Tissue Engineering and Regeneration of the Human Hair Follicle in Androgenetic Alopecia: Literature Review

Abstract

Androgenetic alopecia (AGA) is an androgen-dependent process and represents the most frequent non-scarring alopecia. Treatments for AGA do not always achieve a satisfactory result for the patient, and sometimes cause side effects that lead to discontinuation of treatment. AGA therapeutics currently includes topical and oral drugs, as well as follicular unit micro-transplantation techniques. Tissue engineering (TE) is postulated as one of the possible future solutions to the problem and aims to develop fully functional hair follicles that maintain their cyclic rhythm in a physiological manner. However, despite its great potential, reconstitution of fully functional hair follicles is still a challenge to overcome and the knowledge gained of the key processes in hair follicle morphogenesis and biology has not yet been translated into effective replacement therapies in clinical practice. To achieve this, it is necessary to research and develop new approaches, techniques and biomaterials. In this review, present and emerging hair follicle bioengineering strategies are evaluated. The current problems of these bioengineering techniques are discussed, as well as the advantages and disadvantages, and the future prospects for the field of TE and successful hair follicle regeneration.

Keywords: androgenetic alopecia; bioengineering; hair follicle; regenerative medicine; tissue engineering.

Figure 1

Histological images of the HF. (A) Sebaceous glands and their duct opening into hair follicle; (B) Vertical; (C) Horizontal. M: Medulla. HS: Hair shaft. IRS: Inner root sheath. ORS: Outer root sheath. VM: Hyaline membrane. DS: Dermal sheath. ME: Melanocytes. DP: Dermal papilla. PB: Pilous bulb.

Figure 2

Different approaches to obtain HFs by TE. Adapted from the article ‘Castro, A. R. and Logarinho, E. Tissue engineering strategies for human hair follicle regeneration: How far from a hairy goal?’ First, cell populations are harvested to form the epidermal and dermal components of the HF. If cells are obtained from sites other than the HF, they need to be differentiated appropriately. After initial expansion in culture, trichogenicity will be increased by 3D spheroid culture, biomaterials or by modulation of signalling. Finally, once the HFs have been obtained by follicular or non-follicular techniques, the final step is their implantation and the evaluation of clinical success.