"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. There's a lot more that we don't know than we do know."
Kay said there was "no evidence" that ACell had manipulated the regenerative capabilities of the human body.
"There's no clinical evidence to support the claims," he said. "It really is junk science.
"If you could regenerate body parts like this, your first port of call would be a serious science journal like Nature because it would be a Nobel prize winning revolution."
