Skin is one of the obvious initial targets for tissue engineering, as it is possible to grow in thin sheets without the need to solve the challenge of generating vascular networks to support larger, thicker tissue structures. Researchers have been making progress towards more complete, complex engineered skin, such as through the inclusion of functional hair follicles or sweat gland structures. The research noted here is an example of the type, though one should always be wary of publicity materials that claim researchers to be first to a specific goal in tissue engineering. It is more often the case that several different groups are in progress at at a similar stage for any given advance in this field. It is a very well funded and diverse area of research; few groups are the only ones working on their specific tissue type and methodological focus.
Researchers have cultured the first lab-grown skin tissue complete with hair follicles. This skin model, developed using stem cells from mice, more closely resembles natural hair than existing models. Although various methods of generating skin tissue in the lab have already been developed, their ability to imitate real skin falls short. While real skin consists of 20 or more cell types, these models only contain about five or six. Most notably, none of these existing skin tissues is capable of hair growth.
Researchers originally began using pluripotent stem cells from mice, which can develop into any type of cells in the body, to create organoids that model the inner ear. But the team discovered they were generating skin cells in addition to inner ear tissue, and their research shifted towards coaxing the cells into sprouting hair follicles. The team's recent research demonstrates that a single skin organoid unit developed in culture can give rise to both the epidermis (upper) and dermis (lower) layers of skin, which grow together in a process that allows hair follicles to form the same way as they would in a mouse's body.
While the researchers were unable to identify exactly which types of hairs developed on the surface of the organoid, they believe the skin grew a variety of hair follicle types similar to those present naturally on the coat of a mouse. The skin organoid itself consisted of three or four different types of dermal cells and four types of epidermal cells - a diverse combination that more closely mimics mouse skin than previously developed skin tissues. By observing the development of this more lifelike skin organoid, the researchers learned that the two layers of skin cells must grow together in a specific way in order for hair follicles to develop. As the epidermis grew in the culture medium, it began to take the rounded shape of a cyst. The dermal cells then wrapped themselves around these cysts. When this process was disrupted, hair follicles never appeared.
After discovering this recipe for lab-grown hair follicles, the researchers must now work to overcome a new roadblock in the study of in vitro hair development - physical limitations that prevent the hairs from shedding and regenerating. The shape of the tissue in culture causes the hair follicles to grow into the dermal cysts, leaving them with nowhere to shed. Nonetheless, the team thinks the mouse skin organoid technique could be used as a blueprint to generate human skin organoids.