissue morphology. When the vertical posts were changed to cones, they became tension modulators that dictated when and where tension was released in a large self-organizing tissue. By understanding how elements of mold design control morphology, we can produce better models to study organogenesis, examine 3D cell mechanics, and fabricate building parts for tissue engineering.