Blood is an awkward commodity: hard to collect, highly perishable, prone to carry infections and tricky to transport.

These drawbacks have inspired a half-century of research into blood substitutes, funded principally by the US military. What is required is a lightweight substitute that needs no refrigeration and can be reconstituted on the battlefield by adding water — the blood equivalent of freeze-dried rations.

So far, the best bet has been a plastic-based artificial blood that holds a substitute for haemoglobin — the oxygen-carrying molecule — at the core. Might a blood created from stem cells provide a better alternative? It would avoid several of the drawbacks of donated blood.

Blood donation in healthcare systems such as the NHS has to be timely, since blood has a short shelf life. Maintaining an army of willing donors is critical.

A lab-based system of creating red blood cells from stem cells might provide a more flexible production line, especially for blood that can be used for any recipient without matching. The risks of transmitting viral diseases could be eliminated.

However, unlike the plastic substitutes, the cells produced would be living and would need careful handling. So while production might be simpler — and even possibly cheaper — use would be subject to the same limitations as red blood cells extracted from whole blood.

Unfortunately, blood would still need to be donated for the white cells and plasma fractions. So blood donation systems would have to be kept running, with red cells as essentially a waste material. That could undercut any market for the red blood cells derived from stem cells. So even if the science goes well, economics could prove a significant barrier.

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