Regeneration recipe: Pinch of pig, cell of lizard

‘We're not smart enough ...’
None of this proves the powder was responsible. But those outcomes have helped inspire an effort to try the powder this summer at Fort Sam Houston in San Antonio, on soldiers who have far more disabling finger loss because of burns.

Fingers are particularly vulnerable to burns because they are small and their skin is thin, says David Baer, a wound specialist at the base who’s working on the federally funded project. The five to 10 patients in the project will be chosen because they have major losses in all their fingers and thumbs, preventing them from performing the pinching motion they need to hold a toothbrush, for example.

The soldiers will have the end of a finger stub re-opened surgically, with the powder applied three times a week.

Nobody is talking about regrowing an entire finger. The hope is to grow enough of a finger, maybe even less than an inch, to do pinching.

And it is just a hope.

“This is a real shot in the dark,” says Badylak, who’s participating in the project. “There’s literally nothing else these individuals have to try. They have nothing to lose.”

But from a scientific standpoint, he said, “this isn’t ready for prime time.”

For one thing, it’s not completely clear what happened inside Lee Spievack’s finger.

The broad outline is pretty straightforward. The powder is mostly collagen and a variety of substances, without any pig cells, said Badylak, who’s a scientific adviser to ACell. It forms microscopic scaffolding for incoming human cells to occupy, and it emits chemical signals to encourage those cells to regenerate tissue, he said.

Those signals don’t specifically say “make a finger,” but cells pick up that message from their surroundings, he said.

“We’re not smart enough to figure out how to regrow a finger,” Badylak said. “Maybe what we can do is bring all the pieces of the puzzle to the right place and then let Mother Nature take its course.”

But “we are very uninformed about how all of this works,” Badylak said. “There’s a lot more that we don’t know than we do know.”

No pig powder needed
Some animals, of course, can regenerate tissue without help from any powder. Badylak and other scientists are involved in a separate, Pentagon-funded project to uncover and harness their secrets. This work might someday lead to regenerating entire limbs.

One animal they’re studying is the salamander, a star of the regeneration field. Chop off a salamander’s arm, and it will grow back in a matter of weeks.

Why? The short answer is that rather than making a scar to heal quickly, as people do, the salamander forms a mound of cells called a blastema. This is a regeneration factory: If you cut off a salamander hand and transplant the resulting blastema to the creature’s back, it will grow out a hand there.

David Gardiner at the University of California, Irvine, is studying the secrets of the salamander by growing extra arms on the creatures. That allows for more controlled conditions than amputating arms and trying to follow what happens, he said.

So how do you make a salamander grow an extra arm? Make a shallow wound on the upper arm. Re-route a nerve to the site so it will pump out critical chemical signals that promote the creation of blastema cells. And insert a tiny piece of skin from the other side of limb you just wounded, to help provide a blueprint for what needs to be done.

The recipe sounds like “you put it in a cauldron under a full moon,” Gardiner observed.

The creatures are so lethargic it’s hard to tell if they can use their extra arms, he noted. But the research shows that beyond establishing a blueprint for a new arm, this mix of cells sends out a chemical SOS to attract other kinds of cells from the salamander’s body to help construct a new appendage.

Just how many chemical signals are involved, and what they are, remain to be discovered.

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