Organoid. Coloured scanning electron micrograph (SEM) of a neural organoid (courtesy of Sam Jackson). An organoid is a culture system composed of free-floating clusters of neural stem cells overlying evolving neurones (purple). Since neural stem cells cannot be studied in vivo ( within the body), organoids provide a method to investigate neural precursor cells in vitro (outside the body). Neural stem cells that are transplanted are able to cross the blood-brain barrier and integrate themselves into the host's brain without disrupting normal function. This therapeutic application of neural stem cells derived from organoids is still in its infancy with respect to efficacy, but it has a high potential for success in treating many diseases. Magnification: x300 when printed at 10 centimetres wide.