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The embryo divides into more and more cells and forms a hollow ball of cells called a blastocyst
3 5 TO 7 DAYS
Embryonic stem cells begin to form along the inside of the blastocyst, creating the inner cell mass
4 STEM LINE
The cells are scraped away and grown on a layer of feeder cells and culture medium
5 TISSUE PRODUCTION
Groups of stem cells are nurtured under specialized conditions, with different recipes of nutrients and growth factors that direct the cells to become any of the body's more than 200 various tissues Pancreatic islet cells Could provide a cure for diabetes
Muscle cells Could repair or replace a damaged heart
Nerve cells Could be used to treat Parkinson's, spinal-cord injuries and strokes TIME Graphic