I have seen a few variants of a claim that a man lost a finger/finger tip, and was given an Extracellular Matrix (ECM) treatment, that included a powder (usually based on pig's bladder), and the finger grew back.
(Warning: Some of these links contain confronting medical images.)
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Halpern sought out Dr. Eugenio Rodriguez of the Deerfield Beach Outpatient Surgical Center, who he had heard used a revolutionary procedure called xenograft implantation.
Rodriguez used pig bladder tissue to create a mold of Halpern’s missing finger and attached it to the stump. He then instructed Halpern to apply a powder made from the same pig bladder tissue for two months.
[...]
Weeks later, the finger’s cells, bone, soft tissue, and nail grew into the mold, reports CBS Miami.
“Long story short, it grew back – the majority of it,” Halpern told NBC6. “I’m quite happy.”
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How? Well that's the truly remarkable part. It wasn't a transplant. Mr Spievak re-grew his finger tip. He used a powder - or pixie dust as he sometimes refers to it while telling his story.
Mr Speivak's (sic) brother Alan - who was working in the field of regenerative medicine - sent him the powder.
For ten days Mr Spievak put a little on his finger.
"The second time I put it on I already could see growth. Each day it was up further. Finally it closed up and was a finger.
[...] The "pixie dust" comes from the University of Pittsburgh, though in the lab Dr Stephen Badylak prefers to call it extra cellular matrix.
New York Daily News also about a finger being regenerated.
CBS News, 2014 is similar, but it has to do with regenerating muscle tissue. Fingers are more complicated.
However, The Guardian did a debunking article in 2008, discussing the Spievak case:
Simon Kay, professor of hand surgery at the University of Leeds, saw the before-and-after pictures, and says: "It looked to have been an ordinary fingertip injury with quite unremarkable healing. This is junk science."
Has ECM powder been reliably demonstrated to grow back missing fingers?