Here’s a fun idea: what if we could improve on nature and create more efficient blood? Or at least, artificial blood that is as efficient as natural blood? The medical applications are too numerous and obvious to mention. There are two main approaches to artificial respiratory carriers—artificial ways of transporting oxygen and carbon dioxide around the body: one involves hemoglobin, the protein inside red blood cells that binds CO2 and oxygen. But hemoglobin becomes much less stable outside red blood cells, so various modifications or micro-encapsulations are required. The other approach involves emulsions of fluorocarbons. But both approaches have many inherent flaws.

In 1998, Robert A. Freitas proposed a radical idea: what if nanorobots could carry oxygen around, replacing red blood cells? Freitas’ design involves tiny nanoscale artificial cells fueled by blood sugar that store more than 200 times more oxygen per volume than red blood cells. A nanoengine drives a rotor that sorts molecules and stores the right kinds inside, while a tiny nanocomputer calculates when to release them. Augmenting your blood with a solution of Freitas’ “Respirocytes” could allow you to hold your breath for hours—useful for divers, patients who stop breathing away from hospitals, endurance runners, geriatric patients, and a whole lot more. Being nonbiological in nature, they could sit on the shelf indefinitely and still be ready to go, and once in the body could possibly last a lifetime.

Nanotechnology is far from the kind of precision and efficiency required to actually make respirocytes. And even if we could make them, no amount of theoretical calculations can tell us for sure how they’d behave in living humans. I’m not signing up to have my blood replaced by tiny robots anytime soon. But it’s certainly an interesting idea, if you can look at it with the appropriate amount of skepticism.