I do know which one is safer, as to gain access to blood you have to gain access to a vein, likely by inserting a small tube made of [something] inside the vein, expect it to never break down and enter the bloodstream, become compromised, or be hit with an impact and tear the vein open to create internal bleeding. Then you also have to have a system to get rid of the waste blood (everything but the small amount of oxygen you want) all entirely within a closed system implanted into the arm, thigh, etc.

Artery - not a lot of O2 in veins.

But other than nitpicking defensively, I agree those good points. I'd still like to see what any actual bio-whatever engineers have to say.

> Another possibility, which could prevent the need for immunosuppressive drugs, is to encapsulate the transplanted cells within a flexible device that protects the cells from the immune system. However, finding a reliable oxygen supply for these encapsulated cells has proven challenging.

Hemoglobin is a large molecule. It is difficult to create a barrier that allows it to pass without also allowing in anti-bodies. Trying to extract the oxygen outside of the barrier and that pass just the oxygen through is theoretically another approach. But at that point, doing the same thing with water instead of hemoglobin is just easier.