Despite its ubiquity, hair is surprisingly complicated. The attempt of scientists to engineer it has lagged behind other lab-grown tissues, such as vasculature and intestinal epithelium, mainly because there is no platform in which to foster the right mix of ingredients to grow it. However, with the revolution of micro 3D printing, researchers may now have just what they need.
"When I saw a hair shaft growing out of our engineered skin, I remember running around in the lab and yelling," said Hasan Erbil Abaci, from Columbia University Medical Center, to IFLScience.
The team mimicked the pattern of hair follicles using 3D-printed plastic molds with slender extensions half a millimeter wide. "Previous fabrication techniques have been unable to create such thin projections, so this work was greatly facilitated by innovations in 3D-printing technology," added Erbil Abaci in a statement.
Even with the advent of improved 3D printing, the team faced another challenge. "Cells from rats and mice grow beautiful hairs," said lead researcher Angela Christiano of Columbia University Medical Center. "But for reasons we don’t totally understand, human cells are resistant."
The team used a dash of hair follicle cells from human volunteers in the micropatterned channels and topped them with keratin-producing cells. In a mere three weeks, the formula started sprouting hair.
"It takes about 3 weeks to engineer fully formed human hair follicles entirely in vitro," said Erbil Abaci. "Similarly, when the constructs are grafted onto mice, it takes about 3 weeks to see the hair shafts forming. It is striking to be able to recapitulate the process of hair formation not only in terms of its structure but also its time scale."
"What we've shown is that we can basically create a hair farm: a grid of hairs that are patterned correctly and engineered so they can be transplanted back into that same patient's scalp," said Christiano, whose study is published in Nature Communications.
"That expands the availability of hair restoration to all patients – including the 30 million women in the United States who experience hair thinning and young men whose hairlines are still receding. Hair restoration surgery would no longer be limited by the number of donor hairs."
Other applications of such research include use in skin replacement therapies, substitutions for animal models in drug development and cosmetic testing, and improvements in the appearance of replacement skin in those who have suffered severe skin trauma. Hair restoration surgery for male and female pattern baldness typically requires around 4,400 hairs per patient. The team say their technique yields more than 5,000 hair follicles per human skin construct.
"Current hair restoration techniques rely on transferring one hair from one site of the scalp to another," said Erbil Abaci. "With our approach, which is based on the expansion of donor cells in the lab, it will be possible in the future to graft nearly 2,000 engineered hair follicles from one donor hair follicle."
The method is not perfect yet. Apart from optimizing the process, the team would like to follow up with melanocytes in order to create pigmented hair follicles. Additionally, they'd like to add growth factors and small molecules that target different stages of hair follicle formation. Still, the possible promise of a hair farm – essentially a sustainable source of natural hair for medical use and drug testing – is enticing.
It should be noted that although eight of the 10 researchers in this study have no competing interests, the remaining two (Dr Christiano and Dr Colin Jahoda) are founders of Rapunzel Bioscience Inc., a company that focuses on the development of regenerative therapies for skin and hair disorders.
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