Effects of geometry and structural constraints on the mechanics of 3D engineered microtissues

The structure of the extracellular matrix (ECM) in living tissues plays a critical role in facilitating numerous cellular functions. Hence, understanding and controlling the ECM structure is crucial for modeling various mechanobiological and wound healing processes. We have developed a platform to control ECM alignment in engineered microtissues, while simultaneously measuring their mechanical properties. Tissues are self-assembled from cell-laden collagen gels in microfabricated wells with protruding elastic pillars. The pillars control tissue shape and measure contractile forces. Magnetic material attached to one pillar per well allows application of tensile strain via a magnetic tweezer. Optical tracking of the pillars’ positions and the tissue’s local deformations provides readouts of force generation and the displacement field. Fibroblast populated microtissues grown on elongated isosceles triangular pillar geometries show aligned ECM and increased stiffness compared to microtissues with isotropically organized ECM grown on octagonal pillar structures. Finite element linear elastic modeling of the force and displacement data at low strains provides quantitative measures of the effective elastic moduli, and their spatial variation across the different microtissue geometries.