(602d) Rheology of Adult Stem Cells and Modelling of Flow Induced Deformation

Injection of stem cells for regenerative therapies requires optimal pressure to efficiently deliver cells, but inadequate designs of devices for injection can generate elevated stresses on cells resulting in altered cell response and cell death. However, few studies have examined rheological properties of stem cells to see how these cells deform and rupture under strain. In this study we measure the viscoelastic properties of different types of adult stem cells: mouse and human hematopoietic stem cells, mouse neural stem cell spheres, and human mesenchymal stem cells. We use a combination of fluorescence microscopy and micropipette aspiration to image the deformation of live cells and subcellular components, such as the nucleus. In stem cells, more so than differentiated cells, the nucleus contributes to the overall mechanics due to the high nuclear to cytoplasmic ratio and poorly developed cytoskeletal structure. We quantify elastic, viscoelastic and rupture strain from micropipette aspiration for these cells. We find variation among cells and among cell types (about 60% difference among cell types), but the adult stem cells studied are much softer than reported values for differentiated cells, as expected. We are incorporating this experimental data into 2D and 3D fluid-structure interaction models of flow-induced stem cell deformation to simulate injection systems, which we hope to then use to optimize injection pressures and possibly system design. Also, we will examine the long-term effects of injection shear stress on stem cell differentiation to better determine long-term cell effects of shear stress.