Three-Dimensional bioprinting of in vitro full-thickness skin model incorporating the rete ridge structure

The rete ridges, undulating structures located between the epidermis and dermis, play a crucial role in maintaining the skin’s barrier function, which protects the body from pollutants and ultraviolet (UV) radiation. This formation of rete ridges within in vitro skin models is essential for evaluating the efficacy and safety of pharmaceuticals or cosmetics, replacing the need for animal models. Micro-molding is a prominent technique for recreating the rete ridge structure in in vitro skin models, however, this method is characterized by high technical difficulty. Although three-dimensional (3D) bioprinting technology shows potential for fabricating skin models incorporating the rete ridge structure, it is also limited by the extended time required for structural implementation. In this study, we introduce a methodology for fabricating full-thickness skin equivalents with rete ridges using preset extrusion bioprinting. A polycaprolactone frame was 3D-printed, and the dermal layer was bioprinted in the frame. Subsequently, furrowing steps were undertaken to create a substrate for the stable anchoring of strands produced by the preset extrusion bioprinting, fabricating a dermis layer with a rete ridge structure. Keratinocytes were then seeded and differentiated, resulting in the formation of the stratum corneum. We observed that protein expression was preserved in the valleys of the rete ridge after UV irradiation of the rete ridge full-thickness skin equivalent, demonstrating a similarity to human ex vivo skin models. Therefore, the rete ridge full-thickness skin equivalent generated using our method shows potential as a promising model to replace animal experiments and human ex vivo skin models.