Biologically, this makes sense. Evolution spent an awful lot of time and energy wrapping hemoglobin in a membrane. But so far in animal studies, the immune system rapidly seeks and destroys these neohemocytes. Brave New Blood Vessels Delivery of blood through open vessels is crucial to cardiovascular function. Block a vessel with plaque or a clot, and blood flow backs up, robbing nearby tissues of vital oxygen.
Blood can only flow through a smooth conduit.
So far, none of the several methods to unclog or replace blocked arteries keeps them smooth indefinitely. Plaque that is scraped away or pressed against the artery wall recurs. A transplanted blood vessel may provoke the recipient's immune system to reject it, and taking a vessel from the patient's own body involves surgery at two sites rather than just one. Synthetic blood vessels cause problems too. No small-caliber, synthetic vascular graft presently exists that will remain unplugged by blood clots.