PROJECT SUMMARY Cells and tissues are mechanosensitive. Many and tissues, including the liver, are subjected to mechanical stresses deformed over multiple time and length scales; these can both be altered in disease and drive disease.We have used in vitro experimentation and theory to show that tissue mechanics are an emergent property, arising from and requiring three components: the complex fibrous network of the extracellular matrix (ECM), the cells within that network, and the forces applied to the combined system. Our work in the three years of the past project period has specifically examined the microarchitecture and features of complex fibrous networks, the role of cytoplasmic inclusions and cytoskeletal networks on cell mechanics, and the impact of viscoelasticity on cell and tissue behavior. Collectively, this work has resulted in the development of a multi-axial model of a tissue. Notably, however, while significant strides have been made in understanding tissue elasticity, viscous dissipation and plasticity have been little studied, and the relationship between mechanics and structure – to the point that one can be predicted from the other – remains poorly understood. The overall goal in this competing renewal proposal is to demonstrate the in vivo applicability and predictive value of the concepts we have defined. Specifically, we propose to determine the contribution of the individual components of tissues to emergent tissue mechanics and the impact of these mechanics on cell behavior. Our model tissue in this proposal, as in previous project periods, is the normal, fibrotic, and cirrhotic liver. although our findings will be generally applicable to other organs in the body. We hypothesize that tissue mechanics including viscous dissipation can be described and predicted by integrating the features of the ECM fibrous network, the cells, and the applied forces. There are three specific aims: 1) to determine the relationships between matrix structure and viscous dissipation, elasticity, and plasticity in normal and diseased tissue; 2) to determine the impact of cell properties and cell-matrix organization on tissue mechanics, particularly viscosity; and 3) to measure tissue solid stress and interstitial fluid pressure in normal and diseased tissue and to define the impact of these forces on tissue mechanics, including dissipation. These specific aims will use experimentation and theory as well as machine learning approaches to predict the relationship between structure and mechanics, guide interventions, and generate a unified and therapeutically- targetable model of tissue mechanics in disease. We have previously identified many of the design principles underlying tissue mechanics. In the proposed work, we will further define the critical components of the three elements underlying tissue mechanics, asking whether we can predict mechanics (and their effects on cells and metabolism) from structure. This proposal thus has the potential...