Mapping the mechanome of live stem cells using a novel method to measure local strain fields in situ at the fluid-cell interface

During mesenchymal condensation, the initial step of skeletogenesis, transduction of minute mechanical forces to the nucleus is associated with up or down-regulation of genes, ultimately resulting in formation of the skeletal template and appropriate cell lineage commitment. The summation of these biophysical cues affects the cell's shape and fate. Here, we predict and measure surface strain, in live stem cells, in response to controlled delivery of stresses, providing a platform to direct short-term structure - function relationships and long-term fate decisions. We measure local strains on stem cell surfaces using fluorescent microbeads coated with Concanavalin A. During delivery of controlled mechanical stresses, 4- Dimensional (x,y,z,t) displacements of the bound beads are measured as surface strains using confocal microscopy and image reconstruction. Similarly, micro-particle image velocimetry (m-piv) is used to track flow fields with fluorescent microspheres. The measured flow velocity gradient is used to calculate stress imparted by fluid drag at the surface of the cell. We compare strain measured on cell surfaces with those predicted computationally using parametric estimates of the cell's elastic and shear modulus. Finally, cross-correlating stress - strain data to measures of gene transcription marking lineage commitment enables us to create stress - strain - fate maps, for live stem cells in situ. The studies show significant correlations between live stem cell stress - strain relationships and lineage commitment. The method presented here provides a novel means to probe the live stem cell's mechanome, enabling mechanistic studies of the role of mechanics in lineage commitment as it unfolds

Properties of water confined in hydroxyapatite nanopores as derived from molecular dynamics simulations

N.H. de Leeuw is grateful to ‘Université ParisEst Créteil’ (UPEC) for financial support received during the course of this research. T.T. Pham is grateful to the ‘Institut des sciences de l’ingénierie et des systèmes’ (INSIS) of the ‘Centre national de la recherche scientifique’ (CNRS) for financial support received during the course of this research. D. Di Tommaso would like to thank the Royal Society, UK, for the award of a Royal Society Industry Fellowship