(A) Schematic overview of methodology for the development of HSE. It starts with the embedding of human dermal fibroblasts in collagen I matrix to contract and remodel the gel to form dermal layer. Then the keratinocytes are seeded on the top to form a monolayer and the culture is raised to ALI under 3D cell culture conditions allowing the keratinocytes to differentiate and form epidermal layers. (B) Timeline for the development of HSE.