Medical researchers have made a lot of progress developing artificial versions of organs like the heart, lungs and kidneys, but one thing has stumped them: artificial blood.
Blood is especially hard to recreate because it does so many things, from carrying oxygen to helping the immune system to heating and cooling the body.
Now, some Missouri researchers may have taken a big step forward in creating artificial blood. But the question remains: Will  science ever be able to replace the real thing?