They might look like sperm swimming backwards, but red blood cells have become the first living cells to be fitted with an artificial tail. As the tail whips back and forth, the cell moves tail-first at a cool 6 micrometres per second - about 10 times as slow as sperm swim.
The secret to the cell's motion lies in the composition of the tail - a filament of tiny magnetic beads held rigidly together by strands of DNA. When an oscillating magnetic field is applied to the cells, they move through the fluid as their tails bend to align themselves with the constantly reversing direction of the magnetic field. The microscopic swimmers might one day provide a way to direct medicines through the bloodstream to exactly the right spot.
Respirocytes - Designing an Artificial Red Cell
An artificial nanomedical erythrocyte, or "respirocyte" -- intended to duplicate all of the important functions of the red blood cell -- could serve as a universal blood substitute, preserve living tissue, eliminate "the bends," allow for new sports records, and provide treatment for anemia, choking, lung diseases, asphyxia, and other respiratory problems. [...]
The maximum safe augmentation dosage is probably about 1 liter of 50% respirocyte suspension, which puts 954 trillion devices into your bloodstream. You could then hold your breath for 3.8 hours, at the normal resting metabolic rate. At the maximum human metabolic rate, something like a continuous Olympic-class 50-meter dash exertion level, you could go for a full 12 minutes without taking a breath. Afterwards, your entire capacity is recharged by hyperventilating for just 8 minutes - then you're ready to go again. [...]
By sacrificing one entire natural lung to make room in the thorax, a 3250 cm3 nanolung extends oxygen supply to 4-87 hours. A less-conservative nanolung design could allow you to survive for up to 5 days without drawing a breath. [...]
Respirocytes can also relieve the most dangerous hazard of deep sea diving - decompression sickness ("the bends") or caisson disease, caused by the formation of nitrogen bubbles in blood as a diver rises to the surface. These bubbles come from gas previously dissolved in the blood at higher pressure at greater depths. Safe decompression procedures normally require up to several hours. But a small therapeutic dose of respirocytes reconfigured to absorb nitrogen instead of O2/CO2 gases could allow safe and complete decompression of an N2-saturated human body from a depth of 26 meters (86 feet) in as little as 1 second.