A not-so-hard graft
Transplantable blood vessels can now be grown as desired
ANOTHER advance in the emerging technology of regenerative medicine has just been announced. It should soon be possible to make blood vessels that can be stored and used “off the shelf” for surgery that requires arteries or veins to be bypassed. The vessels, prototypes of which are described this week in a paper in Science Translational Medicine, are made by Humacyte, a small firm based in Durham, North Carolina, that was founded by Shannon Dahl, the paper's principal author, and two colleagues.
The recipe Dr Dahl and her colleagues concocted begins with smooth-muscle cells. Smooth muscle is different from the familiar sort that cloaks bones and enables bodily movement. It is a component of organs such as the gut and the blood vessels that sometimes need to change shape while they are functioning.
To make artificial blood vessels the team took smooth-muscle cells from fresh corpses and cultured them on tubular scaffolds made of a material called polyglycolic acid. Grown this way, smooth muscle secretes collagen, a structural protein that is, among several other things in the body, an important component of the walls of blood vessels. The polyglycolic acid degrades spontaneously over the course of a few weeks with the consequence that it is, in effect, replaced by the collagen. The result is a tube of the length and diameter of the original scaffold, that is composed of collagen and smooth-muscle cells—a structure similar to a natural blood vessel.
Transplanting that into a patient, however, would risk provoking an immune reaction, since the muscle cells are “foreign” tissue. To get around this, Dr Dahl and her colleagues wash the muscle cells away with a detergent, leaving just the collagen. Though the end product is a nonliving simulacrum of a blood vessel rather than an artificial version of the real, biologically active thing, experiments on animals suggest that it works well enough to substitute for a diseased natural vessel (for example, a clogged coronary artery that might otherwise cause a heart attack). It can also act as a “tap” from which the blood of people whose kidneys have failed might be drawn for dialysis.
At the moment, the options for either of these things are limited. The best approach is to use a length of vessel taken from elsewhere in the patient's body (commonly, his leg). But that requires such transplants to be healthy themselves—and each length of transplanted vessel can be used only once. Synthetic vessels made of Teflon exist, but they are prone to infection and blockage by blood clots, and tend to work for only a few months.
The animal experiments suggest the new, all-collagen vessels are capable of lasting at least a year without noticeable deterioration. They are also, once implanted, able to remodel themselves in ways that improve their function—changing shape in response to blood flow, being colonised by cells from the patient's body, and showing signs of incorporating elastin, another structural protein found in natural vessels.
Also, if kept in a suitable saline buffer at 4°C, they can be transplanted a year after they were made without a perceptible degradation of their properties. So, if human trials confirm these results, the surgical-repairer's toolkit will have acquired a useful additional instrument—and the age of the cyborg will be just that little bit nearer.
From the print edition: Science and technology