Reframing hair follicle development through Tissue Engineering Triad for hair organoid construction

Hair follicles are dynamic mini-organs that cyclically regenerate through coordinated epithelial–mesenchymal interactions and precisely regulated molecular signalling. Reconstructing this complexity in vitro remains a central challenge in regenerative dermatology. This review reframes hair-follicle morphogenesis through the Tissue Engineering Triad (TET), which consists of cells, signals, and materials, to provide a design-oriented perspective for organoid construction. Each hair-cycle phase (anagen, catagen, telogen) is analysed in terms of its cellular composition, signalling environment, and extracellular matrix (ECM) dynamics, emphasizing how these triadic components govern homeostasis and regeneration. The telogen-to-anagen transition is highlighted as a natural model of reactivation, linking cellular reprogramming, morphogen signalling, and matrix remodelling. Building on these biological insights, recent advances in hair-follicle organoid engineering are reviewed, covering cell sources, morphogen combinations, ECM scaffolds, and the developmental fidelity of resulting structures. Finally, the challenges of maintaining dermal papilla inductivity, achieving vascularization, and ensuring translational scalability are discussed. Framing hair development through the TET paradigm offers a unifying roadmap for transforming developmental principles into practical strategies for hair regeneration.