You've read about the scientists who grew human blood vessels in mice using progenitor cells, right? Another team of scientists have also created blood from scratch, this time using stem cells.

And it's not just any kind of blood, too. Scientists from the Mayo Clinic and University of Illinois "literally generated whole tubes" of type O-negative blood, a rare blood type that doesn't follow the blood type match rule in blood transfusions, meaning it can be transferred to anyone regardless of the recipient's blood type.

The technique is still in its preliminary stages, though, and according to the Red Cross, there's still a lot of work to be done in order to bring the cultured cells to a stage where they're fully equivalent to natural cells.

Still, this proves really promising, seeing as how only 7 percent of the world's population has type O-negative blood. You can probably imagine the supply problems blood banks are dealing with here.

Then again, these are stem cells we're talking about, so the ethics question is still there. Dr. Robert Lanza, who headed the research, offers a workaround, though: the process could also work with stem cells produced by de-differentiation, an ethically trouble-free process where adult cells are regressed into an embryonic state.

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