Elasticity and viscosity vary widely across tissues and are sometimes hypothesized to relate to collagen-fiber networks that differ in density among adult tissues and are absent in early embryos. Here, second-harmonic generation (SHG) imaging paired with supracellular viscoelasticity measurements shows the mechanics of live adult and embryonic tissues scale above gelation with collagen-fiber densities (with z≈ 1.4 power-law). Addition of ccollagenase establishes the point of network rigidity percolation, while inhibiting cell contractility triggers endogenous collagenous that reveals active strain-stabilization of collagen as an ECM sculpting mechanism in live tissue. For cell-rich soft tissues, scaling indeed aligns best with in vitro results for cellularized collagen-I gels, whereas stronger scaling for collagen-dense tissues such as tendon aligns best with acellular gels. Tissue cell densities and water content across tissues confirm the trends. We also note that nuclear Lamin-A protein and adhesion protein Vinculin scale weakly with collagen-I, and the former conforms to tissue-nucleus compliance-matching. The results reveal how viscoelasticity of tissue-spanning collagen-fiber networks are actively mechanoregulated and also mechanoregulate intracellular factors.
Dennis E. Discher (Sun,) studied this question.