It seems reasonable to expect artificial red blood cells to be widely available in the not too far future. A variety of methodologies have been tried with some success or are presently under development. As the capabilities of nanoscale engineering improve, artificial substitutes for blood cells will only become better. Here is an example of the present cutting edge:
Real red blood cells owe their astonishing agility to their "biconcave" or tyre-like shape. To create synthetic particles with the same agility, Samir Mitragotri of the University of California and his team got their inspiration from the way real red blood cells acquire their final shape in the body.
They start out as spherical cells which then collapse into mature red blood cells following exposure to various substances. Similarly, Mitragotri's team found that if they added small balls made of a polymer called PLGA to a particular solvent, the spheres would collapse into a biconcave shape.
The researchers coated these 7-micrometre across, tyre-shaped particles, in a layer of protein. When they dissolved away the polymer core, a soft biodegradable protein shell was left behind with the same mechanical properties as red blood cells.
When you're building cell-substitutes from scratch the opportunity exists to make them better than the real thing in some regards. For example, giving these artificial cells the ability to carry more oxygen than actual blood cells seems like a very plausible goal. I'm sure you can imagine other enhancements well within the capabilities of today's biotechnology: drug delivery, resistance to infection, control of inflammation, and so forth. But even enhanced delivery of oxygen on its own is a platform that might be capable of slowing the onset of some age-related disease - such as vascular dementia and other conditions related to reduced blood flow in small blood vessels.
Looking further ahead, to the era of medical nanomachinery and synthetic biology that will arrive later this century, red blood cell replacements that are hundreds of times more effective than the real thing are quite possible and plausible:
Each respirocyte can store and transport 236 times more oxygen than natural red blood cells. It can also monitor carbon acidity in the cell. Filled with these respirocytes, an adult human could hold his/her breath underwater for four hours. That person could also sprint at top speed for at least 15 minutes without taking a breath.