Fig. 1.

Conceptual overview of the microspherical stress gauge (MSG) system. Soft (E ~ 0.15 kPa), compressible, and fluorescently labeled hydrogel microspheres can act as sensors of cell-generated mechanical stress. a Changes in the shape of MSGs embedded within model tissues can be used to determine the local cell- and tissue-generated mechanical stresses that arise during complex remodeling, such as during morphogenesis, development, or disease progression. In contrast with conventional traction force microscopy techniques, this approach can be applied to study forces in systems with dynamic tissue mechanical properties, which commonly occur during remodeling processes. b Measuring deformation of the hydrogel microspheres is sufficient to calculate the local isotropic and anisotropic stress components in the surrounding remodeling tissue. In a spheroid culture system, MSGs are expected to deform in a symmetry-simplified combination of axial and radial stresses. c To fabricate the hydrogel MSGs, aqueous polyacrylamide components and fluorescein methacrylate monomers were mechanically dispersed in an immiscible kerosene phase, and allowed to polymerize, producing d fluorescently labeled polydisperse MSGs (green; scale bar = 50 µm). e Functionalization of the MSG surface with collagen I (red) produces an extracellular matrix coating that is limited to the surface of polyacrylamide microspheres (confocal section of different sized beads shown), that facilitates incorporation of the MSGs into engineered tissues (scale bar = 25 μm)