It is well-established that externally applied and endogenously generated mechanical forces are crucial regulators of the structure and function of numerous tissues including cartilage, tendons, ligaments, skin, blood vessels, lungs and the heart. In addition to the important role for these active mechanical components of the environment (i.e., forces and the resulting stresses and strains), it has become increasingly clear over the past decade that the passive mechanical environment (i.e., the local mechanical or material properties of the environment) also impacts cellular function. Based on the Principal Investigators? ongoing work in this area, a conceptual model explaining how the active and passive mechanical environments interact to regulate cellular function has been developed. The proposed studies will critically evaluate this model using two model biological systems - microvascular network formation by endothelial cells and morphological changes / differentiation of mesenchymal stem cells. These studies will utilize an extracellular matrix biomimetic developed by the applicants that allows for independent control of aspects of the active and passive mechanical environments within a three-dimensional cell-compatible setting. The major scientific goals of the proposed work are 1) to expand the capabilities of these existing extracellular matrix biomimetics as a tool to rigorously evaluate the conceptual model of cellular responses to active and passive mechanical environments and 2) to use the extracellular matrix biomimetics to answer important scientific questions related to how cells respond to their mechanical environments, and 3) to integrate research and education to train the next generation of biomedical engineering researchers in mechanobiology. Specific questions to be addressed, which cannot be answered with currently available materials, include the following: What are the independent contributions of matrix stiffness and matrix adhesiveness to cellular function in a 3D environment? For a given cell type in a 3D environment, why does the ideal stiffness for differentiated cell behavior appear to depend on the specific biomaterial? How are the effects of matrix stiffness modulated by cell-matrix adhesion and/or force generation by the cells? What molecular and cellular level processes are modulated by changes in the mechanical stiffness of the matrix and how do these molecular and cellular level processes contribute to observed changes in differentiated multi-cellular structures. The answers to these questions will be explored using microvascular network formation as the primary model system in the proposed studies. Since the formation of multi-cellular, branched microvascular networks involves many coordinated cellular behaviors (e.g., adhesion, elongation, migration, and cell-cell junction formation) important in other physiological, pathological, and tissue engineering settings, the knowledge gained from the proposed studies will likely translate to other important systems including the vascularization of engineered tissues. Additional work with mesenchymal stem cells will provide information about the interplay between the active and passive mechanical environments during cell differentiation in a second relevant cell system.
