Because of their profound regenerative abilities, feather stem cells are of interest to the medical and scientific community. Feather regeneration refers to the cycle by which normal feathers grow, go dormant, molt, and “regenerate” a new feather.
Here's how it works. Dermal papilla, located at the follicle base, controls the regenerative process. The dermal papilla is a permanent structure, while the feather pulp grows and regresses during the feather growth and resting phases. The growth phase is the “blood feather” stage and after the pulp dries up and recedes the feather is in the resting state before the molt begins again.
A bird in nature typically molts twice a year. With more than 20,000 feathers on the average bird, there are a lot of active, ongoing regenerative events in an adult bird. Contemporary studies suggest “reparative regeneration” in avian species is limited to periods during embryonic development.
Early studies show that when the dermal papilla is removed, feather regeneration stopped. Later research revealed that a transplanted dermal papilla would induced feather regeneration in the recipient follicle. Classical work demonstrated that only the bottom layer of the feather follicle would respond while the interfollicular epidermis failed to regenerate new feather follicles. Results from this delicate micro dissection and transplantation study suggest that that the feather dermal papilla induces feather growth.
Scientists were able to control the growth and formation of feathers by manipulating the dermal papilla. So, if specific portion was removed or angled it a certain way, it would make the feather grow at a different angle than the original feather would have. Feather structures can be manipulated (distorted) through removal of a portion of the dermal papilla, which explains why we see bizarre, deformed feathers growing at weird angles on wings that have been operated on, or unnatural regrowth from an injury ... it is likely due to unintended micro dissection of the dermal papilla.