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.)
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.”
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?