It was Seymour Glagov at the University of Chicago who back in the 1970s did the early work in this area, discovering the elastin layer beneath other cells on the wall of anterior (near the heart) arteries. He scraped away the cells, down to the basic elastin, then started putting some of them back. What he found amazed him. When he put a pulsing pressure through the artery—the kind of pulse a heart would exert—the cells started to self-assemble themselves into what looked like the flesh of a normal artery.

“As the wall stretches, those cells get stretched,” says Urry. And cells are connected to each other by microtubule fibers. When you stretch those, he notes, “they trigger chemical signals—which play a part in the release of phosphates and ATP and all the other things that are turning on genes and turning off genes and so on.” As a result, the cell produces materials that will make the arterial walls elastic enough to sustain that force. Urry calls this adaptive restructuring.

You see it in terms of exercise, he observes, where you build bone mass—so that in the next go-round the bone has become stronger. It happens in brain development, too. “In the case of children born with cataracts,” Urry says, “it used to be that we wouldn’t take the cataracts off for a couple of years. By then the child was absolutely blind. But if you let the light in early, so the cells in the brain can receive that light and actively restructure, they will make synapses and networks. Then the next time the light comes in, they can see it even better, and they can get the images better.”

That is adaptive restructuring in response to an energy input, he concludes. “And that’s what, to me, is unique about a living system—the capacity to take the energy input that drives a function, and then adapt in such a way that it can even better receive that energy input. It’s what makes living systems living.”

Urry sees his new biology sheets of elastin as potential patches for use in the repair of artery walls. “For these patches,” he says, “in the protein sequence we’ve designed, we can put in cell-attachment sequences. So the cells can colonize a tube made of artificial elastin, and attach to it just like when they are in a natural artery. And when that tube is stretched out—when the blood pulse goes through it—the artery senses exactly the force it has to sustain and responds to it. The cells then remodel the synthetic scaffolding and integrate it into the natural arterial wall.

“So that is our concept,” he says. “What we put in is ultimately degraded and remodeled. It disappears, and the natural artery simply replaces it.” In response to a question about tissue rejection, a common problem in transplant operations, Urry says, “This is terrific stuff in that regard. The basic sequence is so innocuous that the host doesn’t even know it’s there. The material we introduce is made of amino acids. During the remodeling process the amino acids are eventually degraded—broken down and reincorporated back into new proteins. We talk about a temporary functional scaffolding,” he says, “that the host does not know is foreign. In that context we use the term ‘handshake.’ We make our material so much like the natural material that the handshake is complete.”

The team has confirmed this concept by making an artificial bladder from elastin sheets. When they pulsed it by filling and emptying it, they could see local cell types colonizing and absorbing the scaffold.

Urry calls their work “soft tissue restoration.” Their start-up company is based in Birmingham, Alabama, and there’s a subsidiary in Japan. For now they’re concentrating on soft tissue, but eventually they may make bone as well.

Another term Urry sometimes uses to describe their work is “consilient engineering.” He borrowed the term from Harvard biologist E. O. Wilson, whose popular book Consilience calls for a unity of all knowledge. Urry likes the word because the mechanism he is working with—which causes the protein folding—makes possible not only mechanical work but chemical work and electrical work and other kinds of work in the body. There are, he says, all kinds of energies being interconverted in living organisms by that single means.

Commenting on the importance of natural logic as a replacement for the machine metaphor, he likes to quote from Wilson’s book, which in the final chapter says, “What does it all mean, this is what it all means: To the extent that we depend on prosthetic devices to keep ourselves and the biosphere alive we will render everything fragile.” There are now, Urry points out, operations in which pigs’ heart valves are introduced into humans. These are very sophisticated surgeries, “but then people wander around for the rest of their lives worrying about blood clotting and rejection. They have to take a drug that prevents rejection, and another that prevents the clotting. But then there is a risk of hemorrhage. And so they become very fragile.”

His point, and Wilson’s, is that natural systems are resilient until we introduce mechanistic interfaces—with all their necessary adjustments and compensations—as a means of sustaining ourselves. Those interfaces not only isolate us from nature but at the same time create systems that are brittle and delicate.

Tags: amino acids, bounce back, Consilience, E. O. Wilson, natural systems, prosthetics, proteins, synthetic elastin, tensegrity, Urry

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Posted on May 2nd, 2006 @ 6:00 am