Professor Lin Sung-jan took 10 hair follicles from rodents and cultivated 8 to 10 million dermal papilla cells in vitro in 20 days. Using aggregates of between 3 and 5 million dermal papilla cells, he mixed these with rodent skin cells and transplanted them onto bare rodent skin, which sprouted hair.
Bald skin and haired skin have the same cell populations needed to grow hair, as it turns out, so this sort of cell-based approach has merit. The end of the story will likely be some form of cell signalling treatment to instruct cells already present in the body to form hairs in an area of skin rather than cell transplants - but transplants are first in line for development. The process is not exactly straightforward, unfortunately. Much like the tissue engineering of teeth, some form of guiding technology must be established to ensure that the cells grow as they should - without it, you end up with misshapen or broken structures.
On this subject, the work of a Japanese group on hair regeneration has been in the news of late, and they seem to have established a proof of principle for guiding correct hair growth. You'll find an open access paper and a couple of popular press items to choose from, complete with pictures of a hairless mouse sporting a patch of engineered hair:
Previously, Tsuji and colleagues had bioengineered follicles and hair shafts in the lab using epithelial and mesenchymal cells from mouse embryos. Until now, it was unclear whether these organized clusters of cells would make normal hair if inserted into mouse skin.
In the new work, the team transplanted a group of the engineered follicles into the skin on the backs of hairless mice. After about two weeks, hairs began to sprout. Under the microscope, the hair grown from the bioengineered mouse follicles resembled normal hair, scientists found. And the mouse follicles went through the normal cycle of growing hair, shedding and making new hair.
When researchers injected the region around the bioengineered follicle with acetylcholine, a drug that causes muscles to contract, the hairs perked up. This suggests that the transplanted follicles had integrated with surrounding muscle and nerves like normal hair follicles do.
Importantly, the researchers were able to ensure hair didn't become ingrown or point in the wrong direction by attaching a nylon thread to the engineered follicles and guiding the hair to grow outward.
That guide method doesn't sound very scalable - though given that there is a market for hair restoration techniques that involve moving follicles one by one, I could see it finding use in the clinic. But we can live without our hair and our vanity; a legion of far more serious and life-threatening degenerations accompany aging, and those are where our attention should be directed. The most important long-term effects of this particular line of research will, I think, be the application of the lessons learned to other areas of tissue engineering: guiding the regeneration of small complex structures, of which there are a great many in the body.
The results also mark a step forward in efforts to regenerate organs such as salivary glands that form in a process similar to hair early in their development.