PROJECT SUMMARY Mesenchymal stem/stromal cells (MSCs) have transformative healthcare potential, but to achieve therapeutic cell numbers, MSCs must be culture expanded. On tissue culture poly(styrene), however, MSC expansion is constrained by replicative senescence, and cells experience progressive loss of therapeutic potency with continued expansion. The lack of large numbers of reliably potent therapeutic cells is considered one of the most critical roadblocks to the success of MSC clinical trials. However, screening of improved MSC culture conditions has been hampered by the fact that there are no characterization tools that might allow prediction of cell fitness early in culture. Metabolism is the most dynamic level of cellular response, and metabolomics may enable the identification of early signatures associated with optimal cell product quality. Therefore, it is hypothesized that early metabolomics data from MSCs cultured on biomaterials will allow prediction of cell fitness later in culture and thus promote development of materials to promote a desired cell phenotype during expansion. The objective of this application is to determine the relationship between biomaterial carrier properties, cell metabolism, and maintenance of MSC fitness during expansion. This objective will be approached through the following specific aims: 1) Evaluate the effects of altering ligand type and stiffness of the biomaterial substrate on metabolism and replicative senescence of human MSCs during expansion in serum, and 2) Evaluate the effects of the substrate heparin content and pattern of initial seeding on metabolism and replicative senescence of human MSCs during expansion in serum-free conditions. The proposed work is innovative because it uses early cellular metabolic responses to design material substrates that will promote cell expansion without senescence in a range of media compositions. Results from these studies are expected to have an important positive impact because they will lead to more efficacious expansion protocols for MSCs and thus produce more effective cell-based therapies for a wide variety of diseases.