Elucidating the mechanical milieu of stem cells in situ and delivering mechanical signals to direct cell fate in tissue engineering scaffolds

New approaches to tissue engineering aim to exploit endogenous strategies such as those occurring in prenatal development and recapitulated during postnatal healing. Defining tissue template specifications to mimic the environment of the condensed mesenchyme during development allows for exploitation of tissue scaffolds as delivery devices for exogenous and endogenous cues, including biochemical and mechanical signals, to drive the fate of mesenchymal stem cells seeded within. Although a variety of biochemical signals that modulate stem cell fate have been identified, the mechanical signals conducive to guiding pluripotent cells toward specific lineages are less well characterized. Furthermore, not only is spatial and temporal control of mechanical stimuli to cells challenging, but also tissue template geometries vary with time due to tissue ingrowth and/or scaffold degradation. Recent studies show that delivery of cell volume changing dilational (compression, tension) stresses and cell shape changing deviatoric (shear) stresses can be controlled, through cell seeding density and protocol as well as fluid flow, in immature tissue templates designed to mimic mesenchymal condensations. Taken as a whole, these previous studies present an unprecedented opportunity to engineer immature tissue templates that heal and mature, integrating seamlessly with surrounding tissues after implantation in defect zones. I hypothesize that stem cells adapt to mechanical, i.e. shape and volume changing, cues in their environment. Furthermore, I hypothesize that the adaptation of stem cell structure to prevailing mechanical functional demands relates significantly to cell differentiation and maintenance of phenotype. Hence, I, firstly, elucidate the mechanical milieu of seeded stem cells at a subcellular length scale using Computational Fluid Dynamics modeling (CFD) to predict forces at cell boundaries, as well as micro-particle imaging velocimetry to measure forces at cell boundaries. I, secondly, test the hypothesis that stem cells adapt to density and flow induced shape and volume changing stresses through imaging strain fields at fluid-cell interfaces using 2D and 3D geometries of scaffolds. We, finally, test the hypothesis that delivery of precise mechanical cues inducing stem cell shape changes correlate significantly with stem cell fate commitment using 2D and 3D geometries of scaffolds.