Viscoelasticity during development: What is it? and why should you care?

Viscoelasticity is a fundamental feature of biological tissues and plays a vital role in cells and tissues. This review explores the role of viscoelasticity in mechanobiology, emphasizing its impact on morphogenesis and organogenesis during embryonic development. We discuss the viscoelastic behavior of cells and tissues and its role in how cells and tissues absorb, dissipate, and transmit mechanical energy. We summarize experimental techniques such as Atomic Force Microscopy (AFM), Micropipette Aspiration (MA), and Tissue Stretchers, that have been used to quantify or observe the effects of viscoelasticity. Mathematical models of viscoelasticity, such as the Standard Linear Solid (SLS) model and advanced fractional models are introduced and discussed for their ability to capture the complexity of the viscoelastic behavior of biological systems. The role of subcellular complexes, including the cytoskeleton, extracellular matrix, and nucleus, are also reviewed for their contributions to tissue viscoelastic behavior. We also identify and discuss knowledge gaps, particularly in understanding how dynamic mechanical cues influence viscoelastic responses across cellular and tissue scales. A deeper exploration of these mechanisms, particularly those that determine viscoelastic behavior of cells and tissues, is needed for advancing our understanding of embryonic development and tissue morphogenesis.