Self‐Healing Hydrogel‐Enabled Modular Assembly of Bilayered Skin Construct for Hair Follicle Regeneration

Alopecia remains a pervasive clinical challenge, largely owing to the limited ability of existing therapies to regenerate functional hair follicles. Hair follicle morphogenesis relies on precisely coordinated epithelial-mesenchymal interactions (EMIs) within a spatially defined epidermal-dermal niche, which is difficult to reconstruct using conventional tissue engineering approaches. We present a modular tissue engineering strategy using a self-healing N-carboxyethyl chitosan-oxidized dextran/collagen-genipin hydrogel. The hydrogel exhibits tunable mechanical properties, achieving a mechanically permissive stiffness conducive for hair follicle inductivity (∼32 kPa), and enables the bottom-up assembly of multicellular hair-follicle mimetic tissues. Two independently engineered hydrogel modules, one encapsulating dermal papilla-keratinocyte spheroids filled with singlet keratinocytes and the other containing a dermal fibroblast, spontaneously fuse vertically through self-healing to form a bilayered epidermal-dermal construct. This spatially organized architecture promotes EMIs, enhances folliculogenic signaling, supports in vitro follicle-like morphogenesis, and reproduces pharmacological responses to clinically approved anti-alopecia drugs. In vivo implantation of the bilayered construct accelerates wound healing and promotes de novo hair follicle regeneration, with the implanted human cells contributing to this process. This study establishes a scalable and clinically translatable approach tailored for personalized hair regeneration therapy and the high-throughput pharmacological screening of anti-alopecia drug candidates.