Researchers have successfully used spinach leaves to build functioning human heart tissue, complete with veins that can transport blood.

To tackle a chronic shortage of donor organs, scientists have been working on growing various tissues and even whole organs in the lab. But culturing a bunch of cells is only part of the solution — they simply won’t thrive without a constant blood supply.

It’s notoriously difficult to build a working network of fine blood vessels (also called vasculature), especially when you get down to capillaries, which are only 5 to 10 micrometres wide. Blood vessels transport the oxygen and nutrients that a lab-grown tissue sample needs to grow and function.

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