Stem cells. Coloured scanning electron micrograph (SEM) of human embryonic stem cells (HESCs) that have formed into a horizontal strand. HESCs are pluripotent, which means that they are able to differentiate into any of the 200 cell types in the human body. The type of cell they mature into depends upon the biochemical signals they receive, though the cells seen here have not been exposed to growth factors. HESCs are being studied as a way to repair damaged tissue in diseases such as diabetes and Parkinson's. These cells were grown in 2005 at the Centre for Life, Newcastle Upon Tyne, UK. Magnification: x2100 when printed 10cm wide.