Early Engineered Blood Vessels

Researchers are presently trialing a first generation of tissue engineered blood vessels, and as expected it's at least as good - and probably better - than the other artificial alternatives presently available:

They start by harvesting skin cells known as fibroblasts and growing these in a sheet. They then roll up the sheet and allow the cells to produce an interpenetrating mixture of structural support proteins, known as collagen and elastin.

The trouble with fibroblasts is that they can transform into smooth muscle cells that can eventually clog the vessel. So McAllister's team removed the fibroblasts, leaving behind just the protein scaffold. Then the researchers layered another sheet of fibroblasts on the outside of this scaffold, which is dense enough to prevent the cells from easily migrating to the inside of the engineered vessel. Finally, the team added a layer of the patient's own endothelial cells, which promote smooth blood flow, on the inside of the vessel.

Would the new vessels work? In the current study, McAllister's team implanted them into 10 kidney dialysis patients in Argentina and Poland, all of whom had suffered previous graft failures. Grafts in three patients failed in the first 3 months, a failure rate consistent with a high-risk population, the researchers report today in The Lancet. Two other patients didn't finish the study for reasons unrelated to the grafts. In the remaining five patients, the engineered grafts functioned normally to the study's conclusion, which was between 6 months and 20 months, depending on when the patients enrolled. The ongoing success of the engineered shunts bodes well, McAllister says, because close to half of all plastic shunts fail within 1 year of implantation.

The downside is that this really is a first generation technology - it's very expensive, due to the time taken to grow, and as presently implemented doesn't look like it will scale to tackle the really serious issues revolving around blood vessels in tissue engineering:

Unless you have a way of putting the blood vessels where they need to be, at every scale, or convincing blood vessels to grow according to plan, you simply can't engineer significantly sized pieces of tissue.

A method like the successful one above, wherein manufacturers essentially hand-roll each new section of blood vessel you need, won't scale to stocking new tissue with capillaries. But one step at a time.

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