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Genetic Linkage

A Living Blood Vessel "Stamp"

I still marvel at the interface between a tissue and an organ, even after a quarter century of writing college biology textbooks.

I can easily envision a sheet of epithelium folding itself up into the tiny tube of a capillary. But how do only four basic tissue types connect and contort to fashion such exquisitely eclectic living structures as a bone or a spleen, or the impossibly complex architecture of a lung or heart?

How can a kidney, which resembles from the outside the simple eponymous chili staple, be so incredibly organized on the inside, packed with a million nephrons, aligned by their twists and turns, running into a drainage system that expels wastes, yet shipping back to the bloodstream nearly anything of use?

Breaking the challenge down to its component parts doesn’t, at least to me, tell the whole story.

Cells specialize and grab onto others like themselves, forming tissues, in response to signals, such as hormones and growth factors, or by recognizing compatible surface features. Induced pluripotent stem cells are providing glimpses of that process gone awry, via “diseases-in-a-dish” experiments. And the field of tissue engineering has provided all sorts of replacement parts, with varying degrees of synthetic and borrowed-from-the-body components, since at least the 1980s.

Now, the cover story for the January 2012 issue of Advanced Materials from researchers at the University of Illinois at Urbana-Champaign goes, I think, one step farther by applying a patch to entice formation of blood vessels, structures required nearly everywhere except in cartilage.

Hyunjoon Kong and colleagues fashioned a device resembling a bandage of sorts, which they call a “living microvascular stamp,” that indeed imparts a pattern of blood vessels where it is applied. Why blood vessels? “Any kind of tissue you want to rebuild, including bone, muscle or skin, is highly vascularized,” says Dr. Kong., a chemical and biomolecular engineering professor.

At one centimeter across, the blood vessel stamp is considerably smaller than the postal variety. Like a tiny cube of baklava, the stamp is made of layers, but of a hydrogel material consisting of a jello-y alginate and polyethylene glycol, a polymer found in the vile stuff one chugs the evening before a colonoscopy. The porous synthetic baklava is threaded with carefully-placed channels and houses cells that secrete the precious growth factors.

Place the stamp onto a body part robbed of its blood supply, and circulation is restored, the new blood vessels mirroring those in the stamp, exactly like a stamp used to print an ink design on paper. Instead of a greeting card, the researchers stamped a chicken embryo – and a week later saw the precise pattern of new blood vessels form.

It’s easy to imagine applying the stamp to a wound or body part robbed of its blood supply.
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