Could this be the answer?
I think it theoretically could provide a way to replicate the structure of the hair follicle, where there are at least 6 different distinctly specialized cell types (epithelial cells, stem cells, progenitor cells, dermal papilla cells, keratinocytes, etc.) arranged in a complex 3-dimensional formation.
The problem, again (I’ve mentioned this before), is that the hair follicle is histologically, for its small size, one of the more complex organs in the body. Its proper functioning relies on the perfect spatial arrangement of all these different cell types in a very tiny space.
The problem with 3D printing technology as it exists now, is that it’s very good for printing “big” objects like guns and car chassis and, theoretically, for the bigger human organs that don’t have so many different cell types – like a breast or a heart or the outside part of the ear – but I don’t know how it would perform for a tiny, complex organ like a hair follicle. I think it would be more difficult.
In mice, at least, just two cell types are commonly used for full hair follicle regeneration in vivo: the stem cells (CD34+, Itgb6+ epithelial cells) and the dermal papilla cells. Human follicles may be a bit more difficult to regenerate and may require melanocytes as well (though of course this hasn’t been tried yet in a human, but in vitro seems to work on a limited basis). The human hair follicle stem cells have the capacity to differentiate into all the lineages of the follicle so theoretically all you should need is the stem cells and dermal papilla cells. Someone just needs to come up with a good way of culturing these cells together so that they form new follicles when transplanted. The Japanese group that used nylon thread and cultured human stem cells along with DP cells is going in the right direction, I think, for 3D cultures. Even more simple may be Angela Christiano’s work with dermal papilla spheroids, where she showed that they alone were able to induce new, or de novo, hair follicles. It is very complicated even with just one cell type, which is why it has taken so long to just get to this point. We are close though, I’m sure any year now we will hear of positive human clinical trials for cultured hairs. Fingers crossed!
Hey UW, do you go to University of Washington? Great university. I live near there and work from campus once or twice a week.