A leading plastic surgeon today dismissed claims that a powder made from a pig's bladder caused the regrowth of a man's fingertip.

Professor Simon Kay, professor of hand surgery at the University of Leeds, said the claims by the US company that developed the powder were "junk science".

Lee Spievack, a hobby store salesman in Cincinnati, Ohio, has claimed the treatment stimulated the regrowth of his right hand middle fingertip, which was severed in 2005 by the propeller of a model plane.

Spievack, 69, described the powder as "pixie dust". It was developed by ACell - a company co-founded by his brother Alan, a former Harvard surgeon.

Within four weeks of using the preparation, he said his finger had regained its original length, and four months later "it looked like my normal finger".

But Kay, consultant plastic and hand surgeon at St James' University Hospital, Leeds, said Spievack's injury did not look to have been serious from studying before and after photos.

"It's a ridiculous story – absurd and over-egged in the extreme," Kay said. "It looked to have been an ordinary fingertip injury with quite unremarkable healing. All wounds go through a repair process."

ACell, the company behind the claim, said it had already used the extract of pig bladder to treat ulcers and other wounds, and to help regrow cartilage.

The powder was mostly collagen and a variety of substances, without any pig cells, said Dr Stephen Badylak, a regeneration researcher at the University of Pittsburgh and scientific adviser to ACell.

He said it formed microscopic scaffolding for human cells to occupy, and emitted chemical signals to encourage those cells to regenerate tissue. The signals did not specifically say "make a finger" but cells picked up that message from their surroundings, Badylak 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. 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."

British scientists have led the way in research into genetic treatments that could enable humans to regrow limbs damaged by accidents or surgery and allow patients to recover from wounds without scarring.

A charity, the Healing Foundation, which funds research into pioneering scientific techniques, set up a 25-year project in 2005 with the University of Manchester to advance the understanding of wound healing and tissue regeneration.

The Healing Foundation Centre aims to unravel the genetic quirks that allow certain amphibians, such as frogs and salamanders, to recover from severe injuries by generating fresh body tissue. By identifying the genetic mechanisms involved, the researchers hope to develop medical treatments that do the same in humans.

Professor Enrique Amaya, a tissue engineer at Manchester University and leader of the project, is investigating the regenerative capabilities of frogs. Frog embryos share the human embryo's ability to heal wounds without scars in a matter of hours. Frogs can also regrow appendages.