Hair loss is divided into physiological and pathological. Physiological alopecia refers to the normal shedding of hair. Pathological alopecia refers to abnormal or excessive hair loss. In addition to trauma resulting in partial- or full-thickness skin lesions, increasing pressure on life, environmental degradation, and poor eating habits also make the number of hair loss patients continue to rise. Pathology has a negative impact not only on people’s appearance but also on the mental health of patients . Despite the many strategies and methods of treating hair loss, the treatment is still a worldwide problem, because there is no direct and effective therapeutic agent [84-86]. The development of tissue engineering as a new strategy has begun to emerge, but the reorganization of hair tissue with complete organization and function remains a new challenge. The key to hair regeneration is to repair and rebuild the growth environment of the hair, so the scaffold should support epithelial stem cell proliferation and differentiation and induce the formation of new tissue . In numerous studies of hair tissue engineering, the reinforced scaffold is also a promising tool for repairing and reconstructing hair epithelial tissue.
Itoh et al.  designed a PGA fiber-reinforced collagen scaffold for reconstructing hair. The process of hair growth is that the epithelial cells grow down into the dermal tissue to form a head, called the dermal papilla [88, 89]. Cell implantation position and diffusion movement are necessary condition for hair follicle reconstruction. Collagen is a commonly used material for repair and reconstruction of skin tissue, but the traditional collagen sponge material is not suitable for the repair of scalp tissue [90-92]. Because of poor mechanical property and stability, the pores of the scaffolds formed by the pure collagen sponge decrease with the shrinkage of the collagen sponge, which hinders the diffusion and deposition of the grafted cells, and even leads to the leakage of the cell suspension. To observe the effect of fiber enhancement, pure collagen scaffolds and fiber-reinforced collagen scaffolds transplanted within hair and hair follicles of athymic mice were implanted into the dorsal skin for 3 weeks. The results showed that the nascent hair with a regular arrangement tilted from beginning to end, and the growth of the sebaceous glands on the fiber-reinforced scaffold was normal. Thus, the formation and reconstruction of the hair did not receive the effects of the implant and lasted for 6 months at least. The average hair densities on the collagen scaffold and fiber-reinforced scaffold were 531 ± 179 and 2808 ± 1237 wool/cm 2, respectively, based on the result of quantitative analysis on both implants. There was no significant difference in the shape and size of the two grafts. Since the scaffold has sufficient mechanical properties to maintain the structural stability of the scaffold in vivo, the scaffold-embedded cells can be well preserved and viable. Moreover, the transfer movement of cells could be observed in the reinforced scaffold, which also contributed to the formation of epidermal cysts. In addition, due to the plasticity of the PGA fibers, the addition of them enhanced the ability of collagen sponge scaffolds to be deformed, which was conducive to resist mechanical deformation and increase the possibility of implantation of the reinforced scaffold into an irregularly implanted bed. Therefore, PGA fiber-reinforced collagen scaffolds, as the most typical fiber-reinforced scaffolds, represent the promising to be used in hair tissue repair and regeneration.