Light microscope images of human mesenchymal stem cells. Images taken at the end of the experiment showing the human mesenchymal stem cells in culture 7 days after heat treatment at 48°C for 150 seconds (a), (b) and at 58°C for 45 seconds (c), (d). Normal spindle morphology with cell interactions can be seen after treatment at 48°C for 150 seconds, whereas cell damage is clear 7 days after heat treatment at 58°C for 45 seconds with only cell debris remaining. The threshold for cell survival lies between these two conditions of heat exposure. (a), (c) Scale bar = 500 μm. (b), (d) Scale bar = 250 μm.