Analysis of early and late apoptosis and cell metabolic activity after injection through different gauge needles. Data are shown for viability measured immediately after injection of mesenchymal stem cells (n =3) in D10 through 19G, 20G or 21G needles and in non-injected controls (NI). (a) Annexin V-positive cells expressed as a percentage of the total cell population. (b) Propidium iodide-positive cells expressed as a percentage of the total cell population. (c) Metabolic activity of mesenchymal stem cells measured by alamarBlue® (AbD Serotec, Kidlington, UK) assay.