Figure 1.

A schematic overview of the 2D and 3D in vitro models of the human skin. (A) Different cell types can be isolated from human skin samples. Epidermal keratinocytes are extracted from the epidermal part and fibroblasts from the dermal part of the skin. (B) Fibroblasts and keratinocytes are cultivated separately in a 2D monolayer. (C) Transwell co-culture systems comprise fibroblasts, which are grown on the well bottom, and keratinocytes, which are cultivated in a porous insert. This allows the exchange of soluble factors without direct contact between different cell types. (D) In the reconstructed human epidermis (RHE) model, stratified keratinocytes are cultured in a porous membrane at the air–liquid interface on top of a collagen matrix. (E) In a human skin equivalent (HSE), keratinocytes are cultivated atop a dermal equivalent composed of fibroblasts embedded in an ECM-like matrix [26].